Presence Of Gibberellins Research Articles

Presence of gibberellins in habanero pepper seeds

Presence of gibberellins in habanero pepper seeds

水稲地上部の形質に対する窒素の作用とその作用におけるジベレリンの関与について : 植物生長調節剤の土壌肥料学的研究(第6報)

水稲地上部の形質に対する窒素の作用とその作用におけるジベレリンの関与について : 植物生長調節剤の土壌肥料学的研究(第6報)

Effects of Environmental Factors on Seed Germination and Seedling Emergence of Common Teasel (Dipsacus fullonum)

Common teasel is an invasive and widespread weed in Argentina. Germination experiments were carried out from 2011 to 2014 to determine the effect of various environmental factors on germination and emergence. Germination of recently dispersed seeds was 12% in darkness at constant temperature. In contrast, seed exposure to light and alternating temperatures enhanced germination to 95%. The requirement of light and alternating temperatures suggest that common teasel has physiological dormancy. Several experiments were carried out to determine whether (1) seed responses to light and alternating temperatures have a hormonal basis, (2) seed coats can suppress germination, and (3) time and thermal conditions during seed storage reduce light and alternating temperature requirements. Germination was reduced (≤ 13%) by a gibberellin synthesis inhibitor. In contrast, the presence of gibberellins and an abscisic acid synthesis inhibitor increased germination to 95 and 38%, respectively. Results suggest that a higher ratio among gibberellins and abscisic acid (GA/ABA) leads to a break in dormancy. Germination was 100% when embryos were excised, suggesting that seed coats may suppress germination by mechanical restriction. Likewise, germination was enhanced by hydrogen peroxide (70%). This compound is known to increase GA/ABA ratio in agreement with a hormonal control of dormancy proposed for common teasel. An increment of storage time reduces light and alternating temperature requirements, allowing seeds to germinate in darkness. Taking these results together confirms that common teasel has physiological dormancy. Seedling emergence was progressively reduced from 70 to 8% by increased burial depth from 0 to 3 cm. Information from these experiments may facilitate development of effective management for common teasel.

Sucrose-induced hypocotyl elongation of Arabidopsis seedlings in darkness depends on the presence of gibberellins

In this study, the effects of sucrose on hypocotyl elongation of Arabidopsis seedlings in light and in dark were investigated. Sucrose suppressed the hypocotyl elongation of Arabidopsis seedlings in light, but stimulated elongation in dark. Application of paclobutrazol (PAC, a gibberellin biosynthesis inhibitor) impaired the effects of sucrose on hypocotyl elongation, suggesting that endogenous GAs is required for sucrose-induced hypocotyl elongation in the dark. Exogenous GA 3 application reversed the repression caused by PAC application, indicating that exogenous GA 3 could substitute, at least partially, for endogenous GAs in sucrose-induced hypocotyl elongation. In addition, we found that GA 3-oxidase 1 ( GA3ox1), encoding a key enzyme involved in endogenous bioactive GA biosynthesis, was up-regulated by sucrose in the dark, whereas GIBBERELLIN INSENSITIVE DWARF 1a ( AtGID1a), encoding a GA receptor and playing an important role during GAs degradation to DELLA proteins (DELLAs, repressors of GA-induced plant growth), was down-regulated. These results imply that endogenous bioactive GA levels are expected to be enhanced, but the degradation of DELLAs was inhibited by sucrose in dark. Thus, our data suggest that the sucrose-induced hypocotyl elongation in the dark does not result from GA-induced degradation of DELLAs. We conclude that sucrose can stimulate hypocotyl elongation of Arabidopsis seedlings in the dark in a GA-dependent manner.

Genes involved in ethylene and gibberellins metabolism are required for endosperm-limited germination of Sisymbrium officinale L. seeds

The rupture of the seed coat and that of the endosperm were found to be two sequential events in the germination of Sisymbrium officinale L. seeds, and radicle protrusion did not occur exactly in the micropylar area but in the neighboring zone. The germination patterns were similar both in the presence of gibberellins (GA(4+7)) and in presence of ethrel. The analysis of genes involved in GAs synthesis and breakdown demonstrated that (1) SoGA2ox6 expression peaked just prior to radicle protrusion (20-22 h), while SoGA3ox2 and SoGA20ox2 expression was high at early imbibition (6 h) diminishing sharply thereafter; (2) the accumulation of SoGA20ox2 transcript was strongly inhibited by paclobutrazol (PB) as well as by inhibitors of ET synthesis and signaling (IESS) early after imbibition (6 h), while SoGA3ox2 and SoGA2ox6 expression was slowly depressed as germination progressed; (3) ethrel and GA(4+7) positively or negatively affected expression of SoGA3ox2, SoGA20ox2, and SoGA2ox6, depending on the germination period studied. Regarding genes involved in ET synthesis, our results showed that SoACS7 was expressed, just prior to radicle emergence while SoACO2 expression slowly increased as germination progressed. Both genes were strongly inhibited by PB but were almost unaffected by externally added ethrel or GA(4+7). These results suggest that GAs are more important than ET during the early stages of imbibition, while ET is more important at the late phases of germination of S. officinale L. seeds.

