Salicylic acid-induced physiological and biochemical changes in lemongrass varieties under water stress

Abstract

Salicylic acid (SA) treatment reduces the damaging action by water deficit on growth and accelerates a restoration of growth processes. The aim of the present work was to study the physiological and biochemical alteration induced by SA in lemongrass plants under stress conditions. Therefore, a pot culture experiment was conducted to test whether SA application at concentration of (10^?5 M) through foliar spray could protect lemongrass (Cymbopogon flexuosus Steud. Wats.) varieties (Neema and Krishna), subjected to drought stress on the basis of growth parameters and biochemical constituents, proline metabolism and quality attributes including citral content. The treatments were as follows: (i) 100% FC + 0 SA; (ii) 75% FC + 0 SA; (iii) 50% FC + 0 SA; (iv) 75% FC + 10^?5 M SA; and (v) 50% FC + 10^?5 M SA. The growth parameters were significantly reduced under the applied water stress levels; however, foliar application of salicylic acid (10^?5 M) improved the growth parameters in stress-affected plants. The plants under water stress exhibited a significant increase in activities of nitrate reductase and carbonic anhydrase, and electrolyte leakage, proline content, free amino acid and in PEP carboxylase activity. Content and yield of essential oil also significantly decreased in plants that faced water stress. Thus, it was concluded that variety Neema is the more tolerant variety as compared to Krishna on the basis of content and oil yield and well adapted to drought stress conditions.     

Salicylic acid affects growth,essential oil and chemical compositions of thyme (Thymus daenensis Celak.) under reduced irrigation

Salicylic acid (SA) may reduce the negative impact of water deficit on growth and metabolite yield of Thymus daenensis Celak subsp. daenensis Celak. The effect of foliar application of SA and reduced irrigation on growth, oil yield, chemical components, and antibacterial and antioxidant activities of T. daenensis in field condition were investigated. Treatments comprised 0.0, 1.5 and 3.0 M SA applied to plants under normal irrigation and stressed conditions. Results indicated that irrigation regime had a significant effect on growing degree days (GDD) required to reach early and full flowering. Foliar application of SA influenced GDD from early growing stage to 50 % and full flowering, minimum radius and canopy diameter. The highest values of oil content (3.2 % v/w) and yield (14.9 g m^?2) were obtained from application of 3.0 M SA. Percentage of some chemical constituents in the essential oil extracted from the plants under stress was higher than non-stressed plants. Thymol content was significantly reduced under stressed conditions. Foliar application of SA significantly improved carvacrol, α-thujene, α-pinene and p-cymene contents in the oils, but reduced thymol and, β-caryophyllene amounts. Our results showed that foliar application of SA reduced the negative effect of water deficit on thymol content in the essential oil of T. daenensis. The essential oils of T. daenensis exhibited antioxidant and antibacterial activities when plants were sprayed with 1.5 and 3.0 M SA, respectively.     

Alleviation of salt stress in lemongrass by salicylic acid

Soil salinity is one of the key factors adversely affecting the growth, yield, and quality of crops. A pot study was conducted to find out whether exogenous application of salicylic acid could ameliorate the adverse effect of salinity in lemongrass (Cymbopogon flexuosus Steud. Wats.). Two Cymbopogon varieties, Krishna and Neema, were used in the study. Three salinity levels, viz, 50, 100, and 150 mM of NaCl, were applied to 30-day-old plants. Salicylic acid (SA) was applied as foliar spray at 10^?5 M concentration. Totally, six SA-sprays were carried out at 10-day intervals, following the first spray at 30 days after sowing. The growth parameters were progressively reduced with the increase in salinity level; however, growth inhibition was significantly reduced by the foliar application of SA. With the increase in salt stress, a gradual decrease in the activities of carbonic anhydrase and nitrate reductase was observed in both the varieties. SA-treatment not only ameliorated the adverse effects of NaCl but also showed a significant improvement in the activities of these enzymes compared with the untreated stressed-plants. The plants supplemented with NaCl exhibited a significant increase in electrolyte leakage, proline content, and phosphoenol pyruvate carboxylase activity. Content and yield of essential oil was also significantly decreased in plants that received salinity levels; however, SA overcame the unfavorable effects of salinity stress to a considerable extent. Lemongrass variety Krishna was found to be more adapted to salt stress than Neema, as indicated by the overall performance of the two varieties under salt conditions.     

