Response of barley grains to the interactive e.ect of salinity and salicylic acid

Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na⁺, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca²⁺ and more accumulation of K⁺, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.     

Enhanced salt tolerance of tomatoes by exogenous salicylic acid applied through rooting medium

In Tunisia, like in the other countries of the Mediterranean, tomato is ranked among the important vegetables in the economic sphere. Tunisia ranks as the first consumer of this vegetable in the world. However, tomatoes are exposed to multiple environmental stresses. In particular, salinity is the most stressful limiting factor to productivity. Salt tolerance of the tomato is susceptible to be ameliorated by genetic and physiologic ways. Salicylic acid (SA), a plant phenolic, is now considered as a hormone-like endogenous regulator, and its role in the defense mechanisms against biotic and abiotic stressors has been well documented. So, the aim of this study was to investigate the impact of exogenous application of SA (0.01 mM) on growth, nutritional behavior, and some metabolic parameters (total chlorophyll, soluble sugars, proline, and proteins) of tomato plants cv. Moneymaker exposed to NaCl (100 mM). Our results showed that the application of 0.01 mM SA to tomato plants via root drenching attenuate the depressive effect of salinity on plants. This amelioration results in stimulation of growth and development of plant. Under stress conditions, SA-treated plants exhibited more accumulation of photosynthetic pigments and K(+) contents. Thus, SA induces an increase in soluble sugars in roots and leaves; also, we noted the increase of proteins only in roots. Overall, the adverse effects of salt stress tomato plants were alleviated by the exogenous application of SA at vegetative stage, which upregulated nutrition and the accumulation of some organic solutes and osmoprotectors such sugars, proline, and proteins. So salicylic acid can be greatly used to enhance salt tolerance of tomato plants.     

Composition and Distribution of Free Amino Acids in Flatpea (Lathyrus sylvestris L.) as Influenced by Water Deficit and Plant Age

Drought-stressed flatpea (Lathyrus sylvestris L.) plants from8 to 22 weeks old were analysed for nitrogen, soluble proteinand free amino acids. An increase in nitrogen and free aminoacid concentrations and a decrease in soluble protein levelwere observed in roots of plants up to 16 weeks old. The cumulativeconcentration of free amino acids increased with drought stress.Tissue concentrations of 2, 4-diaminobutyric acid (1.6–2.6%of the dry weight) were highest in leaves. Levels increasedsteadily, nearly doubling, in leaves and stems between weeks10 and 16. Levels in drought-stressed leaves were, on average,11.9% higher than those of controls. Estimated concentrationsof a mixture of 4-aminobutyric acid and an unknown amino acidwere highest in stems, increased in this tissue with age andtended to increase in stems and leaves and decrease in rootsin response to water deficit. Levels of the mixture of homoserineand another unidentified amino acid were not influenced by ageor water status of the plants. Root concentrations of asparagine,arginine, glutamine, aspartate, and another prominent, unidentifiedamino acid increased with plant age and reached a peak at thetime of flowering (14 to 18 weeks). Only the concentration ofthe unknown compound was elevated following drought stress.Concentrations of valine, isoleucine, leucine, phenylalanine,and methionine also increased during this period and were elevatedin drought-stressed plants. Proline levels increased with plantage and drought stress, but proline accounted for only about10% of the total free amino acids in the drought-stressed plants. Key words: 2, 4-Diaminobutyric acid, drought, flatpea     

Influence of arbuscular mycorrhiza on organic solutes in maize leaves under salt stress

A pot experiment was conducted to examine the effect of the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, on plant biomass and organic solute accumulation in maize leaves. Maize plants were grown in sand and soil mixture with three NaCl levels (0, 0.5, and 1.0 g kg⁻¹ dry substrate) for 55 days, after 15 days of establishment under non-saline conditions. At all salinity levels, mycorrhizal plants had higher biomass and higher accumulation of organic solutes in leaves, which were dominated by soluble sugars, reducing sugars, soluble protein, and organic acids in both mycorrhizal and non-mycorrhizal plants. The relative abundance of free amino acids and proline in total organic solutes was lower in mycorrhizal than in non-mycorrhizal plants, while that of reducing sugars was higher. In addition, the AM symbiosis raised the concentrations of soluble sugars, reducing sugars, soluble protein, total organic acids, oxalic acid, fumaric acid, acetic acid, malic acid, and citric acid and decreased the concentrations of total free amino acids, proline, formic acid, and succinic acid in maize leaves. In mycorrhizal plants, the dominant organic acid was oxalic acid, while in non-mycorrhizal plants, the dominant organic acid was succinic acid. All the results presented here indicate that the accumulation of organic solutes in leaves is a specific physiological response of maize plants to the AM symbiosis, which could mitigate the negative impact of soil salinity on plant productivity.     

