Germination of annual celery (Apium graveolens) seeds: Inhibition by paclobutrazol and its reversal by gibberellins and benzyladenine

Plants of annual celery ( Apium graveolens L.) were treated with paclobutrazol during anthesis. Seeds collected from the treated plants showed a marked reduction in germination in light and failed to germinate in the dark. Application of GA_4/7 to the imbibition solution reversed the inhibitory effect of paclobutrazol while gibberellic acid (GA₃) was ineffective. Benzyladenine (BA) interaction with GA_4/7 was light and concentration-dependent. At relatively low concentrations in the dark there was a synergistic effect, but at higher concentrations, especially in the light, BA, antagonized the GA_4/7 effect. Seedlings emerging from the seeds from paclobutrazol-treated plants were only slightly shortened. It is suggested that paclobutrazol applied to the mother plants inhibited the biosynthesis of endogenous GAs, which normally enable the germination of annual seeds under unfavorable conditions. Exogenously applied GA_4/7 fulfills the function of the absent endogenous GAs.     

Factors affecting the induction and release of secondary dormancy in Kalanchoë seeds

Abstract. Several short daily R irradiations are required from the first day of incubation on water to induce germination of Kalanchoë seeds. When the same light treatment is given after a prolonged dark incubation period at 20°C, secondary dormancy prevents germination. Factors controlling the induction and breaking of secondary dormancy have been investigated. The induction of secondary dormancy is very temperature dependent. Locally puncturing the seed coat strongly delays it. Secondary dormancy is not induced in the presence of GA₃ during the first 10 d of dark incubation, although this growth substance cannot induce dark germination. Prolonged or cyclic daily R irradiations can relieve secondary dormancy of seeds kept on water, even after a dark period of 20 d. A 24 h treatment at 4°C restores responsiveness to short R exposures of slightly secondarily dormant seeds. The synergism between GA₃ and Pfr in non-dormant Kalanchoë seeds, leading to high effectiveness of even one short FR irradiation, still occurs in seeds made secondarily dormant before transfer to GA₃, but more R or FR irradiations, in combination with GA₃, are required for the release of secondary dormancy. A combination of red light and 6-benzyl-aminopurine is ineffective in removing dormancy.     

Role of endogenous gibberellins in germination of melon (Cucumis melo) seeds

The effect of the plant growth retardants ancymidol. mefluidide and uniconazole on germination of two melon accessions differing in their ability to germinate at 14°C was examined. The accessions were the cold sensitive Noy Yizre'el and the cold tolerant Persia 202. The three growth retardants were able to delay the germination of intact Noy Yizre'el seeds, but did not affect that of intact Persia 202 seeds. On the other hand germination of decoated seeds of both accessions was unaffected by these inhibitors at normal oxygen concentration, but was inhibited at 5% oxygen. When gibberellin-like activity was measured by a dwarf rice biological assay following HPLC fractionation, it was found that seeds of Persia 202 contained much more gibberellin-like activity than Noy Yizre'el seeds. Among the extracted compounds several endogenous gibberellins were identified by combined gas chromatography-mass spectrometry (GC-MS). They included GA₄, GA₂₀, GA₁ and GA₃ in Noy Yizre'el and GA₃₄, GA₂₀, GA₁ and GA₈ in Persia 202. It is suggested that the better germination of intact Persia 202 seeds, compared to Noy Yizre'el seeds at low temperature and low oxygen concentration, is due to a higher endogenous level of GA and a better seed coat permeability to oxygen.     

Geibberllin and temperature influence carbohydrate content and flowering in Phalaenopsis

When Phalaenopsis amabilis is grown under high temperature (30/25°C, day/night), flowering is blocked, and this can be reversed by gibberellin A₃ (GA₃) treatment. Associated with GA₃ treatment under high temperature are increases in sucrose, glucose and fructose as compared with warm-treated plants. Spraying with sucrose solution alone caused leaf epinasty in plants grown under high temperature. Epinasty was released by about 9 days of GA₃ treatment. In GA₃-treated plants under high temperatures, sucrose application to the source leaves led to an increase in sugar content in both leaves and inflorescence. In contrast, although in warm-treated plants sucrose application to the source leaves increased sugar content in the leaves, it did not increase sucrose content in the inflorescence. These results corroborate our hypothesis that in Phalaenopsis GA₃ stimulates sink activity in the apical meristem and promotes the translocation of sucrose from source leaves to the apex of the inflorescence, where it accumulates. GA₃ treatment led to an increase in sucrose synthase activity and had no effect on invertase activity.     