Influence of ascorbic acid and 24-epibrassinolide on physiological characteristics of pot marigold under water-stress condition*

Water deficit is considered as a major limiting environmental factor for plant growth and yield. To ameliorate the adverse effects of water restriction, an experiment was conducted in the research field of Mohaghegh Ardabili University in two successive years (2014 and 2015). Foliar spraying of different concentration of epibrassinolide (EBL) (0, 10^?8, and 10^?7?M) and ascorbic acid (AsA) (0 and 10?mM) was carried out and water-stress trials included 50 and 100?mm evaporation from class A pan. Water stress significantly enhanced essential oil content, but reduced capitula yield and relative water content (RWC) of leaves. Water-stress damage ameliorated by foliar application of 10?mM AsA with 10^?7?M EBL and the essential oil yield and antioxidant enzymes activity improved significantly. Enhancing of malondialdehyde (MDA) content and electrolyte leakage indicates that water-deficit stress caused oxidative damage to the membrane by enhancing hydrogen peroxide (H₂O₂) level. Combined-application of regulators significantly declined the amounts of H₂O_2, MDA, and electrolyte leakage under water stress. Antioxidant enzymes activity and also proline and protein content were enhanced by drought stress as well as regulators. Also, the application of EBL and AsA induced tolerance to water deficit and reduced the reactive oxygen species by increasing antioxidant enzymes activity and osmotic adjustment.     

Combined effect of salicylic acid and potassium mitigates drought stress through the modulation of physio-biochemical attributes and key antioxidants in wheat

Improving physio-biochemical traits in wheat under drought stress conditions has received more research attention in recent years for better adaptability and higher yield. In this study, we explored the potential bio-physiological mechanisms underlying improved plant growth and water use efficiency in wheat following soil application of potassium (0 and 100 kg ha^?1) and seed primed salicylic acid (SA) (150 mg per L) and SA foliar application (100 mg per L) under drought stresses (100%, 60% and 30% FC). Two years' average data revealed that inducing drought stress resulted in a decrease in plant pigments content, growth traits, and plant water status however, the influence was substantially reduced with the combined application of K and SA under drought stress conditions. The SA foliar spray in combination with K had increased chlorophyll a (174% and 83%), chl b (130% and 192%), chl a + b (156% and 120), carotenoid (22% and 11%), proline contents (24% and 29%) leaf relative water content (24% and 29%) while reduced leaf WSD (17% and 20%), WRC (6% and 7%), and WUC (23% and 28%) under mild and severe drought stresses, respectively. The increase in grain yield by 41% and 37% with enhanced water use efficiency was obtained with combined foliar SA and K under mild and severe drought stress, respectively indicating its vital role in overcoming the deleterious effects of drought via regulation of osmotic and metabolic processes and stabilizes cell components. RDA analysis revealed that the studied traits were completely discriminated under severe stress than mild or no drought stress. A positive and significant association was found between plant pigments with seed yield whereas a negative and significant correlation existed between water leaf traits and plant pigments. It was concluded that both foliar SA and seed primed SA with K fertilization combat the adverse effects of drought and improved plant water status as well as growth and bio-physiological traits of wheat under drought stress conditions.     

Effect of 24-epibrassinolide on growth, protein content and antioxidative defense system of Brassica juncea L. subjected to cobalt ion toxicity

Brassica juncea L. plants were subjected to cobalt (Co) ion (0, 5?×?10^?4, 10^?3, 1.5?×?10^?3 and 2?×?10^?3?M) toxicity and were sprayed with different concentrations of 24-epibrassinolide (24-EBL) (0, 10^?10, 10^?8 and 10^?6?M) at 15-day stage after sowing. They were sampled at 30 and 60?days after sowing and analyzed for growth parameters in terms of shoot length and number of leaves. Thereafter, leaves were excised and content of proteins and the activities of antioxidative enzymes (superoxide dismutase (SOD) (EC 1.15.1.1) catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APOX) (EC 1.11.1.11), guaiacol peroxidase (POD) (EC 1.11.1.7) glutathione reductase (GR) (EC 1.6.4.2), monodehydroascorbate reductase (MDHAR) (EC 1.1.5.4) and dehydroascorbate reductase (DHAR) (EC 1.8.5.1)) were analyzed. The plants exposed to cobalt ion exhibited a significant decline in growth in terms of shoot length and number of leaves. However, foliar spray treatment with 24-EBL was able to alleviate the stress generated by cobalt ion and significantly improved the above parameters. The activities of antioxidative enzymes (SOD, CAT, POD, GR, APOX, MDHAR and DHAR) and protein content were also regulated considerably in leaves of plants treated with 24-EBL alone, 10^?8?M concentration being the most effective. The activities of antioxidative enzymes also increased in leaves of B. juncea plants by the application of cobalt ion to soil and consequently sprayed with 24-EBL. Similarly, the protein content was also regulated in leaves of B. juncea plants treated with 24-EBL as compared to untreated control plants, thereby revealing stress-protective properties of 24-EBL.     

