Exogenous Application Of Gibberellins Research Articles

Seasonal differences in the capacity of perennial ryegrass to respond to gibberellin explained

Perennial ryegrass plants (Lolium perenne) were taken from an established field at two different stages in the season (mid-winter and again at mid-summer). They were then grown in a controlled environment to both "lock in" their contrasting developmental states and to look at the role of nitrogen supply, temperature, and developmental state separately to evaluate the potential of plants to respond to exogenous application of gibberellin. Responses to exogenous gibberellin (gibberellic acid, GA) were significant but were far smaller in summer-derived than winter-derived plants. The major difference in response to GA (compared with controls) between winter-derived and summerderived plants suggests that seasonal changes in plant developmental state have a major effect in the field on the capacity for the plants to respond to exogenous GA application. This effect is greater than that of temperature and N availability. This raises new prospects for making sustained increases in plant growth, but only if the fundamental mechanisms by which plants control their responses to environmental signals (e.g., temperature and soil N status) can be understood. The role of gibberellins (endogenous as well as externally applied) in changes in plant growth strategy presents a new challenge for forage plant science.

The strawberry gene FaGAST affects plant growth through inhibition of cell elongation

The strawberry (Fragaria x ananassa) FaGAST gene encodes a small protein with 12 cysteine residues conserved in the C-terminal region similar to a group of proteins identified in other species with diverse assigned functions such as cell division, elongation, or elongation arrest. This gene is expressed in the fruit receptacle, with two peaks during ripening at the white and the red-ripe stages, both coincident with an arrest in the growth pattern. Expression is also high in the roots but confined to the cells at the end of the elongation zone. Exogenous application of gibberellin increased the transcript level of the FaGAST gene in strawberry fruits. Ectopic expression of FaGAST in transgenic Fragaria vesca under the control of the CaMV-35S promoter caused both delayed growth of the plant and fruits with reduced size. The same growth defect was observed in Arabidopsis thaliana plants overexpressing FaGAST. In addition, the transgenic plants exhibited late flowering and low sensitivity to exogenous gibberellin. Taken together, the expression pattern, the regulation by gibberellin, and the transgenic phenotypes point to a role for FaGAST in arresting cell elongation during strawberry fruit ripening.

Expression of α-amylase in cultured callus of french bean

α-Amylase (EC 3.2.1.1) expression was found in calli of French bean (Phaseolus vulgaris L. cv Goldstar). We examined enzyme activity in the calli to investigate influence of gibberellin and sugars on enzyme expression. After subculture of the calli, α-amylase activity decreased, and then increased at a stationary phase of callus growth. Exogenous application of gibberellin and an inhibitor of gibberellin synthesis, uniconazole, did not have any significant effects on the enzyme expression. Sugar starvation increased the activity, while addition of metabolizable sugars, such as sucrose, glucose and maltose, to the medium repressed expression. Addition of 6% mannitol, a non-metabolizable sugar, to the medium induced higher α-amylase expression as compared to addition of 3% mannitol. This result suggests that osmotic stress enhances α-amylase activity in the calli. Furthermore, high concentrations of agar in the medium increased α-amylase activity in the calli. It is probable that high concentrations of agar prevented incorporation of nutrient into the calli and induced the α-amylase activity in the calli.

Flowers into shoots: photo and hormonal control of a meristem identity switch in Arabidopsis.

Little is known about the signals that govern the network of meristem and organ identity genes that control flower development. In Arabidopsis, we can induce a heterochronic switch from flower to shoot development, a process known as floral meristem reversion, by manipulating photo-period in the floral homeotic mutant agamous and in plants heterozygous for the meristem identity gene leafy. The transformation from flower to shoot meristem is suppressed by hy1, a mutation blocking phytochrome activity, by spindly, a mutation that activates basal gibberellin signal transduction in a hormone independent manner, or by the exogenous application of gibberellins. We propose that LFY and AG play an important role in the maintenance of flower meristem identity and that floral meristem reversion in heterozygous lfy and in ag flowers is regulated by a phytochrome and gibberellin signal transduction cascade.

Gibberellin-Stimulated Changes in Abundance of Two mRNAS in the Developing Shoot of Dwarf Peas (Pisum sativum L.)

