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Changes in abscisic acid, phenols and indoleacetic acid in bulbs of tuberose (Polianthes tuberosa L.) during dormancy and sprouting
SCIEWTIA HORTICULTuRlE Scientia Horticulturae63 ( 1995) 77-82
Changes in abscisic acid, phenols and indoleacetic acid in bulbs of tuberose (Polianthes tuberosa L.) during dormancy and sprouting PK. Nagar Plant Physiology Laboratory, Division of Biotechnology, CSIR Complex, Palampur 176061, India
Accepted5 January 1995
Abstract A high level of free abscisic acid (ABA) was detected in tuberose (Pofiurrthes tuberosa L.) bulbs during their dormant period. With the release of dormancy, the level decreased, suggesting that ABA is involved in the induction and maintenance of dormancy in bulbs. A gradual increase of bound ABA was observed during release of rest periods. Acidic and bound phenols vary with the dormant phases. The levels of indoleacetic acid (IAA) remained low during the early stages of bulb sprouting but increased rapidly thereafter. Changes in ABA, phenols and IAA levels are discussed in relation to the period of dormancy and immediately following its release in tuberose bulbs. Keywords:
Dormancy;Abscisic acid; lndoleaceticacid; Phenols;Tuberose;Polianthus tuberosa L.
1. Introduction Dormancy has been defined as a temporary suspension of external growth occurring under conditions normally favourable for growth (Juntilla, 1988). This period of growth suppression is viewed as a mechanism for species to survive adverse climatic conditions. The regulation of dormancy has attracted considerable interest owing to its basic and applied importance. Fluctuations in growth promoters and inhibitors are generally associated with the control of dormancy (Wareing, 1977). Milborrow ( 1967) regarded abscisic acid (ABA) as a main component of p inhibitor. However, this is not the only inhibiting substance as several coumarins and phenolics have also been detected during dormancy in various tissues (Hamilton and Carpentor, 1976; Rodriguez and Tames, 1986). However, the role of ABA in storage organ formation is still not clear (Powell, 1987). Among ornamental bulbous plants valued for their beauty and fragrance of their flowers, the tuberose (Polianthes tuberosa L.) occupies a very selective and special position. MoreElsevier Science B.V. SSDIO304-4238(95)00773-3
78
P. K. Nagar /Scientia Horticulturae 63 (1995) 77-82
over, the tuberose flower is a very good source of essential oils (Hussain, 1986) that can be used in the production of various perfumes and cosmetics. The tuberose bulb remains in a period of rest for about 3 months in places where the temperature is low (4-5’C) and an early planting is desirable for early crop. Pre-treatment of tuberose bulbs with gibberellic acid (GA,) had no effect on the breaking of dormancy and subsequent sprouting (Pathak et al., 1980). The mechanisms which control dormancy in the tuberose bulb have not yet been elucidated. The purpose of the present work was to measure the level of ABA (free and bound) and total phenols (acidic and residual) during dormancy and levels of indoleacetic acid (IAA) during bulb sprouting in an attempt to understand whether these levels or the relationships between them could be involved in dormancy control in the tuberose bulb.
2. Materials and methods Tuberose bulbs grown on the Institute Floriculture farm were used. Freshly harvested (mid-November) bulbs ( 18-20 g fresh weight (FW) ) were stored at room temperature ( lO-15°C). From these, three bulbs were randomly chosen at 15 day intervals and used for determination of ABA and phenols. The second batch of bulbs was planted in pots 60 days after harvest and allowed to germinate at 15 f 2°C and three sprouted bulbs were chosen at random for IAA determination up to 7 days after sprouting at 1 day intervals. Each sample of whole dormant bulbs (10 g FW) was homogenised with chilled 80% methanol (20 ml g-i) containing butylated hydroxytoluene (BHT) at 100 mg I-‘. The homogenised material was kept in the dark at 4°C for 24 h, filtered and the solid residue reextracted with five volumes of chilled 80% methanol. The resulting aqueous solution was frozen at - 2O”C, thawed and centrifuged at 10 000 rev min- ’ for 40 min at 5°C to remove suspended materials. The supernatant was dried in vacua, and taken in 0.1 M potassium phosphate buffer (pH 8.0) and applied to a PVP column. The column (20 cmX 1.5 cm) was eluted with the buffer (pH 8.0), eluate was adjusted to pH 2.5 with 1 N HCl and partitioned four times against peroxide-free diethyl ether containing BHT ( 100 mg 1-l). The combined organic phases were evaporated to dryness, redissolved in methanol and used for free ABA estimation. The remaining aqueous fraction was hydrolysed at pH 11.0 for 1 h at 60°C. The hydrolysate was adjusted to pH 2.5 with 1 N HCl and partitioned four times against diethyl ether containing BHT. The combined ether phases were evaporated in vacua and taken up in methanol for estimation of bound ABA. Each sample of whole sprouted bulbs was homogenised in 80% chilled methanol ( 15 ml g - ’ FW) containing BHT and kept overnight at 4°C. It was centrifuged at 10 000 rev min - ’ for 20 min at 6°C and supernatant was concentrated in vacua at 30°C. The aqueous phase was purified by PVP column as above. The eluate was adjusted to pH 8.0 and neutral compounds were extracted five times with peroxide-free diethyl ether. The aqueous fraction was acidified to pH 3.0 and partitioned three times against ether. The ether phases (acidic indole fraction containing IAA) were combined, dried over anhydrous Na2S04, evaporated to dryness in vacua and finally taken in methanol for high performance liquid chromatography (HPLC) analysis.
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
79
Reverse phase HPLC method on a Kontron system 600 (Kontron Institute Ltd., Switzerland) for ABA and IAA isolation (Horgan, 198 1) was according to Ciha et al. ( 1977). The partially purified methanolic extracts were filtered through 0.45 pm millipore filter and injected onto 20 ,ul injector loop in a Lichrosorb RP 18 ( 10 pm) column (250 mm X4.6 mm i.d.) protected by a guard column. The elution was carried out with methanol:water (HPLC grade) mixture with a 15 min gradient of 30-70% methanol, followed by 5 min gradient of 70-100% and finally with 100% gradient for 15 min at a flow rate of 1 ml min-‘. Solvents were filtered through 0.45 pm pore size membranes (Whatman) and degassed before use. Column eluants were passed through a UV detector (Kontron 430) at 254 nm and ABA and IAA were measured by reference to external standard of ( f ) ABA and IAA (Sigma Chemical Co.). For phenol estimations, the bulb tissue ( 1 g) was homogenised with 80% cold methanol ( 1: 10 w/v) containing 0.3 N HCl and kept at 4°C for 12 h. The homogenate was centrifuged at 10 000 rev min- ’ for 15 min at 5°C. The supematant was collected and the solid residue re-extracted three times with the solvent as above. The extracts were pooled, evaporated in vacua at 30°C and the residue dissolved in 5 ml of water. The total acidic phenol content was determined following Swain and Hills (1959) using Folin reagent and saturated Na,C03 solution by measuring colour intensity at 630 nm. The residue remaining after methanol extraction was hydrolysed by boiling for 4 h in 2% NaOH. After cooling, the hydrolysate was adjusted to pH 3.0 and extracted with diethyl ether. The ether layer contained the structural phenols and was named residual fraction. This was analysed as for acidic phenol.
3. Results and discussion The changes in levels of free and bound ABA during the dormant period of tuberose bulb are shown in Fig. 1. Initially the levels of free ABA did not show any appreciable increase up to 30 days after harvest but increased thereafter, reaching its peak (4.16 pg gg ’ FW) at
6
”
15
30
60 45 Days After Harvest
75
90
Fig. 1. Changes in the levels of free and bound ABA in tuberose bulbs during dormancy. each sampling (n = 3) is given as a vertical bar.
The standard error for
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
80
Abacrbancalg DwtbOidual)
0.12
Re*leuAl SIwouting
- 0.1
I
0
IS
30
46
80
Fig. 2. Changes in the levels of phenolic compounds each sampling (n = 3) is given as a vertical bar.
90
76
0
in tuberose bulbs during dormancy.
The standard error for
60 days after harvest followed by a rapid decline in subsequent periods. An increase in activity of bound ABA was only visible after 45 day onwards and its level was generally lower than that of free ABA during dormancy. However, at the time of bulb sprouting (90 days) its level was higher than that of free ABA. The level of acidic phenols in the bulb increased up to 60 days after harvest when it reached its peak, and declined thereafter (Fig. 2). However, during this period, the residual phenol fraction showed no significant increase but increased appreciably thereafter. The IAA content increased at a very slow rate up to 3 days after sprouting (Fig. 3) but increased rapidly thereafter, reaching 4.12 pg gg ’ FW 7 days after sprouting, i.e. approximately a four-fold increase during a l-week period. In the present work a good correlation was found between free ABA level and degree of dormancy in tuberose bulbs which decreased with sprouting of bulbs. This suggests that
1
2
3 Day8
4
s
6
7
After Spmutlng
Fig. 3. Changes in the levels of IAA in tuberose bulbs during sprouting. (n = 3) is given as a vertical bar.
The standard error for each sampling
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
81
free ABA decline is a result of dormancy release. In freesia corms (Uyemura and Imanishi, 1987), a direct correlation was noticed between the level of acidic growth inhibitor (ABA) and the degree of dormancy. According to Khan ( 1975), free ABA level alone does not necessarily inhibit growth in dormant seeds and bulbs. In lily bulbs, a threshold level of endogenous ABA is required for the development of dormancy but “an additional unknown factor” may also play a major role (Kim et al., 1994). It seems that ABA may play a role in the early stages of rest in tuberose bulbs and some kind of promoting force becomes dominant during the latter stages to override the possible effects of endogenous ABA. However, as proposed (Suttle and Hulstrand, 1994), the ability of ABA to regulate meristem dormancy in tissues as diverse as seed, bulbs and tubers suggests that its role in dormancy may be more universal than was once generally acknowledged. An increase in bound ABA in the latter part of dormancy (Fig. 1) is suggestive of ABA metabolic interconversions during this period. Although the physiological role of ABA conjugation is not clear, bound ABA is assumed to be an inactive storage form, utilised as and when required, by which free ABA may be sequestered (Milborrow, 1983). The concentrations of at least acidic and residual phenols vary with rest periods (Fig. 2) and they could possibly have a role in the physiological changes of the plant. However, in agreement with Milborrow ( 1967)) ABA could be considered to be the main component of the inhibitory complex, while the phenols could be regarded as enhancing its activity. The most valid explanation for increased levels of IAA during sprouting could be that they are a consequence of intense apical activity and according to Powell (1987) there is no cause/effect relationship between auxin level and the state of dormancy release. Wood ( 1983) noticed in pecan a sharp rise in auxin levels at bud burst from the low levels in the preceding period. Bachelard and Wightman ( 1973) suggested a role for IAA as a possible primary signal for growth activation. The process leading to release of dormancy involves an interaction or balance between endogenous growth promoters and inhibitors. Likewise, the ratio between growth promoters and inhibitors and/or changes in their tissue sensitivity could also be an operative mechanism in dormancy.
Acknowledgements The author isgrateful to the Director, CSIR Complex, Palampur for the facilities necessary to carry out this study and to Anil Kumar for his help in HPLC analysis.
References Bachelard, E.P. and Wightman, F., 1973. Biochemical and physiological studies on dormancy release in tree buds. 1 Changes in degree of dormancy, respiratory activities and major cell constituents in over winter vegetative buds of Populus nigra. Can. J. Bot., 51: 2315-2326. Ciha, A.J., Breneer, M.L. and Brun, W.A., 1977. Rapid separation and quantification of abscisic acid from plant tissues using high performance liquid chromatography. Plant Physiol., 59: 821-826. Hamilton, D.F. and Carpentor, P.I., 1976. Regulation of seed dormancy in Elaeagnus angustifolia by endogenous growth substances. Can. J. Bot., 54: 1068-1073.
