ABA and GA3 affect the growth and pigment composition in Andrographis paniculata Wall.ex Nees., an important folk herb

In this study, 5 μmol·L⁻¹ abscisic acid (ABA) and gibberellic acid (GA₃) were used to study the effect of both growth regulators on the morphological parameters and pigment composition of Andrographis paniculata. The growth regulators were applied by means of foliar spray during morning hours. ABA treatment inhibited the growth of the stem and internodal length when compared with control, whereas GA₃ treatment increased the plant height and internodal length. The total number of leaves per plant decreased in the ABA-treated plants, but GA₃ treatment increased the total number of leaves when compared with the control. Both growth regulators (ABA and GA₃) showed increased leaf area. ABA and GA₃ treatments slightly decreased the total root growth at all the stages of growth. The growth regulator treatments increased the whole plant fresh and dry weight at all stages of growth. ABA enhanced the fresh and dry weight to a larger extent when compared with GA₃. An increase in the total chlorophyll content was recorded in ABA and GA₃ treatments. The chlorophyll-a, chlorophyll-b, and carotenoids were increased by ABA and GA₃ treatments when compared with the control plants. The xanthophylls and anthocyanin content were increased with ABA and GA₃ treatments in A. paniculata plants.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length, shoot length, total leaf area, number of inflorescence per plant, number of flower per inflorescence, whole plant fresh weight and whole plant dry weight. Photosynthetic characteristics were also analyzed based on the same experiment. For this, various photosynthetic pigment contents such as chlorophyll, carotenoid, anthocyanin and xanthophyll content were calculated. The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used. Root length increased due to growth regulator treatment, but shoot length decreased. Leaf area was decreased due to growth regulator treatment. The number of inflorescence increased in ABA treated plants, but it was decreased in PBZ treated plants. In ABA treated plants, the number of flowers per inflorescence was increased. In PBZ treated plants the number of inflorescence was reduced. The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants. There was an increase in chlorophyll content in growth regulator treated plants compared to control, and it was more in PBZ treated plants. The carotenoid content was also increased in ABA and PBZ treated plants.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length,shoot length,total leaf area,number of inflorescence per plant,number of flower per inflorescence,whole plant fresh weight and whole plant dry weight.Photosynthetic characteristics were also analyzed based on the same experiment.For this,various photosynthetic pigment contents such as chlorophyll,carotenoid,anthocyanin and xanthophyll content were calculated.The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used.Root length increased due to growth regulator treatment,but shoot length decreased.Leaf area was decreased due to growth regulator treatment.The number of inflorescence increased in ABA treated plants,but it was decreased in PBZ treated plants.In ABA treated plants,the number of flowers per inflorescence was increased.In PBZ treated plants the number of inflorescence was reduced.The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants.There was an increase in chlorophyll content in growth regulator treated plants compared to control,and it was more in PBZ treated plants.The carotenoid content was also increased in ABA and PBZ treated plants.     

Endogenous hormonal and enzymatic responses of Catharanthus roseus with triadimefon application under water deficits

The effect of triadimefon was investigated in a medicinal plant, Catharanthus roseus subjected to water deficit stress. The abscisic acid (ABA) level, DNA and RNA contents and activities of ATPase and protease were found varying in different parts of the plants under treatment. Drought treatment increased the ABA level more than twofold in all parts of the plants. TDM treatment to the drought stressed plants showed highest contents. In roots, stem and leaves, drought stress caused a decrease in the DNA and RNA contents when compared with control and other treatments. TDM treatment with drought increased the nucleic acid contents to the level of the control roots. The activity of ATPase and protease were increased under drought treatment and lowered due to TDM applications. This information could be useful in the field of soil water deficits reclamation efforts by using plant growth regulators.     