Genomic insights in moss gibberellin biosynthesis

Gibberellins are phytohormones that are essential for proper growth and development of flowering plants. In bryophytes, however, the presence of gibberellins has not been firmly established, because previous reports of gibberellin-like activities were not accompanied by definitive chemical identification. By comparison, the other classical phytohormones auxin, cytokinin, abscisic acid and ethylene have been unambiguously detected in both mosses and liverworts, and their functions have been demonstrated to be very similar to those in flowering plants. The study of gibberellins in bryophytes lagged behind those of other phytohormones presumably because of the bewildering complexity and diversity in their chemical structures. In addition, working with bryophytes becomes even more challenging given their small size and the lack of obvious developmental mutants in the gibberellin signaling pathway. On the other hand, the recent sequencing of the Physcomitrella patens genome provides exciting opportunities to tackle this problem. Genes that may be involved in gibberellin biosynthesis have now been identified, paving the way for molecular genetic experiments that could reveal the role of gibberellins in bryophyte development. As bryophytes represent the earliest diverging lineages of land plants, such studies can also provide insights into how the gibberellin pathway may have evolved in the course of land plant evolution.

Hormonal regulation of tomato seed germination at a supraoptimal temperature

Germination of tomato cv. New Yorker seed is inhibited at 35°C. This thermoinhibition was partially counteracted by application of GA4+7 alone, the compound applied in combination with ACC or ethephon markedly enhancing the process. The latter compound alone was not able to induce germination at 35 °C. Thermoinhibition of seeds at 35 °C was also counteracted by fluridone, an inhibitor of ABA biosynthesis. At 25 °C, an optimal temperature, ABA inhibited germination of New Yorker seeds. Although another known growth inhibitor MeJA, when applied at an optimal temperature (25 °C), had also a slightly inhibitory effect on germination of those seeds and clearly delayed the process, inhibitors of its biosynthetic pathway (ibuprofen, indoprofen, antypiryne and salicylic acid) did not remove thermoinhibition at 35 °C. An increase in endo-β-mannanase activity after 24 hours of incubation at 35 °C was observed in the seeds incubated in the presence of gibberellins, ACC, ethephon, fluridone used alone and in combinations, but it was not clearly correlated with the effects of these compounds on alleviation of seed germination. However, fluridone present in the same incubation medium at 35 °C with ABA was able to counteract the inhibitory effect of ABA on endo-β-mannanase activity. The results of our study suggest that gibberellins, ethylene (produced from ACC or ethephon) and ABA, but not jasmonates, regulate tomato seed germination at supraoptimal temperatures. Alleviation of thermoinhibition of New Yorker seed germination by plant growth regulators and fluridone is partially associated with their controlling endo-β-mannanase activity.

Relationship of Endo-[beta]-D-Mannanase Activity and Cell Wall Hydrolysis in Tomato Endosperm to Germination Rates.

The endosperm tissue enclosing the radicle tip (endosperm cap) governs radicle emergence in tomato (Lycopersicon esculentum Mill.) seeds. Weakening of the endosperm cap has been attributed to hydrolysis of its mannan-rich cell walls by endo-[beta]-D-mannanase. To test this hypothesis, we measured mannanase activity in tomato endosperm caps from seeds allowed to imbibe under conditions of varying germination rates. Over a range of suboptimal temperatures, mannanase activity prior to radicle emergence increased in accordance with accumulated thermal time. Reduced water potential delayed or prevented radicle emergence but enhanced mannanase activity in the endosperm caps. Abscisic acid did not prevent the initial increase in mannanase activity, although radicle emergence was markedly delayed. Sugar composition and percent mannose (Man) content of endosperm cap cell walls did not change prior to radicle emergence under any condition. Man, glucose, and other sugars were released into the incubation solution by endosperm caps isolated from intact seeds during imbibition. Pregerminative release of Man was suppressed and the release of glucose was enhanced when seeds were incubated in osmoticum or abscisic acid; the opposite occurred in the presence of gibberellin. Thus, whereas sugar release patterns were sensitive to environmental and hormonal factors affecting germination, neither assayable endo-[beta]-D-mannanase activity nor changes in cell wall sugar composition of endosperm caps correlated well with tomato seed germination rates under all conditions.

Inhibitory effect of GA3 on the development of thidiazuron-induced somatic embryogenesis in geranium (Pelargonium xhortorum Bailey) hypocotyl cultures

Somatic embryogenesis in geranium (Pelargonium xhortorum Bailey cv 'Scarlet Orbit Improved') can be achieved by incubating hypocotyl explants on MS medium supplemented with thidiazuron (TDZ; 10 μM for 3 days followed by subculture on medium devoid of any plant growth regulators. The presence of gibberellins (GAs) during both the induction and expression phases of embryogenesis was significantly detrimental to somatic embryo formation on the hypocotyl explants. The addition of the GA-synthesis inhibitors paclobutrazol, uniconazole or ancymidol during the period of growth and differentiation of somatic embryos increased the number of somatic embryos formed on each explant. However, paclobutrazol added during the period of induction had no significant influence on somatic embryo formation. Results suggest that both exogenously supplied as well as endogenous GAs play a role, albeit a negative one, on somatic embryogenesis of geranium.

Flowering as metamorphosis: two sequential signals regulate floral initiation in Lolium temulentum.

We investigated floral initiation in the long-day monocot Lolium temulentum, strain Ceres, by culturing apices explanted from photoperiodically induced plants at various times after one inductive long day onto medium with, and without, gibberellin. Apices cultured on the first day after the inductive long day usually required gibberellin in the medium to initiate floral morphogenesis while apices explanted on the second day after induction did not require gibberellin. Apices explanted on the first day after induction onto medium without gibberellin grew vegetatively for many days but a several-day exposure to culture medium with gibberellin at any time caused most apices to initiate floral morphogenesis. The gibberellin synthesis inhibitor, ancymidol, when applied to plants before apex excision and when present in the culture medium reduced floral initiation by more than 50% in the absence of added gibberellin in the medium, but it was ineffective in the presence of gibberellin. These results indicated that floral initiation in photoperiodically induced plants resulted from two signals acting at the apex. The first signal induced the apex into a florally determined state and then the second signal, gibberellin, elicited expression of the florally determined state. Leaf removal and culture of apices from plants previously treated with gibberellin provided evidence that the leaf-applied gibberellin did not itself act on the apex to cause floral determination or initiation. Rather, the exogenous gibberellin appeared to stimulate the production of a signal in the leaves that then led to floral initiation.

Isolation and characterization of a gibberellin-stimulated rice ( Oryza sativa L.) gene encoding a protein that resembles a tumor suppressor

Two rice cDNAs and a genomic clone were isolated and characterized. These genes showed high sequence similarity,72% amino acid similarity, to members of the human QM gene family. The QM gene is known to encode a putative human Wilms' tumor suppressor. Sequence alignments between the genomic and cDNA clones of rice resulted in identifying three introns and four exons in the genomic clone SG12. This gene was constitutively expressed at high levels in the rice tissues examined, including shoots, roots, and germinating seeds. Interestingly, the expression of the rice QM-like gene was stimulated ≥10-fold by the presence of gibberellin in germinating seeds.

In vitro morphogenic characteristics of phytochrome mutants in Nicotiana plumbaginifolia are modified and correlated to high indole-3-acetic acid levels

The involvement of indole-3-acetic acid (IAA) in the integration of the light signal perceived by phytochrome during the morphogenesis of plants was investigated in Nicotiana plumbaginifolia Viviani. The chromophore mutant pew1, deficient in all the phytochrome types, and the aurea-like mutant pew2, which appears to be specifically deficient in phytochromes expressed in darkness, were analysed for IAA-related morphogenic effects such as rooting, shooting and callus formation. We observed, in the absence of exogenously applied hormones, abundant root formation by the pew2 mutant. The pew1 mutant exhibited callus formation in the presence of gibberellins and cytokinins when the wild type did not. The previously described lethality of the double mutant pew1–pew2 was shown to be hormone-dependent since, in the light, exogenously applied auxin and cytokinin (0.1 mg·1−1 each) led to plant regeneration from calli and subsequent normal development. These observations suggested an increase in the auxin/cytokinin ratio as a consequence of the phytochrome mutations. We correlated these morphogenic characteristics with high IAA levels in the mutants. The difference in IAA accumulation in the two mutants indicates that among the different phytochromes expressed by N. plumbaginifolia, the light-expressed isoforms play a major role in the control of IAA levels.

