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Inhibition of Germination by Growth Retardants AMO-1618 and Ancymidol, and its Reversal by Gibberellin A3 in Amaranthus caudatus L. Seeds
J. Plant Physiol. Vol. 132. pp. 584- 587 (1988)
Inhibition of Germination by Growth Retardants AMO-1618 and Ancymidol, and its Reversal by Gibberellin A3 in Amaranthus caudatus L. Seeds JAN K~PCZYNSKII 1
2
and].
STANISLAW KNYPL
2
Department of Plant Physiology, The University of Szczecin, ul. Felczaka 3 a, PL-71412 Szczecin; and Plant Growth Substances Laboratory, The University of Lodz, ul. Banacha 12/16, PL-90 237 Lodz, Poland
Received July 15, 1987 . Accepted November 13, 1987
Summary AMO-1618 and ancymidol, inhibitors of gibberellin biosynthesis, retarded germination of Amaranthus caudatus L. seeds, ancymidol being more active than AMO-1618. Transfer of seeds to ancymidol after imbibition in water for 12 h caused inhibition of germination. Longer imbibition in water led to reduced sensitivity of seeds to subsequently applied ancymidol. The germinating capacity of seeds preincubated in ancymidol for 3 -17 h was restored markedly following transfer to water. Gibberellic acid (GA3) greatly reduced or reversed the germination inhibitory effect of either AMO-1618 or ancymidol. It is suggested that endogenous GAs are required for induction and/or stimulation of early growth of the radicle.
Key words: Amaranthus caudatus L., AMO-1618, ancymidol, gibberellin, seed germination. Abbreviations: AMO-1618, (2-isopropyl-5-methyl-4-trimethylammonium chloride)-phenyl-1-piperidine carboxylate; ancymidol, alpha-cyclopropyl-alpha-{4-methoxyphenyl)-5-pyrimidine methanol; tetcyclacis (code no. BAS 106... W): 5-(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo-5,4,1Q2.6,08.11-dodeca-3,9diene; CCC, (2-chloroethyl)trimethylammonium chloride; GA 3, gibberellic acid; paclobutrazol, (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-l-(1,2,4-triazol-l-yl)pentan-3-ol.
Introduction Plant growth retardants, such as CCC, AMO-1618, ancymidol, tetcyclacis and triazole-type compounds are known to reduce shoot growth in many higher plants Oung and Rademacher, 1983). This is mainly due to inhibition of gibberellin biosynthesis although other metabolic reactions may also be affected (Radamacher et aI., 1984). CCC and AMO1618 have been found to inhibit, in the first order, the biosynthesis of copalylpyrophosphate from geranyl-geranylpyrophosphate, and conversion of copalylpyrophosphate to ent-kaurene (Graebe and Ropers, 1978; Sembdner et aI., 1980); whereas ancymidol, tetcyclacis and triazoles suppress the oxidative reactions that lead from ent-kaurene to ent-kaurenoic acid (Coolbaugh et aI., 1978; Hedden and Graebe, 1985; Hildebrandt et aI., 1982). It has been demonstrated that © 1988 by Gustav Fischer Verlag, Stuttgart
CCC and AMO-1618 were less efficient inhibitors of shoot elongation in rice seedlings than ancymidol or tetcyclacis (Rademacher and Jung, 1981). This study was undertaken in order to obtain more detailed information about the mechanism by which AMO-1618 and ancymidol affect germination of Amaranthus caudatus L. seeds.
Material and Methods Non-dormant seeds of Amaranthus caudatus L., collected in 1982, were used. The seeds were stored at + 7°C in darkness until use in 1985. Groups of 50 seeds were placed in Petri dishes Scm in diameter, each lined with a disc of Whatman No.1 filter paper and
Inhibition of germination by growth retardants moistened with 1.5 cm 3 of distilled water (the control series) or a volume of aqueous solutions of GA 3, AMO-1618 or ancymidol, the latter ones being applied alone at different concentrations or in combinations with GA 3. In some experiments seeds were initially imbibed in water or ancymidol for different periods of time (3 -17 h), then transferred to ancymidol or water, respectively. For germination seeds were incubated at 24°C in darkness. Manipulations were done in physiologically inactive green light. The number of germinated seeds was counted after periods specified for each test. Experimental variants were repeated twice, with 3 - 5 replicates in each series. Growth regulators applied in this study were manufactured by Calbiochem (AMO-1618), Lilly Res. Ctr., Ltd. (ancymidol) and Polfa (GA3).
