Endogenous brassinosteroids in wheat treated with 24-epibrassinolide

The aim of the study was to examine the effect of exogenous 24-epibrassinolide on its uptake and content of endogenous brassinosteroids in wheat seedlings. 24-Epibrassinolide was applied at two concentrations (0.1 and 2.0 μM) and in three different methods: by soaking seeds, by drenching and by spraying plants. Brassinosteroids were determined by high-performance liquid chromatography combined with electrospray mass spectrometry. Three important brassinosteroids, 24-epibrassinolide, brassinolide and castasterone, were detected in the wheat leaves, but their contents varied with leaf insertion and plant age. Increased 24-epibrassinolide content in the leaf tissue was found when this hormone was applied by soaking or drenching. Additionally the seed treatment influenced brassinosteroid balance in seedlings. The growth response of wheat seedlings treated with 24-epibrassinolide has been also investigated.     

Does exogenous application of salicylic acid through the rooting medium modulate growth and photosynthetic capacity in two differently adapted spring wheat cultivars under salt stress?

In order to assess whether exogenous application of salicylic acid (SA) through the rooting medium could modulate the photosynthetic capacity of two wheat cultivars differing in salinity tolerance, a hydroponic experiment was conducted under greenhouse conditions. Seeds of a salt tolerant (S-24) and a moderately salt sensitive (MH-97) cultivar were germinated at 0 or 150 mM NaCl in Hoagland's nutrient solution containing different levels of salicylic acid (SA) (0, 0.25, 0.50, 0.75 and 1.00 mM) for 7d. Seven-day old wheat seedlings were transferred to hydroponics and grown at 0, or 150 mM NaCl for for further 30 d. Different levels of salicylic acid (SA) were also maintained in the solution culture. After 30 d, four plants out of six were harvested and the remaining plants were left for the estimation of yield attributes Salt stress reduced the growth and grain yield of both cultivars. However, cv. S-24 performed better than MH-97 under salt stress with respect to leaf area, and grain yield. Exogenous application of SA promoted growth and yield, and counteracted the salt stress-induced growth inhibition of salt tolerant S-24, whereas for MH-97 there was no improvement in growth or grain yield with SA application. Of the varying SA levels used, the most effective levels for promoting growth and grain yield were 0.75 and 0.25 mM under normal and saline conditions, respectively. The improvement in growth and grain yield of S-24 due to SA application was associated with improved photosynthetic capacity. Changes in photosynthetic rate due to SA application were not due to stomatal limitations, but were associated with metabolic factors, other than photosynthetic pigments and leaf carotenoids.     

Effect of 24-epibrassinolide on biomass, growth and free proline concentration in Spirulina platensis (Cyanophyta) under NaCl stress

In this study, biomass, growth and free proline concentration were investigated in Spirulina platensis treated with different concentrations of NaCl (50, 100, 150, and 200 mM) and 24-epibrassinolide (24-epiBL) hormone (0.5, 1.0, and 3.0 μM) over 5 days. As a result of analysing the cultures under salinity stress, it was determined that biomass and growth rate decreased significantly, while proline concentration increased considerably under salinity stress. The increase in the concentration of proline suggests a role in response to NaCl stress. Among the cultures treated with different concentrations of 24-epiBL, maximum growth was determined at the cultures at 1.0 μM 24-epiBL. Algal growth was also greater at the 0.5 and 3.0 μM concentrations of 24-epiBL with respect to control cultures. With respect to control, 24-epiBL affected growth rate and biomass positively, but proline concentration did not change. Among the cultures supplied with different combinations of NaCl and 24-epiBL, growth rate increased in 150/0.5 and 150/3.0 mM/μM concentrations, but was maximal for the culture containing 150/1.0 mM/μM combination. The increase in algal growth suggests a role for 24-epiBL in partially alleviated to NaCl stress. These results suggest that 24-epiBL may have a protective role for S. platensis reducing the inhibitor effects of salinity stress.     

