Inhibition of Abscisic Acid Biosynthesis in Cercospora rosicola by Inhibitors of Gibberellin Biosynthesis and Plant Growth Retardants

The fungus Cercospora rosicola produces abscisic acid (ABA) as a secondary metabolite. We developed a convenient system using this fungus to determine the effects of compounds on the biosynthesis of ABA. Inasmuch as ABA and the gibberellins (GAs) both arise via the isoprenoid pathway, it was of interest to determine if inhibitors of GA biosynthesis affect ABA biosynthesis. All five putative inhibitors of GA biosynthesis tested inhibited ABA biosynthesis. Several plant growth retardants with poorly understood actions in plants were also tested; of these, six inhibited ABA biosynthesis to varying degrees and two had no effect. Effects of plant growth retardants on various branches of the isoprenoid biosynthetic pathway may help to explain some of the diverse and unexpected results reported for these compounds. Knowledge that certain inhibitors of GA biosynthesis also have the ability to inhibit ABA biosynthesis in C. rosicola indicates the need for further studies in plants on the mode of action of these compounds.     

Inhibition of Gibberellin Production in the Fungi Gibberella fujikuroi and Sphaceloma manihoticola by Plant Growth Retardants

The effect of different types of plant growth retardants on fungal gibberellin (GA) formation has been studied in cultures of Gibberella fujikuroi and Sphaceloma manihoticola. Quaternary ammonium compounds (chlormequat chloride, mepiquat chloride, Amo-1618), triazoles (uniconazole and several experimental compounds), and the norbornanodiazetine tetcyclacis inhibited GA biosynthesis in both fungal species. Concentrations between 2 × 10⁻⁴ and 10⁻⁹m were required for a 50% inhibition of the production of gibberellin A₃ in Gibberella fujikuroi and of giberellin A₄ in Sphaceloma manihoticola. The formation of other prominent GAs was affected at a similar degree of intensity. Tetcyclacis was the most active compound in both fungi. Compared to the growth retardants mentioned above, the biological activity of chlorphonium chloride was low. The acylcyclohexanediones prohexadione and LAB 198 999 had virtually no activity. Most likely, this lack of activity is due to a rapid metabolism of the compounds in the cultures. For the triazole-type compounds and tetcyclacis, a relatively distinct correlation exists in their ability to inhibit GA formation in fungal cultures, to block ent-kaurene oxygenase in a cell-free system, and to reduce shoot growth of rice seedlings. Due to differences in their metabolic fate and species specificities, such conclusions cannot be made for the other compounds.     

Gibberellin and CCC Effects on Flowering and Growth in the Long-day Plant Lemna gibba G3

The application of gibberellic acid (GA₃) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at concentrations of 1 mg/l and higher. On both short and long days GA₃ concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A₇ was used instead of GA₃.     

Nighttime Sugar Starvation Orchestrates Gibberellin Biosynthesis and Plant Growth in Arabidopsis

A plant’s eventual size depends on the integration of its genetic program with environmental cues, which vary on a daily basis. Both efficient carbon metabolism and the plant hormone gibberellin are required to guarantee optimal plant growth. Yet, little is known about the interplay between carbon metabolism and gibberellins that modulates plant growth. Here, we show that sugar starvation in Arabidopsis thaliana arising from inefficient starch metabolism at night strongly reduces the expression of ent-kaurene synthase, a key regulatory enzyme for gibberellin synthesis, the following day. Our results demonstrate that plants integrate the efficiency of photosynthesis over a period of days, which is transduced into a daily rate of gibberellin biosynthesis. This enables a plant to grow to a size that is compatible with its environment.     

植物生长延缓剂对盆栽月季生长发育的影响

采用不同质量浓度的3种植物生长延缓剂多效唑(PP333)、矮壮素(CCC)、缩节胺(DPC),运用叶喷和灌根两种处理方式,通过测定植株的形态指标(株高、节间长、叶片长与宽、花枝长、花梗长、花径及初花期等)和生理生化指标(叶绿素含量、光合速率、蒸腾速率、叶片酶活性及可溶性糖含量等),研究3种药剂对盆栽月季‘世纪之春’生长发育的影响。结果表明:(1)不同药剂的使用浓度和方式对盆栽月季的形态和生理指标有不同程度的影响,适宜浓度和方式处理能缩短植株节间长度来降低株高,使株型饱满,开花正常,提高观赏价值;同时可以增加叶片叶绿素含量,提高光合效率,增加叶片超氧化物歧化酶和过氧化物酶活性及可溶性糖含量,对改善盆栽月季观赏品质有重要影响;(2)叶面喷洒700mg.kg-1 PP333和灌根300mg.kg-1 PP333的调控效果最好,喷洒1 200mg.kg-1CCC和300mg.kg-1 DPC效果次之,均能达到有效降低株高和提高观赏效果的目的。     

Effect of Gibberellin Biosynthesis Inhibitors on Native Gibberellin Content, Growth and Floral Initiation in Sorghum bicolor

CCC, uniconazol, ancymidol, prohexadione-calcium (BX-112), and CGA 163′935, which represent three groups of gibberellin (GA) biosynthesis inhibitors, were applied as a soil drench to Sorghum bicolor cultivars 58M (phyB-1, phytochrome B-deficient mutant) and 90M (phyB-2, equivalent phenotypically to wild type, PHYB, except for small differences in flowering dates). The inhibitors that block steps before GA₁₂ (CCC, uniconazol, and ancymidol) lowered the concentrations of all endogenous early-C13α-hydroxylation pathway GAs found in sorghum: GA₁₂, GA₅₃, GA₄₄, GA₁₉, GA₂₀, GA₁, and GA₈. In contrast, the inhibitors that block the conversion of GA₂₀→ GA₁, (CGA 163′935 and BX-112) drastically reduced GA₁ and GA₈ levels, but they either did not change or caused accumulation of intermediates from GA₁₂ to GA₂₀. Combinations of pre-GA₁₂ inhibitors and GA₃ plus GA₁ strongly reduced GAs other than GA₁ and GA₃. Each of these compounds inhibited shoot growth in both cultivars and delayed floral initiation in 90M. Floral initiation of 58M was also delayed by CCC, uniconazol, and ancymidol but not by CGA 163`935 and BX-112. This separation of shoot elongation from floral initiation in sorghum is novel. Both inhibition of shoot growth and delayed floral initiation were almost completely relieved by a mixture of GA₃ and GA₁ in both 58M and 90M. This observation, plus the much lower levels of endogenous GA₃ than of GA₁ observed in these experiments, implies that GA₁ is the major endogenous GA active in shoot elongation. CGA 163′935 and BX-112 also failed to promote tillering in 58M, whereas inhibitors active before GA₁₂ did so. The possibility that the GA₂₀→ GA₁ inhibitors fail to block flowering and promote tillering in 58M because biosynthetic intermediates between GA₁₂ and GA₂₀ accumulate and/or because 58M is altered in GA metabolism in this same region of the biosynthetic pathway is discussed. Received April 7, 1998; accepted July 31, 1998     

植物赤霉素生物合成和信号传导的分子生物学

赤霉素(GAs)在植物的种子萌发、茎的伸长和花的发育等许多方面起着非常重要的作用。最近几年,对GA生物合成及其信号传导途径相关基因的研究取得了惊人的进展。这些进展促进了对其生物合成及其信号传导途径的认识。GA生物合成相关基因的表达受到多种内源和外源因子的调控, 其中研究较多的是发育阶段、激素水平和光信号等内源及环境因子的调控。GA信号传导通常处于抑制状态, GA信号通过去抑制作用激活该传导途径而促进GA刺激植物生长和发育。     

植物赤霉素生物合成和信号传导的分子生物学

赤霉素 (GAs)在植物的种子萌发、茎的伸长和花的发育等许多方面起着非常重要的作用。最近几年 ,对GA生物合成及其信号传导途径相关基因的研究取得了惊人的进展。这些进展促进了对其生物合成及其信号传导途径的认识。GA生物合成相关基因的表达受到多种内源和外源因子的调控 ,其中研究较多的是发育阶段、激素水平和光信号等内源及环境因子的调控。GA信号传导通常处于抑制状态 ,GA信号通过去抑制作用激活该传导途径而促进GA刺激植物生长和发育。     

The Effect of CCC and Amo-1618 on Growth, Catalase, Peroxidase and Indoleacetic Acid Oxidase Activity of Young Barley Seedlings

Barley seedlings were grown in darkness on filter paper saturated with phosphate buffer or CCC and Amo-1618 buffered solutions. The effects of CCC and Amo-1618 on growth, catalase, peroxidase and lAA-oxidase were studied on coleoptile and primary leaves. Both growth-retarding chemicals cause an inhibition of growth, Amo-1618 being more effective than CCC. They have no effect on catalase activity. Increasing concentrations of CCC and Amo-1618 progressively stimulate peroxidase and IAA-oxidase activities (Amo-1618 more than CCC). The enzymatic activity in short-treated plants is higher than in the corresponding control plants of the same height. It is proposed that CCC and Amo-1618 exert their effect on the growth of barley by acting on auxin catabolism.     

Some Effects of Amo-1618 on Growth, Peroxidase and α-Amylase Which Cannot Be Easily Explained by Inhibition of Gibberellin Biosynthesis

Growth and peroxidase activity of roots and stems of lentil seedlings were compared after treatment with Amo-1618, alone or in combination with gibberellic acid (GA) at varying concentrations. The peroxidase enhancement in Amo-1618 treated stems could not be attributed to a decrease in the gibberellin content since GA alone had no effect on this enzyme. In other experiments, AMO, at low concentrations, was able to induce α-amylase production in barley aleurone layers; the lag period needed for this induction, was longer than for GA. These facts seem to indicate that some growth retardants might act at least in some cases by mechanisms other than inhibition of gibberellin biosynthesis and reversal of GA action.     

Effects of AMO-1618 on Growth, Morphology, and Gibberellin Content of Phaseolus Cocineus Seedlings

A study was made of the effects of AMO-1618 on the endogenousgibberellin (GA) levels and stem, leaf, and root growth of Phaseoluscoccineus seedlings. The data establishes that some of the effectsof AMO-1618 on the growth of Phaseolus seedlings are mediatedby factors other than an inhibition of GA biosynthesis.     

Gibberellin Structure-Dependent Interaction between Gibberellins and Deoxygibberellin C in the Growth of Dwarf Maize Seedlings

The effects of 3-deoxygibberellin C (DGC) on the growth-promoting actions of gibberellins A₁, A₂, A₃, A₄, A₅, A₇, A₈, A₉, A₁₃, A₁₈, A₁₉, A₂₀, and A₂₃ (GAn) as well as 13-deoxygibberellin A₅ (deoxy-GA₅) were tested with seedlings of gibberellin-deficient dwarf mutants (d₂ and d₅) of maize (Zea mays L.). It was found that DGC promoted the actions of gibberellins having both C-1 double bond and C-3 axial hydroxyl group, and it inhibited the action of gibberellins having the saturated ring A and lacking the C-3 axial hydroxyl group, whereas it did not affect that of the ones having the hydroxyl group. The presence of C-2 double bond, as in GA₅ and deoxy-GA₅, diminished the inhibitory action of DGC. The DGC inhibition was alleviated by raising the doses of the relevant GAs, suggesting that it is a competitive inhibition. These results and the finding that the growth of normal maize and rice seedlings are inhibited by DGC indicate that GA₉, GA₁₉, GA₂₀ or other gibberellins having ring A of the same structure are involved in the growth of these plants as active form(s) or as intermediate(s) leading to the active form(s).     

Effects of AMO-1618 and B-995 on Growth and Endogenous Gibberellin Content of Cupressus arizonica seedlings

Soil drenches of 250, 500 or 1000 mg/l of the growth retardants AMO-1618 or B-995 effectively reduced dry matter production and stem elongation in young seedlings of Cupressus arizonica Greene. In seedlings treated with AMO-1618, the acidic, ethyl acetate-soluble gibberellin-like substances (GAs), as detected. by bioassay, were reduced to almost undetectable levels. However, the endogenous GA content in seedlings treated with B-995 were at least 11-fold greater than in control seedlings and differed as well in chromatographic characteristics, being of a more polar nature than the endogenous GAs of control seedlings. It was concluded that while AMO-1618 probably acts through interference with GA biosynthesis, B-995 may act through the interconversion of GAs.     

Effects of Daylength on Endogenous Gibberellins in Solanum andigena III. Gibberellin Production by the Leaves

Using an agar diffusion technique, it was found that leaves from potato plants growing under long days produced more gibberellin-like substances than did leaves from plants growing under short days. Short day plants irradiated with red light during the long dark period and harvested during the ensuing light period, contained levels of gibberellin-like substances approximating those found in long day grown plants. Red irradiation during the long dark period also resulted in an increase in gibberellin production in short day plants. Four zones of gibberellin-like activity (A, B, C, D) were separated by thin layer chromatography in extracts from potato leaves. Red light treatment reduced the levels of peak D and brought about a concomitant increase in the levels of peak A.     

Growth Retardants and the Germination of Light Sensitive Lettuce Seed

The effect of the dwarfing compounds chlormequat, B995, and Phosphon D on the germination of lettuce seed in darkness was found to be a depression which could be overcome in part by red light, GA, and kinetin. There was a marked statistical interaction between the growth retardants and all the mitigating treatments except B995 and GA, and light, at 30°C and GA and Phosphon D at 20°C and this implies a biological interaction at the site of action of the growth retardant. It is suggested that the action of the compounds considered is in the establishment of an ordered system since it is unlikely that there would be a common binding site for kinetin and GA.     

Promotion of Growth and Flowering and Increase in Content of Endogenous Gibberellins in Gladiolus Plants Treated with the Growth Retardant CCC

Application of the growth retardant CCC to gladiolus plants resulted in stimulation of stem lenth, increased number of flowers per spike and a slight advancement of anthesis date. Leaves of treated plants were heavier than control and contained a higher amount of water and chlorophyll. The anthocyanin content in petals was also greatly increased. CCC had little or no effect on the content of the endogenous gibberellins in the acidic ethyl acetate fraction, but markedly increased the content of the native gibberellins in the aqueous fraction. The mode of action of CCC in plants is discussed on the basis of these results and a review of the literature.     

Comparative Effects of Substituted Pyrimidines on Growth and Gibberellin Biosynthesis in Gibberella fujikuroi

The fungicide α-(2,4-dichlorophenyl)-α-phenyl-5-pyrimidine methyl alcohol (triarimol) and four other structural analogs of this substance, in which one or more of the substituents were varied, were tested for their comparative effects on growth and gibberellin biosynthesis in the fungus Gibberella fujikuroi. Each of the five analogs tested was capable of inhibiting growth as measured by dry weight in 5-day-old cultures. Three of them [α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidine methyl alcohol, fenarimol; α-(2-chlorophenyl)-α-(4-fluorophenyl)-5-pyrimidine methyl alcohol, nuarimol; and triarimol] were effective at appreciably lower concentrations than the other two [α-(4-chlorophenyl)-α-(1-methylethyl)-5-pyrimidine methyl alcohol, experimental compound EL 509; and α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methyl alcohol, ancymidol].