Changes in gene expression followed the application of exogenous gibberellin (GA) to dwarf peas, as demonstrated by increases in abundance of a small population of mRNAs. The nature of these changes was investigated by isolating two cDNA clones. The clones were selected by differential screening of a lambda gt 10 cDNA library derived from mRNA that had been extracted from GA-treated dwarf peas. Characterization of the two clones included sequencing and Northern blot hybridizations to compare dwarf and tall pea RNAs. Transcripts with homology to these clones were expressed in both dwarf and tall peas. Northern blotting of mRNAs isolated from 1 to 48 h after GA application revealed a differential expression of the relevant genes. Differences in amounts of RNA at several sampling times between 1 and 48 h were also observed in the dwarf and tall plants. Southern blot hybridizations, using genomic DNA digests with three restriction enzymes, indicated the likelihood that a single gene is represented by one of the cDNAs, and one or more genes by the other cDNA. The hybridizations with the genomic DNA fragments were identical in the dwarf and tall phenotypes for each of the cDNAs.

The influence of photoperiod on the dry matter production of grasses and cereals

summaryPhotoperiod can affect the growth and development of grasses and cereals in three distinct ways: by providing a cue for the start of the reproductive phase, by modifying the rate of reproductive development once established, and by causing changes in the rate of leaf area expansion and of dry‐matter production which are not necessarily related to reproduction. This review, which draws heavily on work with grasses from high latitudes in Scandinavia, deals mainly with this third influence of photoperiod, documenting the range of observed effects on plant development and physiology, and drawing results from other systems to help in exploring the underlying mechanisms.It is difficult to devise experimental treatments which differ only in daylength but involve realistic daily inputs of photosynthetically active radiation (PAR), to avoid possible interactions with shading responses. In the natural environment, photoperiod is confounded with the supply of radiant energy, and the spectral composition of solar radiation at the beginning and end of each day varies with latitude. It is concluded that the use of daylit phytotron chambers with daylength extension by low‐irradiance incandescent lamps is the most practical solution to this complex problem.A survey of experiments conducted under realistic irradiances showed that exposure of plants of a range of temperate and high‐latitude grasses and cereals to longer days, without increasing the supply of PAR, resulted in substantial increases (up to 200%) in dry‐matter production, and even greater increases in leaf area. These effects, which were common to vegetative and reproductive plants, tended to be most marked at lower temperatures. Growth analysis showed that, in general, this enhancement was a consequence of increases in leaf area ratio which, in turn, were caused by increases in specific leaf area rather than in leaf weight ratio. Higher rates of dry‐matter production were, therefore, a result of improved interception of PAR, although, in many experiments, net assimilation rates were lower.Photoperiodic stimulation of growth was generally associated with an unchanged or increased shoot: root ratio, reduction in the number of tillers per plant, unchanged numbers of leaves per tiller, but longer leaf sheaths and blades. Increases in blade length, in turn, were associated with increases in epidermal cell length, although there is also evidence of increased cell division, and in tissue succulence. It was concluded that photoperiodic stimulation of growth is a consequence of a positive feedback system, in which the additional photosynthate from the first leaves which develop under long days is invested in progressively larger leaves. Studies of CO2 exchange rates suggest that the observed decreases in net assimilation rate could be explained in terms of the number of cells or the amount of chlorophyll per unit of leaf area. The fact that increased growth results from increased interception of PAR indicates that, in swards, the effect will only be shown in spring or under regular defoliation.Some experiments have shown that the full range of developmental effects induced by long days can equally be induced by the exogenous application of gibberellins. These findings are consistent with observed effects of gibberellins at the cellular level (loosening of cell walls, etc.) but it is too early to conclude that endogenous gibberellins play a part in the chain of events from the perception of the photoperiodic signal to the cellular changes leading to larger leaves.The fact that photoperiodic stimulation of dry‐matter production is shown by grasses originating from a range of maritime environments from 52° N northwards suggests that this response is not a specific adaptation to the cool long days of the high latitude summer. It is more likely that the related photoperiodic (short‐day) depression of growth, which facilitates the cold‐hardening of these grasses in autumn, is more important. Grasses and cereals from lower latitudes are equipped to grow well during the growing season at high latitudes, but because they are not programmed to recognize the correct photoperiodic cue in autumn, they will be subject to winterkill. CONTENTS Summary 233 I. Introduction 234 II. Experimental approaches 235 III. Stimulation of dry‐matter production 236 IV. Growth analysis 238 V. The role of gibberellins in the photoperiodic stimulation of growth 247 VI. Adaptive significance of photoperiodic stimulation of growth 248 Acknowledgements 251