Effect of 24-epibrassinolide on growth,photosynthesis, and essential oil content of <Emphasis Type="Italic">Pelargonium graveolens</Emphasis> (L.) Herit

The effects of 24-epibrassinolide on growth, photosynthesis, chlorophyll content, carbohydrate fractions, and essential oil content of rose scented geranium (Pelargonium graveolens (L.) Herit) were investigated. Foliar application of 24-epibrassinolide at 0.5, 1, and 3 μM concentrations substantially increased the growth. 24-epibrassinolide at all concentrations improved herbage yield as reflected in the increase of foliar biomass. Exogenous application of 24-epibrassinolide increased the rate of photosynthesis. Growth promotion was also associated with increased chlorophyll content and resulted in the accumulation of carbohydrate fractions. At 3-μM concentration, 24-epibrassinolide increased the total content of essential oils. The quantitative analysis of geranium oil from the geranium plant treated with 3-μM concentration revealed an increase in geraniol content and decrease in citronellol content. The present study demonstrates a positive impact of the new group of phytohormones on the performance of geranium plant, a highly valued aromatic plant.     

Exogenously applied ascorbic acid alleviates salt-induced oxidative stress in wheat

Although ascorbic acid (AsA) is one of the most important and abundantly occurring water soluble antioxidants in plants, relatively little is known about its role in counteracting the adverse effects of salt stress on plant growth. To address this issue that whether exogenous application of ascorbic acid (AsA) through rooting medium could alleviate the adverse effects of salt stress on wheat plants, a hydroponic experiment was conducted under glasshouse conditions using two wheat cultivars, S-24 (salt tolerant) and MH-97 (moderately salt sensitive). Plants of both cultivars were subjected to 0 or 150 mM NaCl solution supplemented with 0, 50, or 150 mg L⁻¹ AsA for 58 days. Imposition of salt stress reduced the growth of both wheat cultivars by causing reduction in photosynthesis, and endogenous AsA level, and enhancing accumulation of Na⁺ and Cl⁻ coupled with a decrease in K⁺ and Ca²⁺ in the leaves and roots of both cultivars thereby decreasing tissue K⁺/Na⁺ ratio. However, root applied AsA counteracted the adverse effects of salt stress on the growth of cv. S-24 only, particularly at 100 mg L⁻¹ AsA level. AsA-induced enhancement in growth of salt-stressed plants of S-24 was associated with enhanced endogenous AsA level and CAT activity, and higher photosynthetic capacity, and accumulation of K⁺ and Ca²⁺ in the leaves. Although root applied AsA did not improve the growth of salt-stressed plants of MH-97, it enhanced endogenous level of AsA, CAT activity, photosynthetic capacity, and leaf K⁺ and Ca²⁺. These findings led us to conclude that root applied AsA counteracts the adverse effects of salt stress on growth of wheat by improving photosynthetic capacity of wheat plants against salt-induced oxidative stress and maintaining ion homeostasis, however, these effects were cultivar specific.     

Does exogenous application of 24-epibrassinolide ameliorate salt induced growth inhibition in wheat (Triticum aestivum L.)?

A greenhouse experiment was conducted to assess whether exogenously applied 24-epibrassionlide (24-epiBL) could alleviate the adverse effects of salt on wheat. Two hexaploid wheat (Triticum aestivum L.) cultivars, S-24 (salt tolerant) and MH-97 (moderately salt sensitive), were grown under control (0 mM NaCl in full strength Hoagland’s nutrient solution) or saline conditions (150 mM of NaCl in full strength Hoagland’s nutrient solution). After 41 days growth of wheat plants under saline conditions, 24-epiBL was applied as a foliar spray. Four levels of BR were used as 0 (water spray), 0.0125, 0.025, and 0.0375 mg l⁻¹. Application of 24-epiBL increased plant biomass and leaf area per plant of both cultivars under non-saline conditions. However, under saline conditions, improvement in growth due to exogenous 24-epiBL was observed only in S-24. Photosynthetic rate was reduced due to salt stress in both cultivars, but this inhibitory effect was ameliorated significantly by the exogenous application of 24-epiBL. Exogenously applied 24-epiBL also enhanced the photosystem-II efficiency in both cultivars measured as F _v /F _m ratio. Although the activities of antioxidant enzymes, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) were increased due to salt stress in both wheat cultivars, exogenously applied 24-epiBL had a varying effect on the antioxidant system. The activity of SOD remained unaffected in both cultivars due to 24-epiBL application, but that of POD and CAT was promoted in the salt stressed plants of cv. S-24 only. In conclusion, improvement in growth in both wheat cultivars due to foliar applied 24-epiBL was found to be associated with 24-epiBL-induced enhancement in photosynthetic capacity. The 24-epiBL-induced regulation of antioxidant enzymes or growth under saline conditions was cultivar specific.     