Cytogerontological studies of biological activity of oregano essential oil

In order to clarify possible cytological mechanisms that underlie the beneficial effects of carvacrol-bearing essential oils on health and mental abilities, we studied one of them (oregano essential oil) in experiments on transformed cultured Chinese hamster cells. Possible cytotoxic or mitogenic effects of the preparation at various concentrations were preliminarily estimated by analyzing the cell culture density after 4 days of cultivation. The preparation concentration in the growth medium (on carvacrol basis) varied from 1 × 10^?15 up to 5 × 10^?4 M (on carvacrol basis). As a result, two concentrations were selected for further experiments, including 2.5 × 10^?5 M as the maximal absolutely non-toxic concentration and 2.5 × 10^?4 M as the concentration at which the oregano essential oil decreased approximately 2-fold the final cell density of the grown culture. It was found that the preparation at 2.5 × 10^?5 M had no effect on either the colony-forming ability of the cells or the saturation density of the culture (which is a marker of its ??biological age??) or kinetics of its ??stationary phase aging?? (degradation of cultured cells in the stationary phase of growth, similar to age-related changes of the cells in aging organism). On the contrary, the oregano essential oil at 2.5 × 10^?4 M abruptly diminished colony-forming ability of the cells and influenced as a ??pro-aging?? factor on the saturation density of the cell culture and kinetics of the cell death induced by ??stationary phase aging.?? Based on our own concept of aging and the data obtained, we assumed that detected increase in the life span of mice under the influence of the oregano essential oil could be determined by certain functional changes at the organismal level only, but is not associated with any geroprotective (anti-aging) activity of the preparation, which is manifested at the cellular level and improves the cell viability.     

Foliar application of plant nutrients and kinetin modifies growth and essential oil profile in <Emphasis Type="Italic">Rosa damascena</Emphasis> under acidic conditions

Rosa damascena Mill. is cultivated for its high-value essential oil in different parts of the world. The flower yield and the composition of essential oil of R. damascena are strongly affected by a number of factors. Nevertheless, the interactive effects of foliar application of plant nutrients and kinetin and its time of application on yield and secondary metabolites profile of R. damascena under acidic conditions are still unclear. Thus, a field experiment comprising two different times of spray and five foliar spray treatments was conducted to test the hypothesis that flowering behavior and secondary metabolites profile can be modified through proper nutrient supply at right time. The foliar spray at flower bud appearance stage (S₂) significantly (P ≤ 0.05) increased flower yield by about 10.0 % compared with the foliar application at axillary bud development stage (S₁) during both years, regardless of plant nutrients. Among the foliar spray treatments, kinetin at 0.20 g L^?1 registered about 23–39 % higher flower yield compared with the water spray control; however, remained statistically at par (P ≤ 0.05) with Ca(NO₃)₂ at 4.06 g L^?1. Moreover, the percentage of major fragrance-bearing compounds of essential oil (β-citronellol + nerol, linalool, E-geraniol, and Z-citral) was marginally increased with Ca(NO₃)₂ compared with kinetin treatment. However, the percentages of major hydrocarbons, nonadecane and heneicosane, were noticeably increased when kinetin was applied at S₁. Foliar application of kinetin and Ca(NO₃)₂ might be done to improve flower yield and essential oil content in R. damascena flowers.     

Plant growth regulators ameliorate the ill effect of salt stress through improved growth,photosynthesis, antioxidant system,yield and quality attributes in <Emphasis Type="Italic">Mentha piperita</Emphasis> L.

The roles of plant growth regulators (PGRs) in plants are well documented. However, there is a little information regarding their roles in alleviating salt stress in plants, particularly peppermint. This necessitated the evaluation of the efficiency of three selected PGRs in counteracting the ill effect of salt stress by conducting a pot experiment on peppermint (Lamiaceae). Three uniform size suckers were transplanted in each pot containing proper nutrients. Thirty day old plants were subjected to 4 levels of salinity, viz. 0, 50, 100 or 150 mM NaCl. Salt stress was given at 30 days after their transplantation (DAT). Plants were sprayed twice, i.e., at 60 and 75 DAT with 10^?6 M each of gibberellic acid (GA₃), salicylic acid (SA) or triacontanol (Tria). The sampling was made at 100 DAT and harvesting at 120 DAT. The graded levels of salinity decreased growth, photosynthesis, carbonic anhydrase (CA) activity, NPK content, peltate glandular trichome (PGT) density, essential oil (EO) and menthol content and herb, EO and menthol yield, but increased catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) activities and proline content linearly. Spray of PGRs particularly SA improved all parameters under both salt and salt free conditions. The maximum values for yields of herb, EO and menthol were noted with 0 mM NaCl?×?SA. However, antioxidants, proline content, PGT density and EO content were found to be maximum with 150 mM NaCl?×?SA.     

Improved Tolerance of Teak (Tectona grandis L.f.) Seedlings to Low-Temperature Stress by the Combined Effect of Arbuscular Mycorrhiza and Paclobutrazol

Low-temperature damage is a common problem for tropical and subtropical plants during their early-growth stage. In this study, an experiment with a L₁₈ (2¹?×?3⁷) mixed orthogonal array in a greenhouse was conducted to determine whether arbuscular mycorrhizal fungi (AMF) inoculation and paclobutrazol (PBZ) application through foliar spray would enhance the chilling tolerance of teak seedlings. One-month-old seedlings of clones 8301, 7544, and 7552 from a Myanmar provenance propagated by tissue culture techniques were inoculated with Glomus versiforme and cultivated for 6?months. The foliar surface of both mycorrhizal and nonmycorrhizal treated plants was sprayed with PBZ at concentrations of 0, 50, and 100?mg?l^?1 once a week for 3?weeks prior to exposure to low temperatures of 6, 3, and 0°C for 12?h in an artificial climate chamber, followed by 12?h of recovery at 20°C room temperature. AMF colonization significantly promoted height and RCD growth and dry biomass accumulation of shoot and root. Under low-temperature stress, AM symbiosis increased leaf chlorophyll content by 22.8%, soluble protein content by 19.6%, superoxide dismutase (SOD) activity by 10.6%, and peroxidase (POX) activity by 9.5%, whereas malondialdehyde content was decreased by 14.1%. Both AMF colonization and the foliar spray PBZ at 50 and 100?mg?l^?1 were capable of alleviating the damage caused by low-temperature stress on teak seedlings by increasing the photosynthetic pigments, accumulation of osmotic adjustment compounds, and antioxidant enzyme (SOD and POX) activity, and by decreasing membrane lipid peroxidation. AMF colonization and foliar spraying of PBZ at 50?mg?l^?1 produced a positive interaction and appears to be a good way to enhance chilling tolerance of teak seedlings experiencing stress at 6, 3 and 0°C for 12?h.     

Response of exogenous salicylic acid on cadmium induced photosynthetic damage,antioxidant metabolism and essential oil production in peppermint

The present inquest was undertaken in view of the alarming increase in the concentration of cadmium, nickel etc., in the arable soils of Uttar Pradesh, India and the little attention paid to the effect of these heavy metals on the performance of pharmaceutically imperative essential oil (EO) producing crops like peppermint (Mentha piperita L.). We devised a pot experiment to study the influence of exogenously sourced salicylic acid (SA) (10^?4 M) in the amelioration of growth, protection of photosynthesis and essential oil production against 30, 60 and 120 mg kg^?1 soil of cadmium (Cd)-accrued stress in peppermint. Plants grown with Cd showed remarkably deleterious effects on growth, photosynthesis, carbon and nitrate assimilating enzymes and yield and active constituents of EO in addition to the marked elevation in the oxidative stress. SA successfully alleviated the Cd induced toxicity in peppermint, improved photosynthesis by enhancing activity of RuBisCo and carbonic anhydrase and minimized the oxidative stress by mitigating the production of free radicals by the maintenance of free radical scavenging enzymes and reduced glutathione (GSH) pool. Furthermore, the decrease in the concentration of EO and menthol due to Cd stress was successfully alleviated by SA application which was evident from the gas chromatograms of EO of Cd stressed SA treated plants.     