Results Both inhibitors of GA biosynthesis delayed or retarded seed germination in Amaranthus caudatus L. (Fig. 1). Much higher concentrations of AMO-1618 than ancymidol were required to produce a comparable degree of inhibition in germination. This suggests that ancymidol is physiologically more efficient than AMO-1618 . Germination in the control series had reached about 95 % after 2 days. Addition of GA3 alone had a slightly stimulatory effect. Simultaneous application of AMO-1618 and GA3 reduced the degree of inhibition in germination as compared with seeds treated with AMO-1618 alone (Table 1). The magnitude of the reversing effect of GA3 was dependent on concentration of AMO-1618. Similarly, the inhibition of seed germination caused by ancymidol could be reversed by GA 3, the effect being dependent on the concentration of GA3 (Fig. 2). Fig. 3 ashows the effect of transferring seeds from water to ancymidol solution after increasing periods of imbibition; Fig. 3 b represents the reverse situation, i.e. the transfer of seeds from ancymidol solution to water at three-hourly intervals. Seeds placed in water germinated well. However, the germination of seeds which were incubated in ancymidol
90
A
B~
~
585
Table 1: Reversing effect of GA3 on the inhibition in germination of Amaranthus caudatus L. seeds caused by AMO-1618. Final germination percentages, as recorded after 7d, are presented.
AMO-1618, M
o 3
X
5
X
10 - 2
Germination, percent GA 3 , M
o
10- 5
94
99 64 26
5
10- 2
or transferred to the ancymidol solution after an initital 12 h imbibition in water was almost completely inhibited. The germination of seeds imbibed for 15 or 17 h in water was also reduced upon subsequent transfer to ancymidol, although not so much as in the former variants (Fig. 3 a). In the other experiment seeds were transferred to water after 3, 6, 9, 12, 15 and 17 h incubation in ancymidol solution. The transfer to water reduced the inhibitory effect of ancymidol, the degree of the final effect being dependent on the period of exposure to the retardant (Fig. 3 b). Even after 17 h incubation in ancymidol solution, 60 % of the seeds could germinate following transfer to water (the final germination percentage was recorded after 6 d).
Discussion The observed inhibition in germination of Amaranthus caudatus L. seeds by AMO-1618 agrees with the data reported by Knypl (1969) for kale (Brassica oleracea L. var. acephala) seeds. A comparison of the physiological efficiency of the two applied inhibitors shows that ancymidol is more active than AMO-1618 (Fig. 1; compare Rademacher and Jung, 1981). The higher sensitivity of seeds and seedlings to ancymidol than to AMO-1618 is possibly associated with the sensitivity of different steps in the pathway of GA biosynthesis, since AMO-1618 blocks the formation of ent-kaurene
3
Co-!
2d
2d
o-l?
5
60
~
~~
z iex
w
~~
C> 30
<>"
0
0 AMO,M
3·10"'
10"5
ANCVMIDOL, M
3·10"5
10-4
0
20h
10-'
10-5
10-4
GA 3 , M
Fig. 1: The effects of different concentrations of AMO-1618 (A), ancymidol (B) and GA3 (C) on the germination of Amaranthus caudatus L. seeds. Id, 2d and 3d mean germination percentages after 1,2 and 3 days, respectively. Results are expressed as arithmetical means; values of S.D. did not exceed 5, 7 and 6 percent for A, Band C, respectively.