Expression levels of the Na + /K + transporter OsHKT2;1 and vacuolar Na + /H + exchanger OsNHX1 , Na enrichment,maintaining the photosynthetic abilities and growth performances of indica rice seedlings under salt stress

Salt affected soil inhibits plant growth, development and productivity, especially in case of rice crop. Ion homeostasis is a candidate defense mechanism in the salt tolerant plants or halophyte species, where the salt toxic ions are stored in the vacuoles. The aim of this investigation was to determine the OsNHX1 (a vacuolar Na+/H+ exchanger) and OsHKT2;1 (Na+/K+ transporter) regulation by salt stress (200 mM NaCl) in two rice cultivars, i.e. Pokkali (salt tolerant) and IR29 (salt susceptible), the accumulation of Na+ in the root and leaf tissues using CoroNa Green® staining dye and the associated physiological changes in test plants. Na+ content was largely increased in the root tissues of rice seedlings cv. Pokkali (15 min after salt stress) due to the higher expression of OsHKT2;1 gene (by 2.5 folds) in the root tissues. The expression of OsNHX1 gene in the leaf tissues was evidently increased in salt stressed seedlings of Pokkali, whereas it was unchanged in salt stressed seedlings of IR29. Na+ in the root tissues of both Pokkali and IR29 was enriched, when subjected to 200 mM NaCl for 12 h and easily detected in the leaf tissues of salt stressed plants exposed for 24 h, especially in cv. Pokkali. Moreover, the overexpression of OsNHX1 gene regulated the translocation of Na+ from root to leaf tissues, and compartmentation of Na+ into vacuoles, thereby maintaining the photosynthetic abilities in cv. Pokkali. Overall growth performance, maximum quantum yield (Fv/Fm), photon yield of PSII (ΦPSII) and net photosynthetic rate (Pn) was improved in salt stressed leaves of Pokkali than those in salt stressed IR29.     

Modulation of Exogenous Glutathione in Phytochelatins and Photosynthetic Performance Against Cd Stress in the Two Rice Genotypes Differing in Cd Tolerance

Greenhouse hydroponic experiments were conducted using Cd-sensitive (Xiushui63) and tolerant (Bing97252) rice genotypes to evaluate genotypic differences in response of photosynthesis and phytochelatins to Cd toxicity in the presence of exogenous glutathione (GSH). Plant height, chlorophyll content, net photosynthetic rate (Pn), and biomass decreased in 5 and 50 μM Cd treatments, and Cd-sensitive genotype showed more severe reduction than the tolerant one. Cadmium stress caused decrease in maximal photochemical efficiency of PSII (Fv/Fm) and effective PSII quantum yield [Y(II)] and increase in quantum yield of regulated energy dissipation [Y(NPQ)], with changes in Cd-sensitive genotype being more evident. Cadmium-induced phytochelatins (PCs), GSH, and cysteine accumulation was observed in roots of both genotypes, with markedly higher level in PCs and GSH on day 5 in Bing97252 compared with that measured in Xiushui63. Exogenous GSH significantly alleviated growth inhibition in Xiushui63 under 5 μM Cd and in both genotypes in 50 μM Cd. External GSH significantly increased chlorophyll content, Pn, Fv/Fm, and Y(II) of plants exposed to Cd, but decreased Y(NPQ) and the coefficient of non-photochemical quenching (qN). GSH addition significantly increased root GSH content in plants under Cd exposure (except day 5 of 50 μM Cd) and induced up-regulation in PCs of 5 μM-Cd-treated Bing97252 throughout the 15-day and Xiushui63 of 5-day exposure. The results suggest that genotypic difference in the tolerance to Cd stress was positively linked to the capacity in elevation of GSH and PCs, and that alleviation of Cd toxicity by GSH is related to significant improvement in chlorophyll content, photosynthetic performance, and root GSH levels.     

