Exogenous Application Of Gibberellins Research Articles

Suppression of highly efficient cadmium translocation by exogenous gibberellin provides insights into the molecular regulation mechanism of hyperaccumulation in Sedum plumbizincicola

Sedum plumbizincicola is a hyperaccumulating species with highly efficient uptake, translocation and distribution system for cadmium (Cd), a non-essential and toxic heavy metal. To understand the molecular regulation mechanisms of Cd transport and accumulation in this hyperaccumulator is still a challenge. In this study, we observed that exogenous gibberellin A3 (GA3) significantly reduced Cd loading efficiency from root to shoot and uploading efficiency from stem to leaves in S. plumbizincicola under Cd treatments, which provided us a remarkable opportunity to study the signaling mechanisms for regulation of highly efficient Cd transport and translocation in S. plumbizincicola. Here, we constructed a de novo full-length transcriptome database with the integration of full-length and next-generation transcriptome sequences for Cd-treated S. plumbizincicola with or without exogenous GA3 application. From this database, we identified 1461 differentially expressed genes (DEGs), which were related to solute transport, cell wall metabolism and signal transduction, and most of them were down-regulated by the exogenous application of gibberellin. In particularly, a substantial number of the downregulated genes belong to calmodulin-like (CML) proteins, calcium-dependent protein kinase, calcium-permeable channel, mitochondrial calcium uniporter (MCU) and Na+/Ca2+ exchanger-like proteins (NCL/EF-CAX). These results indicated that calcium homeostasis and signal transduction may play an important role in the regulation of highly efficient translocation of cadmium in hyperaccumulator S. pumbizincicola.

Gibberellin Increased Yield of Sesbania pea Grown under Saline Soils by Improving Antioxidant Enzyme Activities and Photosynthesis

Crop yield is the ultimate manifestation of all physiological changes of crops and external environmental influence. A controlled study was conducted to investigate the effects of exogenous gibberellin on the morphological and physiological characteristics and yield formation of sesbania pea grown in saline soils. Seeds were presoaked with four levels of Gibberellin (GA3) solutions (0, 202.1, 404.2 and 606.3 µM) for 6 h, and then manually direct-sown with a seeding rate of 45 kg ha−1. The morphological parameters (plant height, root length, dry weight), photosynthesis (chlorophyll a and b content), the activities of antioxidant enzymes (superoxide dismutase (SOD); peroxidase (POD); catalase (CAT)), the contents of soluble protein and NSC (non-structural carbohydrates), and seed yield increased with the application of exogenous gibberellin, especially at the level of 404.2 µM GA3. But GA3 had no significant effects on 1000-seed weight. Our study suggested that the appropriate application of exogenous gibberellin could improve the yield of sesbania pea grown in saline soils by increasing photosynthesis and antioxidative defense.

Light intensity and giberelic acid in the seedling\production of four ornamental species

Ornamental species, especially those involving the use of seedlings in trays to serve residential gardens, need to be produced quickly for commercialization, which requires studies that provide such a condition. The present work aimed to evaluate the effect of light intensity and exogenous application of gibberellin on seedlings of four ornamental species (Calendula officinalis, Gypsophila elegans, Solenostemon scutellarioides and Viola wittrockiana). The experiment was carried out at the Universidade Tecnológica Federal do Paraná, Campus Dois Vizinhos. The seeds were sown in trays containing substrate composed of a mixture of humic Distroferric Red Latosol: medium texture sand: commercial substrate, in the volumetric proportion of 2:1:1, respectively. The trays were kept in shading environments, using black screens with 35%, 50% and 80% shading intensity, red with 35% shading, in addition to full sun. After 30 days of emergence, gibberellic acid solution was applied to the seedlings at concentrations of 0 mg L-1 and 300 mg L-1. Emergence, emergence speed index, mean emergence time, total length, shoot and roots, number of leaves, leaf area, root volume density, shoot, root and total dry matter were evaluated. For each environmental condition of cultivation, the values of temperature and air humidity and light intensity were obtained. The use of gibberellic acid proved to be beneficial for Viola wittrockiana and Solenostemon scutellarioides. The shading environments, regardless of color and light intensity, were more favorable for the formation of seedlings of these four ornamental species.

Generation of Transgene-Free Semidwarf Maize Plants by Gene Editing of Gibberellin-Oxidase20-3 Using CRISPR/Cas9.