586
JAN KIlPCZYNSKI and]. STANISLAW KNYPL
10
~
o
z
eo
o ~
z
~
~ 30
C>
AN
o
24
72
96
168
72
96
TIME. h
A 10
B I-
Fig. 2: The effects of GA3 at 10 - 5 (A) or 3 x 10- 4 (B) on the inhibition of germination of Amaranthus caudatus L. seeds caused by 2x10- 4 ancymidol (AN). Maximal values of S.D. never exceed 8 %.
rf HaO
t-
whole period
3
6
9 12
15 17
HOURS BEFORE TRANSFER
(Graebe and Ropers, 1978; Sembdner et aI., 1980) whereas ancymidol blocks the formation of ent-kaurenoic acid (Coolbaugh et al., 1978). The addition of GA3 markedly counteracted the inhibition caused by AMO-1618 and ancymidol (Fig. 2). In accordance with reports for other growth retardants (Knypl, 1967 a-c and 1969; K~pczynski, 1986; K~pczynski and K~pczynska, 1988; K~pczynski et aI., 1988), which could be counteracted by gibberellins. The results support the earlier formulated idea that the presence of endogenous gibberellins is essential for the germination of Amaranthus caudatus L. seeds (K~pczynski, 1986; K~pczynski et aI., 1988). The production of endogenous gibberellins would appear to be sufficient for germination in «normal» conditions, so that the exogenous addition of GA3 (Fig. 1 c) or GA4 + 7 (K~pczynski, 1986) had only a slight effect on germination. The effect of gibberellin seems to be comparable to the effect of ethylene, another stimulator of Amaranthus caudatus L. seed germination (K~pczynski and Karssen, 1985). Results of the experiment in which seeds were initially incubated in water or ancymidol for different periods (3 -17 h), and then transferred to ancymidol or water, respectively, suggest that responsiveness (or sensitivity) to ancymidol is associated with a late activation phase during the process of germination. Stimulation of radicle
Fig. 3: Germination of Amaranthus caudatus L. seeds transferred after different periods of imbibition in water to ancymidol (AN; 3 x 1O- 4 M) [A] or vice versa [B). «Whole period» means seeds incubated for the whole duration of the experiment either in water or in the ancymidol solution. Final germination percentages, as recorded after 6d, are presented; vertical bars indicate ±S.D.
growth by exogenous gibberellin has been observed in Chenopodium album L. seeds (Karssen, 1976). Acknowledgements We express gratitude to Miss Ewa Maciejewska for skilled technical assistance. This study was supported in part by a grant CPBP 05.02.4.06.
References COOLBAUGH, R. c., S. S. HIRANO, and C. WEST: Studies on the specificity and site of action of ancymidol, a plant growth regulator. Plant Physio!. 62, 571-576 (1978). GRAEBE, J. E. and H. J. ROPERS: Gibberellins. In: D. S. LETHAM, P. B. GOODWIN, and T. J. V. HIGGINS (eds.): Phyohormones and Related Compounds: A Comprehensive Treatise, Elsevier-North Holland, Amsterdam, 1,107-303 (1978). HEDDEN, P. and J. E. GRAEBE: Inhibition of gibberellin biosynthesis by paclobutrazol in cell-free homogenates of Cucurbita maxima endosperm and Malus pumila embryos. J. Plant Growth Regu!. 4, 111-122 (1985). HILDEBRANDT, E.,J. E. GRAEBE, W. RADEMACHER, andJ.JuNG: Mode of action and biological activity of new potent plant growth retardants: BAS 106... W and triazole compounds. Abstracts 11th
Inhibition of germination by growth retardants Int. Conf. on Plant Growth Substances, Aberystwyth, Wales, p. 65 (1982). JUNG, J. and W. RADEMACHER: Plant Growth Regulating chemicals - cereal grains. In: L. G. NICKELL (ed.): Plant Growth Regulating Chemicals. CRC Press, Inc., Boca Raton, 1, 253 -271 (1983). MRSSEN, C. M.: Two sites of hormonal action during germination of Chenopodium album seeds. Physiol. Plant., 36, 264-270 (1976). KIlPCZYNSKI, J.: Ethylene-dependent action of gibberellin in seed germination of Amaranthus caudatus L. Physiol. Plant. 67, 584-587 (1986). KI;PCZYNSKI, J. and e. M. MRSSEN: Requirement for the action of endogenous ethylene during germination of non-dormant seeds of Amaranthus caudatus. Physiol. Plant. 63, 49-52 (1985). KIlPCZYNSKI, J. and E. KI;PCZYNSKA: Reversing inhibitory effect of paclobutrazol on seed germination of Amaranthus paniculatus L. by GA 3 , ethephon or ACe. Plant Growth Regul. (1988) [in press]. KIlPCZYNSKI, J., E. KIlPCZYNSKA, and J. S. KNYPL: Effects of gibberellic acid, ethephon and 1-aminocylopropane-l-carboxylic acid on germination of Amaranthus caudatus L. seeds inhibited by paclobutrazol. J. Plant Growth Regul. (1988) [in press]. KNYPL, J. S.: Synergistic inhibition of kale seed germination by coumarin and (2-chloroethyl)trimethylammonium chloride, and its reversal by kinetin and gibberellic acid. Planta 72, 292-296 (1967 a).