Effects of genotype, explant source, and plant growth regulators on indirect shoot organogenesis in Dieffenbachia cultivars

The capacity for indirect shoot organogenesis of leaf and root explants of four Dieffenbachia cultivars were examined on a modified Murashige and Skoog (MS; Physiol Plant 15:473–495, 1962) medium supplemented with different plant growth regulators in 112 combinations. Callus formation was only observed from leaf explants on MS supplemented with 1–10 μM thidiazuron (TDZ) and 0.5–1.0 μM 2,4-dichlorophenoxyacetic acid (2,4-D) regardless of cultivars. The combination of 5 μM TDZ and 1 μM 2,4-D resulted in the greatest callus formation frequency among the four cultivars tested. Significant differences in callus and shoot formation from leaf explants were also observed among cultivars. Cultivars Camouflage, Camille, Octopus, and Star Bright produced green nodular, brown nodular, yellow friable, and green compact calli with corresponding maximum callus formation frequencies of 96%, 62%, 54%, and 52%, respectively. A maximum of 6.7 shoots/callus was observed in cv. Camouflage, followed by cvs. Camille and Star Bright at 3.7 and 3.5, respectively. Calli of cv. Octopus displayed no capacity for shoot organogenesis. Regardless of cultivar, callus formation was not observed on root explants. Regenerated shoots were successfully acclimatized in a shaded greenhouse condition with 100% survival.     

Foliar applied fullerol differentially improves salt tolerance in wheat through ion compartmentalization,osmotic adjustments and regulation of enzymatic antioxidants

Earlier we reported that seed pre-treatment with PHF promoted early seedling growth and salinity tolerance in wheat. As a way forward, experiments were conducted to investigate whether and to what extent foliar spray of fullerol could influence growth and physio-biochemical responses in salt stressed wheat. In a control experiment, seeds were sown in sand filled pots (500 g) under control and 150 mM NaCl stress. After 15 days, foliar spray of fullerol at 0, 10, 40, 80 and 120 nM concentration was applied and the data for various morpho-biochemical attributes recorded after 2 weeks. Fullerol caused improvements in shoot growth attributes while had least effect on root growth traits. Increase in total chlorophyll while reduction in Car/Chl ratio was evident under salinity in response to fullerol spray. Only 40 and 80 nM spray treatments improved antioxidant activities and reduced H2O2 contents while MDA contents which increased due to salt stress, remained unaffected by foliar spray. Fullerol spray also improved sugars, proline and free amino acids under salinity. During second experiment under natural conditions, 60 day old plants grown in sand filled pots (10 kg) under 0 and 150 mM NaCl were foliar sprayed with selected concentrations (0, 40 and 80 nM) of fullerol. Salinity inhibited gas exchange and grain yield attributes while fullerol-sprayed plants exhibited recovery. Fullerol spray resulted in high root and shoot K+ and shoot Ca2+ contents. Also, increase in shoot and root P, while lesser shoot Na+ was recorded due to 80 nM spray under salt stress. Overall, 40 and 80 nM fullerol spray improved photosynthetic activity, osmolytes accumulation and altered tissue ion compartmentalization which contributed to improvement in grain yield attributes under salinity.     

An Enhancing Effect of Exogenous Mannitol on the Antioxidant Enzyme Activities in Roots of Wheat Under Salt Stress

The role of mannitol as an osmoprotectant, a radical scavenger, a stabilizer of protein and membrane structure, and protector of photosynthesis under abiotic stress has already been well described. In this article we show that mannitol applied exogenously to salt-stressed wheat, which normally cannot synthesize mannitol, improved their salt tolerance by enhancing activities of antioxidant enzymes. Wheat seedlings (3 days old) grown in 100 mM mannitol (corresponding to −0.224 MPa) for 24 h were subjected to 100 mM NaCl treatment for 5 days. The effect of exogenously applied mannitol on the salt tolerance of plants in view of growth, lipid peroxidation levels, and activities of antioxidant enzymes in the roots of salt-sensitive wheat (Triticum aestivum L. cv. Kızıltan-91) plants with or without mannitol was studied. Although root growth decreased under salt stress, this effect could be alleviated by mannitol pretreatment. Peroxidase (POX) and ascorbate peroxidase (APX) activities increased, whereas superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) activities decreased in Kızıltan-91 under salt stress. However, activities of antioxidant enzymes such as SOD, POX, CAT, APX, and GR increased with mannitol pretreatment under salt stress. Although root tissue extracts of salt-stressed wheat plants exhibited only nine different SOD isozyme bands of which two were identified as Cu/Zn-SOD and Mn-SOD, mannitol treatment caused the appearance of 11 different SOD activity bands. On the other hand, five different POX isozyme bands were determined in all treatments. Enhanced peroxidation of lipid membranes under salt stress conditions was reduced by pretreatment with mannitol. We suggest that exogenous application of mannitol could alleviate salt-induced oxidative damage by enhancing antioxidant enzyme activities in the roots of salt-sensitive Kızıltan-91.     