The role of xylopodium in Na+ exclusion and osmolyte accumulation in faveleira [Cnidoscolus phyllacanthus (d. arg.) Pax et K. Hoffm] under salt stress

The aim of this work was to evaluate physiological and biochemical responses of faveleira under salinity. Plants were grown in nutrient solution containing 0, 50, 100 or 150 mM NaCl. After 8 days of stress, plants were harvested and separated into roots, xylopodium, stem + petiole (SP), and basal, median and apical leaves. Salinity reduced the dry weight of all plant parts, although the indicators of water status were not changed. Salt stress increased the content of Na⁺ in the different plant parts, especially in xylopodium, in which it increased approximately eightfold while the content of K⁺ decreased by approximately 40 % under 150 mM NaCl. As a consequence, the K⁺/Na⁺ ratio decreased in all plant organs. In stressed plants, the content of soluble sugars was increased in the roots, SP and leaf strata and the content of soluble proteins increased in all organs. The content of total free amino acids increased in the roots, SP and apical leaves, while the proline content increased in all organs except in xylopodium. It is suggested that the xylopodium may be involved in a mechanism of exclusion and/or compartmentalization of Na⁺ in faveleira under salinity to avoid ionic toxicity in the leaves.     

Accumulation of proline and glycine betaine in Ipomoea pes-caprae induced by NaCl

The present study pertains to the effect of different concentration of NaCl on the contents of proteins, free amino acids, proline and glycine betaine in leaves, stems and roots of Ipomoea pes-caprae. The protein content of the tissues increased in response to salinity upto 200 mM NaCl; the free amino acids content showed a reversal trend. The proline and glycine betaine contents increased with increasing salinity upto 500 mM NaCl. The accumulation of proline and glycine betaine might play a role in the alleviation of salt stress. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mulberry Leaf Metabolism under High Temperature Stress

Effects of high temperature on the activity of photosynthetic enzymes and leaf proteins were studied in mulberry (Morus alba L. cv. BC2-59). A series of experiments were conducted at regular intervals (120, 240 and 360 min) to characterize changes in activities of ribulose-1,5-bisphosphate carboxylase (RuBPC) and sucrose phosphate synthase (SPS), photosystem 2 (PS 2) activity, chlorophyll (Chl), carotenoid (Car), starch, sucrose (Suc), amino acid, free proline, protein and nucleic acid contents in leaves under high temperature (40 °C) treatments. High temperature markedly reduced the activities of RuBPC and SPS in leaf extracts. Chl content and PS 2 activity in isolated chloroplasts were also affected by high temperature, particularly over 360 min treatment. Increased leaf temperature affected sugar metabolism through reductions in leaf starch content and sucrose-starch balance. While total soluble protein content decreased under heat, total amino acid content increased. Proline accumulation (1.5-fold) was noticed in high temperature-stressed leaves. A reduction in the contents of foliar nitrogen and nucleic acids (DNA and RNA) was also noticed. SDS-PAGE protein profile showed few additional proteins (68 and 85 kDa) in mulberry plants under heat stress compared to control plants. Our results clearly suggest that mulberry plants are very sensitive to high temperature with particular reference to the photosynthetic carbon metabolism.     

Inductive responses of some organic metabolites for osmotic homeostasis in peanut (Arachis hypogaea L.) seedlings during salt stress

The salt tolerance of peanut (Arachis hypogaea L.) seedlings was evaluated by analyzing growth, nutrient uptake, electrolyte leakage, lipid peroxidation and alterations in levels of some organic metabolites under NaCl stress. The plant height, leaf area and plant biomass decreased significantly in salt-treated seedlings as compared with control. The relative water content (RWC %) of leaf decreased by 16 % at high concentrations of NaCl. There was an increase in the lipid peroxidation level and decrease in the electrolyte leakage at high concentrations of NaCl. The total free amino acid and proline contents of leaf increased by 5.5- and 43-folds, respectively in 150 mM NaCl-treated plants as compared with control. Total sugar and starch content increased significantly at high concentrations of NaCl. Chl a, Chl b, total chlorophyll and carotenoid contents decreased significantly at high salinity. Na⁺ contents of leaf, stem and root increased in dose-dependent manner. K⁺ content remained unaffected in leaf and root and decreased in stem by salinity. The results from present study reveal that the peanut plants have an efficient adaptive mechanism to tolerate high salinity by maintaining adequate leaf water status associated with growth restriction. In order to circumvent the stress resulting from high salinity, the levels of some organic metabolites such as total free amino acids, proline, total sugars and starch were elevated. The elevated levels of the organic metabolites may possibly have some role in maintenance of osmotic homeostasis, nutrient uptake and adequate tissue water status in peanut seedlings under high-salinity conditions.     

Carbohydrate and Proline Contents in Leaves, Roots, and Apices of Salt-Tolerant and Salt-Sensitive Wheat Cultivars1

Intra-specific variations in nonstructural carbohydrates and free proline were determined in leaves, apices, roots, and maturing seeds of two salt-tolerant cultivars (CR and Kharchia-65) and one salt-sensitive cv. Ghods of spring wheat (Triticum aestivum L.) grown in sand culture at various levels of salinity (0, 100, 200, and 300 mM NaCl and CaCl₂ at 5 : 1 molar ratio) under controlled environmental conditions. The levels of leaf, apex, and root ethanol-soluble carbohydrates, fructans, starch, and proline increased in line with elevating level of salinity in all three cultivars under investigation. The contents of proline, soluble and insoluble carbohydrates in the apex increased to levels exceeding those in the leaves and roots. Soluble carbohydrate content of salt-sensitive cv. Ghods was higher in the leaves, apices, and roots and lower in the maturing seeds than in the other cultivars at all levels of salinity except at 300 mM. The results show considerable variation in the amount of soluble, insoluble sugars, and proline among plant tissues and wheat genotypes in response to salinity. Higher soluble carbohydrates and fructan in leaves, roots and maturing seeds of stressed plants indicate that their accumulation may help plant to tolerate salinity. Salt-sensitive cv. Ghods accumulated less soluble sugars in the maturing seeds and higher soluble sugars in the apices, which might be used as an indicator in screening wheat genotypes for salinity tolerance.     

Counteraction of Salinity Stress on Wheat Plants by Grain Soaking in Ascorbic Acid, Thiamin or Sodium Salicylate

The interactive effects of salinity stress (40, 80, 120 and 160 mM NaCl) and ascorbic acid (0.6 mM), thiamin (0.3 mM) or sodium salicylate (0.6 mM) were studied in wheat (Triticum aestivum L.). The contents of cellulose, lignin of either shoots or roots, pectin of root and soluble sugars of shoots were lowered with the rise of NaCl concentration. On the other hand, the contents of hemicellulose and soluble sugars of roots, starch and soluble proteins of shoots, proline of either shoots or roots, and amino acids of roots were raised. Also, increasing NaCl concentration in the culture media increased Na⁺ and Ca²⁺ accumulation and gradually lowered K⁺ and Mg²⁺ concentration in different organs of wheat plant. Grain soaking in ascorbic acid, thiamin or sodium salicylate could counteract the adverse effects of NaCl salinity on the seedlings of wheat plant by suppression of salt stress induced accumulation of proline.     