Gibberellin levels and cold-induced floral stalk elongation in tulip

To investigate the role of gibberellins (GAs) in the cold requirement of tulip ( Tulipa gesneriana L. cv. Apeldoorn), bulbs were dry-stored at 5°C or at 17°C for 12 weeks prior to planting at 20°C. Only precooled bulbs showed rapid sprout growth and developed a full-grown flower. Endogenous GA levels were measured in sprouts and basal plates at the time of planting and in the second week after planting, by combined gas chromatography-mass spectrometry using deuterated internal standards. GA₄ was the major gibberellin. while GA₁, GA₉ and GA₃₄ were present in lower amounts. At the time of planting, sprouts from non-cooled bulbs contained significantly more GA₄ and GA₁, per sprout than those from precooled bulbs. Hence, there is no direct correlation between rapid sprout growth after planting and high GA levels at planting. In the second week after planting, floral stalks of precooled bulbs contained 2 to 3 times more GA₄ and its metabolite GA₃₄ per floral stalk and per g fresh weight than those of non-cooled bulbs. The results are discussed with regard to the role of gibberellins in the cold-induced floral stalk elongation of tulip.     

Study of the inheritance of seed primary dormancy and the ability to enter secondary dormancy in Petunia: influence of temperature, light and gibberellic acid on dormancy

Abstract. The germination behaviour of two Petunia hybrida lines. M₃₀ and Th₇, and their reciprocal hybrids was studied. Two sets of experimental conditions appeared helped to distinguish between dormant and non-dormant parental lines: (1) 25 and 35 °C in the dark, in the latter case after 2 months of dry storage at 20 °C; (2) 35 and 40 °C in the light. Photosensitivity was tested in the first case and sensitivity to GA₃ in the second case. The predominance of paternal control over dormancy was evident. A maternal or tegumentary control of photosensitivity and of sensitivity to GA₃ was also shown. Transferring the seeds, originally imbibed in conditions expressing primary dormancy, to conditions which previously supported their germination, allowed us to show that secondary dormancy could be easily induced when a deeper primary dormancy had already developed in the seeds.     

Free and conjugated gibberellins in dormancy and germination of apple seeds

Halińska, A. and Lewak, St. 1987. Free and conjugated gibberellins in dormancy and germination of apple seeds.
The presence of gibberellin A₄ (GA₄) was confirmed in partly stratified seeds of apple ( Malus domestica Borb., cv. Antonówka) by mass spectrometry of the methyl ester. Levels of free and conjugated gibberellins A₄₊₇ and A₉ changed during drying of mature seeds, during cold and warm stratification, as well as during germination of dormant and non-dormant embryos. The temporary rise in GA₄₊₇ during cold stratification and during the culture of dormant embryos as well as the lack of it under conditions of warm stratification, allowed us to postulate a role for GA₄₊₇ in the removal of dormancy. In addition, GA₉ was absent in dormant embryos and increased during cold stratification and during the culture of non-dormant embryos. This suggests the involvement of GA₉, in induction of normal development of the seedling. The equivalence between changes in free and conjugated GAs suggests that formation and hydrolysis of conjugates are involved in the control of the physiologically active levels of free GA₄₊₇ and GA₉.     