Effects of CCC and GA on internodal development of barley

Summary The effect of applying (2-chloroethyl)trimethylammonium chloride (CCC) or gibberellic acid (GA) as foliar sprays on internodal development of barley was studied. CCC applied to the whole plant at main tiller leaf stages 1, 2 or 3 decreased shoot elongation, and prevented elongation of internode 6 (internode 5 subtended the head). CCC at all stages delayed senescence of the lower leaves. CCC sprayed at all 6 leaf stages and GA sprayed at main tiller leaf stages 1, 2, 3 or 4 reduced plant height at maturity. GA treatment at leaf stages 2, 3 or 4 initially stimulated internodal elongation; elongation of later developed internodes was inhibited resulting in shorter plants at maturity. Only the treatment with GA at leaf stages 5 and 6 resulted in increased plant height.     

Augmented Phytoextraction of Lead (Pb2+)-Polluted Soils: A Comparative Study of the Effectiveness of Plant Growth Regulators,EDTA, and Plant Growth–Promoting Rhizobacteria

Abstract

The role of gibberellic acid (GA3), indole-3-acetic acid (IAA), plant growth–promoting bacteria (Rhizobium and Azotobacter), and a synthetic chelator (EDTA; ethylenediaminetetraacetic acid) in lead (Pb) phytoextraction was evaluated using Parthenium hysterophorus (dicot, unpalatable noncrop) and Zea mays (monocot food/forage crop) plants at the flowering stage. Various plant parts were analyzed by atomic absorption/flame spectrophotometer for their Pb content. Both plant growth regulators and both growth-promoting bacteria significantly increased the plant growth in Pb-polluted soils, whereas EDTA significantly decreased growth and biomass of both plants. EDTA increased the Pb uptake (μg g^?1 dry biomass), but the total plant Pb accumulation was decreased. GA3 and IAA significantly increased both uptake and translocation, and the maximum total Pb in the entire plant of Parthenium was found with GA3 foliar spray, whereas in Z. mays the total Pb was maximum in the plant treated with GA3 in combination with EDTA, followed by the GA3 foliar spray treatment. Overall, the GA3 foliar application showed superior response compared with all other treatments. Further research is recommended to observe the role of endogenous GA3 levels in correlation with metal phytoextraction in different plants.     

On the role of abscisic Acid and gibberellin in the regulation of growth in rice

Submergence induces rapid elongation of rice coleoptiles (Oryza sativa L.) and of deepwater rice internodes. This adaptive feature helps rice to grow out of the water and to survive flooding. Earlier, we found that the growth response of submerged deepwater rice plants is mediated by ethylene and gibberellin (GA). Ethylene promotes growth, at least in part, by increasing the responsiveness of the internodal tissue to GA. In the present work, we examined the possibility that increased responsiveness to GA was based on a reduction in endogenous abscisic acid (ABA) levels. Submergence and treatment with ethylene led, within 3 hours, to a 75% reduction in the level of ABA in the intercalary meristem and the growing zone of deepwater rice internodes. The level of GA₁ increased fourfold during the same time period. An interaction between GA and ABA could also be shown by application of the hormones. ABA inhibited growth of submerged internodes, and GA counteracted this inhibition. Our results indicate that the growth rate of deepwater rice internodes is determined by the ratio of an endogenous growth promoter (GA) and a growth inhibitor (ABA). We also investigated whether ABA is involved in regulating the growth of rice coleoptiles. Rice seedlings were grown on solutions containing fluridone, an inhibitor of carotenoid and, indirectly, of ABA biosynthesis. Treatment with fluridone reduced the level of ABA in coleoptiles and first leaves by more than 75% and promoted coleoptile growth by more than 60%. Little or no enhancement of growth by fluridone was observed in barley, oat, or wheat. The involvement of ABA in determining the growth rate of rice coleoptiles and deepwater rice internodes may be related to the semiaquatic growth habit of this plant.     