The “green revolution” gene gibberellin oxidase contributes to the semidwarf phenotype, improving product and lodging resistance. Dissecting the function of GA biosynthetic genes would be helpful for dwarf maize breeding. In this study, we edited the maize GA20ox3 gene and generated semidwarf maize plants using CRISPR/Cas9 technology. Application of exogenous gibberellin can recover the dwarf phenotype, indicating that the mutants are gibberellin deficient. The contents of GA12 and GA53 were elevated in the mutants due to the disruption of GA20 oxidase, whereas the contents of other GA precursors (GA15, GA24, GA9, GA44, and GA20) were decreased in the mutants, and the accumulation of bioactive GA1 and GA4 was also decreased, contributing to the semidwarf phenotype. Transgene-free dwarf maize was selected from T2-generation plants and might be useful for maize breeding in the future.

Bacteria-derived diacetyl enhances Arabidopsis phosphate starvation responses partially through the DELLA-dependent gibberellin signaling pathway

ABSTRACTPlant growth-promoting rhizobacteria (PGPR) are naturally occurring soil microorganisms that colonize roots and stimulate plant growth. Some PGPR strains can directly regulate plant growth in the absence of physical contact with the plant, via volatile organic compounds (VOCs) emissions. Recently, we have described that Arabidopsis thaliana respond differentially to diacetyl, a VOC from Bacillus amyloliquefaciens strain GB03 (GB03), through integral modulation of the immune system and the phosphate-starvation response (PSR) system, resulting in either mutualism or immunity. Under phosphate deficient conditions, diacetyl enhances salicylic acid- and jasmonic acid-mediated immunity and consequently causes plant hyper-sensitivity to phosphate deficiency. Here, we show that application of exogenous gibberellin (GA) partially alleviates the deleterious effect caused by either B. amyloliquefaciens GB03 VOCs or diacetyl in Arabidopsis under phosphate deficient conditions, while DELLA quadruple mutant exposed to GB03 VOCs exhibits a partial reduction on the stress symptoms. Moreover, diacetyl appears to enhance DELLA protein accumulation and increase the expression of several GA deactivation-related genes. These findings suggest that the DELLA-mediated GA signaling pathway is involved in the bi-faceted role of GB03 VOCs in regulating plant growth.

AtHSPR is involved in GA- and light intensity-mediated control of flowering time and seed set in Arabidopsis.

Flowering is a dynamic and synchronized process, the timing of which is finely tuned by various environmental signals. A T-DNA insertion mutant in Arabidopsis HEAT SHOCK PROTEIN-RELATED (AtHSPR) exhibited late-flowering phenotypes under both long-day (LD) and short-day (SD) conditions compared to the wild-type, while over-expression of AtHSPR promoted flowering. Exogenous application of gibberellin (GA) partially rescued the late-flowering mutant phenotype under both LD and SD conditions, suggesting that AtHSPR is involved in GA biosynthesis and/or the GA signaling that promotes flowering. Under SD or low-light conditions, the Athspr mutant exhibited late flowering together with reduced pollen viability and seed set, defective phenotypes that were partially rescued by GA treatment. qRT-PCR assays confirmed that GA biosynthetic genes were down-regulated, that GA catabolic genes were up-regulated, and that the levels of bioactive GA and its intermediates were decreased in Athspr under both SD and low-light/LD, further suggesting that AtHSPR could be involved in the GA pathway under SD and low-light conditions. Furthermore, AtHSPR interacted in vitro with OFP1 and KNAT5, which are transcriptional repressors of GA20ox1 in GA biosynthesis. Taken together, our findings demonstrate that AtHSPR plays a positive role in GA- and light intensity-mediated regulation of flowering and seed set.

Exogenous application of phytohormones mitigates the effect of salt stress on Carica papaya plants

ABSTRACT The salinity has complex effects on the physiological, nutritional and hormonal interactions of plants. This study aimed to evaluate the mitigating action of exogenous application of different types and concentrations of phytohormones on Carica papaya under salt stress. The experiment was conducted in greenhouse, using a randomized block design with treatments formed from a 2 x 3 x 5 factorial scheme, relative to two concentrations of salts in the irrigation water (0.6 and 2.4 dS m-1), three types of phytohormones [Auxin = indole-3-acetic acid; Cytokinin = CPPU (N-(2-chloro-pyridyl)-N-phenylurea) and Gibberellin = gibberellic acid(AG3)], and five concentrations of the phytohormone (0, 12.5, 25.0, 37.5 and 50.0 µM L-1), with three repetitions, totaling 90 plots, and the experimental unit consisted of six plants. C. papaya cv. ‘Sunrise Solo’ was grown on polyethylene trays of 162 cells, with capacity for 50 mL. The plants were evaluated for survival percentage and phytomass accumulation until 25 days after sowing. Increase in irrigation water salinity has deleterious effects on C. papaya plants regardless of the application of phytohormones. Exogenous application of gibberellin has a positive effect in mitigating salt stress on C. papaya plants, greater than the effects of auxins and cytokinins. Exogenous application of gibberellin and auxin at concentration of 37.5 µM L-1 mitigates the effects of salinity on C. papaya plants. Exogenous application of cytokinin at concentrations of 12.5 to 50.0 µM L-1 is not viable for C. papaya plants.