铜胁迫条件下AMF对海州香薷光合色素含量、抗氧化能力和膜脂过氧化的影响

以盆栽海州香薷为研究对象,模拟Cu胁迫条件下,接种丛枝菌根真菌(AMF)对海州香薷叶片光合色素含量、抗氧化酶活性、抗氧化剂含量、膜脂过氧化程度的影响。结果表明:(1)与对照相比,Cu胁迫使海州香薷叶片叶绿素a(Chl a)、叶绿素b(Chl b)、总叶绿素(Chl(a+b))、类胡萝卜素(Car)含量以及叶绿素a/b(Chl a/b)均显著降低,抗氧化酶活性和抗氧化剂含量也显著下降,质膜相对透性(MRP)和丙二醛(MDA)含量显著增大。(2)与Cu胁迫相比,Cu胁迫下接种AMF可使海州香薷叶片叶绿素含量显著增加;超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)活性显著提高;还原型谷胱甘肽(GSH)、抗坏血酸(As A)含量显著增加;MDA含量、MRP显著下降。总之,接种AMF可提高Cu胁迫下海州香薷叶片光合色素含量和抗氧化能力,降低膜脂过氧化水平,从而缓解Cu胁迫对植株造成的伤害,增强海州香薷对Cu胁迫的适应性,提高了植株的生物量。     

Sugar and Amino Acid Content of Poa pratensis Infected with Ustilago striiformis and Urocystis agropyri

Leaf and root tissues of Poa pratensis L. showing distinct morphological changes associated with infection by Ustilago striiformis (West.) Niessl var. poae (stripe smut) or Urocystis agropyri (Pruess) Schroet. (flag smut) were analyzed for total soluble sugars and free amino acids. Decreases in the quantity of soluble sugars in stripe-smutted plants were not significant, indicating that the presence of U. striiformis sori in leaf tissue does not interfere with photosynthesis of the host. Severe decreases in the quantity of soluble sugars in flag-smutted plants suggest that U. agropyri either directly impairs photosynthesis or effectively metabolizes the photosynthate. Both pathogens caused significant decreases in total free amino acids in leaf and root tissues. The negligible decrease in soluble sugars in stripe-smutted plants was associated with a disproportionate decrease in free amino acids, suggesting that the pathogen either metabolizes amino acids or inhibits their synthesis. The severe decrease in amino acids in leaves and roots of U. agropyri-infected plants is believed due to carbohydrate starvation. It is probable that morphological changes in U. agropyri-infected plants, including reduced branching, dwarfed leaves and root systems, and the inability to produce inflorescences, are probably the direct result of severely reduced levels of sugars and amino acids. The reduced branching, somewhat smaller root systems, and inhibition of inflorescence production on plants infected by U. striiformis probably are associated to some extent with decreases in amino acids. The upright elongated leaves of U. striiformis-infected plants, however, cannot be attributed to the decrease in amino acid content and are suggestive of hyperauxiny.     

Organic substances responsible for salt tolerance inEruca sativa

Responses of a salt tolerant and a normal population of an oilseed crop,Eruca sativa Mill. were assessed after four weeks growth in sand culture salinized with 0 (control), 100, 200, or 300 mol m^?3 NaCl. The salt tolerant plants produced significantly greater dry biomass than the normal population. The populations did not differ significantly in leaf osmotic potential, relative water content and leaf soluble proteins. However, the tolerant population accumulated significantly greater amounts of soluble sugars, proline and free amino acids in the leaves compared with the non-tolerant population. It is established that leaf soluble sugars, proline, and free amino acids are important components of salt tolerance inEruca sativa.     

Effects of copper on the growth,photosynthesis and nutrient concentrations of Phaseolus plants

Bean plants (Phaseolus vulgaris L. var. Zargana Kavala) were grown under conditions of increasing Cu concentrations in the growth medium (0.5-160.5 µM). Generally, the Cu concentrations between 0.5-1.5 µM were deficient, 1.5-10.5 µM were optimal, and 10.5-160.5 µM were toxic to plant growth. The Cu toxicity was associated with marked increases in plant tissue Cu concentrations. Under the Cu-deficient and optimal growth conditions, Cu was located primarily in the leaves. Under Cu toxicity, it was primarily sequestered in the roots. With increasing Cu in the growth medium, there was a positive correlation between Cu concentrations in the roots, stems and leaves, Ca in the roots, and K and Mg in the leaves. In contrast, Ca concentrations in the leaves and stems showed a negative correlation. The chlorophyll (Chl) concentration increased with increasing leaf Cu concentration, however, the Chl a/b ratio decreased. Since with an increasing leaf Cu concentration the leaf area decreased more markedly than the leaf dry mass, the net photosynthetic rate (PN) per leaf area increased and per dry mass decreased. The increase in PN per leaf area was almost entirely accounted for by the increase in Chl concentration. The initial Chl fluorescence (F0) increased with increasing leaf Cu concentration. The ratio of variable to maximum fluorescence (Fv/Fm) under Cu toxicity decreased. The half-time for the rise from F0 to Fm (t1/2) remained relatively unchanged with increasing leaf Cu concentration. Therefore the Cu-stress caused a small decrease in the efficiency of photosystem 2 photochemistry, but its primary effect was on growth.     