Gibberellin status and responsiveness in shoots of tall and dwarf genotypes of diploid rye (Secale cereale)

The recessive dwarfing alleles of rye ( Secale cereale L.), ct1 and ct2 , caused a 35–55% reduction in the length of leaf 2 compared with corresponding tall lines grown at both 10°C and 20°C. The dwarf lines were 45–50% as responsive to applied GA₃ as the tall lines at 20°C but the absolute GA-responsiveness of the dwarfs was greater at 10°C than at 20°C. There was no significant difference in the contents of GA₁₉, GA₂₀, GA₂₉, GA₁, GA₃ and GA₈ in the leaf extension zone of tall and dwarf seedlings grown at 20°C. It was concluded that the mechanism whereby GA homeostasis is maintained is functional in both tall and dwarf lines despite marked differences in leaf extension rate. The recessive rye mutations may cause loss of function late in the GA-cell elongation pathway or, alternatively, indirectly affect GA-responsiveness in vegetative tissues. The genetic and physiological evidence indicates that ct1 and ct2 are unrelated to the GA-insensitive Rht genes in hexaploid bread wheat.     

Ethylene-dependent action of gibberellin in seed germination of Amaranthus caudatus

The role of gibberellins in the germination of seeds of Amaranthus caudatus L. was examined. Tetcyclacis (BAS 106), an inhibitor of gibberellin biosynthesis, inhibited germination of the seeds. The inhibition caused by BAS 106 was antagonised by gibberellin A₄₊₇ (GA₄₊₇). Ethephon (2-chloroethylphosphonic acid) and 1-aminocyclopropane-1-carboxylic acid (ACC) could replace GA₄₊₇. Ethephon and ACC counteracted also the side effects of BAS 106 that are not reversible by GA₄₊₇. The rate of seed germination was not increased by gibberellin in the presence of aminoethoxyvinylglycine (AVG). AVG increased the effect of BAS 106. GA₄₊₇ could not reverse the effect of BAS 106 when AVG was simultaneously applied. The results indicate that the biosynthesis of endogenous gibberellins may be required for germination of A. caudatus seeds and that main physiological effects of GA₄₊₇ on seed germination may depend on ethylene biosynthesis.     

Identification and quantitation of gibberellins in fruits of Lycopersicon esculentum, and their relationship to fruit size in L. esculentum and L. pimpinellfolium

GA₁, GA₈, GA₁₇, GA₁₉, GA₂₀ and GA₂₉ were identified by combined gas chromatography-mass spectrometgry (GC-MS) in immature seeds and pericarp of Lycopersicon esculentum Mill. (tomato). Higher levels of these GAs were present in the seeds than in the pericarp; seeds in addition contained GA₁₅, GA₂₄, GA₂₅, and GA₄₄. Fruits of the Lycopersicon pimpinellifolium Mill. mutant I were smaller and contained lower GA₁ concentrations, but higher GA₂₀ concentrations, than those of mutants III and IV. In contrast, differences in fruit size in L. esculentum due to position on the truss did not correlate with GA₁ concentration in either the pericarp or seeds.     

Effects of sodium chloride on prevention of thermodormancy, ethylene and protein synthesis and respiration in Grand Rapids lettuce seeds

Grand Rapids lettuce ( Lactuca saliva L.) seeds entered into a state of secondary dormancy (thermodormancy) when they were imbibed at 40°C for 72 h. The effect of 40°C in inducing thermodormancy was largely reduced by imbibing seeds at 40°C in solutions of polyethylene glycol (PEG), mannitol and NaCl. Despite similar water potentials of solutions, NaCl pretreatment was more effective. Subsequent germination in the dark at 25°C of saline, high-temperature-pretreated seeds required only gibberellic acid (GA₃), as was the case with nonthermodormant seeds. Thermodormancy reduced total respiratory capacity (V_T) and increased the ratio of alternate pathway (V_alt) to cytochrome pathway (V_cyt) respiration. This was prevented by saline pretreatment. Ethylene production and protein synthesis were depressed in thermodormant seeds, and this was partly alleviated by saline pretreatment. The patterns of protein synthesis in saline- and nonsaline-freated seeds at 40°C were similar, differing only in that the saline treated seeds produced in addition a 78 kDa polypeptide. The pattern of protein synthesis at 40°C differed significantly from that at 25°C.     