Physiological effects and transport of 24-epibrassinolide in heat-stressed barley

This paper presents a study of the metabolic response (dark respiration intensity, photosystem II efficiency, metabolic activity) and the yield of barley treated with 24-epibrassinolide and subjected to high-temperature stress. Transport of exogenously applied 24-epibrassinolide in barley and changes in the profile of brassinosteroids that may occur in tissues after 24-epibrassinolide application were also studied. The water solution of 24-epibrassinolide (0.005 and 0.25 mg dm⁻³) was applied via infiltration of the first and second leaves of 12-day-old seedlings. Control plants were treated with water solution of hormone solvent (ethanol). Fifteen-day-old plants were subjected to high-temperature stress (42°C for 3 h). The influence of hormone treatment and stress conditions was investigated in the first and second leaves based on measurements of PSII efficiency. The aftereffect of plant treatment was investigated in the seventh leaf (measurements of PS II efficiency, dark respiration intensity, metabolic activity). The transport efficiency of 24-epibrassinolide exogenously applied to the first and second leaves, as well as the profile of other brassinosteroids, was also measured on the seventh leaf. Finally, yield formation was estimated. 24-epibrassinolide showed protective action, which manifested itself in the improved functioning of PSII, but this was observed in case of higher hormone concentration and only for the first, older leaf. The PSII efficiency of the seventh leaf was similar in plants treated with brassinosteroid and in the control plants, whereas the respiration intensity and metabolic activity decreased in plants previously treated with higher concentration of 24-epibrassinolide. The use of a higher hormone concentration at the seedling phase ultimately resulted also in lower crop yield. Brassinosteroids—brassinolide and castasterone—were detected in barley leaves. 24-epibrassinolide was found only in trace amounts in control plants. Its exogenous application directly to the apoplast of the first and second leaves resulted in an increase in the 24-epibrassinolide content in the seventh leaf, but did not depend on whether a high or low concentration had been applied to the plants.     

Cadmium-induced stress on the seed germination and seedling growth of <Emphasis Type="Italic">Brassica napus</Emphasis> L., and its alleviation through exogenous plant growth regulators

Because of its prolific growth, oilseed rape (Brassica napus L.) can be grown advantageously for phytoremediation of the lands contaminated by industrial wastes. Therefore, toxic effect of cadmium on the germination of oilseed rape, the capability of plants for cadmium phytoextraction, and the effect of exogenous application of plant growth regulators to mitigate phytotoxicity of cadmium were investigated. For the lab study of seedlings at early stage, seeds were grown on filter papers soaked in different solutions of Cd²⁺ (0, 10, 50, 100, 200 and 400 μM). In greenhouse study, seedlings were grown in soil for 8 weeks, transferred to hydroponic pots for another 6 weeks growth, and then treated with plant growth regulators and cadmium. Four plant growth regulators viz. jasmonic acid (12.5 μM), abscisic acid (10 μM), gibberellin (50 μM) and salicylic acid (50 μM); and three levels of Cd²⁺ (0, 50 and 100 μM) were applied. Data indicated that lower concentration of Cd²⁺ (10 μM) promoted the root growth, whereas the severe stresses (200 or 400 μM) had negative effect on the establishment of germinating seedlings. Plants treated with any of the tested plant growth regulators alleviated cadmium toxicity symptoms, which were reflected by more fresh weight, less malondialdehyde concentration in leaves and lower antioxidant enzyme activities. The application of abscisic acid to the plants cultivated in the medium containing 100 μM Cd²⁺ resulted in significantly lower plant internal cadmium accumulation. Huabing Meng and Shujin Hua contributed equally to this paper.     