Effects of NaCl-salinity on amino acid and carbohydrate contents of Phragmites australis

The effects of NaCl-salinity on growth, free amino acid and sugar content and composition were assayed in roots, rhizomes and leaves of Phragmites australis (Cav.) Trin. ex Steud. Juvenile plants produced from freshwater clones, were cultured under greenhouse hydroponic conditions for 21 days. Relative growth rates were highest at a salinity level of 0 and 1.5‰, respectively, but decreased significantly at 10‰. All plants cultured at 35‰ salinity died. The osmolality in rhizomes and leaves increased with salinity. The total contents of free amino acids were highest in rhizomes>leaves>roots. In rhizomes, the amino acid content increased significantly up to four-fold from 0 to 10‰ salinity. This increase was caused by up to 200-fold increase of proline and 11-fold increase of glutamine at 10‰, whilst the share of asparagine and glutamate decreased. Leaves showed a similar response to salinity with increasing amino acid contents, and shares of proline and glutamine whereas roots did not react significantly. The contents of sucrose, glucose and fructose were highest in leaves>rhizomes>roots. In rhizomes of all three clones, the sugar contents increased up to 3.5-fold from 1.5 to 10‰ salinity level, but were lower at 1.5‰ versus the control (0‰). Sugar contents were lowest (roots) and highest (leaves) at 1.5‰ salinity. The sugar composition did not vary significantly except for leaves where the fraction of sucrose decreased with increasing salinity level at all three clones from 89.1 to 61.7% of total dissolved sugar (pooled data). The importance of free amino acids and sugars as osmolytes was similar in rhizomes and leaves (13–15% of total osmolality at 10‰). In rhizomes, free amino acids were more important as osmolyte than sugars, while the opposite was true for leaves. Proline contributed up to 2.7% to total osmolality. It is hypothesised that a strong proline accumulation indicates the exceeding of a critical salinity level.     

Exogenous salicylic acid improves salinity tolerance of <Emphasis Type="Italic">Nitraria tangutorum</Emphasis>

In the present study, the physiological responses of Nitraria tangutorum Bobr. seedlings to NaCl stress and the regulatory function of exogenous application of salicylic acid (SA) were investigated. NaCl in low concentration (100 mM) increased while in higher concentrations (200–400 mM) decreased the individual plant dry weights (wt) of seedlings. Decreased relative water content (RWC) and chlorophyll content were observed in the leaves of seedlings subjected to salinity stress (100–400 mM NaCl). Furthermore, NaCl stress significantly increased electrolyte leakage and malondialdehyde (MDA) content. The levels of osmotic adjustment solutes including proline, soluble sugars, and soluble protein were enhanced under NaCl treatments as compared to the control. In contrast, exogenous application of SA (0.5–1.5 mM) to the roots of seedlings showed notable amelioration effects on the inhibition of individual plant dry wt, RWC, and chlorophyll content. The increases in electrolyte leakage and MDA content in the leaves of NaCl-treated seedlings were markedly inhibited by SA application. The SA application further increased the contents of proline, soluble sugars, and soluble protein. The activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were up-regulated by NaCl stress and the activities of SOD, POD, and CAT were further enhanced by SA treatments. Application of SA in low concentration (0.5 mM) enhanced while in higher concentrations (1.0 and 1.5 mM) inhibited APX activities in leaves of NaCl-treated seedlings. These results indicate that SA effectively alleviated the adverse effects of NaCl stress on N. tangutorum.     