Improving Papaya Seedling Emergence by Matriconditioning and Gibberellin Treatment

Papaya (Carica papaya L.) seeds germinated poorly at 25C in the presence of gibberellin (GA4+7) or following matriconditioning at 25C for 4 days. However, a combined treatment of matriconditioning and GA4+7 for 4 days synergistically promoted germination and seedling emergence. Drying the seeds after conditioning reduced the percentage of seedling emergence in the combined treatment involving 400 μm GA4+7 only. Combining matriconditioning with 100 or 200 μm GA4+7could effectively reduce germination time and improve seedling emergence and is recommended as a standard procedure for testing papaya seed germination.

Enhancement by Putrescine of Gibberellin-Induced Elongation in Hypocotyls of Lettuce Seedlings

Effects of diamines, polyamines, and other basic amino acids on the growth of lettuce hypocotyls were investigated. Putrescine, cadaverine and agmatine enhanced the hypocotyl growth in the presence of gibberellin, while spermidine and spermine were non-effective. Arginine and ornithine, which may be precursors of putrescine, had similar effect. While the growth inhibition due to arcaine (1,4-diguanidinobutane), which is a agmatine iminohydrolase inhibitor, was recovered by agmatine, cadaverine, putrescine, and spermidine, putrescine most effectively recovered its growth-enhancing effect.

Increase in the gibberellin response by low temperature pretreatment of azuki bean epicotyls

Epicotyl segments cut from azuki bean (Vigna angularis) seedlings grown at 27 C for 5 days and then treated at 15 C for 2 days were compared with those cut from seedlings not receiving the 15-C treatment, for their response to auxin and auxin plus gibberellin. The segments cut from 15C-treated seedlings showed greater elongation than the segments cut from untreated seedlings both in the absence and in the presence of gibberellin. The 15-C treatment increased the elongation caused by auxin plus gibberellin to a greater extent than it did the elongation caused by auxin alone; the gibberellin response of epicotyl was increased by the treatment.Diffusates from leaves and buds inhibited both the elongation caused by auxin and that caused by auxin plus gibberellin. The diffusates inhibited the latter more strongly than the former; the gibberellin response was decreased by the diffusates. Leaves or buds appear to supply epicotyls with a substance which decreases the gibberellin response. The supply of this substance was found to be temperature dependent. The diffusates obtained at 15 C caused no inhibition, while those obtained at 27 C decreased the gibberellin response.The lack of the supply of this substance at 15 C may account for the increase in the gibberellin response by the 15-C treatment.

Fractionation of Gibberellins in Plant Extracts by Reverse Phase High Performance Liquid Chromatography

In studies on endogenous plant gibberellins (GAs), reverse phase (Bondapak C(18)) high performance liquid chromatography (HPLC) has proved to be a useful method for the fractionation of plant extracts. The behavior of 18 authentic GAs in such a chromatographic system is described. The main factors determining chromatographic behavior are the degree and the position of hydroxylation of the GA. Generally, dihydroxylated GAs elute before monohydroxylated GAs, whereas 13-hydroxylated GAs elute before 3-hydroxylated GAs. The number of carboxyl groups and the degree of saturation of the A-ring have little effect. For 20-carbon GAs, the oxidation state at C-20 is only relevant insofar as GAs having a methyl group at this position elute later than those with other groups (lactone, aldehyde, or carboxyl).As an illustration of the use of reverse phase HPLC, the endogenous GAs of immature seeds of Pharbitis nil L., strain "Violet," were reinvestigated. The presence of gibberellins A(3), A(5), A(17), A(20), and A(29) was confirmed by gas-liquid chromatography-mass spectrometry. In addition, two other GAs, A(19) and A(44), were also identified in extracts of this material.

Role of Indole-3-acetic Acid and Gibberellin in the Control of Internodal Elongation in Avena Stem Segments

Exogenous application of indoleacetic acid results in a significant suppression of the linear growth that is promoted by exogenous gibberellic acid in Avena stem segments in a fashion similar to that previously noted in Avena leaf base segments (van Overbeek and Dowding, 1961, Fourth International Conference Plant Growth Regulation). Treatment with the auxin transport inhibitors, methyl-2-chloro-9-hydroxyfluorene-(9)-carboxylate (CFM) or 2,3,5-triiodobenzoic acid (TIBA), alone promotes elongation growth of the stem segments over that of control growth. This effect is interpreted as being due to the interference in the transport of native indoleacetic acid by CFM and TIBA, thus removing the inhibitory effect of native indoleacetic acid on gibberellin-promoted growth in the internodal intercalary meristem. This results in a greater promotion of internodal growth by native gibberellins. In the presence of (2-chloroethyl) trimethylammonium chloride (CCC), the growth-promoting effects of CFM and TIBA are decreased, and the antiauxin, PCIB (4-chloro-phenoxyisobutyric acid), has no growth-promoting effects whatsoever. These results indicate that the CFM and TIBA-promoted growth require the continuous presence of gibberellins. They further support the view that native indoleacetic acid acts as a growth suppressor hormone in its regulation of gibberellin-promoted internodal extension in Avena shoots.

Preferential stimulation of the plant mRNA synthesis by gibberellic acid.

1. Treatment of the etiolated maize seedlings with the plant hormone, gibberellic acid results in a significant enhancement of heavy polyribosome formation. 2. This is accompanied by highly increased incorporation of the labelled RNA precursors into RNA engaged in the polyribosomal complex, as well as by an increased rate of protein synthesis in vivo. 3. Determination of the specific radioactivity of particular RNA classes isolated from polyribosomes reveals that gibberellic acid stimulates mostly the synthesis of the rapidly labelled, non-ribosomal RNA fraction. 4. A considerable amount of this rapidly labelled RNA fraction, whose synthesis is preferentially stimulated by exogenous gibberellic acid contains poly(A) sequences, as shown by affinity chromatography on oligo (dT)-cellulose indicating that phytohormone causes an increased transcription of mRNA in etiolated maize seedlings. 5. When [3H]adenosine served as the RNA precursor it was found that the ratio between the heteropolymeric and polyadenylic parts of the poly(A)-RNA chain markedly changed under gibberellin treatment, suggesting that, in addition to an increased rate of mRNA synthesis, the plant hormone also affects the process of post-transcriptional polyadenylation of the newly made mRNA precursors. Possible extension of the polyadenylate segment in the presence of gibberellin may account for a longer functional half-life of the mRNA synthesized in plants treated with the phytohormone, and may explain significantly enhanced heavy polyribosome formation, as well as a higher efficiency of protein synthesis in plants treated with gibberellic acid.

Embryoless Wheat Grain

Yorkstar wheat, grown in New York State, has a high percentage (10-11) of grains without embryos. The embryoless grains have viable aleurone layers and show no sign of injury. These grains are able to support alpha-amylase synthesis only in the presence of gibberellin A(3) (GA(3)). In the absence of GA(3) some protein synthesis occurs in embryoless grains during the early hours of soaking, indicating that such activity occurs prior to and independent of GA(3) induction of alpha-amylase. The level of beta-amylase on a dry weight basis is the same in embryoless and normal grains and decreases with time of soaking. In the presence of GA(3), beta-amylase decreases at a slower rate. Isoenzymes of alpha-amylase from GA(3)-treated embryoless and normal grains show quantitative as well as qualitative differences. Cycloheximide (60 mug/ml) completely inhibits the synthesis of alpha-amylase by embryoless grains. Of the RNA synthesis inhibitors, actinomycin D (60 mug/ml) was ineffective while 6-methylpurine (60 mug/ml) gave 65% inhibition without decreasing the number of isoenzymes.

Hormonal regulation of germination and early seedling development in Acer pseudoplatanus (L.)

Dormancy of intact sycamore (Acer pseudoplatanus) seeds was broken by chilling (5°C) for several weeks in moist conditions. Treatment of unchilled seeds with kinetin induced some germination, but gibberellin was ineffective. This stimulation by kinetin was not suppressed by the added presence of abscisic acid during incubation.The chilling requirement of intact seeds was eliminated by removal of the testa, and the naked embryos developed with no morphological abnormalities. During early growth of isolated embryos in the light, two distinct developmental processes were recognised. One involved initial elongation of the radicle accompanied by geotropic curvature and was stimulated by kinetin but not by gibberellin, while the other involved unrolling of the cotyledons, which was accelerated by gibberellin but much less by kinetin. Abscisic acid strongly suppressed both developmental processes when applied alone, inhibited cotyledon expansion in the presence of gibberellin, but failed to overcome the promotory effects of kinetin on radicle growth. Experiments with CCC indicated that under natural conditions the unrolling of the cotyledons is dependent upon endogenous gibberellin. Radicle growth of isolated embryos was unimpaired by incubation in the dark, but cotyledon expansion of water incubated embryos was poor, and although it was accelerated by gibberellin, the responses in all treatments were slower than in the corresponding light grown samples.It is suggested that endogenous cytokinins are primary factors in the initiation of radicle growth, while gibberellins are important in cotyledon expansion. Abscisic acid appears to have an inhibitory role in both processes, and the interactions of these regulators in the control of germination and development are discussed.