Seed coat structure and oxygen availability control lowtemperature germination of melon (Cucumis melo) seeds

The involvement of the seed coat in low-temperature germination of melon seeds was examined in two accessions differing in their ability to germinate at 14°C: Noy Yizre'el (a cold-sensitive cultivar) and Persia 202 (a cold-tolerant breeding line). Decoating resulted in full germination of Noy Yizre'el at 14°C, but splitting the coat increased germination only partially. Thus, the inhibition of Noy Yizre'el germination at 14°C is not due to physical constraint on radicle protrusion. At 25°C, seeds of both accessions submerged in water or agar germinated fully as long as the hilum aperture remained uncovered. Submerging the whole seed, or covering the hilum with lanolin, strongly depressed germination of Noy Yizre'el but not of Persia 202. Accessions differed in germination response to decreasing O₂ concentration, with Noy Yizre'el showing higher sensitivity to hypoxia. These differences were correlated with differences in seed coat structure as well as in embryo sensitivity to hypoxia. Intercellular spaces in the outer layer of the seed coat were evident in the more tolerant Persia 202, while in the sensitive Noy Yizre'el this layer was completely sealed. Sensitivity to hypoxia increased at 15°C as compared with 25°C, the increase being greater in Noy Yizre'el. It is proposed that the seed coat-imposed dormancy at low temperature in Noy Yizre'el is the combined result of more restricted oxygen diffusion through the seed coat and a greater embryo sensitivity to hypoxia, rather than to physical constraints of radicle break-through or impairment of imbibition.     

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.     

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.     

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.     

The effect of some growth regulators on light-induced germination of Paulownia tomentosa seeds

Grubišié, D., Konjevié, R. and Neškovié, M. 1988. The effect of some growth regulators on light-induced germination of Paulownia tomentosa seeds. - Physiol. Plant. 72: 525–528.
The germination of Paulownia tomentosa Steud. (Empress tree) seeds can be induced either by red light (R) or by exogenously applied gibberellic acid (GA₃). The R induced germination is completely suppressed by far red irradiation, abscisic acid (ABA) or by growth retardants such as ancymidol, tetcyclacis and paclobutrazol, though not by AMO 1618 or chloro-choline chloride (CCC). The inhibition caused by far red light (FR) and growth retardants can be overcome by GA₃, while the ABA-induced inhibition can be reversed by fusicoccin (FC), which does not reverse the inhibition caused by FR or growth retardants. It is noteworthy that the germination of light insensitive wheat, corn, alfalfa and mung bean seeds is not inhibited by growth retardants.     

Internode length in Pisum. IV. The effect of the Le gene on gibberellin metabolism

The highly active, polar gibberellin-like substance found in the apical region of shoots of tall (genotype Le ) peas ( Pisum sativum L.) is shown by combined gas chromatography-mass spectrometry (GC/MS) to be GA₁. This substance is either absent or present at only low levels in dwarf ( le ) plants. Multiple ion monitoring (MIM) tentatively suggests that GA₈ may also be present in shoot tissue of tall peas. Gibberellin A₁ is the first 3 β-hydroxylated gibberellin positively identified in peas, and its presence in shoot tissue demonstrates the organ specificity of gibberellin production since GA₁ has not been detected in developing seeds. Application of GA₁ can mask the Le/le gene difference. However, whilst Le plants respond equally to GA₂₀ and GA₁, le plants respond only weakly to GA₂₀, the major biologically active gibberellin found in dwarf peas. These results suggest that the Le gene controls the production of a 3 β-hydroxylase capable of converting GA₂₀ to GA₁. Further support for this view comes from feeds of [³H] GA₂₀ to Le and le plants. Plants with Le metabolise [³H] GA₂₀ to three major products whilst le plants produce only one major product after the same time. The metabolite common to Le and le plants co-chromatographs with GA₂₉. The additional two metabolites in Le peas co-chromatograph with GA₁ and GA₈.     

The effect of light and exogenous gibberellic acid on respiration pathways during germination of tomato seeds

Tomato (Lycopersicon esculenlum Mill. cv. Taiwan Red) seeds are typical lightsensitive seeds where light requirement can be substituted by gibberellic acid (GA₃). During the initial stage of germination, the hexose monophosphate pathway (HMP) in seeds incubated for 24 h under white light or 12 h in 0.3 mW GA₃ solution acidified with 1 M HCI for 1 h in the dark (HCl→GA₃) was much greater than in seeds incubated for 24 h in the dark. The results were obtained from measurements of the respiration rate by man metric method of Warburg with or without iodoacetic acid, and from activities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and aldolase (EC 4.1.2.13). Although the HMP tended to decrease at the later stage (72 h under white light or in the dark, or 36 h in HCl→GA₃), it remained greater in light- than in dark-incubated seeds. CN-resistant respiration increased from 27–30% to 57–64% of the total respiration in seeds incubated under white light or in HCI→GA₃, while respiration of non-germinating, dark-incubated seeds remained zero. Benzohydrox–amic acid (BHAM), an inhibitor of the alternative pathway, inhibited both respiration and seed germination. It is concluded that the enhancement of HMP and the CN–resistant pathways are both controlled by P_fr, but there is no direct connection between them.     

The effects of phosphate supply on uptake of potassium ions, 2,4-D and atrazine by wheat and maize

The germination percentage of peach [ Prunus persica (L.) Batsch cv. Halford] seeds at 20°C was low (< 20%) after incubation at 5°C for as long as 35 days, but then increased considerably (> 40%) when the seeds were maintained at 5°C for longer than 42 days. Four zones of gibberellin-like activity were found in partially purified seed extracts. Gibberellin-like activity remained low in seeds incubated at 5°C for as long as 28 days, but increased significantly in three of these zones after 35 days, and in the fourth zone after 49 days. The increase in gibberellin-like activity was evident prior to the transfer of the seeds to 20°C. Moreover, seeds maintained at 5°C germinated at this temperature after 63 days. For seeds incubated and germinated at 20°C, both the germination percentage and the gibberellin-like activity remained low throughout the experimental period. Application of the growth retardant paclobutrazol to seeds after 28 days of a 49 day total incubation period at 5°C did not substantially reduce seed germination, although the increase in gibberellin-like activity was prevented. Seeds did, however, require a longer time to germinate after transfer to 20°C and were dwarfed in appearance. Application of GA₃ to seeds prior to stratification increased the percentage germination of seeds only when they had been incubated at 5°C for at least 35 days. The major changes in gibberellin-like activity are, therefore, associated not so much with the processes which allow germination to take place in peach, but more with those processes which allow normal growth and development of the seedling.     

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.     

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.     

Interactions between hydrogen cyanide, gibberellin, abscisic acid and red light in germination of lettuce seeds

Germination of lettuce ( Lactuce sativa L. cy. Grand Rapids) seeds was promoted by red light and by pulse treatments with gibbercllie acid (GA₃) or hydrogen cyanide, whereas it was inhibited by short exposure of seeds to absusic acid (ABA). The eflects of unsalLirating red light and of 10 μ M GA₃ on lettuce germination were completely reversed the effect of ABA (100 μ M ). In contrast, hydrogen cyanide did not reverse the effect of 100 μ M ABA and only partly eliminated the effect of 10μ M ABA, independently of the sequence of treatments. Possible interactions between HCN GA₃, ABA and red light were discussed. It was concluded thai light GA₃ and HCN affect different mechanisms involved in lettuce germination: ABA counteracts the stimulatory action of all these faclors. being the most effective against cvanide Additional key words - Lactuca sativa, pholodormancy, phylohormoncs.     

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.     

The role of hormones in regulating the germination of polymorphic seeds and early seedling growth of Atriplex triangularis under saline conditions

Germination of the polymorphic seeds and seedling growth of Atriplex triangularis under various salinity, gibberellic acid and kinetin treatments were determined. Gibberellic acid (GA₃; 2.9 m M ) promoted germination and growth at high NaCl concentrations (345 m M ). Kinetin (4.7 μ M ) stimulated germination at all salinities and seed sizes tested. GA₃ and kinetin generally increased seedling growth at all concentrations of salinity studied. Higher concentrations of kinetin were found to be inhibitory.     

Improved germination in seeds of guayule (Parthenium argentatum Gray) following polyethylene glycol and gibberellic acid pretreatments

Suitable conditions for the pretreatment of seeds of guayule were determined with a view to improving germination. These included the addition of thiram (500 mg litre^-1), and applications of GA₄₊₇ alone, or in combination with polyethylene glycol. Significant improvements in the seed germination were seen following applications of PEG at -0.10 MPa. Simultaneous application of GA₄₊₇ with priming improved soil emergence and germination over a wide range of temperatures. No beneficial effects of PEG priming were evident on seed storage.     

Internode length in Pisum. III The effect and interaction of the Na/na and Le/le gene differences on endogenous gibberellin-like substances

In the garden pea ( Pisum sativum L.), shoots of the extremely short plants with the mutant na (phenotype nana) are found by bioassay to contain undetectable levels of gibberellin-like substances. This is confirmed by the use of near isogenic lines differing at the Na locus. Thus, mutant na appears to block a step early in the pathway of gibberellin synthesis. It is suggested that the polar gibberellin-like substance found in the apical portion of shoots of tall ( Le ) but not dwarf ( le ) peas could be GA₁. Extracts of shoots of na Le peas treated with GA₂₀ (the major active gibberellin in dwarf peas) possess a large amount of GA₁-like activity whereas extracts of shoots of na le peas treated with GA₂₀ possess a much reduced amount. Thus, gene Le may allow the conversion of a less active gibberellin (GA₂₀) into one more active in stimulating elongation in the pea (the GA₁-like compound). In contrast to their influence in the shoot, the na and Le genes do not appear to be operative in controlling the gibberellin content of developing seed, indicating that organ specific gibberellin biosynthesis and metabolism occur in peas.     

Gibberellin-biosynthesis and -sensitivity mediated stimulation of seed germination of Sisymbrium officinale by red light and nitrate

Light stimulated seed germination of Sisymbrium officinale (L.) Scop, (hedge mustard) by means of two different mechanisms. Light effect I was absolutely dependent on the simultaneous presence of nitrate. Without nitrate, red (R) irradiated seeds did not escape from the antagonizing action of far-red (FR) irradiation. The data indicated that nitrate acted as a cofactor at the level of the FR absorbing form of phy-tochrome (P_fr). The combined action of R and nitrate could be replaced by addition of the gibberellins 4 and 7 (GA,₄₊₇). This action could be inhibited by the growth re-tardant tetcyclacis, an inhibitor to GA biosynthesis in cell free systems and intact plants. The action of tetcyclacis was fully neutralized by GA₄₊₇. It is concluded that the combination of R and nitrate stimulated GA biosynthesis. Omission of nitrate from the incubation medium enabled the study of light effects apart from G A biosynthesis. In such conditions R stimulated the sensitivity to GA₄₊₇, (light effect II). The two light effects could also be distinguished by their different reactions to the temperature of a pre-treatment in water and darkness. The sensitivity to R and nitrate was subject to breaking and induction of dormancy. Both processes were stimulated at rising temperatures. Due to a different optimum, breaking of dormancy prevailed at lower temperatures and induction of secondary dormancy at more elevated temperatures. The sensitivity to GA₄₊₇ rose and fell in a comparable way during dark incubation at a broad range of temperatures. The capacity of light to stimulate GA₄₊₇, action did not diminish at higher temperatures, it even tended to rise. The study indicated that seed germination is regulated by an increase in both the levels of GAs and the sensitivity to GAs.     

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.     

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.     

Effects of the triazole plant growth retardant BAS 111¨W on gibberellin levels in oilseed rape, Brassica napus

Three-week-old shoots of the spring oilseed rape cv. Petranova ( Brassica napus L. ssp. napus ) were found by combined gas chromatography-mass spectrometry to contain GA₁, GA₈, GA₁₅, GA₁₇, GA₁₉, GA₂₀, GA₂₄, GA₂₉, 3-epi-GA₁ and a previously uncharacterised C₁₉ dicarboxylic acid that is probably structurally related to GA₂₄. Shoots of the winter cultivar Belinda, harvested at the early flowering stage, contained the same GAs with the exception of the C₁₉ dicarboxylic acid and, in addition, GA₃₄ and GA₅₁ were identified. All material contained higher levels of GA₂₀ than of GA₁; the ratio of GA₁ to GA₂₀ was highest in shoots containing the largest proportion of young immature tissues. Soil treatment of cv. Petranova seedlings with the growth retardant BAS 111¨W [1-phenoxy-5,5-dimethyl-3-(1,2,4-triazol-1-yl)-hexan-4-ol] caused 80% reduction in height 18 days after treatment and the levels of all GAs were 20% or less that of control plants. Foliar treatment at the same dosage reduced height by 50% and caused an 85% or greater reduction in the concentrations of the GA₁ precursors GA₂₀, GA₁₉ and GA₄₄. However, the levels of GA₁, GA₈ and GA₂₉ were affected to a much smaller extent. Foliar application of BAS 111¨W to cv. Belinda 1 month after sowing resulted in only a 20% height reduction at flowering, but no uniform decrease in the concentrations of endogenous GAs at this stage.