The role of amino acids and sugars in supporting of osmotic homeostasis in maize seedlings under salinization conditions and treatment with synthetic growth regulators

Stress state in plants caused by salinization conditions is characterized by the disturbance of ionic and osmotic homeostasis. The maintenance of the latter is reached by accumulation of osmolytes including free amino acids and soluble sugars in cells. The free amino acid level in the 8-day-old control seedling leaves was higher, than in the roots, whereas the contrary picture was observed in 17-day-old plant tissues. At the same time 8-day-old seedling roots contained more total sugars, than leaves, although the reduced sugar content was nearly a half of the total sugar content. A decrease of both total and reduced sugar levels was observed in 17-day-old seedling tissues. One-day exposure of 7-day-old seedlings to 0.1 M NaCl increased the free amino acid content especially in roots, than in leaves, and the total sugar content in maize leaves, whereas in roots this level remained without changes. The prolongation of salt exposure to 10 days leads to osmolyte content decrease. The seed treatment with Methyure and Ivine intensified accumulation of free amino acids and soluble sugars in the root and leaf tissues under salinization conditions.     

Calcium-mediated enhancement of copper tolerance in Elodea canadensis

The alleviative effects of exogenous calcium on copper phytotoxicity were investigated in Elodea canadensis plants. There was a significant accumulation of Cu in the plants after their exposure to 0.01 mM Cu accompanied by many symptoms of toxicity. Increased uptake of Cu severely reduced content of photosynthetic pigments, soluble proteins, and free proline. The total antioxidant capacity (T-AOC), reduced glutathione (GSH), and non-protein thiol (NP-SH) were severely suppressed in Cu-stressed plants resulting in a rapid increase in content of superoxide anion (O₂ ^·?), hydrogen peroxide, lipid peroxidation, and cell death. Simultaneous application of Ca markedly increased the content of photosynthetic pigments, soluble proteins, free proline, T-AOC, GSH, and NP-SH, and reduced oxidative damage as indicated by lowered content of MDA, O₂ ^·?, and H₂O₂; and decreased cell death. Furthermore, application of Ca reduced Cu uptake and effectively reversed the Cu-induced nutrient imbalance.     

Effects of lead and kinetin on the growth, and some physiological components of safflower

Pollution of the root environment with excess of Pb retarded shoot growth, decreased chlorophyll (Chl) content and reduced Chl stability (CSI) to heat. Plants growing in Pb polluted soil accumulated much more free amino acids and less soluble sugars than the control plants. Stability of leaf membranes to heat (51 °C) or dehydration stresses (40% polyethylene glycol, 6000) decreased in response to Pb pollution where the membranes of leaf discs excised from Pb-treated plants were damaged more than those taken from plants growing in Pb free soil. Supplying kinetin ameliorated the deleterious effects of Pb pollution on the parameters tested. Kinetin-treated plants had higher Chl, soluble sugars content and produced more biomass in their shoots. Also, kinetin increased leaf membrane stability especially in Pb-treated plants, effectively protected chlorophyll degradation by heat and increased Chl a and b stability index; the most effective concentration was 10 mg L^–1. The effects of Pb and kinetin as well as their interaction (Pb × Kin) on the parameters tested were statistically significant. Applied kinetin had a dominant role (as indicated by ²) in affecting shoot growth, soluble sugars, Chl a and b contents, stability of leaf membranes to dehydration stress as well as the Chl stability index. Pb had a dominant role on total free amino acids (TAA) and leaf relative water content (RWC). The interaction between Kin × Pb influenced the stability of leaf membranes to heat stress in a major way.     

Modulation of endogenous levels of some key organic metabolites by exogenous application of glycine betaine in drought stressed plants of sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.)

The present study was conducted to examine the changes in some key metabolites in drought-stressed sunflower plants supplied with glycine betaine externally. Imposition of drought stress at the vegetative or reproductive growth stages decreased the plant dry matter production and increased the accumulation of organic solutes (glycine betaine, proline, soluble proteins, free amino acids and soluble sugars) in two sunflower lines, i.e., Glushan-98 and Suncross. In general, decrease in dry matter production and increase in the endogenous levels of organic solutes, were more pronounced when drought stress applied at the vegetative stage than at the reproductive stage. Glycine betaine applied as a pre-sowing seed treatment was not found to be effective in reducing the negative effects of drought stress in sunflower plants. Foliar application of GB further enhanced the leaf endogenous levels of GB, soluble proteins and total soluble sugars in drought stressed plants without exerting any negative effects on other osmotica. However, this GB-induced increase in endogenous levels of organic solutes was found to be not associated with plant dry matter production under stress conditions.