Effects of root pruning on the growth and water use efficiency of winter wheat

A pot experiment was conducted to study the effects of root pruning at the stem elongation stage on the growth and water use efficiency (WUE) of winter wheat (Triticum aestivum). The results showed that stomatal conductance (g) and transpiration (E) of wheat were very sensitive to root pruning. After root pruning, they declined rapidly and but returned to pre-pruning values 15 days after treatment. Under well-watered conditions, there was no significant difference in leaf water potential (ψ_leaf) between root pruned and control plants after root pruning. Under moderate drought stress, ψ_leaf of root pruned plants declined significantly compared to the control 3 days after root pruning. After 15 days, ψ_leaf of root pruned plants was similar to the controls. Under different soil moisture levels, net assimilation rate (A) of root pruned plants was lower than controls 3–7 days after root pruning, but was similar to the controls 15 days after pruning. At anthesis (50 days after root pruning), root pruned plants showed significantly higher A compared with the control. Leaf area per tiller and tiller number of root pruning plants was significant lower than the control at booting stage, which showed that root pruning restrained the growth of plants in the early growing stage, but leaf area per stem, of root pruned plants, was similar to the control at anthesis. Under both soil moisture levels, there was no significant difference in grain yield between root pruned and the control plants in the monoculture. In mixture with the control plants, the root pruned plants was less productive and had a lower relative yield (0.92 and 0.78, respectively) compared with the control (1.13 and 1.19, respectively), which suggested that the pruned plants lost some of its competing ability and showed a lower ability to acquire and use the same resources in the mixture compared with the control plant. Over the whole growing cycle, root pruning reduced water consumption (by 10% under well-watered conditions and 16% under moderate drought stress) of wheat significantly compared to the control (P < 0.05), and but there was no significant difference in grain yield between root pruned and control plants. Therefore root pruned wheat had a higher WUE with respect to grain yield compared with the controls. In conclusion, lowering water consumption by root pruning in the early growing stage is an effective way to improve water use efficiency in arid and semi arid areas.     

Micropropagation of Hemidesmus indicus for cultivation and production of 2-hydroxy 4-methoxy benzaldehyde

Caulogenic responses of various explant types from 12-month-old plants of Hemidesmus indicus were tested. Second and third visible nodes (0.5 cm) from the apex and root segments (0.5 cm) were the most and least regenerative respectively, with the formation of 9.37 and 2.6 shoots in 4 weeks on half strength MS medium supplemented with 2.22 μM BA and 1.07 μM NAA and 4.44 μM BA and 2.69 μM NAA respectively. Caulogenic ability of the nodes decreased with increasing maturity. Shoot buds initiated upon the young nodes on day 10 developed into 7.2 cm long shoots within 4 weeks thereby making a shoot elongation phase unnecessary. Nodal explants of the in vitro raised shoots subcultured in the same medium produced 9.32 shoots of 7.1 cm length in 3–4 weeks, similar to those of the mature plant-derived nodes. Multiplication through subculture of the nodes up to 25 passages of 4 weeks each was achieved without decline. Shoot cultures were rooted in quarter salt strength MS medium containing 9.8 μM IBA and the rooted plants were hardened for establishment in pots at 96% rate. Four months after establishment, the micropropagated plants were stable and showed uniform morphological and growth characteristic. After 12 months of cultivation in the field, on an average micropropagated plant consisted of 4–5 shoots, 5–8 branches per shoot and increased root biomass (13.5 g) compared to the poor growth (single shoot and 2–3 branches) and root production (4.6 g) values obtained with plants raised from conventional rooted stem cuttings. The concentration of the root specific compound, 2-hydroxy 4-methoxy benzaldehyde per plant was 2–3 fold higher in micropropagated plants though on unit dry root biomass (0.12% per g dry wt) basis it remained the same between two sources of plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparative effectiveness of <Emphasis Type="Italic">Pseudomonas</Emphasis> and <Emphasis Type="Italic">Serratia</Emphasis> sp. containing ACC-deaminase for improving growth and yield of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) under salt-stressed conditions

Ethylene synthesis is accelerated in response to various environmental stresses like salinity. Ten rhizobacterial strains isolated from wheat rhizosphere taken from different salt affected areas were screened for growth promotion of wheat under axenic conditions at 1, 5, 10 and 15 dS m⁻¹. Three strains, i.e., Pseudomonas putida (N21), Pseudomonas aeruginosa (N39) and Serratia proteamaculans (M35) showing promising performance under axenic conditions were selected for a pot trial at 1.63 (original), 5, 10 and 15 dS m⁻¹. Results showed that inoculation was effective even in the presence of higher salinity levels. P. putida was the most efficient strain compared to the other strains and significantly increased the plant height, root length, grain yield, 100-grain weight and straw yield up to 52, 60, 76, 19 and 67%, respectively, over uninoculated control at 15 dS m⁻¹. Similarly, chlorophyll content and K⁺/Na⁺ of leaves also increased by P. putida over control. It is highly likely that under salinity stress, 1-aminocyclopropane-1-carboxylic acid-deaminase activity of these microbial strains might have caused reduction in the synthesis of stress (salt)-induced inhibitory levels of ethylene. The results suggested that these strains could be employed for salinity tolerance in wheat; however, P. putida may have better prospects in stress alleviation/reduction.     