Effects of prohexadione (BX-112) and gibberellins on shoot growth in seedlings of Salix pentandra

Effects of gibberellins A₁, A_4/7, A₉, A₁₉ and A₂₀ and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth-retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX-112), which is suggested to block 3β-hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA₁, but not GA₁₉ and GA₂₀, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA₁₉, GA₂₀ and GA₁ are native in S. pentandra , and the results are compatible with the hypothesis that GA₁ is active per se in shoot elongation, and that the effect of GA₁₉ and GA₂₀ is dependent on their conversion to GA₁.
A mixture of GA₄ and GA₇ was as active as GA₁ in promoting shoot elongation in seedlings treated with prohexadione, while GA₉ showed slight activity only when applied at high doses.     

Antagonistic effects of abscisic acid and gibberellic acid on the breaking of dormancy of Fagus sylvatica seeds

Study of the factors involved in the dormancy of Fagus sylvatica seeds shows that such dormancy is due partly to the seed coats and partly to endogenous factors. Seed coat removal accelerates both the release from dormancy and the effects of the other treatments that abolish it. The dormancy of these seeds is eliminated by cold treatment at 4°C over a period longer than 8 weeks, and exogenous application of abscisic acid (ABA) reverses the effects of low temperature, the seeds remaining in an ungerminated state. Additionally, ABA reduces protein synthesis but slightly increases RNA synthesis, which suggests its involvement in the synthesis of RNAs related to this process. In vitro translation of the RNAs isolated from these seeds shows that ABA delays the disappearance of at least 2 polypeptides (of ca 22 and 24 kDa), which are abundant in dormant seeds and under conditions that prevent the release from dormancy, but which disappear under treatments that abolish it. Exogenous application of gibberellic acid (GA₃) proved to be efficient in breaking the dormancy of these seeds and in substituting for cold treatment as well as in antagonizing the effects of ABA on the synthesis of both DNA and proteins. GA₃ also accelerates the disappearance of the two polypeptides abundant in dormant seeds and in ABA-treated seeds. These findings suggest that both ABA and GA₃ could be involved in the regulation of nucleic acid and protein metabolism during dormancy, acting antagonistically in these processes and, specifically, in the regulation of the synthesis of the two proteins that appear to play a role in the maintenance of dormancy in these seeds.     

Biological activity, identification and quantification of gibberellins in seedlings of Norway spruce (Picea abies) grown under different photoperiods

Short photoperiod induces growth cessation in seedlings of Norway spruce ( Picea abies (L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA₉ and GA₂₀ can not induce growth. In contrast application of GA, and GA₄ induced shoot elongation. The results indicate that 3β-hydroxylation of GA₉ to GA₄ and of GA₂₀ to GA₁ is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA₁, GA₃, GA₄, GA₇, GA₉, GA₁₂, GA₁₅, GA₁₅, GA₂₀, GA₂₉, GA₃₄ and GA₅₁ were identified by combined gas chromatography-mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and ¹⁴C-labelled GAs as intermal standards. In short days, the amounts of GA₉, GA₄ and GA₁ are less than in plants grown in continuous light. There is no significant difference in the amounts of GA₃, GA₁₂, and GA₂₀ between the different photoperiods. The lack of accumulation of GA₉ and GA₂₀ under short days is discussed.     

Vernalization,photoperiod and GA3 interact to affect flowering of Japanese radish (Raphanus sativus Chinese Radish Jumbo Scarlet)

Raphanus sativus L. Chinese Radish Jumbo Scarlet has characteristics that make it an excellent plant model for vernalization studies. This study further characterizes flower induction of R. sativus Chinese Radish Jumbo Scarlet. Seed were imbibed in distilled water containing 0, 10⁻⁵ M or 10⁻³ M GA₃ for 24 h and were then exposed to 6 ± 0.5°C (vernalized) for 0, 2, 4, 6, or 8 days. Seedlings were then grown under a short- (8 h) or long-day photoperiod (8 h with or without a 4-h night interruption; 2200–0200 h). Of unvernalized plants grown under long- and short-day conditions, 45 and 3% flowered, respectively. Saturation of the vernalization response occurred after a 4- or 8-day vernalization treatment when plants were placed under long- or short-days, respectively. Basal leaf number and days to anthesis decreased when seeds were cooled for 2 or 4 days and were imbibed with 10⁻³ M GA₃ compared to distilled water only. These data indicate that R. sativus Chinese Jumbo Scarlet has principally an obligate vernalization requirement when grown under short-days. GA₃ application only facilitated flowering when the length of the vernalization treatment was marginal. Taken together, these data support the use of this plant as a model plant for identifying vernalization responses under short-day conditions.     