Seed Germination Traits of Loquat (Eriobotrya japonica Lindl.) As Affected by Various Pre-Sowing Treatments (Cutting of Cotyledons, Removal of Perisperm, Moist Chilling and/or Exogenous Application of Gibberellin)

The purpose of this study was to investigate the effects of various presowing treatments on the germinability (final germination percentage) and germination rate of loquat seeds in order to increase seedling production in nurseries (applied research) as well as provide answers for important physiological issues related to loquat seeds and their seed coat (basic research). Three experiments were carried out with various pre-sowing treatments. These treatments included full or partial removal of seed coat (perisperm), partial cutting of cotyledons as well as moist chilling at 5°C for 13 days and/or soaking the seeds in water or 250 ppm gibberellic acid (GA3) solution for 24 h. According to the results, cotyledons excision resulted in delayed germination, regardless of the presence or absence of the seed coat in comparison with the decoated seeds that demonstrated the highest germination rate amongst them. In addition, even the partial excision of seed coats affected positively both the germinability and the germination rate, compared to the control-intact seeds. Furthermore, control-intact seeds had a higher germination percentage when exposed to moist chilling independently of the application or not of gibberellin; while the combination of gibberellin application and moist chilling improved both the percentage and the rate of germination of decoated seeds. In conclusion, the role of perisperm (seed coat) in the germination procedure of loquat seeds seems to be important, indicating the existence of seed coat-imposed dormancy on loquat seeds. Finally, the existence of a mild endogenous embryo-dormancy on loquat is also discussed.

Functional identification of apple MdMYB2 gene in phosphate-starvation response

Inorganic phosphate (Pi) starvation severely affects the normal growth and development of plants. Here, a Pi-responsive gene, named MdMYB2 (MDP0000823458), was cloned and functionally identified in apple. Overexpression of MdMYB2 regulated the expression of Pi starvation-induced (PSI) genes and then promoted phosphate assimilation and utilization. The ectopic expression of MdMYB2 in Arabidopsis influenced plant growth and flowering, which was partially rescued by application of exogenous gibberellin (GA). These results indicated that MdMYB2 may be an essential regulator in phosphate utilization and GA-regulated plant growth and development.

Co-suppression of NbClpC1 and NbClpC2 alters plant morphology with changed hormone levels in Nicotiana benthamiana.

Co-suppression of chaperonic ClpC1 and ClpC2 in Nicotiana benthamiana significantly affect the development and exogenous application of gibberellin partially rescue the developmental defects. Over the past decade, the Clp protease complex has been identified as being implicated in plastid protein quality control in plant cells. CLPC1 and CLPC2 proteins form the chaperone subunits of the Clp protease complex and unfold protein substrates to thread them into the ClpP complex. Here, using the technique of virus-induced gene silencing (VIGS), we suppressed both Nicotiana benthamiana ClpC1 and ClpC2 (NbClpC1/C2) functioning as chaperone subunits in the protease complex. Co-suppression of NbClpC1/C2 caused chlorosis and retarded-growth phenotype with no seed formation and significantly reduced root length. We found that co-suppression of NbClpC1/C2 also affected stomata and trichome formation and vascular bundle differentiation and patterning. Analysis of phytohormones revealed significant alteration and imbalance of major hormones in the leaves of NbClpC1/C2 co-suppressed plant. We also found that application of gibberellin (GA3) partially rescued the developmental defects. Co-suppression of NbClpC1/C2 significantly affected the development of N. benthamiana and exogenous application of GA3 partially rescued the developmental defects. Overall, our findings demonstrate that CLPC1 and CLPC2 proteins have a pivotal role in plant growth and development.