Interaction of Daylength and Applied Gibberellins on Stem Growth and Leaf Production in Three Varieties of Celery

Pressman, E. and Negbi, M. 1987. Interaction of daylength and applied gibberellins on stem growth and leaf production in three varieties of celery.—J. exp. Bot. 38: 968-971. Exogenous application of gibberellins (GAs) stimulated stem length. The extent of this stimulation was less in long photoperiods, as long days (LD) or as long nights interrupted by night breaks (NB), than it was in short days (SD). Long photoperiods increased the length and erectness of leaves and reduced leaf number. Similar morphological changes were stimulated by applied GAs, which were more effective on plants grown in SD than on those in LD. It is suggested that long photoperiods cause these morphological changes via the production or metabolism of endogenous GAs, but it is not clear how endogenous GAs interact with the applied Key words—Daylength, gibberellins, stem growth, leaf production, celery. Correspondence to: Department of Vegetable Crops, Agricultural Research Organization, The Volcani Centre, Bet Dagan, Israel. INTRODUCTION Celery (Apium graveolens L.) is a short-day-long-day plant with a vernalization requirement. LD or NB during vernalization reduces bolting and flowering, while after vernalization LD promotes them (Pressman and Negbi, 1980). Biennial rosette plants grown under non-inductive conditions will bolt in response to gibberellin application (Lang, 1965). Metzger (1985) found that in the cold-requiring annual field pennycress (Thlaspi arvense L.), stems grew faster and taller when GA3 was applied to non-thermo-induced plants in LD rather than in SD. Similar effects of day length were obtained with other rosette LDP plants pretreated with Amo-1618; i.e. Silene armeria L. (Cleland and Zeevaart, 1970) and spinach (Spinacia oleracea L.) (Zeevaart, 1971) after GA3 treatment and Agrostemma githago (Jones and Zeevaart, 1980) after GA20 treatment. Long photoperiod caused upright presentation of spinach leaves and increased elongation 1 Contribution from the Agricultural Research Organization, The Volcani Centre, Bet Dagan, Israel. No. 1804-E, 1986 series. © Oxford University Press 1987 This content downloaded from 157.55.39.59 on Sat, 15 Oct 2016 04:15:07 UTC All use subject to http://about.jstor.org/terms Pressman and Negbi—Photoperiod and Gibberellin Interactions 969 of the petioles (Zeevaart, 1971). Davis (1967) showed that Proserpinaca palustris L. when maintained on LD grows erect, while in SD it tends to grow prostrate. Wallenstein and Albert (1963) reported that application of GA3 caused P. palustris L. plants grown in SD to grow erect. The leaf number of Arabidopsis thaliana strain ZU was reduced by GA3 or GA7 (Napp-Zinn, 1971). In celery, GA3 caused longer and more erect leaves (Aloni and Pressman, 1980). The present work examined the interaction between photoperiod and applied GAs on bolting and other morphological changes in the three varieties of celery. MATERIALS AND METHODS Plants of leaf celery (Apium graveolens L. var. dulce cv. Florida), an Israeli wild celery (var. lusitanicum) and root celery (var. rapaceum cv. Alabaster) were grown in a glasshouse, in day and night temperatures of 27 °C and 17 °C, respectively, for 70-80 d (up to 8-9 leaves). At this age plants were removed to the phytotron. In the phytotron of the Faculty of Agriculture of the Hebrew University, plants were held in a controlled temperature glasshouse, with day and night temperatures of 27 °C and 22 °C, under natural light. LD (16 h) was obtained by adding incandescent illumination (103 pW cm 2 at plant level) before sunrise and after sunset, and SD (8 h) by transferring the plants to a dark room from 16.00 h to 08.00 h. Night breaks (NB) for plants under the SD conditions, lasted from 23.00 h to 01.00 h. Fluorescent (40 W Tadiran, Israel) cool white tubes provided 200 pW cm-2 at plant level. Gibberellin (in water plus 0 05% Tween 20) was applied directly to the apex using a micropipette in two equal applications 48 h apart. In the first experiment a total of 320 pg was applied per plant. In the second and third experiments 160 pg was applied. In the fourth experiment 80 fig of GA3 or GA4/7 was applied to each plant. RESULTS Stems formed under SD in response to GA3 treatment were almost twice as long as those under LD in the three varieties examined (Table 1). Plants produced a few more leaves under SD than under LD. Application of GA3 reduced the leaf number under the two day length regimes, especially under SD. In Experiment 2 cv. 'Florida' plants maintained under three photoperiods were treated Table 1. The effect of day length on the response to GA3 (320 pg per plant) in celery plants of three varieties. Experiment 1