The role of abscisic acid in disturbed stomatal response characteristics of Tradescantia virginiana during growth at high relative air humidity

In this study, the role of abscisic acid (ABA) in altered stomatal responses of Tradescantia virginiana leaves grown at high relative air humidity (RH) was investigated. A lower ABA concentration was found in leaves grown at high RH compared with leaves grown at moderate RH. As a result of a daily application of 20 microM ABA to leaves for 3 weeks during growth at high RH, the stomata of ABA-treated leaves grown at high RH showed the same behaviour as did the stomata of leaves grown at moderate RH. For example, they closed rapidly when exposed to desiccation. Providing a high RH around a single leaf of a plant during growth at moderate RH changed the stomatal responses of this leaf. The stomata in this leaf grown at high RH did not close completely in response to desiccation in contrast to the stomata of the other leaves from the same plant. The ABA concentration on a fresh weight basis, though not on a dry weight basis, of this leaf was significantly lower than that of the others. Moreover, less closure of stomata was found in the older leaves of plants grown at high RH in response to desiccation compared with younger leaves. This was correlated with a lower ABA concentration in these leaves on a fresh weight basis, though not on a dry weight basis. Stomata of leaves grown at moderate RH closed in response to short-term application of ABA or sodium nitroprusside (SNP), while for leaves grown at high RH there was a clear difference in stomatal responses between the leaf margins and main-vein areas. The stomatal aperture in response to short-term application of ABA or SNP at the leaf margins of leaves grown at high RH remained significantly wider than in the main-vein areas. It was concluded that: (i) a long-term low ABA concentration in well-watered plants during growth at high RH could be a reason for less or no stomatal closure under conditions of drought stress; and (ii) the long-term ABA concentration on a fresh weight basis rather than on a dry weight basis is likely to be responsible for structural or physiological changes in stomata during leaf growth.     

Growth Substances and Dormancy in Ceratophyllum demersum

Ceratophyllum demersum L. occurs in winter in the dormant form, in summer in the vegetative form. Factors that affect growth and dormancy in Ceratophyllum were studied. After several weeks of severe winter conditions the plants changed from dormant to quiescent state. Under natural conditions Ceratophyllum plants remain quiescent for several months, due to unfavourable growth conditions. Experimentally the dormant could also be broken by high and low temperature treatments (shocks), and most effectively by addition of GA, An attempt to induce dormancy in full grown plants by the addition of ABA under extreme summer or winter conditions proved unsuccessful. The IAA and ABA contents in the plants were measured during the year. In winter the concentration of ABA was high and that of IAA low, whereas in summer the IAA concentration increased and that of ABA was variable. IAA only slightly antagonized the inhibition of growth by ABA. Both the growth regulators were readily taken up from the culture medium, as was confirmed by a study with the radioactive labelled compounds. The uptake rate of IAA was significantly higher than that of ABA. being 762 μg and 3.26, μg per plant in 24 h, respectively. GA, was found to have a strong antagonistic effect on the ABA induced growth inhibition. The total GA activity in dormant and quiescent plants was similar, in full grown plants it was much lower. In the dormant state a large part of GA was in a bound form, whereas during quiescence relatively more GA occurred in a free state in the plants.     

Improved growth,productivity and quality of tomato (Solanum lycopersicum L.) plants through application of shikimic acid

A field experiment was conducted to investigate the effect of seed presoaking of shikimic acid (30, 60 and 120 ppm) on growth parameters, fruit productivity and quality, transpiration rate, photosynthetic pigments and some mineral nutrition contents of tomato plants. Shikimic acid at all concentrations significantly increased fresh and dry weights, fruit number, average fresh and dry fruit yield, vitamin C, lycopene, carotenoid contents, total acidity and fruit total soluble sugars of tomato plants when compared to control plants. Seed pretreatment with shikimic acid at various doses induces a significant increase in total leaf conductivity, transpiration rate and photosynthetic pigments (Chl. a, chl. b and carotenoids) of tomato plants. Furthermore, shikimic acid at various doses applied significantly increased the concentration of nitrogen, phosphorus and potassium in tomato leaves as compared to control non-treated tomato plants. Among all doses of shikimic acid treatment, it was found that 60 ppm treatment caused a marked increase in growth, fruit productivity and quality and most studied parameters of tomato plants when compared to other treatments. On the other hand, no significant differences were observed in total photosynthetic pigments, concentrations of nitrogen and potassium in leaves of tomato plants treated with 30 ppm of shikimic acid and control plants. According to these results, it could be suggested that shikimic acid used for seed soaking could be used for increasing growth, fruit productivity and quality of tomato plants growing under field conditions.     

The effects of gibberellic acid and nutrient sprays on growth and yield of brussels sprout

Young plants of brussels sprout, cv. Cambridge Special, growing in pots in a glasshouse, were sprayed on ten occasions with gibberellic acid (GA) at 0, 25, 100 and 400 p.p.m. and ammonium nitrate (NH₄NO₃) at 0, 0·0125, 0·025 and 0·05 M concentrations in all combinations. In 24 days both GA and NH₄NO₃ increased leaf area, leaf number, dry weights of leaf, stem and root, and fresh weights of leaf and stem. GA increased stem height and decreased fresh weight/unit leaf area (leaf thickness), whereas NH₄NO₃ did not affect stem height and increased leaf thickness. Of the GA treatments, 100 p.p.m. gave the largest plants as judged by fresh weight of the whole plant and leaf area, and of the N treatments 0·05 M NH₄NO₃ increased growth most. The best treatment combination was 0·05 M NH₄NO₃ with 100 p.p.m. GA, which gave the greatest fresh and dry weights of the whole plant, leaf area and leaf dry weight as well as increasing leaf thickness. Significant interactions were found between GA and N for dry weight of leaf, fresh and dry weight of root, and leaf thickness but not for leaf area or stem growth (fresh weight, dry weight, height). The combination of levels of GA and N that can be expected to increase leaf area, leaf dry weight and leaf thickness simultaneously, may lie within narrow limits for a particular crop. In a second experiment plants were sprayed with all combinations of GA (0 and 100 p.p.m.) seven times under glass in pots and ten times in the field, and three levels of KH₂PO₄ on twelve occasions in the field. Sprouts (axillary buds) were harvested in October and February. At the first harvest GA did not affect fresh weight or number, but increased both the total number of sprouts picked (with GA = 80·7; without GA = 69·8 per plant) and the total fresh weight of saleable sprouts (with GA = 2·59; without GA = 2·33 lb/plant). KH₂PO₄ also increased the weight and number of sprouts at the final harvest and the number of small sprouts at the first. There were interactions between GA and KH₂PO₄ (P= < 0·001) for both tota weight and number of saleable sprouts.     

Abscisic acid mimics effects of dehydration on area expansion and photosynthetic partitioning in young soybean leaves

Abstract. Leaf area expansion, photosynthetic carbon dioxide uptake and leaf dry mass accumulation were compared for expanding leaves of well-watered soybean ( Glycine max [L.] Merr.) plants, mildly dehydrated plants and well-watered plants treated with abscisic acid (ABA). Both ABA treatment and dehydration reduced area expansion in the light and over a 24 h period without decreasing the photosynthetic rates of expanding leaves. Dry mass accumulation during the light was less in ABA-treated and water-stressed leaves than in control leaves, with no differences among treatments in leaf mass per unit of area. ABA treatment and water stress both increased export of carbon from expanding leaves in the light. ABA applied near the end of the light period also increased export of carbon during the following dark period. However, it is unlikely that decreased availability of photosynthate caused slow expansion in the ABA and dehydration treatments, because expansion rates were not slowed in plants kept in dim light, even though photosynthetic rates and dry mass accumulation rates were greatly reduced. The data suggest that ABA may mediate the effects of mild dehydration on leaf area expansion and partitioning of photosynthate.     

植物生长调节剂对西南桦苗木生长的影响

用 ABT6 和 GA3对西南桦苗木进行叶面喷施试验。试验结果表明 ,GA3的 3种浓度即 2 0× 10 - 6 m g/L、50× 10 - 6 m g/L、80× 10 - 6 m g/L在苗木高生长、地径大小、苗木干鲜重及苗木根系生长发育方面都比清水对照( CK)有明显地提高。ABT6 各浓度特别是 50× 10 - 6 m g/L处理的在苗木分枝数、单株叶面积、苗木干鲜重及苗木根系生长发育方面也比对照有显著的提高。综合各指标 ,用 A BT6 生长调节剂的 50× 10 - 6 mg/L比 2 0× 10 - 6mg/L、80× 10 - 6 mg/L处理及 GA3生长调节剂各浓度处理在生产实践上更适宜用于培育西南桦苗木。     

CONTROL OF THE INTERNODAL INTERCALARY MERISTEM OF CYPERUS ALTERNIFOLIUS

In the growing culm of C. alternifolius, surgical removal of parts indicated that the stimulus for the prolonged activity of the internodal intercalary meristem (IM) came from the matured leaves and upper internode and that buds were not involved in maintaining internodal growth. Decapitation of the culm resulted in cessation of internodal extension. Various growth regulators were applied to the decapitated internode, and both the total extension and growth rates were analyzed statistically. Gibberellin A₃ (GA) and benzyladenine (BA) substituted for the excised parts in their effect on internodal extension. Indoleacetic acid (IAA) had little effect. (2-chloroethyl) trimethylammonium chloride (CCC) inhibited internodal growth, and its effects were reversed by GA. IAA was antagonistic to BA but not to GA. BA and GA were somewhat antagonistic. The quantitative effects of growth regulators on epidermal and ground parenchyma cell length and number of interstomatal cells were examined. Extension induced by GA was due to both cell division and cell elongation in the IM. Cells were longer, and fewer stomates differentiated than in the control. In internodes induced to extend by GA + BA cell division, cell length, and stomate differentiation were similar to the control. The results indicate that prolonged internodal IM activity is maintained by cytokinins and gibberellins coming from the matured upper portions of the culm. Changes in the levels of these regulators during growth presumably result in the histological gradient in the internode.     

Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants

Salinization is one of the most important causes of crop productivity reduction in many areas of the world. Mechanisms that control leaf growth and shoot development under the osmotic phase of salinity are still obscure, and opinions differ regarding the Abscisic acid (ABA) role in regulation of biomass allocation under salt stress. ABA concentration in roots and leaves was analyzed in a genotype of processing tomato under two increasing levels of salinity stress for five weeks: 100 mM NaCl (S10) and 150 mM NaCl (S15), to study the effect of ABA changes on leaf gas exchange and dry matter partitioning of this crop under salinity conditions. In S15, salinization decreased dry matter by 78% and induced significant increases of Na⁺ and Cl⁻ in both leaves and roots. Dry matter allocated in different parts of plant was significantly different in salt-stressed treatments, as salinization increased root/shoot ratio 2-fold in S15 and 3-fold in S15 compared to the control. Total leaf water potential (Ψ_w) decreased from an average value of approximately −1.0 MPa, measured on control plants and S10, to −1.17 MPa in S15. In S15, photosynthesis was reduced by 23% and stomatal conductance decreased by 61%. Moreover, salinity induced ABA accumulation both in tomato leaves and roots of the more stressed treatment (S15), where ABA level was higher in roots than in leaves (550 and 312 ng g⁻¹ fresh weight, respectively). Our results suggest that the dynamics of ABA and ion accumulation in tomato leaves significantly affected both growth and gas exchange-related parameters in tomato. In particular, ABA appeared to be involved in the tomato salinity response and could play an important role in dry matter partitioning between roots and shoots of tomato plants subjected to salt stress.     

Protective effect of jasmonic acid and potassium against cadmium stress in peas (Pisum sativum L.)