The effect of 5-azacytidine on wheat seedlings responses to NaCl stress

The effect of 5-azacytidine (5-azaC) on the alleviation of damaging effects of NaCl treatment was studied in two wheat (Triticum aestivum L.) cultivars differing in salt tolerance (salt-tolerant Dekang-961 and sensitive Lumai-15). The plants were pre-treated or not with 50 μM 5-azaC and then subjected to salt stress induced by 100 or 150 mM NaCl. Salinity caused reduction in biomass accumulation and increase in malondialdehyde content in root tissues in both cultivars, but less in pre-treated seedlings. The activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in the roots of both cultivars increased during salt stress, but the rate of increase was higher in Dekang-961. Plants treated with 5-azaC had higher root SOD, CAT and POD activities under salt stress than untreated plants. Content of 5-methylcytosine (5mC) decreased in both cultivars under salt stress, and the level of demethylation was higher in Dekang-961 than that in Lumai-15. Moreover, the degree of methylation was lower in both cultivars under salt stress after 5-azaC application compared to only salt-treated groups. These findings suggested that 5-azaC could protect plants from salt stress.     

Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars During Grain Filling: Changes in Flag Leaf Photosynthetic Activity,ABA Levels,and Grain Yield

Water status parameters, flag leaf photosynthetic activity, abscisic acid (ABA) levels, grain yield, and storage protein contents were investigated in two drought-tolerant (Triticum aestivum L. cv. MV Emese and cv. Plainsman V) and two drought-sensitive (cvs. GK élet and Cappelle Desprez) wheat genotypes subjected to soil water deficit during grain filling to characterize physiological traits related to yield. The leaf water potential decreased earlier and at a higher rate in the sensitive than in the tolerant cultivars. The net CO₂ assimilation rate (P _N) in flag leaves during water deficit did not display a strict correlation with the drought sensitivity of the genotypes. The photosynthetic activity terminated earliest in the tolerant cv. Emese, and the senescence of flag leaves lasted 7 days longer in the sensitive Cappelle Desprez. Soil drought did not induce characteristic differences between sensitive and tolerant cultivars in chlorophyll a fluorescence parameters of flag leaves during post-anthesis. Changes in the effective quantum yield of PSII (Φ_PSII) and the photochemical quenching (qP) depended on the genotypes and not on the sensitivity of cultivars. In contrast, the levels of ABA in the kernels displayed typical fluctuations in the tolerant and in the sensitive cultivars. Tolerant genotypes exhibited an early maximum in the grain ABA content during drought and the sensitive cultivars maintained high ABA levels in the later stages of grain filling. In contrast with other genotypes, the grain number per ear did not decrease in Plainsman and the gliadin/glutenin ratio was higher than in the control in Emese during drought stress. A possible causal relationship between high ABA levels in the kernels during late stages of grain filling and a decreased grain yield was found in the sensitive cultivars during drought stress.     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

The effect of isoproturon on root growth and ultrastructure of the photosynthetic apparatus of two wheat cultivars and a weed

The effect of isoproturon [N,N-dimethyl N'4-(1-methyl-ethyl) phenyl urea] on the germination, growth of root and ultrastructure of the photosynthetic apparatus was investigated in two wheat cultivars ( Triticum sativum L. cvs Castan and Esquilache) and a weed ( Lolium rigidum Gaud.). No inhibition of germination was apparent in any of the three plants studied. The inhibition of root growth was considerably significant, especially in cv. Esquilache. After 48 h treatment with isoproturon (340 μ M ), the chloroplasts of the two wheat cultivars were found to be similar, showing a higher number of grana with fewer thylakoids per granum (lower stacking degree), broader grana stacks than in the control and an absence of starch. However, after 60 h of treatment, swelling of the thylakoids occurred in the Esquilache cultivar.
The rye grass was the most affected by the herbicide; at low concentration (3.4 μ M ) the number and size of the grana decreased considerably and the stroma thylakoids were destroyed. At higher concentration (17 μ M ), there was a strong accumulation in certain areas of the stroma of a substance with a lipid-like appearance, probably derived from the disintegrating thylakoids. At the same concentrations some chloroplast envelopes were completely desintegrated.
The Hill reaction of the three plants exhibited a similar sensitivity towards the herbicide.