Studies on the Stellaria longipes complex: phenotypic plasticity. II. Gibberellins, abscisic acid, and stem elongation

Clonal material of one genotype of Stellaria longipes Goldie s.l. was used to investigate whether environmental regulation of the phenotype was mediated through phytohormones. Photoperiod and temperature modified the response of this species to exogenous application of gibberellins (GAs) and abscisic acid (ABA). Application of GAs to ramets in short or long days and low temperature increased stem elongation but did not induce elongation equivalent to that seen in control ramets in long warm days. Application of GAs to ramets in short days (warm or cold) induced elongation equivalent to that of ramets in long days at a similar temperature. Application of (2-chloroethyl)-trimethylammonium chloride resulted in dwarfing at some concentrations, while exposure to other concentrations initially stimulated elongation. Application of ABA reduced elongation in short, cold days but showed no effect under other conditions. Metabolism of radiolabeled ABA and GA3 was similar in both short cold days and long warm days. It was concluded that photoperiodically induced stem elongation could be partially mediated through endogenous levels of GAs. However, a hypothesis based on the idea that temperature-induced changes in elongation are controlled by suboptimal levels of GAs or supraoptimal levels of ABA is inadequate.

The Chemistry and Microstructure of Protein Bodies in Celery Endosperm

Anatomical variations in regions of the endosperm and the structure and composition of protein bodies of ungerminated celery (A pium graveolens) fruits were examined by histochemistry, light microscopy, electron microscopy, and X-ray analysis. Protein bodies contained either phytin globoids with Mg and P and lesser amounts of Ca and K or Ca oxalate druse crystals that had only Ca peaks. Most of the Ca in the fruit is stored in the druse crystals, which are broken down more slowly than the globoids during germination. Cells in the central region of the endosperm, distal to the cotyledons, contained enlarged protein bodies and other cellular features, indicating that they had already undergone some autolysis prior to the onset of germination. Such cells would be expected to appear to respond earlier to the application of exogenous gibberellin than more peripheral cells in the endosperm. The apparent early response of central cells in isolated endosperm halves may therefore not depend on an inherent differen...

The Gibberellins as Hormones

Publisher Summary The gibberellins are now recognized as being an important group of plant hormones, regulating growth and morphogenesis, distinct chemically and functionally from the more familiar indole auxins. Nine structurally related gibberellins are known (structures I-IX). They are conventionally named gibberellins A 1 to A 9 . The chapter focuses on the status, function, and mode of action of the gibberellins as native plant hormones, and on their interactions with the indole auxins. The gibberellins differ from the auxins in many ways, but most markedly by the variety of responses which they are capable of eliciting from intact plants. Exogenous application of gibberellin to plants induces a variety of responses involving growth or differentiation, which suggests that they are functional hormones. Rigid proof, about being them hormones, involving demonstration that endogenous gibberellins control one or another phase of growth or development, and that the site of production of the gibberellins is removed from the site of action, is likely to be difficult to obtain. But there is circumstantial evidence of some weight from positive correlations between endogenous gibberellin levels (and of changes in level) and certain developmental trends. Examples of such evidence are described in the chapter.