587
- Growth retardants in relation to to the germination of seeds. I. A paradoxical concentration effect of N,N-dimethylaminosuccinamic acid on the germination of kale seeds affected with coumarin. Can. J. Bot. 45, 903 -913 (1967 b). - Kinetin reversal of the synergistic inhibitory effect of 2,4-dichlorobenzyltributyl phosphonium chloride and coumarin on the germination of Brassica oleracea L. var. acephala seeds. BioI. Plant. Bohemoslov. 9, 212-221 (1967 c). - Kinetin and gibberellin reversal of the synergistic inhibition of germination of the seeds of kale, Brassica oleracea L. var. acephala, by AMO-1618 and coumarin. Acta Soc. Bot. Polon. 38,653-661 (1969). RADEMACHER, W. and J. JUNG: Comparative potency of various synthetic plant growth retardants on the elongation of rice seedlings. J. Agron. Crop Sci. 150, 363 -371 (1981). RADEMACHER, W., J. JUNG, J. E. GRAEBE, and L. SCHWENEN: On the mode of action of tetcyclacis and triazole growth retardants. In: MENHENETT, R. and D. K. LAWRENCE (eds.). Biochemical Aspects of Synthetic and Naturally Occurring Plant Growth Regulators. Monograph 11, British Plant Growth Regulator Group, Wantage, 1-11 (1984). SEMBDNER, G., D. GROSS, G. W. LIEBISCH, and G. SCHNEIDER: Biosynthesis and metabolism of plant hormones. In: J. MACMILLAN (ed.). Hormonal Regulation of Development. 1. Molecular Aspects of Plant Hormones. Springer Verlag, Berlin, 1, 281- 444 (1980).
Inhibition of Germination by Growth Retardants AMO-1618 and Ancymidol, and its Reversal by Gibberellin A3 in Amaranthus caudatus L. Seeds JAN K~PCZYNSKII 1
2
and].
STANISLAW KNYPL
2
Department of Plant Physiology, The University of Szczecin, ul. Felczaka 3 a, PL-71412 Szczecin; and Plant Growth Substances Laboratory, The University of Lodz, ul. Banacha 12/16, PL-90 237 Lodz, Poland
Received July 15, 1987 . Accepted November 13, 1987
Summary AMO-1618 and ancymidol, inhibitors of gibberellin biosynthesis, retarded germination of Amaranthus caudatus L. seeds, ancymidol being more active than AMO-1618. Transfer of seeds to ancymidol after imbibition in water for 12 h caused inhibition of germination. Longer imbibition in water led to reduced sensitivity of seeds to subsequently applied ancymidol. The germinating capacity of seeds preincubated in ancymidol for 3 -17 h was restored markedly following transfer to water. Gibberellic acid (GA3) greatly reduced or reversed the germination inhibitory effect of either AMO-1618 or ancymidol. It is suggested that endogenous GAs are required for induction and/or stimulation of early growth of the radicle.
Key words: Amaranthus caudatus L., AMO-1618, ancymidol, gibberellin, seed germination. Abbreviations: AMO-1618, (2-isopropyl-5-methyl-4-trimethylammonium chloride)-phenyl-1-piperidine carboxylate; ancymidol, alpha-cyclopropyl-alpha-{4-methoxyphenyl)-5-pyrimidine methanol; tetcyclacis (code no. BAS 106... W): 5-(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo-5,4,1Q2.6,08.11-dodeca-3,9diene; CCC, (2-chloroethyl)trimethylammonium chloride; GA 3, gibberellic acid; paclobutrazol, (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-l-(1,2,4-triazol-l-yl)pentan-3-ol.
Introduction Plant growth retardants, such as CCC, AMO-1618, ancymidol, tetcyclacis and triazole-type compounds are known to reduce shoot growth in many higher plants Oung and Rademacher, 1983). This is mainly due to inhibition of gibberellin biosynthesis although other metabolic reactions may also be affected (Radamacher et aI., 1984). CCC and AMO1618 have been found to inhibit, in the first order, the biosynthesis of copalylpyrophosphate from geranyl-geranylpyrophosphate, and conversion of copalylpyrophosphate to ent-kaurene (Graebe and Ropers, 1978; Sembdner et aI., 1980); whereas ancymidol, tetcyclacis and triazoles suppress the oxidative reactions that lead from ent-kaurene to ent-kaurenoic acid (Coolbaugh et aI., 1978; Hedden and Graebe, 1985; Hildebrandt et aI., 1982). It has been demonstrated that © 1988 by Gustav Fischer Verlag, Stuttgart
CCC and AMO-1618 were less efficient inhibitors of shoot elongation in rice seedlings than ancymidol or tetcyclacis (Rademacher and Jung, 1981). This study was undertaken in order to obtain more detailed information about the mechanism by which AMO-1618 and ancymidol affect germination of Amaranthus caudatus L. seeds.
Material and Methods Non-dormant seeds of Amaranthus caudatus L., collected in 1982, were used. The seeds were stored at + 7°C in darkness until use in 1985. Groups of 50 seeds were placed in Petri dishes Scm in diameter, each lined with a disc of Whatman No.1 filter paper and
Inhibition of germination by growth retardants moistened with 1.5 cm 3 of distilled water (the control series) or a volume of aqueous solutions of GA 3, AMO-1618 or ancymidol, the latter ones being applied alone at different concentrations or in combinations with GA 3. In some experiments seeds were initially imbibed in water or ancymidol for different periods of time (3 -17 h), then transferred to ancymidol or water, respectively. For germination seeds were incubated at 24°C in darkness. Manipulations were done in physiologically inactive green light. The number of germinated seeds was counted after periods specified for each test. Experimental variants were repeated twice, with 3 - 5 replicates in each series. Growth regulators applied in this study were manufactured by Calbiochem (AMO-1618), Lilly Res. Ctr., Ltd. (ancymidol) and Polfa (GA3).
Results Both inhibitors of GA biosynthesis delayed or retarded seed germination in Amaranthus caudatus L. (Fig. 1). Much higher concentrations of AMO-1618 than ancymidol were required to produce a comparable degree of inhibition in germination. This suggests that ancymidol is physiologically more efficient than AMO-1618 . Germination in the control series had reached about 95 % after 2 days. Addition of GA3 alone had a slightly stimulatory effect. Simultaneous application of AMO-1618 and GA3 reduced the degree of inhibition in germination as compared with seeds treated with AMO-1618 alone (Table 1). The magnitude of the reversing effect of GA3 was dependent on concentration of AMO-1618. Similarly, the inhibition of seed germination caused by ancymidol could be reversed by GA 3, the effect being dependent on the concentration of GA3 (Fig. 2). Fig. 3 ashows the effect of transferring seeds from water to ancymidol solution after increasing periods of imbibition; Fig. 3 b represents the reverse situation, i.e. the transfer of seeds from ancymidol solution to water at three-hourly intervals. Seeds placed in water germinated well. However, the germination of seeds which were incubated in ancymidol
90
A
B~
~
585
Table 1: Reversing effect of GA3 on the inhibition in germination of Amaranthus caudatus L. seeds caused by AMO-1618. Final germination percentages, as recorded after 7d, are presented.
AMO-1618, M
o 3
X
5
X
10 - 2
Germination, percent GA 3 , M
o
10- 5
94
99 64 26
5
10- 2
or transferred to the ancymidol solution after an initital 12 h imbibition in water was almost completely inhibited. The germination of seeds imbibed for 15 or 17 h in water was also reduced upon subsequent transfer to ancymidol, although not so much as in the former variants (Fig. 3 a). In the other experiment seeds were transferred to water after 3, 6, 9, 12, 15 and 17 h incubation in ancymidol solution. The transfer to water reduced the inhibitory effect of ancymidol, the degree of the final effect being dependent on the period of exposure to the retardant (Fig. 3 b). Even after 17 h incubation in ancymidol solution, 60 % of the seeds could germinate following transfer to water (the final germination percentage was recorded after 6 d).
Discussion The observed inhibition in germination of Amaranthus caudatus L. seeds by AMO-1618 agrees with the data reported by Knypl (1969) for kale (Brassica oleracea L. var. acephala) seeds. A comparison of the physiological efficiency of the two applied inhibitors shows that ancymidol is more active than AMO-1618 (Fig. 1; compare Rademacher and Jung, 1981). The higher sensitivity of seeds and seedlings to ancymidol than to AMO-1618 is possibly associated with the sensitivity of different steps in the pathway of GA biosynthesis, since AMO-1618 blocks the formation of ent-kaurene
3
Co-!
2d
2d
o-l?
5
60
~
~~
z iex
w
~~
C> 30
<>"
0
0 AMO,M
3·10"'
10"5
ANCVMIDOL, M
3·10"5
10-4
0
20h
10-'
10-5
10-4
GA 3 , M
Fig. 1: The effects of different concentrations of AMO-1618 (A), ancymidol (B) and GA3 (C) on the germination of Amaranthus caudatus L. seeds. Id, 2d and 3d mean germination percentages after 1,2 and 3 days, respectively. Results are expressed as arithmetical means; values of S.D. did not exceed 5, 7 and 6 percent for A, Band C, respectively.
586
JAN KIlPCZYNSKI and]. STANISLAW KNYPL
10
~
o
z
eo
o ~
z
~
~ 30
C>
AN
o
24
72
96
168
72
96
TIME. h
A 10
B I-
Fig. 2: The effects of GA3 at 10 - 5 (A) or 3 x 10- 4 (B) on the inhibition of germination of Amaranthus caudatus L. seeds caused by 2x10- 4 ancymidol (AN). Maximal values of S.D. never exceed 8 %.
rf HaO
t-
whole period
3
6
9 12
15 17
HOURS BEFORE TRANSFER
(Graebe and Ropers, 1978; Sembdner et aI., 1980) whereas ancymidol blocks the formation of ent-kaurenoic acid (Coolbaugh et al., 1978). The addition of GA3 markedly counteracted the inhibition caused by AMO-1618 and ancymidol (Fig. 2). In accordance with reports for other growth retardants (Knypl, 1967 a-c and 1969; K~pczynski, 1986; K~pczynski and K~pczynska, 1988; K~pczynski et aI., 1988), which could be counteracted by gibberellins. The results support the earlier formulated idea that the presence of endogenous gibberellins is essential for the germination of Amaranthus caudatus L. seeds (K~pczynski, 1986; K~pczynski et aI., 1988). The production of endogenous gibberellins would appear to be sufficient for germination in «normal» conditions, so that the exogenous addition of GA3 (Fig. 1 c) or GA4 + 7 (K~pczynski, 1986) had only a slight effect on germination. The effect of gibberellin seems to be comparable to the effect of ethylene, another stimulator of Amaranthus caudatus L. seed germination (K~pczynski and Karssen, 1985). Results of the experiment in which seeds were initially incubated in water or ancymidol for different periods (3 -17 h), and then transferred to ancymidol or water, respectively, suggest that responsiveness (or sensitivity) to ancymidol is associated with a late activation phase during the process of germination. Stimulation of radicle
Fig. 3: Germination of Amaranthus caudatus L. seeds transferred after different periods of imbibition in water to ancymidol (AN; 3 x 1O- 4 M) [A] or vice versa [B). «Whole period» means seeds incubated for the whole duration of the experiment either in water or in the ancymidol solution. Final germination percentages, as recorded after 6d, are presented; vertical bars indicate ±S.D.
growth by exogenous gibberellin has been observed in Chenopodium album L. seeds (Karssen, 1976). Acknowledgements We express gratitude to Miss Ewa Maciejewska for skilled technical assistance. This study was supported in part by a grant CPBP 05.02.4.06.