Glyoxylate cycle and reactive oxygen species metabolism are involved in the improvement of seed vigor in watermelon by exogenous GA3

Exogenous application of gibberellins (GA) is a simple and effective way to improve seed vigor, which is probably achieved through its stimulation on the glyoxylate cycle activity and reactive oxygen species (ROS) metabolism in germinating seeds. However, the physiological mechanism of the stimulation still remains unclear. Here, we show that pre-soaking with GA3 enhanced seed vigor and seedling growth of watermelon. GA3 initiated the seed metabolic processes earlier, increased the respiration rate, and thus enhanced the respiration activity. Meanwhile, exogenous GA3 increased the activity of isocitrate lyase (ICL), one of the key enzymes in the glyoxylate cycle, and activities of malate dehydrogenase (MDH), succinate dehydrogenas (SDH) and isocitrate dehydrogenase (IDH) as well. Also, exogenous GA3 led to an enhancement in gene expression of ICL, MDH and IDH. Accompanied by the enhancement of glyoxylate cycle and tricarboxylic acid cycle, the production of O2·‾and H2O2 was promoted by GA3. In addition, GA3 induced the activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPOD), promoted the expression of CSD and POD, so as to scavenge the excess ROS. Our results suggest that seed vigor of watermelon increased by exogenous GA3 may be related to GA function in activation of the glyoxylate cycle and the regulation of ROS metabolism during seed germination.

Enhanced vacuolar invertase activity and capability for carbohydrate import in GA-treated inflorescence correlate with increased fruit set in grapevine

Application of exogenous gibberellin (GA) has been widely used to improve fruit set in grapevine, although the underlying molecular mechanism remains unknown. In this work, GA application at 10 days before anthesis promoted fruit set of grapevine “Fenghou” (Vitis vinifera × V. labrusca) and increased sugar content and acid invertase activity in the ovary, especially vacuolar invertase (VIN) activity during fruit set, compared with the control. However, the GA biosynthesis inhibitor paclobutrazol (PAC) had the opposite effect. Tissue-specific expression analysis and in situ hybridization showed that transcripts of three acid invertase genes were primarily detected in the phloem of the flower and fruitlet. In contrast to the expression of the cell wall invertase gene, which was only induced before blooming, transcript accumulation of the VIN genes VvGIN1 and VvGIN2 was enhanced during fruit set by GA application. Nevertheless, PAC treatment reduced VvGIN1 transcript accumulation after anthesis, but had no significant effect on the VvGIN2 transcript level at the same time point. Interestingly, the effect of GA and PAC application on expression of VvPIN1-like and VvPIN3-like (auxin transporters) was similar to that on VvGIN1 after blooming. In addition, the inducibility of the VvGIN1 and VvGIN2 promoters by GA was demonstrated using transient expression assays in tobacco leaves. These results indicated that enhanced VIN activity and carbohydrate import into grapevine fruitlets by GA application contribute to the increased fruit set through increasing sink strength and sugar signaling activities, possibly by regulating polar auxin transport.

TaERECTAResponses to Phytohormones, Mg2+Stress and Dehydration and Its Correlation with Stomatal Density in Bread Wheat

ERECTA is an ancient family of leucine-rich repeat receptor-like kinases (RLKs) that coordinate growth and development of plant. TaERECTA, one copy of the ERECTA homologs in wheat, was isolated from bread wheat Chinese Spring. The Ser/Thr kinase of TaERECTA was expressed in E. coli after IPTG induction and confirmed by immunoblot. TaERECTA showed higher expression in younger organs with rapid development, as well as great expression in younger spikes at booting stage. Under exogenous application of gibberellin (GA3) and abscisic acid (ABA), and Mg2+ stress, the expression of TaERECTA was largely suppressed, whereas under exogenous application of indole acetic acid (IAA) and brassinolide (BR), and dehydration stress, its expression was initially suppressed and then up-regulated. Natural variation was apparent in the relative expression of TaERECTA among 9 different bread wheat lines, and its expression level was negatively correlated with the stomatal density. These results suggested that TaERECTA could be...

NO FLOWERING IN SHORT DAY (NFL) is a bHLH transcription factor that promotes flowering specifically under short-day conditions in Arabidopsis.

Flowering in plants is a dynamic and synchronized process where various cues including age, day length, temperature and endogenous hormones fine-tune the timing of flowering for reproductive success. Arabidopsis thaliana is a facultative long day (LD) plant where LD photoperiod promotes flowering. Arabidopsis still flowers under short-day (SD) conditions, albeit much later than in LD conditions. Although factors regulating the inductive LD pathway have been extensively investigated, the non-inductive SD pathway is much less understood. Here, we identified a key basic helix-loop-helix transcription factor called NFL (NO FLOWERING IN SHORT DAY) that is essential to induce flowering specifically under SD conditions in Arabidopsis. nfl mutants do not flower under SD conditions, but flower similar to the wild type under LD conditions. The no-flowering phenotype in SD is rescued either by exogenous application of gibberellin (GA) or by introducing della quadruple mutants in the nfl background, suggesting that NFL acts upstream of GA to promote flowering. NFL is expressed at the meristematic regions and NFL is localized to the nucleus. Quantitative RT-PCR assays using apical tissues showed that GA biosynthetic genes are downregulated and the GA catabolic and receptor genes are upregulated in the nfl mutant compared with the wild type, consistent with the perturbation of the endogenous GA biosynthetic and catabolic intermediates in the mutant. Taken together, these data suggest that NFL is a key transcription factor necessary for promotion of flowering under non-inductive SD conditions through the GA signaling pathway.

APLICAÇÃO FOLIAR DE GA3 NO CRESCIMENTO E DESENVOLVIMENTO DE Passiflora edulis Sims f. flavicarpa Degener

RESUMO Com o conhecimento de que a aplicação exógena de giberelinas pode alterar os processos fisiológicos, modificando o crescimento e o desenvolvimento das plantas, vistoque funcionam como regulador da divisão e do alongamento das células, objetivou-se com estetrabalho avaliar o crescimento e o desenvolvimento de Passiflora edulis Sims f. flavicarpa Degener cultivadosob luminosidade de 650 µmol m-2 s-1, por nove meses, e submetido a pulverizações semanais com GA3. Odelineamento experimental foi inteiramente casualizado, com cinco tratamentos (0,0; 1,5; 3,0; 15,0 e 30,0 mgL-1 de GA3) e dez repetições. O substrato utilizado foi constituído por uma mistura (1:1:1, em volume) de areia grossa lavada, moinha de carvão lavado e Latossolo Vermelho distroférrico disposto em vasos com capacidadepara 5L. As concentrações de GA3 influenciaram (p<0,05) na maioria das variáveis analisadas, com exceção do comprimento do caule principal até a inserção do primeiro caule lateral, do número de cauleslaterais, do número de nós do caule principal até à inserção do primeiro caule lateral, do número de nós do caule principal até a inserção da primeira gavinha e da primeira folha trilobada, do início da floração, donúmero de caules laterais emitidos pela planta no início da floração e do número de nós da base do caule principal até à inserção do primeiro botão floral. Concentração em torno de 15 mg L-1 propiciou maior comprimento da planta, maior número de nós da planta e maior massa fresca e seca das plantas. A utilização de 30 mg L d-1e GA3 antecipou a emissão da primeira gavinha e da primeira folha trilobada, e produziu maior número de botões florais. A utilização exógena de GA3 em concentrações de até 30 mg L-1 foi mais eficaz na indução do que na evocação floral dePassiflora edulis Sims f. flavicarpa Degener.