82
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
Horgan, R., 1981. Modem methods for plant hormone analysis. In: L. Reinhald, J.B. Harbome and T. Swain (Editors), Progress in Phytochemistry. Pergamon Press, New York, pp. 137-170. Hussain, A., 1986. Ornamental Horticulture. ICAR, New Delhi, India, 136 pp. Juntilla, 0.. 1988. To be or not to be bud dormant: some comments on the new dormancy nomenclature. Hortic. Sci., 23: 805-806. Khan, A.A., 1975. Primary, preventive and permissive roles of hormones in plant system. Bot. Rev., 4: 391420. Kim, K.S., Devalaar, E. and De Klerk, G.J., 1994. Abscisic acid controls dormancy, development and bulb formation in lily plantlets regenerated in vitro. Physiol. Plant., 90: 59-64. Milborrow, B.V., 1967. The identification of ( + ) abscisin II ( + ) dormin in plants and measurements of its concentrations. Planta, 76: 93-113. Milborrow, P.V., 1983. Pathway to and from abscisic acid. In: F.T. Addicott (Editor), Abscisic Acid. Praeger, New York, pp. 79-l 12. Pathak, S., Chaudhary, M.A. and Chaudhary, S.K., 1980. Germination and flowering in different sized bulbs of tuberose (Polianthes tuberosa L.). Indian J. Plant Physiol., 23: 47-54. Powell, L.E., 1987. Hormonal aspects of bud and seed dormancy in temperate zone woody plants. Hortic. Sci., 22: 845-850. Rodriguez, A. and Tames, R., 1986. Dormancy and seasonal changes of plant growth regulators in hazel buds. Physiol. Plant., 66: 288-292. Suttle, J.C. and Hulstrand, J.F., 1994. Role of endogenous abscisic acid in potato microtuber dormancy. Plant Physiol., 105: 891-896. Swain, T. and Hills, W.E., 1959. The phenolic constituents of Prunus domesfica. I. The quantitative analysis of phenolic constituents. J. Sci. Food Agric., 10: 63-68. Uyemura, S. and Imanishi, H., 1987. Changes in abscisic acid during dormancy in freesia corms. Plant Growth Regul., 5: 99-103. Wareing, P.F., 1977. Growth substances integration in the whole plant. In: D.H. Jennings (Editor), Integration of Activity in Higher Plants. Symposium XxX1. Society of Experimental Biology, pp. 337-365. Wood, B.W., 1983. Changes in indoleacetic acid, abscisic acid, gibberellins and cytokinins during bud break in pecan. J. Am. Sot. Hortic. Sci., 108: 333-338.
Changes in abscisic acid, phenols and indoleacetic acid in bulbs of tuberose (Polianthes tuberosa L.) during dormancy and sprouting PK. Nagar Plant Physiology Laboratory, Division of Biotechnology, CSIR Complex, Palampur 176061, India
Accepted5 January 1995
Abstract A high level of free abscisic acid (ABA) was detected in tuberose (Pofiurrthes tuberosa L.) bulbs during their dormant period. With the release of dormancy, the level decreased, suggesting that ABA is involved in the induction and maintenance of dormancy in bulbs. A gradual increase of bound ABA was observed during release of rest periods. Acidic and bound phenols vary with the dormant phases. The levels of indoleacetic acid (IAA) remained low during the early stages of bulb sprouting but increased rapidly thereafter. Changes in ABA, phenols and IAA levels are discussed in relation to the period of dormancy and immediately following its release in tuberose bulbs. Keywords:
Dormancy;Abscisic acid; lndoleaceticacid; Phenols;Tuberose;Polianthus tuberosa L.
1. Introduction Dormancy has been defined as a temporary suspension of external growth occurring under conditions normally favourable for growth (Juntilla, 1988). This period of growth suppression is viewed as a mechanism for species to survive adverse climatic conditions. The regulation of dormancy has attracted considerable interest owing to its basic and applied importance. Fluctuations in growth promoters and inhibitors are generally associated with the control of dormancy (Wareing, 1977). Milborrow ( 1967) regarded abscisic acid (ABA) as a main component of p inhibitor. However, this is not the only inhibiting substance as several coumarins and phenolics have also been detected during dormancy in various tissues (Hamilton and Carpentor, 1976; Rodriguez and Tames, 1986). However, the role of ABA in storage organ formation is still not clear (Powell, 1987). Among ornamental bulbous plants valued for their beauty and fragrance of their flowers, the tuberose (Polianthes tuberosa L.) occupies a very selective and special position. MoreElsevier Science B.V. SSDIO304-4238(95)00773-3
78
P. K. Nagar /Scientia Horticulturae 63 (1995) 77-82
over, the tuberose flower is a very good source of essential oils (Hussain, 1986) that can be used in the production of various perfumes and cosmetics. The tuberose bulb remains in a period of rest for about 3 months in places where the temperature is low (4-5’C) and an early planting is desirable for early crop. Pre-treatment of tuberose bulbs with gibberellic acid (GA,) had no effect on the breaking of dormancy and subsequent sprouting (Pathak et al., 1980). The mechanisms which control dormancy in the tuberose bulb have not yet been elucidated. The purpose of the present work was to measure the level of ABA (free and bound) and total phenols (acidic and residual) during dormancy and levels of indoleacetic acid (IAA) during bulb sprouting in an attempt to understand whether these levels or the relationships between them could be involved in dormancy control in the tuberose bulb.
2. Materials and methods Tuberose bulbs grown on the Institute Floriculture farm were used. Freshly harvested (mid-November) bulbs ( 18-20 g fresh weight (FW) ) were stored at room temperature ( lO-15°C). From these, three bulbs were randomly chosen at 15 day intervals and used for determination of ABA and phenols. The second batch of bulbs was planted in pots 60 days after harvest and allowed to germinate at 15 f 2°C and three sprouted bulbs were chosen at random for IAA determination up to 7 days after sprouting at 1 day intervals. Each sample of whole dormant bulbs (10 g FW) was homogenised with chilled 80% methanol (20 ml g-i) containing butylated hydroxytoluene (BHT) at 100 mg I-‘. The homogenised material was kept in the dark at 4°C for 24 h, filtered and the solid residue reextracted with five volumes of chilled 80% methanol. The resulting aqueous solution was frozen at - 2O”C, thawed and centrifuged at 10 000 rev min- ’ for 40 min at 5°C to remove suspended materials. The supernatant was dried in vacua, and taken in 0.1 M potassium phosphate buffer (pH 8.0) and applied to a PVP column. The column (20 cmX 1.5 cm) was eluted with the buffer (pH 8.0), eluate was adjusted to pH 2.5 with 1 N HCl and partitioned four times against peroxide-free diethyl ether containing BHT ( 100 mg 1-l). The combined organic phases were evaporated to dryness, redissolved in methanol and used for free ABA estimation. The remaining aqueous fraction was hydrolysed at pH 11.0 for 1 h at 60°C. The hydrolysate was adjusted to pH 2.5 with 1 N HCl and partitioned four times against diethyl ether containing BHT. The combined ether phases were evaporated in vacua and taken up in methanol for estimation of bound ABA. Each sample of whole sprouted bulbs was homogenised in 80% chilled methanol ( 15 ml g - ’ FW) containing BHT and kept overnight at 4°C. It was centrifuged at 10 000 rev min - ’ for 20 min at 6°C and supernatant was concentrated in vacua at 30°C. The aqueous phase was purified by PVP column as above. The eluate was adjusted to pH 8.0 and neutral compounds were extracted five times with peroxide-free diethyl ether. The aqueous fraction was acidified to pH 3.0 and partitioned three times against ether. The ether phases (acidic indole fraction containing IAA) were combined, dried over anhydrous Na2S04, evaporated to dryness in vacua and finally taken in methanol for high performance liquid chromatography (HPLC) analysis.
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
79
Reverse phase HPLC method on a Kontron system 600 (Kontron Institute Ltd., Switzerland) for ABA and IAA isolation (Horgan, 198 1) was according to Ciha et al. ( 1977). The partially purified methanolic extracts were filtered through 0.45 pm millipore filter and injected onto 20 ,ul injector loop in a Lichrosorb RP 18 ( 10 pm) column (250 mm X4.6 mm i.d.) protected by a guard column. The elution was carried out with methanol:water (HPLC grade) mixture with a 15 min gradient of 30-70% methanol, followed by 5 min gradient of 70-100% and finally with 100% gradient for 15 min at a flow rate of 1 ml min-‘. Solvents were filtered through 0.45 pm pore size membranes (Whatman) and degassed before use. Column eluants were passed through a UV detector (Kontron 430) at 254 nm and ABA and IAA were measured by reference to external standard of ( f ) ABA and IAA (Sigma Chemical Co.). For phenol estimations, the bulb tissue ( 1 g) was homogenised with 80% cold methanol ( 1: 10 w/v) containing 0.3 N HCl and kept at 4°C for 12 h. The homogenate was centrifuged at 10 000 rev min- ’ for 15 min at 5°C. The supematant was collected and the solid residue re-extracted three times with the solvent as above. The extracts were pooled, evaporated in vacua at 30°C and the residue dissolved in 5 ml of water. The total acidic phenol content was determined following Swain and Hills (1959) using Folin reagent and saturated Na,C03 solution by measuring colour intensity at 630 nm. The residue remaining after methanol extraction was hydrolysed by boiling for 4 h in 2% NaOH. After cooling, the hydrolysate was adjusted to pH 3.0 and extracted with diethyl ether. The ether layer contained the structural phenols and was named residual fraction. This was analysed as for acidic phenol.
3. Results and discussion The changes in levels of free and bound ABA during the dormant period of tuberose bulb are shown in Fig. 1. Initially the levels of free ABA did not show any appreciable increase up to 30 days after harvest but increased thereafter, reaching its peak (4.16 pg gg ’ FW) at
6
”
15
30
60 45 Days After Harvest
75
90
Fig. 1. Changes in the levels of free and bound ABA in tuberose bulbs during dormancy. each sampling (n = 3) is given as a vertical bar.
The standard error for
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
80
Abacrbancalg DwtbOidual)
0.12
Re*leuAl SIwouting
- 0.1
I
0
IS
30
46
80
Fig. 2. Changes in the levels of phenolic compounds each sampling (n = 3) is given as a vertical bar.
90
76
0
in tuberose bulbs during dormancy.
The standard error for
60 days after harvest followed by a rapid decline in subsequent periods. An increase in activity of bound ABA was only visible after 45 day onwards and its level was generally lower than that of free ABA during dormancy. However, at the time of bulb sprouting (90 days) its level was higher than that of free ABA. The level of acidic phenols in the bulb increased up to 60 days after harvest when it reached its peak, and declined thereafter (Fig. 2). However, during this period, the residual phenol fraction showed no significant increase but increased appreciably thereafter. The IAA content increased at a very slow rate up to 3 days after sprouting (Fig. 3) but increased rapidly thereafter, reaching 4.12 pg gg ’ FW 7 days after sprouting, i.e. approximately a four-fold increase during a l-week period. In the present work a good correlation was found between free ABA level and degree of dormancy in tuberose bulbs which decreased with sprouting of bulbs. This suggests that
1
2
3 Day8
4
s
6
7
After Spmutlng
Fig. 3. Changes in the levels of IAA in tuberose bulbs during sprouting. (n = 3) is given as a vertical bar.
The standard error for each sampling
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
81
free ABA decline is a result of dormancy release. In freesia corms (Uyemura and Imanishi, 1987), a direct correlation was noticed between the level of acidic growth inhibitor (ABA) and the degree of dormancy. According to Khan ( 1975), free ABA level alone does not necessarily inhibit growth in dormant seeds and bulbs. In lily bulbs, a threshold level of endogenous ABA is required for the development of dormancy but “an additional unknown factor” may also play a major role (Kim et al., 1994). It seems that ABA may play a role in the early stages of rest in tuberose bulbs and some kind of promoting force becomes dominant during the latter stages to override the possible effects of endogenous ABA. However, as proposed (Suttle and Hulstrand, 1994), the ability of ABA to regulate meristem dormancy in tissues as diverse as seed, bulbs and tubers suggests that its role in dormancy may be more universal than was once generally acknowledged. An increase in bound ABA in the latter part of dormancy (Fig. 1) is suggestive of ABA metabolic interconversions during this period. Although the physiological role of ABA conjugation is not clear, bound ABA is assumed to be an inactive storage form, utilised as and when required, by which free ABA may be sequestered (Milborrow, 1983). The concentrations of at least acidic and residual phenols vary with rest periods (Fig. 2) and they could possibly have a role in the physiological changes of the plant. However, in agreement with Milborrow ( 1967)) ABA could be considered to be the main component of the inhibitory complex, while the phenols could be regarded as enhancing its activity. The most valid explanation for increased levels of IAA during sprouting could be that they are a consequence of intense apical activity and according to Powell (1987) there is no cause/effect relationship between auxin level and the state of dormancy release. Wood ( 1983) noticed in pecan a sharp rise in auxin levels at bud burst from the low levels in the preceding period. Bachelard and Wightman ( 1973) suggested a role for IAA as a possible primary signal for growth activation. The process leading to release of dormancy involves an interaction or balance between endogenous growth promoters and inhibitors. Likewise, the ratio between growth promoters and inhibitors and/or changes in their tissue sensitivity could also be an operative mechanism in dormancy.
Acknowledgements The author isgrateful to the Director, CSIR Complex, Palampur for the facilities necessary to carry out this study and to Anil Kumar for his help in HPLC analysis.
References Bachelard, E.P. and Wightman, F., 1973. Biochemical and physiological studies on dormancy release in tree buds. 1 Changes in degree of dormancy, respiratory activities and major cell constituents in over winter vegetative buds of Populus nigra. Can. J. Bot., 51: 2315-2326. Ciha, A.J., Breneer, M.L. and Brun, W.A., 1977. Rapid separation and quantification of abscisic acid from plant tissues using high performance liquid chromatography. Plant Physiol., 59: 821-826. Hamilton, D.F. and Carpentor, P.I., 1976. Regulation of seed dormancy in Elaeagnus angustifolia by endogenous growth substances. Can. J. Bot., 54: 1068-1073.
82
P.K. Nagar /Scientia Horticulturae 63 (1995) 77-82
Horgan, R., 1981. Modem methods for plant hormone analysis. In: L. Reinhald, J.B. Harbome and T. Swain (Editors), Progress in Phytochemistry. Pergamon Press, New York, pp. 137-170. Hussain, A., 1986. Ornamental Horticulture. ICAR, New Delhi, India, 136 pp. Juntilla, 0.. 1988. To be or not to be bud dormant: some comments on the new dormancy nomenclature. Hortic. Sci., 23: 805-806. Khan, A.A., 1975. Primary, preventive and permissive roles of hormones in plant system. Bot. Rev., 4: 391420. Kim, K.S., Devalaar, E. and De Klerk, G.J., 1994. Abscisic acid controls dormancy, development and bulb formation in lily plantlets regenerated in vitro. Physiol. Plant., 90: 59-64. Milborrow, B.V., 1967. The identification of ( + ) abscisin II ( + ) dormin in plants and measurements of its concentrations. Planta, 76: 93-113. Milborrow, P.V., 1983. Pathway to and from abscisic acid. In: F.T. Addicott (Editor), Abscisic Acid. Praeger, New York, pp. 79-l 12. Pathak, S., Chaudhary, M.A. and Chaudhary, S.K., 1980. Germination and flowering in different sized bulbs of tuberose (Polianthes tuberosa L.). Indian J. Plant Physiol., 23: 47-54. Powell, L.E., 1987. Hormonal aspects of bud and seed dormancy in temperate zone woody plants. Hortic. Sci., 22: 845-850. Rodriguez, A. and Tames, R., 1986. Dormancy and seasonal changes of plant growth regulators in hazel buds. Physiol. Plant., 66: 288-292. Suttle, J.C. and Hulstrand, J.F., 1994. Role of endogenous abscisic acid in potato microtuber dormancy. Plant Physiol., 105: 891-896. Swain, T. and Hills, W.E., 1959. The phenolic constituents of Prunus domesfica. I. The quantitative analysis of phenolic constituents. J. Sci. Food Agric., 10: 63-68. Uyemura, S. and Imanishi, H., 1987. Changes in abscisic acid during dormancy in freesia corms. Plant Growth Regul., 5: 99-103. Wareing, P.F., 1977. Growth substances integration in the whole plant. In: D.H. Jennings (Editor), Integration of Activity in Higher Plants. Symposium XxX1. Society of Experimental Biology, pp. 337-365. Wood, B.W., 1983. Changes in indoleacetic acid, abscisic acid, gibberellins and cytokinins during bud break in pecan. J. Am. Sot. Hortic. Sci., 108: 333-338.