References COOLBAUGH, R. c., S. S. HIRANO, and C. WEST: Studies on the specificity and site of action of ancymidol, a plant growth regulator. Plant Physio!. 62, 571-576 (1978). GRAEBE, J. E. and H. J. ROPERS: Gibberellins. In: D. S. LETHAM, P. B. GOODWIN, and T. J. V. HIGGINS (eds.): Phyohormones and Related Compounds: A Comprehensive Treatise, Elsevier-North Holland, Amsterdam, 1,107-303 (1978). HEDDEN, P. and J. E. GRAEBE: Inhibition of gibberellin biosynthesis by paclobutrazol in cell-free homogenates of Cucurbita maxima endosperm and Malus pumila embryos. J. Plant Growth Regu!. 4, 111-122 (1985). HILDEBRANDT, E.,J. E. GRAEBE, W. RADEMACHER, andJ.JuNG: Mode of action and biological activity of new potent plant growth retardants: BAS 106... W and triazole compounds. Abstracts 11th
Inhibition of germination by growth retardants Int. Conf. on Plant Growth Substances, Aberystwyth, Wales, p. 65 (1982). JUNG, J. and W. RADEMACHER: Plant Growth Regulating chemicals - cereal grains. In: L. G. NICKELL (ed.): Plant Growth Regulating Chemicals. CRC Press, Inc., Boca Raton, 1, 253 -271 (1983). MRSSEN, C. M.: Two sites of hormonal action during germination of Chenopodium album seeds. Physiol. Plant., 36, 264-270 (1976). KIlPCZYNSKI, J.: Ethylene-dependent action of gibberellin in seed germination of Amaranthus caudatus L. Physiol. Plant. 67, 584-587 (1986). KI;PCZYNSKI, J. and e. M. MRSSEN: Requirement for the action of endogenous ethylene during germination of non-dormant seeds of Amaranthus caudatus. Physiol. Plant. 63, 49-52 (1985). KIlPCZYNSKI, J. and E. KI;PCZYNSKA: Reversing inhibitory effect of paclobutrazol on seed germination of Amaranthus paniculatus L. by GA 3 , ethephon or ACe. Plant Growth Regul. (1988) [in press]. KIlPCZYNSKI, J., E. KIlPCZYNSKA, and J. S. KNYPL: Effects of gibberellic acid, ethephon and 1-aminocylopropane-l-carboxylic acid on germination of Amaranthus caudatus L. seeds inhibited by paclobutrazol. J. Plant Growth Regul. (1988) [in press]. KNYPL, J. S.: Synergistic inhibition of kale seed germination by coumarin and (2-chloroethyl)trimethylammonium chloride, and its reversal by kinetin and gibberellic acid. Planta 72, 292-296 (1967 a).
587
- Growth retardants in relation to to the germination of seeds. I. A paradoxical concentration effect of N,N-dimethylaminosuccinamic acid on the germination of kale seeds affected with coumarin. Can. J. Bot. 45, 903 -913 (1967 b). - Kinetin reversal of the synergistic inhibitory effect of 2,4-dichlorobenzyltributyl phosphonium chloride and coumarin on the germination of Brassica oleracea L. var. acephala seeds. BioI. Plant. Bohemoslov. 9, 212-221 (1967 c). - Kinetin and gibberellin reversal of the synergistic inhibition of germination of the seeds of kale, Brassica oleracea L. var. acephala, by AMO-1618 and coumarin. Acta Soc. Bot. Polon. 38,653-661 (1969). RADEMACHER, W. and J. JUNG: Comparative potency of various synthetic plant growth retardants on the elongation of rice seedlings. J. Agron. Crop Sci. 150, 363 -371 (1981). RADEMACHER, W., J. JUNG, J. E. GRAEBE, and L. SCHWENEN: On the mode of action of tetcyclacis and triazole growth retardants. In: MENHENETT, R. and D. K. LAWRENCE (eds.). Biochemical Aspects of Synthetic and Naturally Occurring Plant Growth Regulators. Monograph 11, British Plant Growth Regulator Group, Wantage, 1-11 (1984). SEMBDNER, G., D. GROSS, G. W. LIEBISCH, and G. SCHNEIDER: Biosynthesis and metabolism of plant hormones. In: J. MACMILLAN (ed.). Hormonal Regulation of Development. 1. Molecular Aspects of Plant Hormones. Springer Verlag, Berlin, 1, 281- 444 (1980).