Plant growth regulators involved in abiotic stress: preface

An ever-expanding world population and globally changing diet preferences have put considerable pressure on the worldwide agricultural community to produce more food, feed and bio-energy crops. As a result, marginal land areas will need to be used to meet the increasing requirement of future generations, especially in developing countries. These marginal areas commonly impose abiotic stresses on crops due to factors such as salinity, drought, temperature extremes, flooding, low nutrients and aluminium or heavy metal toxicity. As a consequence, the growth and yield of crops from such areas is typically low and their quality poor, limiting farmer income. Therefore, it is important to gain knowledge and insight of the intrinsic flexibility by which plants respond to these abiotic stresses. Throughout evolution, plants have developed a dazzling array of complex strategies for coping with abiotic stresses and adapting to a wide range of environments. Biochemical, physiological and molecular genetic studies of these strategies have been initiated, and, as in many plant research fields, those on Arabidopsis pave the way. However, the contributions in this special issue illustrate the progress made on other species and highlight the insights into this research field. The calcineurin B-like (CBL) and CBL-interacting protein kinase (CIPK) signalling pathway is a flexible, Ca signalling network that allows plants to fine-tune their stress mitigation responses. Thoday-Kennedy et al. (2015) provide a critical account of our current knowledge of CBL and CIPK interactions and their roles in ion transport under abiotic stress. Han et al. (2014) review the signalling pathways and key mechanisms of sodium detoxification mediated by ion transporters and antiporters, and give an overview of practical strategies and methodologies for functional characterisation of high-affinity potassium transporters. In addition, they discuss how to alleviate salt stress through the exogenous application of gibberellins and nitric oxide. Li et al. (2014a) focus on salt cress (Thellungiella halophila), a close relative of Arabidopsis, a species that has emerged as a model halophyte for the molecular elucidation of abiotic stress tolerance. Its seed germination is highly regulated by environmental and hormonal signals; thus, it provides opportunities to study how such external conditions are sensed. The mung bean (Vigna radiata) is salinity-sensitive and suffers considerably from soil salinity; as a consequence, reductions in germination, chlorophyll content, vigour and yield have been reported. Patel et al. (2014) draw attention to interactions that occur with this species in the rhizosphere and report on those with halotolerant Bacillus spp. These species were isolated from saline habitats and alleviate salt stress in mung beans thereby increasing germination and partially restoring root and shoot growth. Xuan et al. (2014) characterise the response of seedlings of yellowand black-seeded rape to salt and cadmium stresses, and show how tolerance is associated with flavonoid content. Li et al. (2014b) demonstrate how improvement of endogenous polyamine levels by exogenous spermidine application may promote drought tolerance of plants. Waterlogging is also a major constraint to crop production in many parts of the world due to anoxic conditions in the root zone. Najeeb et al. (2015) investigate the mechanisms of waterlogging tolerance in cotton induced by aminoethoxyvinylglycine and show the how leaf growth and fruit production can be enhanced under these & Stefaan P. O. Werbrouck Stefaan.Werbrouck@UGent.be

Towards plant salinity tolerance-implications from ion transporters and biochemical regulation

Crop production is adversely affected by soil salinization and therefore, development of crop cultivars with salt tolerance is crucial for better utilization of saline soil and enhancement of sustainable agricultural productivity. High salt concentration induces various physiological and biochemical responses in plants, while plants employ mechanisms in adaptation to salinity stress at cellular, metabolic and whole-plant levels, including stress signalling, ion balancing, osmotic regulation and antioxidant protection. In this review, we discuss the signalling pathways and key mechanisms of Na+ detoxification mediated by ion transporters and antiporters, and make an overview of practical strategies and methodologies for functional characterization of high-affinity potassium transporters. In addition, recent research advances in improvement of plant salt tolerance through biochemical regulation, particularly alleviating salt stress by exogenous application of gibberellins and nitric oxide, are reviewed. We also propose key research perspectives that remain to be addressed in future.

Genome-wide analysis of the cyclin gene family in tomato.

Cyclins play important roles in cell division and cell expansion. They also interact with cyclin-dependent kinases to control cell cycle progression in plants. Our genome-wide analysis identified 52 expressed cyclin genes in tomato. Phylogenetic analysis of the deduced amino sequences of tomato and Arabidopsis cyclin genes divided them into 10 types, A-, B-, C-, D-, H-, L-, T-, U-, SDS- and J18. Pfam analysis indicated that most tomato cyclins contain a cyclin-N domain. C-, H- and J18 types only contain a cyclin-C domain, and U-type cyclins contain another potential cyclin domain. All of the cyclin genes are distributed throughout the tomato genome except for chromosome 8, and 30 of them were found to be segmentally duplicated; they are found on the duplicate segments of chromosome 1, 2, 3, 4, 5, 6, 10, 11 and 12, suggesting that tomato cyclin genes experienced a mass of segmental duplication. Quantitative real-time polymerase chain reaction analysis indicates that the expression patterns of tomato cyclin genes were significantly different in vegetative and reproductive stages. Transcription of most cyclin genes can be enhanced or repressed by exogenous application of gibberellin, which implies that gibberellin maybe a direct regulator of cyclin genes. The study presented here may be useful as a guide for further functional research on tomato cyclins.

Effect of exogenous gibberellic acid on germination, seedling growth and phosphatase activities in Lettuce under salt stress

The effect of gibberellic acid on germination and seedling growth of lettuce variety, Vista, under salinity conditions was studied. A reduction in germination percentage, roots and shoots length and fresh weight were observed under salt stress. At the same time, acid phosphatase and phytase activities in roots were reduced by NaCl. The exogenous application of gibberellin increased germination percentage and improved length and fresh weight of roots and shoots under salt treatment. It also increased both acid phosphatase and phytase activities in roots under this constraint. The application of gibberellic acid compensated for the negative effect of salinity. Keywords: Acid phosphatase, germination, gibberellic acid, lettuce, phytase, salinity, seedling growth

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.