A combination of mineral nutrients and plant growth regulators should be assessed to improve crop performance under various abiotic stresses. There is a need to include plant growth regulators in fertilization regime of various crops along with essential mineral nutrients, especially when they are irrigated with polluted water with higher levels of heavy metals. The performance of pea was evaluated under cadmium (Cd) stress coupled with potassium (K) and jasmonic acid (JA) supplementation. The Cd stress (50 μM) was applied to soil (sandy loam) grown pea plants as basal dose after a month of sowing. The control and stressed plants were then supplemented with K (5 M), JA (0.5 mM) and their collective application along with control as distilled water. Cd stress showed a marked reduction in growth pattern, however, the collective supplementation sufficiently improved the growth pattern of stressed peas plants as evidenced by improvement in shoot length (cm), root length (cm), number of leaves per plant, leaf area (cm²), plant fresh and dry weight (gm). Potassium application under Cd stress significantly enhanced internodal distance (cm) while the number of seeds per pod and relative water contents remained nonsignificant. The applied treatment (JA + K) under Cd stress prominently improved enzymatic activities, which were measured as nitrate reductase activity (NRA), nitrite reductase activity (NiRA), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Cd stress impacted the biochemical profile by enhancing antioxidant capacity (AC), antioxidant activity (AA), total phenols (TP), while reducing total soluble protein (TSP), chlorophyll ‘a’, chlorophyll ‘b’ and carotenoids. The combined application of JA and K under Cd stress enhanced AC, AA, TP, Chl a and b, TSP and carotenoids. The results indicate that foliar application of JA and K efficiently negated the harmful effects of Cd stress on peas.     

Abscisic acid and osmotic relations in Phaseolus vulgaris L. Shoots under salt stress

The exogenous application of abscisic acid (ABA) to well-watered plants may be of interest in imitating the effects of salinity on shoot growth. In this paper we have determined the time course of ABA accumulation in control and salt-stressed Phaseolus vulgaris plants and its possible relation to the accumulation of solutes and other physiologic conditions. The effect on shoot parameters of the application of exogenous ABA to the root system has also been checked. The addition of exogenous ABA to control plants caused a retardation of growth. The amount of ABA applied to the growth medium caused tissue ABA concentrations to become close to those of salinized plants. The addition of exogenous ABA to plants under control conditions resulted in a profile of proline and total sugar accumulation very similar to that observed in salinized plants. It was also found that NaCl treatment decreased the stomatal conductance and transpiration rate of leaves as well as the osmotic and turgor potentials. The addition of exogenous ABA also mimicked these responses, resulting in qualitatively and quantitatively similar results. These results, particularly those showing that the early transient rise in ABA upon exposure to NaCl coincides with the period of proline and total sugar accumulation, and that treatment of plants with exogenous ABA mimics these effects, are discussed around the idea that ABA stimulates the cellular processes of osmotic adjustment in P. vulgaris.Abbreviations ABA abscisic acid - HPLC high performance liquid chromatography - DW dry weight - FW fresh weight.     

Application of bioreactor system for large-scale production of Eleutherococcus sessiliflorus somatic embryos in an air-lift bioreactor and production of eleutherosides

Embryogenic callus was induced from leaf explants of Eleutherococcus sessiliflorus cultured on Murashige and Skoog (MS) basal medium supplemented with 1 mg l(-1) 2,4-dichlorophenoxyacetic acid (2,4-D), while no plant growth regulators were needed for embryo maturation. The addition of 1 mg l(-1) 2,4-D was needed to maintain the embryogenic culture by preventing embryo maturation. Optimal embryo germination and plantlet development was achieved on MS medium with 4 mg l(-1) gibberellic acid (GA(3)). Low-strength MS medium (1/2 and 1/3 strength) was more effective than full-strength MS for the production of normal plantlets with well-developed shoots and roots. The plants were successfully transferred to soil. Embryogenic callus was used to establish a suspension culture for subsequent production of somatic embryos in bioreactor. By inoculating 10 g of embryogenic cells (fresh weight) into a 3l balloon type bubble bioreactor (BTBB) containing 2l MS medium without plant growth regulators, 121.8 g mature somatic embryos at different developmental stages were harvested and could be separated by filtration. Cotyledonary somatic embryos were germinated, and these converted into plantlets following transfer to a 3l BTBB containing 2l MS medium with 4 mg l(-1) GA3. HPLC analysis revealed that the total eleutherosides were significantly higher in leaves of field grown plants as compared to different stages of somatic embryo. However, the content of eleutheroside B was highest in germinated embryos. Germinated embryos also had higher contents of eleutheroside E and eleutheroside E1 as compared to other developmental stages. This result indicates that an efficient protocol for the mass production of E. sessiliflorus biomass can be achieved by bioreactor culture of somatic embryos and can be used as a source of medicinal raw materials.     

A study on soybean responses to drought stress and rehydration

To investigate soybean responses to drought stress and growth through metabolism compensation after rehydration, and for the establishment of an optimal water-saving irrigation model, we used the soybean variety Suinong 14 as experimental material and adopted a weighing method for water control in potted plants. We exposed soybean plants to stress treatments at different growth stages using different stress levels and durations. We then studied the effects of drought stress and rehydration on soybean growth and development, osmoregulation, and endogenous hormonal regulations, as well as antioxidant systems. The results showed that drought stress inhibited increases in the soybean plant height and leaf area. This inhibition became more significant as the level, duration, and frequency of the drought stress increased. After rehydration, the soybean plant heights and leaf areas exhibited rapid increases and partial compensation for their decreased sizes. As the level, duration, and frequency of drought stress increased, the compensation effect decreased, but it did not return to the control level. Drought stress reduced the chlorophyll content and relative water content in the soybean leaves and increased the osmolyte contents, antioxidant potential, and peroxidation of the membrane lipids. In addition, the changes mentioned above became more dramatic as the drought stress level, duration, and frequency increased. Upon rehydration, various levels of growth compensation were observed in each physio-biochemical parameter. As the drought stress level, duration, and frequency increased, the compensation effect also increased. Overall, the compensation effect for drought stress that occurred at the early growth stages was higher than that at the later growth stages. Drought stress led to decreases in the ZR/IAA and ZR/ABA ratios in soybean leaves and an increase in the ABA/(IAA + GA + ZR) ratio; thus, the plant growth was inhibited. These hormone ratios exhibited more dramatic changes when the drought stress level became more severe and the stress duration was prolonged. After rehydration, these hormone ratios produced equal compensation effects. Therefore, the compensatory effect of rewatering after drought stress is conditional. Severe stress, especially long-term severe stress, will reduce the compensatory effect. At the same time, drought resistance treatment at seedling stage can improve the adaptability and compensatory effect of re-drought at grain filling stage.     

EFFECTS OF SINGLE AND MULTIPLE EXPOSURES OF FERULIC ACID ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF PHASEOLUS VULGARIS BBL-290

Phaseolus vulgaris BBL-290 plants were grown in growth chambers in the Southeastern Plant Environment Laboratory and exposed to either single (at seedling, flower, or podfill) or multiple (biweekly or weekly) treatments of ferulic acid (FA). In the first experiment, plants were harvested one week after FA treatment (0, 1.0, 2.0 mM) and at final harvest (56 days old). FA delayed leaf expansion during the seedling and flowering stages. The total plant leaf area and the plant dry weight of plants treated with 1.0 and 2.0 mM FA as seedlings were reduced one week after treatment by 38–48%. The total plant leaf area and the plant dry weight of plants treated at flowering with 2.0 mM FA were reduced by 25% one week after treatment. Treatment with 2.0 mM FA at podfill caused the senescence and abscission of older leaves and reduced total plant leaf area, plant dry weight and mean pod dry weight by 54, 40, and 48%, respectively, one week after treatment. The plants treated at the seedling and flowering stages recovered by final harvest. In a subsequent experiment, FA (0, 0.50, 1.0, 1.5 mM) reduced total plant leaf area at the seedling and flowering stages but not at podfill. The youngest expanding leaves were most sensitive to FA at flowering. The leaf area of these leaves was reduced by 35 and 25%, one and two weeks after treatment, respectively. Their absolute growth rates were reduced from 31 to 56% one week after treatment at flowering. Their relative growth rates were reduced by 50% one week after treatment. Growth rates then recovered within two weeks after treatment. In the final experiment, biweekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area but did not affect any other growth parameters. Weekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area up to 34%, absolute growth rate up to 58%, leaf number up to 31% and pod number up to 58%. As the frequency of exposure to FA increased, the concentration necessary to affect bean plant growth and development decreased.