Effect of fungicidal essential oils against Botrytis cinerea and Rhizopus stolonifer rot fungus in vitro conditions

The development of natural crop protection products as alternatives to the use of synthetic fungicides is currently popular. The aim of this study is to evaluate the antifungal effects of several essential oils against the fungal pathogens, Botrytis cinerea and Rhizopus stolonifer, under in vitro condition. Four essential oils (fennel, black caraway, peppermint and thyme) were each tested at five concentrations (0, 200, 400, 600 or 800 μl l^?1). In vitro results showed that the essential oil of black caraway and fennel had the highest fungicidal effect against B. cinerea and R. stolonifer, respectively. The growth of B. cinerea was completely inhibited by the essential oil of black caraway at 400 μl l^?1. Fennel oil perfectly inhibited growth of R. stolonifer fungus colonies at concentration higher than 600 μl L^?1 in potato dextrose agar medium. Percentage of spores germination was the lowest in medium of Fennel and black caraway essential oils, and was the highest in Thyme ones. These results show that plant essential oils can have a strong effect on reducing post-harvest decay. These plant essential oils could provide an alternative to synthetic chemicals to control post-harvest phytopathogenic fungi on fruit.     

Salicylic acid mitigates salinity stress by improving antioxidant defence system and enhances vincristine and vinblastine alkaloids production in periwinkle [<Emphasis Type="Italic">Catharanthus roseus</Emphasis> (L.) G. Don]

A pot experiment was conducted to find out whether the foliar spray of salicylic acid (SA) could successfully ameliorate the adverse effects of salinity stress on periwinkle. Thirty-day-old plants were supplied with Control; 0 mM NaCl + 10⁻⁵ M SA (T₁); 50 mM NaCl + 0 SA (T₂); 100 mM NaCl + 0 SA (T₃); 150 mM NaCl + 0 SA (T₄); 50 mM NaCl + 10⁻⁵ M SA (T₅); 100 mM NaCl + 10⁻⁵ M SA (T₆); 150 mM NaCl + 10⁻⁵ M SA (T₇). The plants were sampled 90 days after sowing to assess the effect of SA on stressed and unstressed plants. Salt stress significantly reduced the growth attributes including plant height, leaf-area index, shoot and root fresh weights, shoot and root dry weights. Increasing NaCl concentrations led to a gradual decrease in photosynthetic parameters and activities of nitrate reductase and carbonic anhydrase. Ascorbic acid, total alkaloids and antioxidants enzymes superoxide dismutase, catalase and peroxidase also declined in NaCl-treated plants. The plants, undergoing NaCl stress, exhibited a significant increase in electrolyte leakage and proline content. Foliar application of SA (10⁻⁵ M) reduced the damaging effect of salinity on plant growth and accelerated the restoration of growth processes. It not only improved the growth parameters but also reversed the effects of salinity. Total alkaloid content was improved by SA application both in unstressed and stressed plants. The highest level of total alkaloid content recorded in leaves of SA-treated stressed plants was 11.1%. Foliar spray of SA overcame the adverse effect of salinity by improving the content of vincristine (14.0%) and vinblastine (14.6%) in plants treated with 100 M NaCl.     

Salicylic acid induces amelioration of chromium toxicity and affects antioxidant enzyme activity in Sorghum bicolor L.

Aim: Chromium (Cr(VI)) would inflict serious morphological, metabolic, and physiological anomalies in plants ranging from chlorosis of shoot to lipid peroxidation and protein degradation. Cr(VI) toxicity is often associated with oxidative stress, caused by the excessive formation of reactive oxygen species (ROS). In response, plants are equipped with a repertoire of mechanisms to counteract heavy metal (HM) toxicity. Salicylic acid (SA) plays a key role in the signal transduction pathways of various stress responses, demonstrating the protective effect of SA against abiotic stress factors. So, the present investigation was carried out to study the amelioration of pernicious effects of different concentration of Cr(VI) (0.0, 2.0, and 4.0?mg Cr(VI) kg^?1 soil in the form of potassium dichromate) by treatments of salicylic acid solution viz. pretreatment and foliar spray via antioxidative enzymes and their metabolites.

Results: With different treatments of salicylic acid solution, the reinstatement from ill effects of Cr(VI) toxicity was contemplated but the most conspicuous effect was observed when salicylic acid solution was supplied through the foliar spray (0.50?mM). This was accompanied with an increase in ascorbate peroxidase activity and hydrogen peroxide content and decrease in peroxidase activity and ascorbic acid content.

Significance of the study: This study suggests that salicylic acid when applied through pre-treatment of seeds or through a foliar spray can be used to ameliorate the toxic effects of chromium (VI). Salicylic acid has the great potential for reducing the toxicity of heavy metals without negatively impacting the growth of the plants.     

Sulphur application improves the growth, seed yield and oil quality of canola

Sulphur (S) nutrition is very important for harvesting potential seed and oil yield of rapeseed. This study evaluated response of foliage applied thiourea on the performance of two canola cultivars Shiralee and Dunkeld. Sulphur was applied to soil (40 kg ha^?1) or foliage (500 and 1,000 mg L^?1) at rosette, bud initiation and flowering stages using elemental S or thiourea as source, respectively; no S application was taken as control. Among all the treatments, soil application of S improved the crop growth, yield and oil quality in both cultivars and was followed by foliar application of thiourea at 1,000 mg L^?1 compared with no application. Soil applied S and foliar thiourea (1,000 mg L^?1) delayed the flowering and maturity. Soil and foliar applied S significantly improved leaf area index, crop growth rate, net assimilation rate and chlorophyll contents. Plant height, number of branches, siliqua per plant, seed number per siliqua, 1,000-seed weight, biological and seed yield were also increased by soil applied S and foliage applied thiourea (1,000 mg L^?1). Nonetheless, improvement in harvest index, seed oil, protein and glucosinolate contents was only observed from foliage applied thiourea (1,000 mg L^?1). Response of cv. Shiralee to sulphur application was better than cv. Dunkeld. In conclusion, foliar applied thiourea (1,000 mg L^?1) can have potential to improve growth, yield and oil quality in canola and can be economically viable and attractive alternative source.     

Synthesis and biological activity of the probable biosynthetic precursors of 241-norbrassinolide

A series of 24¹-norbrassinolide biosynthetic precursors containing 3??-OH, 3-keto, ??²- or 2??,3??-epoxy functional groups less polar than 2??,3??-diol group in A-ring, and (22R,23R)-diol group in the side chain, was synthesized. Their biological activity as the proliferation regulators in MCF-7 human breast cancer and LNCaP human prostate adenocarcinoma cells was studied. It was shown that the majority of the derivatives obtained effectively suppress cell proliferation. The dependence of proliferation on the concentration of the studied compounds was found in LNCaP human prostate adenocarcinoma cells (IC₅₀ = 13?C28 ??M at 72 h of incubation in a medium containing 10% FBS, and suppression of DNA biosynthesis). Some compounds stimulated apoptosis (23?C33%), blocked the cell cycle in S- and G2/M-phases, and induced a partial detachment of cells during a prolonged incubation.     

Depolymerised carrageenan enhances physiological activities and menthol production in Mentha arvensis L.

Irradiated carrageenan (IC) could elicit plant growth promoting activities in plants. The effect of foliar spray of five concentrations of IC (20, 40, 60_, 80 and 100 mg L⁻¹) was studied on Mentha arvensis L. in terms of plant growth, physiological attributes, herbage yield and the content and yield of essential oil and its components. Un-irradiated carrageenan and deionized water had no effect on the attributes studied. GPC study revealed formation of low molecular weight fractions in irradiated samples containing less than 20,000 molecular weight oligomers which are responsible for plant growth promotion in this study. 80 mg L⁻¹ of IC was the most effective concentration which resulted in the highest values of growth attributes, herbage yield and the content and yield of essential oil and menthol content of the oil. It also improved the leaf-nutrient contents, photosynthetic rate and other physiological parameters. 100 mg L⁻¹ of IC did not further improve the attributes studied, but it was always better than the control.     

Sugars,antioxidant enzymes and IAA mediate salicylic acid to prevent rice spikelet degeneration caused by heat stress

Salicylic acid (SA) can alleviate damage to rice plants induced by heat stress, but its role in preventing spikelet degeneration under high-temperature stress has not been documented. Rice plants pretreated with SA (0–50 mmol L^?1) were subjected to heat stress at 40?°C at the pollen mother cell meiosis stage for 10 days. The results indicated that there were no significant differences in grain yields and yield components among rice plants that were exogenously sprayed with SA (0–50 mmol L^?1) under natural conditions. Under heat stress, the grain yield, spikelet number per panicle and setting rate in response to SA treatments were higher than under the control (0 mmol L^?1 SA or NON-SA) treatment, especially with 1 and 10 mmol L^?1 SA. A higher grain yield, spikelet number per panicle and setting rate were recorded in these two SA treatments compared with the NON-SA treatment. During this process, soluble sugars, proline, phytohormones including ABA, GA₃, BRs, IAA, ZR and JA, and antioxidant enzymes, such as superoxide dismutase, peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), were induced by SA. Moreover, soluble sugars, IAA, POD and APX in the spikelets with SA treatments were not only higher than with the NON-SA treatment but the changing patterns were also similar to that of the spikelet number per panicle under natural conditions and heat stress. Therefore, our results suggest that sugars, antioxidant enzymes and IAA might mediate SA to prevent spikelet degeneration caused by heat stress.     

Paclobutrazol Improved the Reproductive Growth and the Quality of Seed Oil of Jatropha curcas

Jatropha curcas was treated by soil drench paclobutrazol (PBZ) (0, 2, and 3 g m^?1 of canopy diameter) and foliar spray PBZ (0, 500, 800, and 1,200 ppm). The results showed that PBZ treatments greatly retarded vegetative growth and improved reproductive growth. The lengths of new branches were greatly decreased, whereas the number of fruits per inflorescence, fruit-bearing branches per tree, and total fruit load per tree were increased. Only the 2-g soil drench and the 1,200-ppm foliar PBZ spray significantly increased fruit load. The 2-g soil drench PBZ treatment resulted in a decrease in seed S and Cu contents of J. curcas, whereas Mn and B were greatly or moderately increased. A higher dose (3-g soil drench PBZ) reversed the improvement in reproductive growth and alleviated the negative effects on element contents in seeds compared with the 2-g soil drench PBZ. Finally, soil drench PBZ treatments significantly improved seed oil content and oil quality by reducing the oil acid value, increasing stearic acid and oleic acid contents, and reducing palmitic acid and linoleic acid content. The optimum drench dose was below 2 g m^?1 of canopy diameter. The optimum foliar spray concentration of PBZ was not determined in this study but our results suggest that it is higher than 1,200 ppm.     

Morpho-physiological and phytochemical traits of (<Emphasis Type="Italic">Thymus daenensis</Emphasis> Celak.) in response to deficit irrigation and chitosan application

Thymus daenensis Celak. is an aromatic herb used as a popular medicine and its natural products in the form of extracts and essential oil have significant economic values in Iran. We hypothesized that spraying plants grown under deficit irrigation system with chitosan can be considered as an applicable method to enhance essential oil and antioxidant activity in thyme. Response of thyme to three irrigation regimes including well-watered, moderate stress, and severe stress along with three levels of chitosan application rates 0, 200, and 400 μL L^?1 was evaluated in a 2-year study in 2014 and 2015. Drought stress condition significantly shortened phenologic stages, more specifically in the first (establishment) year. All growth parameters were reduced dramatically as drought stress intensified. Imposing even moderate stress reduced leaf area as much as 59 and 44% in the first year and the second year, respectively. Biomass yield of plants grown under severe drought stress decreased substantially, whereas essential oil content and the share of thymol in thyme oil which possesses the greatest degree of biological activity improved. Maximum oil yield (1.50 g plant^?1) was obtained from plants under mild drought stress when sprayed with 400 μL L^?1 chitosan in the second year when plants were well-established. Foliar applications of chitosan reduced the adverse effect of water deficit on oil yield and improved thymol content of the essential oil. Chitosan also increased secondary metabolites including α-terpinene, p-cymene, γ-terpinene, thymol, carvacrol and β-caryophyllene. Leaf flavonoid reduced under deficit irrigation while more phenol was found in plants grown under deficit irrigation. The essential oil of thyme exhibited antioxidant property when the plants were sprayed with 400 μL L^?1 chitosan. The results of this study indicated that thyme can be grown successfully under moderate stress and that application of chitosan elicitor can to some degree compensate the negative impact of deficit irrigation on its biomass and essential oil yield.