Effects of different gibberellins on elongation growth under short day conditions in seedlings of Salix pentandra

Fifteen different gibberellins (GA's) were tested for their ability to induce elongation growth under short day conditions in seedlings of Salix pentandra L. GA's were applied either to the apex or they were injected into a mature leaf. GA₃ was highly active and also GA₄₊₇ and GA₄ showed high activity. GA₁, GA₂, GA₅, GA₉, GA₁₃, GA₂₀, GA₃₆ and GA₄₇ showed moderate activity. GA₁₆, GA₁₇, GA₂₇ and GA₄₁ exhibited low or no activity in doses up to 10 μg per plant. In general, a better growth response was obtained with an application to the apex than with an injection into the leaf.     

Embryonal dormancy in apple seeds is controlled by free and conjugated gibberellin levels in the embryonic axis and cotyledons

Halińska, A., Sińska, I. and Lewak, St. 1987. Embryonal dormancy in apple seeds is controlled by free and conjugated gibberellin levels in the embryonic axis and cotyledons.
Free and conjugated gibberellins (GAs) A₄₊₇ and A₉ were determined in embryonic axes and in cotyledons of seeds of apple ( Malus domestica Borb., cv. Antonó wka) during breaking of dormancy under cold stratification. In both organs, the maximum level of free GA₄₊₇ was found at day 30 of stratification, but the concentration was 700 times higher in axes than in cotyledons. Comparison of changes in free and conjugated GA₄₊₇ levels during stratification allow us to suggest that the accumulation of free hormone in axes is, at the most, to 40% due to release from conjugates already present in the axis; that maximally 20% is derived from hydrolysis of cotyledonary conjugates translocated to axes; and that at least 40% originate from the novo biosynthesis of the hormone. Free and conjugated GA₉ levels were similarly altered in axes and in cotyledons, markedly increasing at the end of afterripening. Both release of the free hormone from conjugates and biosynthesis of GA₉, appeared to be involved in that increase; no translocation of free or bound GA₉, between axes and cotyledons was demonstrated.     

Response of genetic dwarf apple plants to GA3

High temperature has been implicated as the major factor responsible for dwarfing of selected apple ( Malus domestica Borkh.) trees of a hybrid population of cv. Goldspur Delicious x cv. Redspur Delicious. Dwarf plants grew only 2.2 cm in 63 days under a ramped temperature regime (night 15°C, day ramped up to 38°C, held for 2 h and ramped down to 15°C—14 h daylength), whereas semi-dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi-dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi-dwarf plants grew nearly 50 cm. The gibberellin biosynthesis inhibitor, paclobutrazol, retarded growth of semi-dwarf plants in both ramped and constant environments and dwarf plants in the constant 27°C environment. It did not further reduce the size of dwarf plants growing under the ramped regime. Gibberellin (GA₃) treatment reversed the inhibition of growth caused by paclobutrazol for all plants except it did not restore growth of dwarf plants in the ramped environment. These data suggest that neither pacobutrazoltreated nor untreated dwarf plants growing in the ramped environment (or in the orchard during hot summer months) are able to respond to GA₃. In constrast, GA₃ was utilized by the paclobutrazol-inhibited dwarf plants growing at constant 27°C, enabling shoot elongation to take place. It appears that high temperature may have caused alterations in GA target tissues in dwarf plants so that they no longer had the capacity to respond to GA.     

Interaction of gibberellic acid and photoperiod on leaf sheath elongation in normal and gibberellin-insensitive genotype of wheat

Effect of gibberellic acid (GA₃) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin(GA)-insensitive (cv. Siete Cerros) genotype of wheat ( Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA₃ both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA₃ was additive, and there was no statistically signficant interaction between photoperiod and GA₃ concentrations. Leaf sheath length in cv. Siete Cerros was not significantly affected by GA₃ under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin.