Interactions of Abscisic Acid, Cytokinin and Gibberellin in the Control of Betacyanin Synthesis in Seedlings of Amaranthus caudatus

In de-rooted seedlings of Amaranthus caudatus L., betacyanin synthesis induced by white light or cytokinin was inhibited by abscisic acid (ABA) or a mixture of gibberellins A₄ and A₇ (GA_4/7). The GA_4/7 and ABA effects were additive. Thus ABA inhibited the cytokinin action but had no effect on the gibberellin response.     

Activity of Various Growth Substances in the Avena First Internode Test

The elongation growth of the Avena first internode segments was studied in the presence of one or several of the following growth substances: indoleacetic acid (IAA), 6-fur-furylamino purine (FAP, kinetin), 6-benzylamino purine (BAP), gibberellin A₃ (GA₃) and A₄₊₇ (GA₄₊₇), and abscisic acid (ABA). The cytokinins at concentrations of 10^?7 to 10^?6M stimulated growth with 4 to 6 per cent but this effect was not statistically significant. Concentrations higher than 5 × 10^?6M inhibited growth. FAP and BAP (from 10^?8M to 10^?6M) had no significant interaction with any other growth substance used. The two-factor interactions of IAA × ABA, IAA × GA₃, and GA₃× ABA, as well as the three-factor interaction IAA × ABA × GA₃ were significant. However, the IAA × ABA interaction was significant only when high concentration (10^?6M) of ABA was used. The growth inhibition produced by 10^?7 and 10^?6M ABA was overcome by about equimolar concentrations of IAA. The stimulation of growth by GA₃ and GA₄₊₇ (10^?9 to 10^?7M) was prevented by simultaneous application of ABA, and it was reduced significantly by application of IAA (10^?7 to 10^?8M). GA3 at 10^?8M combined with different concentrations of IAA gave slightly higher elongation than IAA alone but the observed values were significantly lower than expected assuming independent additive action.     

Interaction of jasmonic acid with some plant growth regulators in the control of apple (Malus domestica) embryo germination

Embryos isolated from dormant apple seeds were treated with jasmonic acid (JA), gibberellin A₃ (GA₃), abscisic acid (ABA) and hydrogen cyanide in darkness and in light. The chemicals were present in the culture medium continuously and simultaneously or applied for 2 days and in different sequences. All treatments stimulated embryo germination except ABA, which was strongly inhibitory. Additive effects of JA with light and with GA₃ on embryo germination were observed, whereas ABA interacted synergically with JA, HCN and light. ABA and GA₃ were most effective when applied early during embryo incubation, but the late JA treatment was more stimulatory. It is concluded that JA does not act on the regulatory pathway that is initiated by light and which leads to embryo germination through gibberellin accumulation and alkaline lipase activation. ABA and HCN appear to be involved in the control of this pathway. JA and ABA may be involved in the control of alkaline lipase activity, independently of this regulatory chain.Abbreviations ABA abscisic acid - GA₃ gibberellin A₃ - JA jasmonic acid     

Two Sites of Hormonal Action during Germination of Chenopodium album Seeds

During the overall germination process in the light-requiring seeds of Chenopodium album L. two sites of hormonal action can be distinguished. The start of visible growth is induced in darkness by the gibberellins 4 and 7 (GA₄₊₇) or by ethylene. Added cytokinins are inactive although 8-¹⁴C-kinetin shows rapid penetration into the seed and rapid turnover. The induction of growth by GA₄₊₇ and the uptake of 8-methylene-¹⁴C-GA₃ are enhanced at lower pH values. Prolonged incubation in darkness results in a decreased responsiveness of the seeds towards GA₄₊₇ and ethylene. A second site of hormonal action is located during the progress of growth inside the covering structures. ABA inhibits radicle growth, while GA₄₊₇, GA₃, kinetin, zeatin and ethylene reduce the inhibition.     

In vitro propagation of caper (Capparis spinosa L.)

Summary A twenty fold multiplication per twenty days of caper was achieved by culturing nodal shoot segments in the presence of BAP (4 μM) plus IAA (0.3 μM) and GA₃ (0.3 μM). The use of a modified MS medium facilitated this response. Plantlet regeneration was induced on single shoots taken from proliferating clusters subcultured for 20 days on a reduced BAP (2 μM) without auxin and gibberellin Higher rooting responses (70%) were obtained after a 20-day incubation period in darkness on solid half-strength MS1 medium plus IAA (30 μM), followed by a subsequent 20 day culture period on half-strength MSI basal medium. Proliferation was mainly due to axillary shoot-bud development as revealed by histological studies. The extensive meristematic activities observed indicated the enormous morphological potential of this species.     

The roles of inorganic nitrogen salts in maintaining phytochrome- and gibberellin A3-mediated germination control in skotodormant lettuce seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A₃ (GA₃). Inorganic nitrogen salts in the imbibition solutions reduced seed skotodormancy. Ten-day DS seeds, imbibed in 25 mm salt solutions followed by terminal R, germinated 99% if imbibed in NH₄NO₃, 70% if imbibed in KNO₃ or NH₄Cl, and 55% if imbibed in NaNO₃. Seeds imbibed in higher salt concentrations germinated fully upon terminal R treatment. Seeds imbibed in 25 mm NH₄Cl or in 50 mm NH₄NO₃ germinated completely upon GA₃ treatment. Osmotic effects of imbibition media accounted for only part of the effect, since seeds imbibed in 50 mm CaCl₂ or NaCl germinated poorly following R or GA₃ treatment. Seeds imbibed in 500 mm polyethylene glycol (PEG) 1000 or mannitol solutions for 10 days still exhibited skotodormancy. Treatments of R or GA₃ did not stimulate germination in seeds imbibed in mannitol, but germination was complete if seeds were given 1-h acid immersion plus a water rinse before the terminal R or GA₃ treatment. Seeds imbibed in 50–500 mm PEG during 10-day DS germinated significantly better in response to terminal R. Terminal GA₃ significantly improved germination only in seeds imbibed at 500 mm PEG. P_fr appeared to function in mannitol-imbibed seed only after an acid treatment. Seed exposure to inorganic nitrogen salts during the 10-day DS maintained seed sensitivity to terminal R or GA₃ treatment. The depth of seed skotodormancy was related to the availability of inorganic nitrogen and also involved the levels of P_fr or endogenous GA₃.Abbreviations FR far red - DS dark storage - R red - GA₃ gibberellin A₃ - PEG polyethylene glycol - SHAM salicylhydroxamic acid - ANOVA analysis of variance - GLM general linear model - LSD least squares difference - P_fr far-red absorbing form of phytochrome     

Growth regulators differentially affect photosensitivity induced by low temperature and osmotic stresses in germinating white clover seeds

Negative photoblastism induced in white clover seeds at 5°C or by lowered water potential (–0.3 MPa, polyethylene glycol) was affected by ethrel, gibberellin A₃, benzylaminopurine and kinetin treatments. The effects were different for water and temperature stressed seeds. The observed synergistic and additive effects of light and growth regulators confirm the earlier suggestion that there are two different mechanisms involved in the light inhibition of white clover seed germination induced by various adverse environmental conditions.Abbreviations ABA abscisic acid - BAP benzylaminopurine - GA₃ gibberellin A₃ - PEG polyethylene glycol     

The isolation of abscisic acid (ABA) deficient mutants by selection of induced revertants in non-germinating gibberellin sensitive lines of Arabidopsis thaliana (L.) heynh.

Summary By selecting for germinating seeds in the progeny of mutagen-treated non-germinating gibberellin responsive dwarf mutants of the ga–1 locus in Arabidopsis thaliana, germinating lines (revertants) could be isolated. About half of the revertants were homozygous recessive for a gene (aba), which probably regulates the presence of abscisic acid (ABA). Arguments for the function of this gene were obtained from lines homozygous recessive for this locus only, obtained by selection from the F₂ progeny of revertant X wild-type crosses. These lines are characterized by a reduced seed dormancy, symptoms of withering, increased transpiration and a lowered ABA content in developing and ripe seeds and leaves.Abbreviations ABA Abscisic acid - GA₄₊₇ Mixture of gibberellin A₄ and A₇ - EMS Ethylmethanesulfonate - NG Non-germinating - G Germinating     

Profile of Plant Hormones and their Metabolites in Germinated and Ungerminated Canola (Brassica napus) Seeds Imbibed at 8°C in either GA4+7, ABA, or a Saline Solution

Abscisic acid (ABA) and gibberellins (GAs) are two major phytohormones that regulate seed germination in response to internal and external factors. In this study we used HPLC-ESI/MS/MS to investigate hormone profiles in canola (Brassica napus) seeds that were 25, 50, and 75% germinated and their ungerminated counterparts imbibed at 8°C in either water, 25 μM GA₄₊₇, a 80 mM saline solution, or 50 μM ABA, respectively. During germination, ABA levels declined while GA₄ levels increased. Higher ABA levels appeared in ungerminated seeds compared to germinated seeds. GA₄ levels were lower in seeds imbibed in the saline solution compared to seeds imbibed in water. Ungerminated seeds imbibed in ABA had lower GA₄ levels compared to ungerminated seeds imbibed in water; however, the levels of GA₄ were similar for germinated seeds imbibed in either water or ABA. The ABA metabolites PA and DPA increased in seeds imbibed in either water, the saline solution, or ABA, but decreased in GA₄₊₇-imbibed seeds. In addition, ABA inhibited GA₄ accumulation, whereas GA had no effect on ABA accumulation but altered the ABA catabolism pathway. Information from our studies strongly supports the concept that the balance of ABA and GA is a major factor controlling germination.     

Roles of Soluble Sugars in Protecting Phytochrome- and Gibberellin A3-Mediated Germination Control in Skotodormant Lettuce Seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A₃ (GA₃). Soluble sugars in the imbibition solutions influenced the depth of skotodormancy. Ten-day DS seeds, imbibed in 50–500 mm sucrose or 100–500 mm glucose and given terminal GA₃ germinated completely and germinated about 80% when imbibed in 100 mm galactose, mannose, lactose, or maltose. In contrast, terminal R applied to 10-day DS seeds caused only 20–50% germination. If given R at day 0 and imbibed for 10 days in darkness in 500 mm sucrose or glucose, seeds washed free of exogenous glucose or sucrose then germinated about 50% in darkness in water. These seeds responded to terminal R or GA₃ with complete germination. When seeds were given FR at day 0, germination responses following terminal R or GA₃ were significantly lower when the duration of DS was increased from 7–10 day DS to 15 days. In 10-day DS seeds given initial FR and imbibed in either solutions of 50 or 100 mm sucrose and KNO₃, either terminal R or GA₃ treatment gave complete or near complete germination. It is concluded that seed exposure to certain soluble sugars and/or nitrate during a 10-day DS protected certain substrates and thereby extended the sensitivity of the seeds to terminal R or GA₃ treatment. The study provides substantial evidence for nonhormonal factors associated with light and GA action in the control of seed skotodormancy. Received October 30, 1996; accepted April 22, 1997     

Enhancement of Gibberellin Activity by Ethylenediaminetetraacetic Acid in Celery Seeds and Embryoless Barley Seeds

The phytochrome-controlled dormancy of celery seeds (Apium graveolens L.) can be broken by exogenously applied growth regulators. Gibberellins, especially the mixture of GA₄ and GA₇ appeared to be the primary stimuli for germination of darkincubated seeds. However, concentrations less than 1 mM were ineffective in replacing the light requirement in one celery cultivar (cv.Utah), and in another cultivar (cv.Lathom Blanching), concentrations above 1 mM were insufficient. The addition of ethylenediaminetetraacetic acid (EDTA) to gibberellins, increased markedly their activity and reduced by several orders of magnitude the gibberellin concentrations needed to stimulate a light treatment. This synergistic activity is similar to the effect of benzyladenine (BA) or Succinic acid-2,2-dimethylhydrazide (SADH) when added to gibberellins. In a diverse plant system, the mixture of gibberellin with EDTA increased significantly the amount of reducing sugars released by embryoless barley seeds.     

Differential effects of camptothecin and interactions with plant hormones on seed germination and seedling growth

Effects of camptothecin, a naturally occurring alkaloid, on seed germination varied from promotive to inhibitory, depending on the species used. It markedly inhibited seedling root growth but its inhibition of hypocotyl growth varied among species. Camptothecin inhibited GA₃-induced dark germination of lettuce (Lactuca sativa L.) seeds and hypocotyl elongation of seedlings. In contrast to ABA, the camptothecin inhibition of GA₃-induced germination could not be overcome by cytokinin. When seeds were germinated at 29C with a 0.5 h light treatment, little or no germination occurred in the camptothecin treatment, but addition of cytokinin overcame this inhibition.     

Low temperature, gibberellin and acid lipase activity in removal of apple seed dormancy

The activity of acid lipase and the level of gibberellin A₄ (GA₄) were determined in apple embryos excised from seeds after different time periods of stratification and subsequently cultured in darkness at 4°C or at 25°C. Enzyme activity and GA₄ content were higher at 4°C. Exogenous gibberellin stimulated lipase activity, while AMO-1618, an inhibitor of gibberellin biosynthesis, inhibited, to the same degree, both the enzyme activity and the GA₄ accumulation. The involvement of GA₄ and lipolytic enzymes in cold-mediated removal of embryonal dormancy has been discussed and compared with the role of these two factors in light-stimulated germination of dormant apple embryos, described earlier (Smoleńska and Lewak 1974).     

Nitrate,abscisic acid and gibberellin interactions on the thermoinhibition of lettuce seed germination

Germination of lettuce seeds has obvious thermoinhibition, but the mechanism for thermoinhibition of seed germination is poorly understood. Here, we investigated the interactions of nitrate, abscisic acid (ABA) and gibberellin on seed germination at high temperatures to understand further the mechanism for thermoinhibition of seed germination. Our results showed that lettuce (Lactuca sativa L. ‘Jianye Xianfeng No. 1’) seeds exhibited notable thermoinhibiton of germination at ≥17°C in darkness, and at ≥23°C in light, but the thermoinhibited seeds did not exhibit secondary dormancy. Thermoinhibition of seed germination at 23 or 25°C in light was notably decreased by 5 and 10 mM nitrate, and the stimulatory effects were markedly prevented by nitric oxide (NO) scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. The sensitivity of seed germination to exogenous ABA increased with increasing temperature. Thermoinhibition of seed germination was markedly decreased by fluridone (an inhibitor of ABA biosynthesis) and GA₃, and was increased by diniconazole (an inhibitor of the ABA-catabolizing enzyme ABA 8′-hydroxylase) and paclobutrazol (an inhibitor of GA biosynthetic pathway). The effect of fluridone in decreasing thermoinhibition of seed germination was obviously antagonized by paclobutrazol, and that of GA₃ was notably added to by fluridone, and that of nitrate was antagonized by paclobutrazol, diniconazole and ABA and was added to by GA₃ and fluridone. Our data show that thermoinhibition of lettuce seed germination is decreased by nitrate in a NO-dependent manner, which is antagonized by ABA, diniconazole and paclobutrazol and added by fluridone.     

The role of endogenous gibberellins in the formation of α-amylase by aleurone layers of germinating barley caryopses

Using sensitive and selective immunological assays we have shown that in germinating caryopses of Hordeum vulgare L. cv. Himalaya, the level of gibberellin A₄ (GA₄) rises approximately 18-to 20-fold shortly (2–4 h) before -amylase activity increases. Gibberellin A₄ is the predominant immunoreactive gibberelin during these developmental stages and reaches a peak amount of approximately 9 pmol per caryopsis about 48 h after imbibition. Isolated aleurone layers produce GA₄ in the presence of an exogenous gibberellin, such as GA₁, which is not a biosynthetic precursor for GA₄. Experiments with inhibitors of gibberellin biosynthesis indicate that gibberellin synthesis is required in this tissue for the induction of -amylase. The inductive effect of exogenously applied GA₁ is indirect and appears to be mediated by GA₄. Embryos form predominantly GA₁; however, very little of this material is released by isolated embryos into the incubation medium. The results presented make it unlikely that the role of the embryo in the process of -amylase induction in aleurone layers is to provide gibberellins or gibberellin precursors.Abbreviations ABA abscisic acid - GA gibberellin - GA₃ gibberellic acid - RIA radioimmunoassay - TLC thin-layer chromatography     

Phytochrome inhibits the effectiveness of gibberellins to induce cell elongation in rice

Red light controls cell elongation in seedlings of rice (Oryza sativa L.) in a far-red-reversible manner (Nick and Furuya, 1993, Plant Growth Regul. 12, 195–206). The role of gibberellins and microtubules in the transduction of this response was investigated in the rice cultivars Nihon Masari (japonica type) and Kasarath (indica type). The dose dependence of mesocotyl elongation on applied gibberellic acid (GA₃) was shifted by red light, and this shift was reversed by far-red light. In contrast, coleoptile elongation was found to be independent of exogenous GA₃. Nevertheless, it was inhibited by red light, and this inhibition was reversed by far-red light. The content of the active gibberellin species GA₁ and GA₄ was estimated by radio-immunoassay. In the mesocotyl, the gibberellin content per cell was found to increase after irradiation with red light, and this increase was far-red reversible. Conversely, the cellular gibberellin content in japonica-type coleoptiles did not exhibit any significant light response. Microtubules reoriented from transverse to longitudinal arrays in response to red light and this reorientation could be reversed by subsequent far-red light in both the coleoptile and the mesocotyl. This movement was accompanied by changes in cell-wall birefringence, indicating parallel reorientations of cellulose deposition. The data indicate that phytochrome regulates the sensitivity of the tissue towards gibberellins, that gibberellin synthesis is controlled in a negative-feedback loop dependent on gibberellin effectiveness, and that at least two hormone-triggered signal chains are linked to the cytoskeleton in rice.Abbreviations D darkness - FR far-red light - GA₃ gibberellic acid - GC-SIM gas chromatography-selected ion monitoring - R red light This work was supported by a grant of the Human Frontier Science Organization to P.N. Advice and organizational support by Prof. M. Furuya (Hitachi Advanced Research Laboratory, Hatoyama, Japan) and Prof. N. Murofushi (Department of Agricultural Chemistry, University of Tokyo, Japan) is gratefully acknowledged. Seeds of both rice cultivars were kindly provided by Dr. O. Yatou (Institute for Radiation Breeding, Hitachi-Ohmiya, Japan), and the antiGA₁ Me-antiserum for the radio-immunoassays by Dr. I. Yamaguchi (Department of Agricultural Chemistry, University of Tokyo, Japan).     

Induction of Secondary Dormancy in Chenopodium bonus-henricus L. Seeds by Osmotic and High Temperature Treatments and Its Prevention by Light and Growth Regulators

Factors controlling the establishment and removal of secondary dormancy in Chenopodium bonus-henricus L. seeds were investigated. Unchilled seeds required light for germination. A moist-chilling treatment at 4 C for 28 to 30 days removed this primary dormancy. Chilled seeds now germinated in the dark. When chilled seeds were held in the dark in −8.6 bars polyethylene glycol 6000 solution at 15 C or in water at 29 C a secondary dormancy was induced which increased progressively with time as determined by subsequent germination. These seeds now failed to germinate under the condition (darkness) which previously allowed their germination. Continuous light or daily brief red light irradiations during prolonged imbibition in polyethylene glycol solution at 15 C or in water at 29 C prevented the establishment of the secondary dormancy and caused an advancement of subsequent germination. Far red irradiations immediately following red irradiation reestablished the secondary dormancy indicating phytochrome participation in “pregerminative” processes. The growth regulator combination, kinetin + ethephon + gibberellin A₄+A₇ (GA₄₊₇), and to a relatively lesser extent GA₄₊₇, was effective in preventing the establishment of the secondary dormancy and in advancing the germination or emergence time. Following the establishment of the secondary dormancy by osmotic or high temperature treatments the regulator combination was relatively more active than light or GA₄₊₇ in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA₄₊₇ control. The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant. These changes appear to be modulated by light and hormones.     

Evidence for Phytochrome Regulation of Gibberellin A(20) 3beta-Hydroxylation in Shoots of Dwarf (lele) Pisum sativum L

The effect of light on the dwarfing allele, le, in Pisum sativum L. was tested as the growth response to gibberellins prior to or beyond the presumed block in the gibberellin biosynthetic pathway. The response to the substrate (GA₂₀), the product (GA₁), and a nonendogenous early precursor (steviol) was compared in plants bearing the normal Le and the deficient lele genotypes in plants made low in gibberellin content genetically (nana lines) or by paclobutrazol treatment to tall (cv Alaska) and dwarf (cv Progress) peas. Both genotypes responded to GA₁ under red irradiation and in darkness. The lele plants grew in response to GA₂₀ and steviol in darkness but showed a much smaller response when red irradiated. The Le plants responded to GA₂₀ and steviol in both light and darkness. The red effects on lele plants were largely reversible by far-red irradiation. It is concluded that the deficiency in 3β-hydroxylation of GA₂₀ to GA₁ in genotype lele is due to a Pfr-induced blockage in the expression of that activity.     

GA3 induced flowering in Podophyllum hexandrum Royle: A rare alpine medicinal herb

Podophyllum hexandrum Royle, an important alpine herb, is the source of highly valued podophyllotoxin. The effect of some plant growth substances (GA₃, BAP & ABA), uniconazole (an inhibitor of GA biosynthesis), and a combination of GA₃ and uniconazole were examined in respect to influence on sprouting in rhizomes of P. hexandrum and on induction of flowering at a lower altitude. Amongst the various chemicals tested, GA₃ had a marked effect resulting in uniform sprouting and also induced flowering in about half of the treated rhizomes. While BAP also promoted early sprouting, delayed sprouting was seen in rhizomes treated with ABA. Uniconazole treatment, either alone or with GA₃ was found to inhibit flowering and also resulted in reduced plant height. GA₃ treatment of rhizomes from plants that was maintained for up to 30 months at a lower altitude also induced flowering thus replacing the normal chilling requirement of plants. These results suggest that treatment of GA₃ could be effectively used for inducing uniform sprouting and flowering in rhizomes of P. hexandrum grown at lower altitudes.     

Interactions of phytochrome and exogenous gibberellic acid on germination of Lamium amplexicaule L. seeds

Summary In henbit (Lamium amplexicaule L.) seeds, micromolar levels of gibberellic acid (GA₃) introduced at the onset of imbibition markedly stimulated germination. Sensitivity to GA₃ stimulation is rapidly lost if the seeds are pretreated in darkness at 15° for 1 day or more on a water substrate. Loss in responsiveness to GA₃ is hastened by pretreatment in far-red or by dark pretreatment at higher (25°) temperatures and is reduced by pretreatments at 5°. A portion of the lost responsiveness to GA₃ at 15° or higher is attributable to onset of a secondary dormancy, but the results of far-red treatment at 5°, where secondary dormancy is not a factor, clearly indicate that some phytochrome in the far-red absorbing form increased the effectiveness of gibberellic acid action.Abbreviations GA gibberellin - GA₃ gibberellic acid - R red light - FR far-red - P_r red-absorbing form of phytochrome - P_fr far-red-absorbing form of phytochrome Mention of a trade name or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable