Effects of silicon on defense of wheat against oxidative stress under drought at different developmental stages

The effects of silicon application before sowing on the drought-induced oxidative stress and antioxidant defense in wheat (Triticum aestivum L.) were investigated. Drought stress was applied by withholding watering till sampling at booting or filling stage. Application of Si increased the water potential of drought-stressed plants at filling stage, whereas it did not at booting stage. The superoxide dismutase (SOD) activity was inhibited and peroxidase (POD) activity was enhanced by drought at booting stage, and no differences were observed due to the Si treatment. At filling stage, however, application of Si increased the SOD activity and decreased the POD activity of drought-stressed plants. The catalase (CAT) activity was slightly increased by drought only in the absence of Si and at booting stage. The activity of glutathione reductase (GR) was not greatly influenced. Application of Si did not change the contents of H₂O₂, total soluble protein and protein carbonyl of drought-stressed plants at booting stage, whereas at filling stage, it decreased the content of H₂O₂ and protein carbonyl and increased the content of total soluble protein. The content of thiobarbituric acid reactive substances (TBARS) and the activities of acid phospholipase (AP) and lipoxygenase (LOX) in drought-stressed plants were also decreased by application of Si at both stages.     

Exogenous jasmonic acid modulates the physiology,antioxidant defense and glyoxalase systems in imparting drought stress tolerance in different Brassica species

This study examined the ability of jasmonic acid (JA) to enhance drought tolerance in different Brassica species in terms of physiological parameters, antioxidants defense, and glyoxalase system. Ten-day-old seedlings were exposed to drought (15 % polyethylene glycol, PEG-6000) either alone or in combination with 0.5 mM JA. Drought significantly increased lipoxygenase activity and oxidative stress, levels of malondialdehyde and H₂O₂. Drought reduced seedling biomass, chlorophyll (chl) content, and leaf relative water content (RWC). Drought increased proline, oxidized ascorbate (DHA) and glutathione disulfide (GSSG) levels. Drought affected different species differently: in B. napus, catalase (CAT) and glyoxalase II (Gly II) activities were decreased, while glutathione-S-transferase (GST) and glutathione peroxidase (GPX) activities were increased in drought-stressed compared to unstressed plants; in B. campestris, activities of glutathione reductase (GR), glyoxalase I (Gly I), GST, and GPX were increased, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), CAT and other enzymes were decreased; in B. juncea, activities of ascorbate peroxidase, GR, GPX, Gly I were increased; Gly II activity was decreased and other enzymes did not change. Spraying drought-stressed seedlings with JA increased GR and Gly I activities in B. napus; increased MDHAR activity in B. campestris; and increased DHAR, GR, GPX, Gly I and Gly II activities in B. juncea. JA improved fresh weight, chl, RWC in all species, dry weight increased only in B. juncea. Brassica juncea had the lowest oxidative stress under drought, indicating its natural drought tolerance capacity. The JA improved drought tolerance of B. juncea to the highest level among studied species.     

Brassinolide alleviated the adverse effect of water deficits on photosynthesis and the antioxidant of soybean (<Emphasis Type="Italic">Glycine max</Emphasis> L.)

Brassinolide (BR) is a relatively new plant growth regulator. To test whether BR could be used to increase tolerance to water deficits in soybean, the effects of BR application on photosynthesis, assimilate distribution, antioxidant enzymes and seed yield were studied. BR at 0.1 mg l⁻¹ was foliar applied at the beginning of bloom. Two levels of soil moisture (80% field capacity for well-watered control and 35% for drought-stressed treatment) were applied at pod initiation. BR treatment increased biomass accumulation and seed yield for both treatments. Drought stress inhibited translocation of assimilated ¹⁴C from the labeled leaf, but BR increased the translocation for both treatments. Drought stress depressed chlorophyll content and assimilation rate (A), while chlorophyll content and A of BR-treated plants were greater than that of drought-stressed plants. BR treatment increased maximum quantum yield of PS II, the activity of ribulose-1,5-bisphosphate carboxylase, and the leaf water potential of drought-stressed plants. Treatment with BR also increased the concentration of soluble sugars and proline, and the activities of peroxidase and superoxide dismutase of soybean leaves when drought-stressed. However, it decreased the malondialdehyde concentration and electrical conductivity of leaves under drought stress. This study show that BR can be used as a plant growth regulator to enhance drought tolerance and minimize the yield loss of soybean caused by water deficits.     

Effect of salicylic acid pretreatment on drought stress responses of zoysiagrass (Zoysia japonica)

The present study was carried out to examine the effects of exogenous salicylic acid (SA) on growth, activities of antioxidant enzymes, and some physiological and biochemical characteristics of zoysiagrass (Zoysia japonica Steud.) plants subjected to drought. Aqueous 0.1, 0.5, or 1.0 mM SA solution was sprayed on the leaves of zoysiagrass for 3 days. Drought was induced by withholding watering for 16 days after SA application. Biomass, chlorophyll content, net photosynthetic rate (P _n), activities of antioxidant enzymes (e.g., superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), MDA and proline contents were determined. Pretreatments with 0.1 and 0.5 mM SA significantly increased fresh and dry weights and chlorophyll content, while 1 mM SA pretreatment did not show significant change compared to controls. SA pretreatments showed a marked increase in P _n compared with controls from the 7th to 16th day after drought start. Activities of SOD, POD, and CAT were increased by SA pretreatments. MDA and proline contents after 0.1 and 0.5 mM pretreatments were lower than those of controls from the 6th to 12th day of drought, while 1 mM SA pretreatment did not show significant change from the 0th to 9th day of drought. This work suggests that suitable exogenous SA (0.5 mM) helps zoysiagrass to perform better under drought stress by enhancing the net photosynthetic rate and antioxidant enzyme activities while decreasing lipid peroxidation as compared to the controls. SA could be used as a potential growth regulator for improving plant growth under drought stress.     

Physiological and biochemical changes by nitric oxide and brassinosteroid in tomato (<Emphasis Type="Italic">Lycopersicon esculentum</Emphasis> Mill.) under drought stress

Drought stress produces many physiological and biochemical changes in plant affecting its life cycle and production. Oxidative damage and antioxidant defense responses are two components of plant to survive under drought stress. Nitric oxide (sodium nitroprusside, SNP) and brassinosteroid (24-epibrassinolide, EBL) were used in this experiment as single and combined application as foliar spray to study the mitigating effect of drought stress in two tomato genotypes EC-625652 (drought susceptible) and EC-620419 (drought tolerant). Drought stress produced harmful effect on number of leaves plant^?1, RWCL, fruit set percent, days to first fruit set, number of cluster plant^?1, lycopene content, fruit diameter and fruit yield. Plant produces reactive oxygen species (ROS), such as H₂O₂ in response to drought stress. Exogenous application of SNP and EBL, both in single and combined application, mitigated the deleterious effects of drought and improved drought tolerance by increasing SOD activity, fruit yield, and other physiological processes.     

Time‐course analysis of salicylic acid effects on ROS regulation and antioxidant defense in roots of hulled and hulless barley under combined stress of drought,heat and salinity

Greater crop losses can result from simultaneous exposure to a combination of drought, heat and salinity in the field. Salicylic acid (SA), a phenolic phytohormone, can affect a range of physiological and biochemical processes in plants and significantly impacts their resistance to these abiotic stresses. Despite numerous reports involving the positive effects of SA by applying each abiotic stress separately, the mechanism of SA‐mediated adaptation to combined stresses remains elusive. This study, via a time‐course analysis, investigated the role of SA on the roots of hulled and hulless (naked) barley (Hordeum vulgare L. ‘Tarm’ and ‘Özen’, respectively), which differed in salt tolerance, under the combined stress of drought, heat and salt. The combined stress caused marked reductions in root length and increases in proline content in both genotypes; however, Tarm exhibited better adaptation to the triple stress. Under the first 24 h of stress, superoxide dismutase (SOD; EC.1.15.1.1) and peroxidase (POX; EC.1.11.1.7) activity in the Tarm roots increased remarkably, while decreasing in the Özen roots. Furthermore, the Tarm roots showed higher catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) activity than the Özen during the combined stresses. The sensitivity of hulless barley roots may be related to decreasing SOD, POX, CAT and GR activity under stress. Over 72 h of stress, the SA pretreatment improved the APX and GR activity in Tarm and that of POX and CAT in Özen, demonstrating that exogenously applied SA regulates antioxidant defense enzymes in order to detoxify reactive oxygen species. The results of this study suggest that SA treatment may improve the triple‐stress combination tolerance in hulled and hulless barley cultivars by increasing the level of antioxidant enzyme activity and promoting the accumulation of proline. Thus, SA alleviated the damaging effects of the triple stress by improving the antioxidant system, although these effects differed depending on characteristic of the hull of the grain.     

Mycorrhizal colonization alleviates drought-induced oxidative damage and lignification in the leaves of drought-stressed perennial ryegrass (Lolium perenne)

To investigate the effects of arbuscular mycorrhizal (AM) fungus Glomus intraradices on antioxidative activity and lignification under drought‐stressed (DS) conditions, the enzyme activities, growth, lignin contents and some stress symptomatic parameters as affected by drought treatment were compared in AM colonized or non‐colonized (non‐AM) perennial ryegrass plants for 28 days. Drought significantly decreased leaf water potential (Ψ_w), photosynthesis rate and biomass. The negative impact of drought on these parameters was much highly relived in AM plants compared to non‐AM ones. Drought increased H₂O₂, lipid peroxidation, phenol and lignin levels, with significantly higher in non‐AM relative to AM plants at day 28 after drought treatment. The enhanced activation of guaiacol peroxidase (GPOX), coniferyl alcohol peroxidase (CPOX), syringaldazine peroxidase (SPOX) and polyphenol oxidase (PPO) was closely related with the decrease in Ψ_w in both AM and non‐AM plants. GPOX, CPOX, SPOX and PPO highly activated with a concomitant increase in lipid peroxidation and lignin as the Ψ_w decreased below ?2.11 MPa in non‐AM plants, while much less activated by maintaining Ψ_w≥?1.15 MPa in AM ones. These results indicate that AM symbiosis plays an integrative role in drought stress tolerance by alleviating oxidative damage and lignification, which in turn mitigate the reduction of forage growth and digestibility under DS conditions.     

Salicylic acid pretreatment induces drought tolerance and delays leaf rolling by inducing antioxidant systems in maize genotypes

Salicylic acid (SA) acts as an endogenous signal molecule responsible for inducing abiotic stress tolerance in plants. In this study, the role of SA in improving drought tolerance in two maize cultivars (Zea mays L.) differing in their tolerance to drought was evaluated. The plants were regularly watered per pot and grown until the grain filling stage (R2) under a rainout shelter. At stage R2, parts of the plants were treated with SA, after which drought stress was applied. Leaf samples were harvested on the 10th and 17th days of the drought. Some antioxidant enzyme activity, such as the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content, was measured during the drought period. Exogenous SA prevented water loss and delayed leaf rolling in comparison with control leaves in both cultivars. As a consequence of drought stress, lipid peroxidation, measured in terms of malondialdehyde content, was prevented by SA. SA pretreatment induced all antioxidant enzyme activities, and to a greater extent than the control leaves, during drought. SA also caused a reduction in the ascorbate (ASC) and glutathione (GSH) content in two maize cultivars. The H₂O₂ level was higher in SA pretreated plants than the controls in both cultivars. Pretreatment with SA further enhanced the activities of antioxidant enzymes and the concentrations of non-enzymatic antioxidants in the tolerant cultivar compared with the sensitive cultivar. Results suggested that exogenous SA could help reduce the adverse effects of drought stress and might have a key role in providing tolerance to stress by decreasing water loss and inducing the antioxidant system in plants with leaf rolling, an alternative drought protection mechanism.     

Effects of salicylic acid on the photosystem 2 of barley seedlings under osmotic stress

The effects of exogenous salicylic acid (SA) on photosystem 2 (PS 2) in barley (Hordeum vulgare L.) seedlings were investigated. SA pretreatment provided protection against subsequent osmotic stress. The highest protective effect of 0.25 mM SA was confirmed by determination of chlorophyll fluorescence, electrolyte leakage, malonyldialdehyde contents, PS 2 mRNAs and proteins. SA pretreatment increased reactive oxygen species (ROS), decreased net photosynthetic rate and stomatal conductance immediately, but prevented ROS accumulation during subsequent osmotic stress by activating antioxidant enzymes. Elimination of H₂O₂ during SA pretreatment inhibited almost all above mentioned SA effects. Therefore, SA pretreatment enhanced osmotic stress tolerance in barley seedlings mainly through ROS signals, rather than SA itself. The only SA-dependent and ROS-independent effect of exogenous SA on PS 2 was reduction of non-photochemical quenching.     

Photosynthetic and antioxidative upregulation in drought-stressed sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) subjected to foliar-applied salicylic acid

Insufficient attention has been paid to the physiological responses of sesame to drought and it is unclear if exogenous plant growth regulators are beneficial to drought-stressed sesame. Thus, a field study was conducted on seven Sesamum indicum genotypes affected by two levels of irrigation (60 and 80% depletions in available soil water) and by foliar-applied salicylic acid (SA; 0 and 0.6 mM). Water deficit led to depressions in net photosynthetic rate, stomatal conductance, leaf area index, chlorophyll a, b, and total chlorophyll contents, maximum quantum efficiency of PSII, and plant dry matter and seed yield, despite increases in carotenoid concentration, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase activities. SA was found beneficial in ameliorating the depressions in all of the above characteristics, indicating that it could be applied for lessening the harmful effects of the drought stress.     

Physiological and biochemical adaptations in lentil genotypes under drought stress

Drought is a major restrictive factor for declining grain yield in lentil globally. Present investigation was conducted by taking microsperma (HUL-57) and macrosperma (IPL-406) genotypes of lentil (Lens culinaris Medik.) as information regarding physiological and biochemical basis of differences in drought resistance in macrosperma (bold-seeded) and microsperma (small-seeded) are not well understood. Pot grown plants were exposed to drought stress at specific phenophase viz. mid-vegetative, flower initiation and pod formation stage by withholding irrigation till the plants experienced one cycle of permanent wilting (PWP). Genotypes exhibited substantial differences for most of the measured traits under drought irrespective of the phenophase of stress imposed. Under drought HUL-57 had lower CMI, higher CSI, lower values of Δ¹³C, maintained higher SLN, accumulated more N and efficiently remobilized accumulated N to developing seeds. Higher chlorophyll content, increased accumulation of osmotically active solutes viz. soluble sugars and proline under drought stress was evident in HUL-57. Drought induced H₂O₂ accumulation and lipid peroxidation in both genotypes, but increments were of lesser magnitudes in HUL-57. Drought stress of pod formation stage followed by flower initiation stage was most damaging than the stress imposed at mid-vegetative stage in both genotypes. HUL-57 showed a better drought resistance capacity than IPL-406. Drought indices viz. DSI, STI and MP are proposed as criterion to identify and breed lentil genotypes for drought conditions.     

Photosynthesis and antioxidative defense mechanisms in deciphering drought stress tolerance of crop plants

Crop plants are regularly exposed to an array of abiotic and biotic stresses, among them drought stress is a major environmental factor that shows adverse effects on plant growth and productivity. Because of this these factors are considered as hazardous for crop production. Drought stress elicits a plethora of responses in plants resulting in strict amendments in physiological, biochemical, and molecular processes. Photosynthesis is the most fundamental physiological process affected by drought due to a reduction in the CO₂ assimilation rate and disruption of primary photosynthetic reactions and pigments. Drought also expedites the generation of reactive oxygen species (ROS), triggering a cascade of antioxidative defense mechanisms, and affects many other metabolic processes as well as affecting gene expression. Details of the drought stress-induced changes, particularly in crop plants, are discussed in this review, with the major points: 1) leaf water potentials and water use efficiency in plants under drought stress; 2) increased production of ROS under drought leading to oxidative stress in plants and the role of ROS as signaling molecules; 3) molecular responses that lead to the enhanced expression of stress-inducible genes; 4) the decrease in photosynthesis leading to the decreased amount of assimilates, growth, and yield; 5) the antioxidant defense mechanisms comprising of enzymatic and non-enzymatic antioxidants and the other protective mechanisms; 6) progress made in identifying the drought stress tolerance mechanisms; 7) the production of transgenic crop plants with enhanced tolerance to drought stress.     

Drought stress induces oxidative stress and the antioxidant defense system in ascorbate-deficient vtc1 mutants of Arabidopsis thaliana

Drought stress has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). To increase our understanding of the effects of drought stress on antioxidant processes, we investigated the response of the ascorbate-deficient Arabidopsis thaliana vtc1 mutant to drought stress. After drought stress, vtc1 mutants exhibited increases in several oxidative parameters, including H₂O₂ content and the production of thiobarbituric acid reactive substances. Decreases in chlorophyll content and chlorophyll fluorescence parameters were also observed. The vtc1 mutants had higher total glutathione than did wild-type (WT) plants after 48 h of drought stress. A reduced ratio of glutathione/total glutathione and an increased ratio of dehydroascorbate/total ascorbate were observed in the vtc1 mutants compared with the WT plants. In addition, the activities of enzymes that are responsible for ROS scavenging, including superoxide dismutase, catalase, and ascorbate peroxidase, were decreased in the vtc1 mutants compared with the WT plants. Similar reductions in activity in the vtc1 mutant were observed for the enzymes that are responsible for the regeneration of ascorbate and glutathione, including monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. These results suggest that low intrinsic ascorbate and impaired ascorbate–glutathione cycling in the vtc1 mutant induced a decrease in the reduced form of ascorbate, which enhanced sensitivity to drought stress.     

Drought stress and cereal aphid performance

The performance of clones of Rhopalosiphum padi and Sitobion avenae from England and Spain was examined on drought-stressed tillering winter wheat in an environment chamber at 14 ± 1°C. Two different levels of drought stress and an unstressed control were established by different watering regimes which resulted in drought-stressed plants being smaller at the end of the experiment. The effect of drought stress to plants on aphid performance was not significantly different between the clones tested. Drought stress had no effect on aphid development time, nymphal mortality, the weight of teneral adults and the number of embryos in teneral adults up to the onset of reproduction in the first F₁ generation. The subsequent reproductive capacity, as measured by the effective and potential fecundity, and the reproductive rate, were much reduced on drought-stressed plants. However, there was only a small decrease in the intrinsic rate of increase (r_m). Overall the clone of R. padi from Spain performed better than that from England, the development and prereproductive times being shorter and the fecundity higher in the Spanish clone, giving a higher r_m. There were no differences in the fecundity and the r_m between the Spanish and the English clones of S. avenae. The proportion of the F₂ generation that was alate differed greatly between clones, and only the English S. avenae produced significantly more alatae on drought-stressed than on unstressed plants.     

Salt-Induced Changes in Physio-Biochemical and Antioxidant Defense System in Mustard Genotypes

Salinity stress is a major factor limiting plant growth and productivity of many crops including oilseed. The present study investigated the identification of salt tolerant mustard genotypes and better understanding the mechanism of salinity tolerance. Salt stresses significantly reduced relative water content (RWC), chlorophyll (Chl) content, K⁺ and K⁺ /Na⁺ ratio, photosynthetic rate (P_N), transpiration rate (Tr), stomatal conductance (gs), intercellular CO₂ concentration (Ci) and increased the levels of proline (Pro) and lipid peroxidation (MDA) contents, Na⁺ , superoxide (O₂^•− ) and hydrogen peroxide (H₂O₂) in both tolerant and sensitive mustard genotypes. The tolerant genotypes maintained higher Pro and lower MDA content than the salt sensitive genotypes under stress condition. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione peroxidase (GPX), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were increased with increasing salinity in salt tolerant genotypes, BJ-1603, BARI Sarisha-11 and BARI Sarisha-16, but the activities were unchanged in salt sensitive genotype, BARI Sarisha-14. Besides, the increment of ascorbate peroxidase (APX) activity was higher in salt sensitive genotype as compared to tolerant ones. However, the activities of glutathione reductase (GR) and glutathione S-transferase (GST) were increased sharply at stress conditions in tolerant genotypes as compared to sensitive genotype. Higher accumulation of Pro along with improved physiological and biochemical parameters as well as reduced oxidative damage by up-regulation of antioxidant defense system are the mechanisms of salt tolerance in selected mustard genotypes, BJ-1603 and BARI Sarisha-16.     

Selenium Pretreatment Upregulates the Antioxidant Defense and Methylglyoxal Detoxification System and Confers Enhanced Tolerance to Drought Stress in Rapeseed Seedlings

In order to observe the possible regulatory role of selenium (Se) in relation to the changes in ascorbate (AsA) glutathione (GSH) levels and to the activities of antioxidant and glyoxalase pathway enzymes, rapeseed (Brassica napus) seedlings were grown in Petri dishes. A set of 10-day-old seedlings was pretreated with 25 μM Se (Sodium selenate) for 48 h. Two levels of drought stress (10% and 20% PEG) were imposed separately as well as on Se-pretreated seedlings, which were grown for another 48 h. Drought stress, at any level, caused a significant increase in GSH and glutathione disulfide (GSSG) content; however, the AsA content increased only under mild stress. The activity of ascorbate peroxidase (APX) was not affected by drought stress. The monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) activity increased only under mild stress (10% PEG). The activity of dehydroascorbate reductase (DHAR), glutathione S-transferase (GST), glutathione peroxidase (GPX), and glyoxalase I (Gly I) activity significantly increased under any level of drought stress, while catalase (CAT) and glyoxalase II (Gly II) activity decreased. A sharp increase in hydrogen peroxide (H₂O₂) and lipid peroxidation (MDA content) was induced by drought stress. On the other hand, Se-pretreated seedlings exposed to drought stress showed a rise in AsA and GSH content, maintained a high GSH/GSSG ratio, and evidenced increased activities of APX, DHAR, MDHAR, GR, GST, GPX, CAT, Gly I, and Gly II as compared with the drought-stressed plants without Se. These seedlings showed a concomitant decrease in GSSG content, H₂O₂, and the level of lipid peroxidation. The results indicate that the exogenous application of Se increased the tolerance of the plants to drought-induced oxidative damage by enhancing their antioxidant defense and methylglyoxal detoxification systems.     

Improvement of heat and drought photosynthetic tolerance in wheat by overaccumulation of glycinebetaine

Within their natural habitat, crops are often subjected to drought and heat stress, which suppress crop growth and decrease crop production. Causing overaccumulation of glycinebetaine (GB) has been used to enhance the crop yield under stress. Here, we investigated the response of wheat (Triticum aestivum L.) photosynthesis to drought, heat stress and their combination with a transgenic wheat line (T6) overaccumulating GB and its wild-type (WT) Shi4185. Drought stress (DS) was imposed by controlling irrigation until the relative water content (RWC) of the flag leaves decreased to between 78 and 82%. Heat stress (HS) was applied by exposing wheat plants to 40°C for 4 h. A combination of drought and heat stress was applied by subjecting the drought-stressed plants to a heat stress as above. The results indicated that all stresses decreased photosynthesis, but the combination of drought and heat stress exacerbated the negative effects on photosynthesis more than exposure to drought or heat stress alone. Drought stress decreased the transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO₂ concentration (Ci), while heat stress increased all of these; the deprivation of water was greater under drought stress than heat stress, but heat stress decreased the antioxidant enzyme activity to a greater extent. Overaccumulated GB could alleviate the decrease of photosynthesis caused by all stresses tested. These suggest that GB induces an increase of osmotic adjustments for drought tolerance, while its improvement of the antioxidative defense system including antioxidative enzymes and antioxidants may be more important for heat tolerance.     

Effect of penconazole and drought stress on the essential oil composition and gene expression of Mentha pulegium L. (Lamiaceae) at flowering stage

Effect of penconazole (PEN) on the expression level of two genes in the biosynthesis pathway of monoterpenes, isopiperitenone reductase (iPR) and pulegone reductase (PR), and essential oil (EO) compounds were studied at flowering stage of Mentha pulegium L. under drought stress. Plants were grown with different levels of field capacity (100 and 50 %) with or without PEN (15 mg l^?1). Results showed that drought stress decreased the growth and productivity parameters. PEN treatment to drought-stressed plants decreased the negative effects of drought stress on these parameters. The EO yield increased by about 1.6 times under drought stress, and the highest amount of EO was obtained in drought-stressed with PEN. Drought stress increased pulegone and decreased menthone percentage, and the highest pulegone percentage (78.2 % of total constituents) was obtained in drought-stressed with PEN treatment. Semi-quantitative RT-PCR showed drought stress increased the expression level of iPR and PR genes. PEN treatment promoted the impact of drought stress on iPR gene expression and repressed PR gene expression. Our results suggest that PEN may be a useful tool for the regulation of monoterpene metabolism in M. pulegium under stress condition.     

Influence of nitric oxide in protection of tomato seedling against oxidative stress induced by osmotic stress

Osmotic stress associated with drought and salinity is a serious problem that inhibits the growth of plants mainly due to disturbance of the balance between production of ROS and antioxidant defense and causes oxidative stress. In this research, sodium nitroprusside (SNP) was used as NO donor in control and drought-stressed plants, and the role of NO in reduction of oxidative damages were investigated. In this study, we observed that SNP pretreatment prevented drought-induced decrease in RWC and membrane stability index, increase in lipid peroxidation and lipoxygenase activity and increase in hydrogen peroxide content. However, pretreatment of plants with SNP and phenyl 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (a NO scavenger) reversed the protective effects of SNP suggesting that protective effect by SNP is attributable to NO release. In addition, the relationship between these defense mechanisms and activity of antioxidant enzymes were checked. Results showed that in drought-stressed plants ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase activities were elevated over the controls, while GR decreased under drought condition. Activity of GPX was inhibited under SNP pretreatment in drought-stressed plants specially, while the activity of APX and GR increased under SNP pretreatment and it seems that under this condition APX had a key role of detoxification of ROS in tomato plants. This result corresponded well with ASA and total acid-soluble thiols content. Therefore, reduction of drought-induced oxidative damages by NO in tomato leaves is most likely mediated through either NO ability to scavenge active oxygen species or stimulation of antioxidant enzyme such as APX.