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Increasing flower longevity in Alstroemeria
Postharvest Biology and Technology 29 (2003) 324 /332 www.elsevier.com/locate/postharvbio
Increasing flower longevity in Alstroemeria U. Chanasut a,1, H.J. Rogers b, M.K. Leverentz c,2, G. Griffiths c, B. Thomas c, C. Wagstaff b, A.D. Stead a,* b
a School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK Cardiff School of BioSciences, Main Building, University of Cardiff, PO Box 915, Cardiff CF10 3TL, UK c HRI, Wellsbourne, Warwick CV35 9EF, UK
Received 21 October 2002; accepted 7 March 2003
Abstract The vase-life of Alstroemeria (cv. Rebecca) flowers is terminated when the tepals abscise. Abscission was accelerated by both chloroethylphosphonic acid (CEPA) and 1-aminocyclopropane-1-carboxylic acid (ACC). Petals abscised 24 h earlier compared with controls, when isolated cymes were placed in 340 nM CEPA, and earlier still when higher concentrations were used. This suggests that flowers of this Alstroemeria cultivar are very ethylene sensitive. Treatment with silver thiosulphate (STS) overcame the effects of exposure to CEPA and delayed perianth abscission of untreated isolated flowers by 3 /4 days. The inclusion of 1% sucrose in the vase solution also extended longevity but not by as much as STS treatment; combined STS and sucrose treatments did not increase longevity beyond that of either treatment alone. However, removal of the young buds from the axil of the first flower was the most effective treatment to extend vase-life and encouraged the growth and development of the remaining flower. Flowers on cut inflorescences from which young axillary buds were trimmed more than doubled in fresh weight 6 days after flower opening compared with an increase of only 70 /80% in those untreated or treated with STS and/or sucrose. Growth was less in isolated cymes but followed a similar pattern. The effect of STS and/or sucrose treatment was synergistic with the trimming treatment and thus the vase-life of trimmed, STS and sucrose-treated flowers was over 7 days longer than that for untreated controls. # 2003 Elsevier B.V. All rights reserved. Keywords: Alstroemeria ; Vase-life; Ethylene; Silver; Flower removal
1. Introduction * Corresponding author. Tel.: /44-1784-44-3761; fax: /441784-47-0756. E-mail address: [email protected] (A.D. Stead). 1 Present address: Biology Department, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. 2 Present address: Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Wilmslow Road, Manchester M20 4BX, UK.
Several authors have reported that leaf yellowing is one of the first indicators of the deterioration of flowering Alstroemeria stems. Moreover, leaf yellowing occurs quickly if, as is often the case, cut stems are held or transported in the dark (Dai and Paull, 1991; Hicklenton, 1991; van Doorn et al., 1992). Postharvest treatments to delay leaf yellow-
0925-5214/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-5214(03)00048-6
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ing have, therefore, been suggested. These include pre-treatment of cut stems with gibberellins with or without other growth regulators (Hicklenton, 1991; van Doorn et al., 1992; Jordi et al., 1993, 1994) or with chemicals that have cytokinin-like activity (Ferrante et al., 2002). These studies have not reported the effects on floral longevity and although Nowak and Rudnicki (1990) reported that the use of silver thiosulphate (STS) was recommended for Alstroemeria it is not clear whether this relates to improving the longevity of the flowers or to delaying leaf senescence. The use of STS is, of course, a common practice for extending the flower longevity of ethylene-sensitive species (Veen, 1979), but the literature suggests that flowers of Alstroemeria are only weakly sensitive to ethylene (Woltering and van Doorn, 1988). Collier (1997) reported the changes in several biochemical constituents during Alstroemeria petal development and flower senescence but did not consider floral ethylene production, thus the importance of ethylene in the control of flower longevity in Alstroemeria has not been fully elucidated. However, the lack of recommendations for the use of either STS or 1-methylcyclopropane (1-MCP), to prolong flower longevity suggests that ethylene is not considered an important factor in regulating the vase-life of this species. Floral preservatives usually include a biocide and a carbohydrate supply since, once detached from the plant and held under relative low light intensities, flowering stems have little opportunity for photosynthesis. Apart from normal respiratory requirements for carbohydrates, the development of the ovary and the development of axillary flowering shoots, as occur in Alstroemeria , represent further sinks. Certainly it has been shown in several species that translocation of metabolites from the senescing petals occurs and that these may contribute to the growth of the ovary (Nichols and Ho, 1975a,b) or developing flowers (Waithaka et al., 2001). However, the extent of such mobilisation may depend upon whether the petals abscise with minimal loss of turgor or whether they wilt prior to abscission (Stead and van Doorn, 1994). This paper examines the effect of removing the axillary buds on the development and longevity of
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the single remaining flower and investigates the sensitivity of Alstroemeria cv. Rebecca flowers to applied ethylene. The benefits of three postharvest treatments (STS pulse; continuous sucrose; removal of young buds), used individually or in combination, on floral longevity is discussed.
2. Material and methods 2.1. Plant material Flowers of Alstroemeria cv. Rebecca were harvested from Oak Tree Nurseries, Virginia Water, UK at a stage just after the outer sepals separated (Stage 0, Stead et al., 2003), thus showing good sepal colour development, and thereafter were maintained as described by Wagstaff et al. (2002). A minimum of ten individual cymes was treated for each experiment and each experiment repeated at least twice. Data collected were either for flower longevity, where longevity was defined as being terminated when at least one tepal had abscised; alternatively the percentage abscission of tepals was recorded at least once daily. All chemicals were from Sigma (Poole, Dorset) unless otherwise stated. 2.2. Comparison of the vase-life of cymes and stems The development and longevity of individual cyme flowers was compared with that of cyme flowers remaining attached to cut flowering stems (recut to 50 cm length) and to flowers remaining on growing plants. For this comparison all cut flower material was maintained alongside the growing plants in the greenhouse to ensure identical environmental conditions. 2.3. Effect of CEPA or ACC on vase-life Cymes, prepared immediately after harvest (Stage 0) were placed individually in solutions of chloroethylphosphonic acid (CEPA) (34 nM /3.4 mM; equivalent to 5 ppb /500 ppm) or 1-aminocylcopropane-1-carboxylic acid (ACC) (0.1, 1.0, 10.0 mM) to investigate if ethylene, released from either CEPA or ACC, influenced flower longevity.
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2.4. Effect of STS on vase-life Once isolated, individual cymes were stood in freshly prepared 2 mM STS (Veen, 1979). Cymes were then removed after 1, 3, 6 or 24 h and placed in DI water. The flowers were examined at least once daily to determine flower longevity. Cut stems were treated similarly for comparison. 2.5. Effect of applied sugar on vase-life Isolated cymes were placed, continuously, in either 0.5, 1.0, 2.0 or 5.0% sucrose and the flowers were examined at least once daily to determine flower longevity. 2.6. Effects of combined STS/sugar with or without trimming on vase-life and floral appearance The effect of removing all floral buds, with the exception of the largest bud, on each cyme was investigated since the development of the younger buds represents a significant sink for metabolites. This trimming treatment was investigated in combination with STS pre-treatment and/or holding flowers in 1% sucrose. Flower longevity was determined for both isolated cymes and cut inflorescence stems.
3. Results
petals of intact plants persisted for more than 12 days after flower opening, whereas those of cut flowers lasted only 8/9 days, with the isolated cymes lasting only slightly less than flowers on cut stems (Table 1). In subsequent experiments, however, vase-life differed slightly. For example, the first tepals abscised from the untreated cymes used as controls in Fig. 3 approximately 10.4 days after harvest or 12.1 days for cut stems compared with 10.6 and 11.4 days for the flowers used to collect data for Table 1. The longevity of flowers remaining on the plant was approximately 4 days longer than cut flowers and they were much larger and had a greater weight (Fig. 1a and b), and were more deeply pigmented (data not shown). The dry weight of flowers remaining on the plant continued to increase for several days after complete flower opening. In contrast, the dry weight of flowers on cut stems remained almost unchanged for about 6/8 days after opening but that of the isolated cymes declined from the time of harvesting (i.e. before flower opening). 3.2. Effect of CEPA or ACC on vase-life Keeping isolated cymes in 34 nM CEPA had no significant effect on petal abscission, however, greater concentrations of CEPA accelerated petal abscission. With 340 nM the time for 50% of all petals to drop was approximately 24 h earlier than
3.1. Comparison of the vase-life of cymes and stems When cv. Rebecca flowers are harvested at a commercial stage the buds are swollen and the sepals coloured but not separated, and, in the present study, it was about 2.5 days before the flowers were fully open. This was the same for isolated cymes, cymes on detached flowering stems and for flowers remaining attached to the plant. The total vase-life of flowers of this variety was determined by petal drop (abscission) rather than leaf yellowing as occurs in certain other Alstroemeria varieties. However, they were differences in the time between flower opening and petal abscission depending on whether isolated cymes, cut stems or intact, growing plants were studied. The
Table 1 Flower longevity for flowers held either as isolated cymes, cut inflorescence stems or remaining intact on the plant Vase-life (days) Type of flower Cyme
Cut stem
Intact plant
Harvest0/opening 2.59/0.2 2.49/0.2 2.69/0.1 Fully open0/abscission 8.19/0.3 9.09/0.2 12.49/0.1 Total flower or vase-life 10.69/0.4a 11.49/0.3a 15.09/0.1b Flowers were harvested at a normal commercial stage just prior to the sepals parting. Values are the means (9/S.E.) of at least 15 flowers, values for total flower or vase-life, followed by different letters are significantly different from one another at the 95% level (Tukey’s test).
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Fig. 1. Fresh weight (a) and dry weight (b) of flowers attached to cymes (j), inflorescences (') and intact plants (m) (n/30).
for the controls, whilst at 3.4 mM the time difference was approximately 48 h, and at 34 mM the difference was approximately 96 h (Fig. 2a). Higher concentrations of CEPA not only accelerated petal abscission still further but prevented the normal development of the flower such that those that opened were small with paper-like petals (data not shown) reminiscent of the opening of the axillary bud of the control flowers. Application of concentrations greater than 0.1 mM ACC, the immediate precursor of ethylene in plant tissues, similarly reduced the time to 50% petal drop (Fig. 2b), with 1.0 mM reducing the time to abscission by more than 96 h. Such sensitivity to CEPA or ACC suggests that this cultivar is very sensitive to ethylene.
Fig. 2. (a) Effects of CEPA on % tepal abscission (n/150 tepals); (b) effect of ACC (' 10 mM; " 1 mM; I 0.1 mM) on the time to tepal abscission from isolated single cyme flowers (n/120 tepals).
3.3. Effect of STS on vase-life A 1 or 3 h pre-treatment with 2 mM STS increased the time to tepal abscission relative to water-treated controls (Fig. 3). A 6-h pretreatment similarly increased longevity but caused blackening of the bracts and was thus toxic. Longer treatments with STS not only caused discolouration of the bracts but also failed to increase longevity beyond that of the controls.
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3.4. Effect of applied sugar on vase-life Concentrations of sucrose in excess of 0.5% increased floral longevity (Table 2), with the greatest increase being with 5% sucrose. However, bract yellowing occurred within 5 days when flowers were treated with 5% sucrose, and similar, but less marked, damage was observed when flowers were held in 2% sucrose. Therefore, the maximum strength sucrose that could be used without inducing yellowing of the bracts was 1%. Fig. 3. Effect of pulsing with 2 mM STS on the subsequent time to abscission of the first tepal from cyme flowers (n/209/S.E.) or flowers on cut inflorescences (n/209/S.E.).
Since 3 h was not detrimental, further studies, using combinations of treatments, used a 3 h pretreatment to ensure that sufficient STS was taken up by the isolated cymes. For intact inflorescence stems a shorter pre-treatment (1 h) was optimal (Fig. 3), probably because of the greater transpiration from cut inflorescences compared with single cymes. A 3 h treatment for cymes completely reversed the deleterious effects of 340 mM CEPA (Fig. 4), both when 340 mM CEPA was applied as a 24 h treatment following the STS pulse and when applied continuously.
3.5. Combined STS/sugar with or without trimming Combining an STS pre-treatment with the addition of 1% sucrose in the vase solution did not significantly alter the vase-life (as determined by tepal abscission) of either isolated cymes or cut inflorescence stems relative to those only treated with STS (Table 3). Removing unopened buds from the individual cyme branches prolonged the vase-life of the remaining flowers of cyme branches and inflorescence stems. The untrimmed and untreated cyme branches or inflorescence stems (as the control treatments) kept in the constant temperature room had a vase-life of about 10.1 and 11.8 days, respectively. The results of trimming treatment alone improved the vase-life of cyme flowers by about 4.3 to 14.4 days and also extended the vase-life of inflorescence flowers by about 4.8 to 16.6 days (Table 3). The combination of trimming and chemical treatments had a greater effect on the longevity of both cyme and inflorescence flowers compared with those treated only with chemicals. For example, the flowers from untrimmed and non STS-treated cyme branches lasted about 10.1 days Table 2 The effect of applying sucrose on the time to abscission of first tepal for isolated Alstroemeria cymes (n/209/S.E.)
Fig. 4. The reversal of the effect of 340 mM CEPA (applied for 24 h or continuously) by a 3 h pre-treatment with 2 mM STS (n/159/S.E.).
Sucrose conc. (%)
Time to abscission (days)9/S.E.
0 0.5 1.0 2.0 5.0
10.49/0.32 10.99/0.53 11.29/0.55 12.09/0.51 12.79/0.15
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Table 3 Effect of sucrose, STS pre-treatment and combined STS and sucrose treatment on the vase-life of trimmed or untrimmed cyme and inflorescence Alstroemeria flowers (n /209/S.E.) Treatment
Vase-life (days) Cyme flowers
DI water 1% Sucrose STS/DI water STS/1% Sucrose
Inflorescence flowers
Untrimmed
Trimmed
Untrimmed
Trimmed
10.19/0.4a 13.09/0.1b 14.89/0.5c 15.29/0.4c
14.49/0.2bc 15.69/0.2cd 17.09/0.3d 17.89/0.4d
11.89/0.4ab 13.69/0.2b 16.69/0.2c 15.09/0.3c
16.69/0.2cd 17.69/0.2d 19.89/0.4e 17.69/0.2d
Different superscript letters denote significant differences at the 95% level (Tukey’s test) in vase-life between treatments.
in DI water, but lasted almost seven days longer when trimmed of unopened buds, pre-treated with STS and held in DI water or 1% sucrose. The trimmed inflorescence flowers pre-treated with STS and kept in DI water had the longest vaselife compared with the other treatments. The treatments also enhanced floral weight (Table 4) and improved the visual appearance of the flowers (Fig. 5). Regardless of whether cymes or inflorescences were studied the % increase in flower weight was greatest when the axillary buds were trimmed off. Indeed in the case of the cut inflorescences, trimming resulted in at least a doubling of the flower fresh weight.
Table 4 The % increase in flower fresh weight 6 days after opening relative to that at the time of harvest (2 days before being fully open) for isolated cyme flowers and flowers on cut inflorescence stems treated with STS, sucrose and trimming or combinations thereof Treatment
Controls STS STS/trimming 1% sucrose 1% sucrose/trimming STS/1% sucrose STS/1% sucrose/trimming
% fwt. change Cymes
Inflorescences
20.6 58.8 89.0 36.8 73.5 50.0 79.4
75.0 77.2 125.0 89.0 105.9 75.0 127.9
Fig. 5. The appearance of untreated control flowers on cymes (left side) compared with that of flowers in which the axillary buds were removed, pre-treated with STS and placed in 1% sucrose (right side). The photograph was taken six days after flower opening.
4. Discussion The use of small floral units, or indeed floral parts, offers many advantages for postharvest studies relative to whole cut inflorescences since it is possible to ensure that only flowers of comparative ages are included. Moreover, a greater number of replicates can be maintained under controlled environmental conditions. Several authors have previously advocated the use of isolated petals (Garrod and Harris, 1978; Wulster et al. 1982a,b; Woodson et al., 1985; Sacalis, 1986), and even petal segments (Kende and Baumgartner, 1974) have been shown to behave in a similar way to that of the intact flowers. In the present study the vase-life of isolated cymes was not statistically different from that of cymes remaining on cut inflorescences although the vase-life of both was
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less than the longevity of flowers on growing plants. It is thus reasonable to anticipate that the maximum vase-life extension that could be obtained with cut Alstroemeria flowers is probably no more than four days, i.e. equal to those on the growing plant, when held under similar environmental conditions. Flower weight continued to increase after flower opening in flowers remaining on the plant, thus individual flower fresh and dry weight was reduced in both cymes and inflorescences; if flower growth were to be maintained in cut flowers there is also potential to improve the quality of cut Alstroemeria flowers. Vase-life differed slightly depending upon time of year, for example, the first tepals abscised from the untreated cymes (Fig. 3) approximately 10.4 days after harvest or 12.1 days for cut stems compared with 10.6 and 11.4 days for the flowers used to collect data for Table 1. This difference is, most likely, due to variations in the growing conditions at different times of the year since stems produced in early spring and in the autumn were thicker, had more terminal cyme-like branches and possessed the longest vase-life compared with flowers produced at other times of the year. Ethylene production from isolated Alstroemeria flowers was undetectable by gas chromatography (data not shown). However, exogenous application of either CEPA or ACC accelerated petal abscission. Indeed acceleration of petal abscission was induced by as little as 340 nM CEPA, higher concentrations causing petals to abscise even earlier, in some cases before the flowers were properly open, suggesting that Alstroemeria are highly ethylene-sensitive. The ability to respond to ethylene possibly also explains why, in Alstroemeria, treatment with STS can extend the time to tepal abscission in this and other varieties (data not shown) since STS will inhibit the effects of exogenous ethylene. In the present study a 3 h pre-treatment completely overcame the effect of subsequent treatment with 340 mM CEPA. As with many other species (Serek et al., 1994; Eason et al., 1997; Ichimura, 1998), provision of a carbohydrate source (sucrose) increased the vaselife, weight and colour of detached cymes and inflorescences. However, removal of the developing buds was even more effective; in isolated cymes
the growth of the remaining flower was enhanced such that six days after flower opening the flower fresh weight was approximately 80% greater than when harvested compared with only a 20% increase in the untrimmed control flowers. The effect on flowers on cut inflorescences was even greater as the flowers remaining after trimming, 6 days after opening, were more than double their weight at the time of harvest. Following other treatments (STS and/or sucrose) the fresh weight of flowers on cut stems was about 80% greater than when harvested. Combining STS and sucrose treatments did not increase vase-life or flower weight above that following either treatment separately, in this respect Alstroemeria flowers are similar to Gladiolus (Serek et al., 1994). In comparison, the weight gain in treated, but untrimmed, isolated cymes varied between 30 and 60%, considerably lower than the increase seen in flowers remaining attached to cut stems. The failure of cut flowers to develop as well when the younger buds remain suggests that there is internal competition for a limited supply of nutrients. Both STS and sucrose only partially overcame this, presumably by different means, although the effects of the two treatments are not synergistic. Despite the differences in size, the vase-life of isolated cymes was not significantly reduced relative to that of cymes on cut inflorescence stems. In Gladiolus it is evident that material is transported from senescing to developing florets since removal of the lowermost open flowers on cut flower spikes reduces the size of the upper flowers when they open (Waithaka et al., 2001). Export from flowers has been demonstrated in several other species too (Nichols and Ho, 1975a,b; Yamane et al., 1993; Bieleski, 1995). Although higher concentrations of sucrose did further increase the vase-life of Alstroemeria flowers, such solutions also caused accelerated chlorophyll loss in the bracts. Addition of sucrose to cut Narcissus flowers has been shown to be ineffectual at delaying leaf yellowing (Ichimura and Goto, 2002) but, as in the present study, sucrose usually extends floral life in most, but not all species (Ichimura, 1998; Redman et al., 2002). In Alstroemeria it may be possible to combine the
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beneficial effects of higher sucrose concentrations with other treatments to fully exploit the sucroseinduced extension in floral longevity without inducing leaf yellowing. However, there is a dilemma here since the current data relate only to the first flower on each flowering cyme. If conditions were perfect then most flowering shoots (cymes) could produce a succession of flowers as they do when growing on the plant, thus increasing the vase-life of the inflorescence as a whole. However, when the first flower senesces the overall attractiveness of the inflorescence is reduced. In conclusion it appears that whilst flowers of Alstroemeria may produce very low amounts of ethylene (undetectable in the present study using GC) they are sensitive to exogenous ethylene and this can be overcome by a pre-treatment with STS. Whilst STS and 1% sucrose delay the time to tepal abscission and enhance flower growth, the effects of both of these treatments are less than the effect of removing the small, young buds found in the axil of each flower. Similarly the remaining flower achieves a greater size and better colouration when the young axillaries are removed, but once removed there is no possibility of extending the vaselife of the inflorescence beyond that of the initial flower.
Acknowledgements One of us (U. Chanasut) was funded by a scholarship from the Thai Government, whilst two of us (C. Wagstaff and M. Leverentz) received funding from MAFF (DEFRA). This funding is gratefully acknowledged.
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van Doorn, W.G., Hibma, J., de Wit, J., 1992. Effect of exogenous hormones on leaf yellowing in cut flowering branches of Alstroemeria pelegrina L. Plant Growth Regul. 11, 445 /448. Veen, H., 1979. Effects of silver on ethylene synthesis and action in cut carnations. Planta 145, 467 /470. Wagstaff, C., Leverentz, M.K., Griffiths, G., Thomas, B., Chanasut, U., Stead, A.D., Rogers, H.J., 2002. Protein degradation during senescence of Alstroemeria petals. J. Exp. Bot. 53, 233 /240. Waithaka, K., Dodge, L.L., Reid, M.S., 2001. Carbohydrate traffic during opening of gladiolus florets. J. Hort. Sci. Biotechnol. 76, 120 /124. Woltering, E.J., van Doorn, W.G., 1988. Regulation of ethylene in senescence of petals */morphological and taxonomic relationships. J. Exp. Bot. 39, 1605 /1616.
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Increasing flower longevity in Alstroemeria U. Chanasut a,1, H.J. Rogers b, M.K. Leverentz c,2, G. Griffiths c, B. Thomas c, C. Wagstaff b, A.D. Stead a,* b
a School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK Cardiff School of BioSciences, Main Building, University of Cardiff, PO Box 915, Cardiff CF10 3TL, UK c HRI, Wellsbourne, Warwick CV35 9EF, UK
Received 21 October 2002; accepted 7 March 2003
Abstract The vase-life of Alstroemeria (cv. Rebecca) flowers is terminated when the tepals abscise. Abscission was accelerated by both chloroethylphosphonic acid (CEPA) and 1-aminocyclopropane-1-carboxylic acid (ACC). Petals abscised 24 h earlier compared with controls, when isolated cymes were placed in 340 nM CEPA, and earlier still when higher concentrations were used. This suggests that flowers of this Alstroemeria cultivar are very ethylene sensitive. Treatment with silver thiosulphate (STS) overcame the effects of exposure to CEPA and delayed perianth abscission of untreated isolated flowers by 3 /4 days. The inclusion of 1% sucrose in the vase solution also extended longevity but not by as much as STS treatment; combined STS and sucrose treatments did not increase longevity beyond that of either treatment alone. However, removal of the young buds from the axil of the first flower was the most effective treatment to extend vase-life and encouraged the growth and development of the remaining flower. Flowers on cut inflorescences from which young axillary buds were trimmed more than doubled in fresh weight 6 days after flower opening compared with an increase of only 70 /80% in those untreated or treated with STS and/or sucrose. Growth was less in isolated cymes but followed a similar pattern. The effect of STS and/or sucrose treatment was synergistic with the trimming treatment and thus the vase-life of trimmed, STS and sucrose-treated flowers was over 7 days longer than that for untreated controls. # 2003 Elsevier B.V. All rights reserved. Keywords: Alstroemeria ; Vase-life; Ethylene; Silver; Flower removal
1. Introduction * Corresponding author. Tel.: /44-1784-44-3761; fax: /441784-47-0756. E-mail address: [email protected] (A.D. Stead). 1 Present address: Biology Department, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. 2 Present address: Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Wilmslow Road, Manchester M20 4BX, UK.
Several authors have reported that leaf yellowing is one of the first indicators of the deterioration of flowering Alstroemeria stems. Moreover, leaf yellowing occurs quickly if, as is often the case, cut stems are held or transported in the dark (Dai and Paull, 1991; Hicklenton, 1991; van Doorn et al., 1992). Postharvest treatments to delay leaf yellow-
0925-5214/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-5214(03)00048-6
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ing have, therefore, been suggested. These include pre-treatment of cut stems with gibberellins with or without other growth regulators (Hicklenton, 1991; van Doorn et al., 1992; Jordi et al., 1993, 1994) or with chemicals that have cytokinin-like activity (Ferrante et al., 2002). These studies have not reported the effects on floral longevity and although Nowak and Rudnicki (1990) reported that the use of silver thiosulphate (STS) was recommended for Alstroemeria it is not clear whether this relates to improving the longevity of the flowers or to delaying leaf senescence. The use of STS is, of course, a common practice for extending the flower longevity of ethylene-sensitive species (Veen, 1979), but the literature suggests that flowers of Alstroemeria are only weakly sensitive to ethylene (Woltering and van Doorn, 1988). Collier (1997) reported the changes in several biochemical constituents during Alstroemeria petal development and flower senescence but did not consider floral ethylene production, thus the importance of ethylene in the control of flower longevity in Alstroemeria has not been fully elucidated. However, the lack of recommendations for the use of either STS or 1-methylcyclopropane (1-MCP), to prolong flower longevity suggests that ethylene is not considered an important factor in regulating the vase-life of this species. Floral preservatives usually include a biocide and a carbohydrate supply since, once detached from the plant and held under relative low light intensities, flowering stems have little opportunity for photosynthesis. Apart from normal respiratory requirements for carbohydrates, the development of the ovary and the development of axillary flowering shoots, as occur in Alstroemeria , represent further sinks. Certainly it has been shown in several species that translocation of metabolites from the senescing petals occurs and that these may contribute to the growth of the ovary (Nichols and Ho, 1975a,b) or developing flowers (Waithaka et al., 2001). However, the extent of such mobilisation may depend upon whether the petals abscise with minimal loss of turgor or whether they wilt prior to abscission (Stead and van Doorn, 1994). This paper examines the effect of removing the axillary buds on the development and longevity of
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the single remaining flower and investigates the sensitivity of Alstroemeria cv. Rebecca flowers to applied ethylene. The benefits of three postharvest treatments (STS pulse; continuous sucrose; removal of young buds), used individually or in combination, on floral longevity is discussed.
2. Material and methods 2.1. Plant material Flowers of Alstroemeria cv. Rebecca were harvested from Oak Tree Nurseries, Virginia Water, UK at a stage just after the outer sepals separated (Stage 0, Stead et al., 2003), thus showing good sepal colour development, and thereafter were maintained as described by Wagstaff et al. (2002). A minimum of ten individual cymes was treated for each experiment and each experiment repeated at least twice. Data collected were either for flower longevity, where longevity was defined as being terminated when at least one tepal had abscised; alternatively the percentage abscission of tepals was recorded at least once daily. All chemicals were from Sigma (Poole, Dorset) unless otherwise stated. 2.2. Comparison of the vase-life of cymes and stems The development and longevity of individual cyme flowers was compared with that of cyme flowers remaining attached to cut flowering stems (recut to 50 cm length) and to flowers remaining on growing plants. For this comparison all cut flower material was maintained alongside the growing plants in the greenhouse to ensure identical environmental conditions. 2.3. Effect of CEPA or ACC on vase-life Cymes, prepared immediately after harvest (Stage 0) were placed individually in solutions of chloroethylphosphonic acid (CEPA) (34 nM /3.4 mM; equivalent to 5 ppb /500 ppm) or 1-aminocylcopropane-1-carboxylic acid (ACC) (0.1, 1.0, 10.0 mM) to investigate if ethylene, released from either CEPA or ACC, influenced flower longevity.
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2.4. Effect of STS on vase-life Once isolated, individual cymes were stood in freshly prepared 2 mM STS (Veen, 1979). Cymes were then removed after 1, 3, 6 or 24 h and placed in DI water. The flowers were examined at least once daily to determine flower longevity. Cut stems were treated similarly for comparison. 2.5. Effect of applied sugar on vase-life Isolated cymes were placed, continuously, in either 0.5, 1.0, 2.0 or 5.0% sucrose and the flowers were examined at least once daily to determine flower longevity. 2.6. Effects of combined STS/sugar with or without trimming on vase-life and floral appearance The effect of removing all floral buds, with the exception of the largest bud, on each cyme was investigated since the development of the younger buds represents a significant sink for metabolites. This trimming treatment was investigated in combination with STS pre-treatment and/or holding flowers in 1% sucrose. Flower longevity was determined for both isolated cymes and cut inflorescence stems.
3. Results
petals of intact plants persisted for more than 12 days after flower opening, whereas those of cut flowers lasted only 8/9 days, with the isolated cymes lasting only slightly less than flowers on cut stems (Table 1). In subsequent experiments, however, vase-life differed slightly. For example, the first tepals abscised from the untreated cymes used as controls in Fig. 3 approximately 10.4 days after harvest or 12.1 days for cut stems compared with 10.6 and 11.4 days for the flowers used to collect data for Table 1. The longevity of flowers remaining on the plant was approximately 4 days longer than cut flowers and they were much larger and had a greater weight (Fig. 1a and b), and were more deeply pigmented (data not shown). The dry weight of flowers remaining on the plant continued to increase for several days after complete flower opening. In contrast, the dry weight of flowers on cut stems remained almost unchanged for about 6/8 days after opening but that of the isolated cymes declined from the time of harvesting (i.e. before flower opening). 3.2. Effect of CEPA or ACC on vase-life Keeping isolated cymes in 34 nM CEPA had no significant effect on petal abscission, however, greater concentrations of CEPA accelerated petal abscission. With 340 nM the time for 50% of all petals to drop was approximately 24 h earlier than
3.1. Comparison of the vase-life of cymes and stems When cv. Rebecca flowers are harvested at a commercial stage the buds are swollen and the sepals coloured but not separated, and, in the present study, it was about 2.5 days before the flowers were fully open. This was the same for isolated cymes, cymes on detached flowering stems and for flowers remaining attached to the plant. The total vase-life of flowers of this variety was determined by petal drop (abscission) rather than leaf yellowing as occurs in certain other Alstroemeria varieties. However, they were differences in the time between flower opening and petal abscission depending on whether isolated cymes, cut stems or intact, growing plants were studied. The
Table 1 Flower longevity for flowers held either as isolated cymes, cut inflorescence stems or remaining intact on the plant Vase-life (days) Type of flower Cyme
Cut stem
Intact plant
Harvest0/opening 2.59/0.2 2.49/0.2 2.69/0.1 Fully open0/abscission 8.19/0.3 9.09/0.2 12.49/0.1 Total flower or vase-life 10.69/0.4a 11.49/0.3a 15.09/0.1b Flowers were harvested at a normal commercial stage just prior to the sepals parting. Values are the means (9/S.E.) of at least 15 flowers, values for total flower or vase-life, followed by different letters are significantly different from one another at the 95% level (Tukey’s test).
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Fig. 1. Fresh weight (a) and dry weight (b) of flowers attached to cymes (j), inflorescences (') and intact plants (m) (n/30).
for the controls, whilst at 3.4 mM the time difference was approximately 48 h, and at 34 mM the difference was approximately 96 h (Fig. 2a). Higher concentrations of CEPA not only accelerated petal abscission still further but prevented the normal development of the flower such that those that opened were small with paper-like petals (data not shown) reminiscent of the opening of the axillary bud of the control flowers. Application of concentrations greater than 0.1 mM ACC, the immediate precursor of ethylene in plant tissues, similarly reduced the time to 50% petal drop (Fig. 2b), with 1.0 mM reducing the time to abscission by more than 96 h. Such sensitivity to CEPA or ACC suggests that this cultivar is very sensitive to ethylene.
Fig. 2. (a) Effects of CEPA on % tepal abscission (n/150 tepals); (b) effect of ACC (' 10 mM; " 1 mM; I 0.1 mM) on the time to tepal abscission from isolated single cyme flowers (n/120 tepals).
3.3. Effect of STS on vase-life A 1 or 3 h pre-treatment with 2 mM STS increased the time to tepal abscission relative to water-treated controls (Fig. 3). A 6-h pretreatment similarly increased longevity but caused blackening of the bracts and was thus toxic. Longer treatments with STS not only caused discolouration of the bracts but also failed to increase longevity beyond that of the controls.
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3.4. Effect of applied sugar on vase-life Concentrations of sucrose in excess of 0.5% increased floral longevity (Table 2), with the greatest increase being with 5% sucrose. However, bract yellowing occurred within 5 days when flowers were treated with 5% sucrose, and similar, but less marked, damage was observed when flowers were held in 2% sucrose. Therefore, the maximum strength sucrose that could be used without inducing yellowing of the bracts was 1%. Fig. 3. Effect of pulsing with 2 mM STS on the subsequent time to abscission of the first tepal from cyme flowers (n/209/S.E.) or flowers on cut inflorescences (n/209/S.E.).
Since 3 h was not detrimental, further studies, using combinations of treatments, used a 3 h pretreatment to ensure that sufficient STS was taken up by the isolated cymes. For intact inflorescence stems a shorter pre-treatment (1 h) was optimal (Fig. 3), probably because of the greater transpiration from cut inflorescences compared with single cymes. A 3 h treatment for cymes completely reversed the deleterious effects of 340 mM CEPA (Fig. 4), both when 340 mM CEPA was applied as a 24 h treatment following the STS pulse and when applied continuously.
3.5. Combined STS/sugar with or without trimming Combining an STS pre-treatment with the addition of 1% sucrose in the vase solution did not significantly alter the vase-life (as determined by tepal abscission) of either isolated cymes or cut inflorescence stems relative to those only treated with STS (Table 3). Removing unopened buds from the individual cyme branches prolonged the vase-life of the remaining flowers of cyme branches and inflorescence stems. The untrimmed and untreated cyme branches or inflorescence stems (as the control treatments) kept in the constant temperature room had a vase-life of about 10.1 and 11.8 days, respectively. The results of trimming treatment alone improved the vase-life of cyme flowers by about 4.3 to 14.4 days and also extended the vase-life of inflorescence flowers by about 4.8 to 16.6 days (Table 3). The combination of trimming and chemical treatments had a greater effect on the longevity of both cyme and inflorescence flowers compared with those treated only with chemicals. For example, the flowers from untrimmed and non STS-treated cyme branches lasted about 10.1 days Table 2 The effect of applying sucrose on the time to abscission of first tepal for isolated Alstroemeria cymes (n/209/S.E.)
Fig. 4. The reversal of the effect of 340 mM CEPA (applied for 24 h or continuously) by a 3 h pre-treatment with 2 mM STS (n/159/S.E.).
Sucrose conc. (%)
Time to abscission (days)9/S.E.
0 0.5 1.0 2.0 5.0
10.49/0.32 10.99/0.53 11.29/0.55 12.09/0.51 12.79/0.15
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Table 3 Effect of sucrose, STS pre-treatment and combined STS and sucrose treatment on the vase-life of trimmed or untrimmed cyme and inflorescence Alstroemeria flowers (n /209/S.E.) Treatment
Vase-life (days) Cyme flowers
DI water 1% Sucrose STS/DI water STS/1% Sucrose
Inflorescence flowers
Untrimmed
Trimmed
Untrimmed
Trimmed
10.19/0.4a 13.09/0.1b 14.89/0.5c 15.29/0.4c
14.49/0.2bc 15.69/0.2cd 17.09/0.3d 17.89/0.4d
11.89/0.4ab 13.69/0.2b 16.69/0.2c 15.09/0.3c
16.69/0.2cd 17.69/0.2d 19.89/0.4e 17.69/0.2d
Different superscript letters denote significant differences at the 95% level (Tukey’s test) in vase-life between treatments.
in DI water, but lasted almost seven days longer when trimmed of unopened buds, pre-treated with STS and held in DI water or 1% sucrose. The trimmed inflorescence flowers pre-treated with STS and kept in DI water had the longest vaselife compared with the other treatments. The treatments also enhanced floral weight (Table 4) and improved the visual appearance of the flowers (Fig. 5). Regardless of whether cymes or inflorescences were studied the % increase in flower weight was greatest when the axillary buds were trimmed off. Indeed in the case of the cut inflorescences, trimming resulted in at least a doubling of the flower fresh weight.
Table 4 The % increase in flower fresh weight 6 days after opening relative to that at the time of harvest (2 days before being fully open) for isolated cyme flowers and flowers on cut inflorescence stems treated with STS, sucrose and trimming or combinations thereof Treatment
Controls STS STS/trimming 1% sucrose 1% sucrose/trimming STS/1% sucrose STS/1% sucrose/trimming
% fwt. change Cymes
Inflorescences
20.6 58.8 89.0 36.8 73.5 50.0 79.4
75.0 77.2 125.0 89.0 105.9 75.0 127.9
Fig. 5. The appearance of untreated control flowers on cymes (left side) compared with that of flowers in which the axillary buds were removed, pre-treated with STS and placed in 1% sucrose (right side). The photograph was taken six days after flower opening.
4. Discussion The use of small floral units, or indeed floral parts, offers many advantages for postharvest studies relative to whole cut inflorescences since it is possible to ensure that only flowers of comparative ages are included. Moreover, a greater number of replicates can be maintained under controlled environmental conditions. Several authors have previously advocated the use of isolated petals (Garrod and Harris, 1978; Wulster et al. 1982a,b; Woodson et al., 1985; Sacalis, 1986), and even petal segments (Kende and Baumgartner, 1974) have been shown to behave in a similar way to that of the intact flowers. In the present study the vase-life of isolated cymes was not statistically different from that of cymes remaining on cut inflorescences although the vase-life of both was
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less than the longevity of flowers on growing plants. It is thus reasonable to anticipate that the maximum vase-life extension that could be obtained with cut Alstroemeria flowers is probably no more than four days, i.e. equal to those on the growing plant, when held under similar environmental conditions. Flower weight continued to increase after flower opening in flowers remaining on the plant, thus individual flower fresh and dry weight was reduced in both cymes and inflorescences; if flower growth were to be maintained in cut flowers there is also potential to improve the quality of cut Alstroemeria flowers. Vase-life differed slightly depending upon time of year, for example, the first tepals abscised from the untreated cymes (Fig. 3) approximately 10.4 days after harvest or 12.1 days for cut stems compared with 10.6 and 11.4 days for the flowers used to collect data for Table 1. This difference is, most likely, due to variations in the growing conditions at different times of the year since stems produced in early spring and in the autumn were thicker, had more terminal cyme-like branches and possessed the longest vase-life compared with flowers produced at other times of the year. Ethylene production from isolated Alstroemeria flowers was undetectable by gas chromatography (data not shown). However, exogenous application of either CEPA or ACC accelerated petal abscission. Indeed acceleration of petal abscission was induced by as little as 340 nM CEPA, higher concentrations causing petals to abscise even earlier, in some cases before the flowers were properly open, suggesting that Alstroemeria are highly ethylene-sensitive. The ability to respond to ethylene possibly also explains why, in Alstroemeria, treatment with STS can extend the time to tepal abscission in this and other varieties (data not shown) since STS will inhibit the effects of exogenous ethylene. In the present study a 3 h pre-treatment completely overcame the effect of subsequent treatment with 340 mM CEPA. As with many other species (Serek et al., 1994; Eason et al., 1997; Ichimura, 1998), provision of a carbohydrate source (sucrose) increased the vaselife, weight and colour of detached cymes and inflorescences. However, removal of the developing buds was even more effective; in isolated cymes
the growth of the remaining flower was enhanced such that six days after flower opening the flower fresh weight was approximately 80% greater than when harvested compared with only a 20% increase in the untrimmed control flowers. The effect on flowers on cut inflorescences was even greater as the flowers remaining after trimming, 6 days after opening, were more than double their weight at the time of harvest. Following other treatments (STS and/or sucrose) the fresh weight of flowers on cut stems was about 80% greater than when harvested. Combining STS and sucrose treatments did not increase vase-life or flower weight above that following either treatment separately, in this respect Alstroemeria flowers are similar to Gladiolus (Serek et al., 1994). In comparison, the weight gain in treated, but untrimmed, isolated cymes varied between 30 and 60%, considerably lower than the increase seen in flowers remaining attached to cut stems. The failure of cut flowers to develop as well when the younger buds remain suggests that there is internal competition for a limited supply of nutrients. Both STS and sucrose only partially overcame this, presumably by different means, although the effects of the two treatments are not synergistic. Despite the differences in size, the vase-life of isolated cymes was not significantly reduced relative to that of cymes on cut inflorescence stems. In Gladiolus it is evident that material is transported from senescing to developing florets since removal of the lowermost open flowers on cut flower spikes reduces the size of the upper flowers when they open (Waithaka et al., 2001). Export from flowers has been demonstrated in several other species too (Nichols and Ho, 1975a,b; Yamane et al., 1993; Bieleski, 1995). Although higher concentrations of sucrose did further increase the vase-life of Alstroemeria flowers, such solutions also caused accelerated chlorophyll loss in the bracts. Addition of sucrose to cut Narcissus flowers has been shown to be ineffectual at delaying leaf yellowing (Ichimura and Goto, 2002) but, as in the present study, sucrose usually extends floral life in most, but not all species (Ichimura, 1998; Redman et al., 2002). In Alstroemeria it may be possible to combine the
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beneficial effects of higher sucrose concentrations with other treatments to fully exploit the sucroseinduced extension in floral longevity without inducing leaf yellowing. However, there is a dilemma here since the current data relate only to the first flower on each flowering cyme. If conditions were perfect then most flowering shoots (cymes) could produce a succession of flowers as they do when growing on the plant, thus increasing the vase-life of the inflorescence as a whole. However, when the first flower senesces the overall attractiveness of the inflorescence is reduced. In conclusion it appears that whilst flowers of Alstroemeria may produce very low amounts of ethylene (undetectable in the present study using GC) they are sensitive to exogenous ethylene and this can be overcome by a pre-treatment with STS. Whilst STS and 1% sucrose delay the time to tepal abscission and enhance flower growth, the effects of both of these treatments are less than the effect of removing the small, young buds found in the axil of each flower. Similarly the remaining flower achieves a greater size and better colouration when the young axillaries are removed, but once removed there is no possibility of extending the vaselife of the inflorescence beyond that of the initial flower.
Acknowledgements One of us (U. Chanasut) was funded by a scholarship from the Thai Government, whilst two of us (C. Wagstaff and M. Leverentz) received funding from MAFF (DEFRA). This funding is gratefully acknowledged.
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