Exogenous salicylic acid alleviates oxidative damage of barley plants under drought stress

This paper reports the effects of 500 μM salicylic acid (SA) application on drought stress acclimation of barley (Hordeum vulgare L. cv Nosrat) plants grown in soil culture. In these experiments the following treatments were used: CK (control), DR (drought), SA (500 μM) and DSA (SA+drought). The results showed that drought stress decreased the dry mass and net CO2 assimilation rate (A) of plants, which were all increased by the addition of SA. Under drought conditions, the improvement of photosynthesis of barley plants treated with SA was associated with an increase in gs, whereas the maximal quantum yield of PSII (Fv/Fm) did not change with SA treatment. Malondialdehyde (MDA) content remained unchanged in DSA plants because of an efficient scavenging of reactive oxygen species (ROS) following a significant enhancement of some antioxidative enzyme activities. The present work suggests that the improvement of SA on drought tolerance of barley plants was associated with the increase of antioxidant defense abilities and maintenance of photosynthesis under drought, which may elucidate the physiological mechanism of SA in improvement of drought tolerance of barley plants

Effects of soil- and foliar-applied silicon on the resistance of grapevine plants to freezing stress

Grapes are frequently injured by freezing stress. Silicon (Si) is reported to reduce the effects of freezing on various crops. The main objective of this study was to elucidate the role of foliar- and soil-applied Si in enhancing grape (Vitis vinifera L.) tolerance to cold stress. The results indicated that the freezing stress dramatically decreased leaf fresh mass, relative water content, and caused an increased necrotic leaf area, but these effects were alleviated by both soil and foliar-applied Si. Foliar-applied Si reduced significantly damaging effects of freezing stress on maximum quantum yield of PSII after 2 and 96 h recovery after freezing treatment, while soil application of Si could not. This may be attributed to the enhancement of non-photochemical quenching, because of its effect on elevation of protective pigments; carotenoids, and more protection of PSII from photodamage following a foliar spray of Si. In addition, freezing stress increased membrane damage, as estimated by malondialdehyde content, while foliar Si application significantly decreased the membrane damage, because of an efficient scavenging by peroxidase, but soil application of Si could not. We conclude that foliar-applied Si can effectively alleviate adverse effects of freezing via maintenance of membrane integrity and alleviating photoinhibition during recovery

Effects of mild and severe drought stress on the biomass, phenolic compounds production and photochemical activity of Aloe vera (L.) Burm.f.

In this study, the biomass, compatible solutes, PSII functioning and phenolic profiles of Aloe vera (L.) Burm.f. leaves were investigated at different time intervals after drought stress (20, 40 and 80 % of the field capacity). While the impaired ability of leaves for synthesis of assimilates caused growth inhibition in A. vera under severe drought stress, we observed that the content of proline, soluble sugars, total phenolic and flavonoids tended to increase in plants treated with mild drought stress. Under mild drought stress, the increased leaf thickness correlated with the higher productivity in terms of leaf biomass and gel production. Also, mild drought stress enhanced photochemical activity in Aloe leaves, and changed the entire quantity of secondary metabolite of vanillic acid produced, which may be considered to obtain better growth and considerable secondary metabolite of the medicinal Aloe plants treated with mild drought stress.</p

Exogenous ascorbate improves antioxidant defense system and induces salinity tolerance in soybean seedlings

Germination, growth and antioxidant defense system were investigated under salinity stress and pre-treatment with ascorbate (ASC) in two soybean cultivars SAHAR and DPX. Sterilized seeds were soaked in distilled water or ASC solution (0, 400 mg L-1) for 4 hrs before they were sown in distilled water or NaCl solution (0, 12.5 and 50 mM). Salt stress reduced the growth of both cultivars through reduction in percentage of germination, shoot and root length and dry weight of seedling. ASC induced enhancement in growth of salt-stressed plants coupled with an increase in catalase and peroxidase activity in seedlings only in SAHAR cultivar, and an increase in superoxide dismutase activity in both cultivars. These findings led us to conclude that applied ASC counteracts the adverse effects of salt stress on growth of soybean; however, these effects were cultivar specific

Contrastive response of Phlomis tuberosa to salinity and UV radiation stresses

Growth, photosynthetic characteristics and antioxidant defense system were investigated under salinity stress and UV radiation in Phlomis tuberosa (Lamiaceae) grown under environmentally controlled conditions for two weeks. Salinity at 40 mM results in significant reduction of shoot growth up to 20%, while UV radiation at 10 kJ m-2 d-1 did not affect plants dry matter production. Salinity did not influnce PSII photochemistry, while UVA+B radiation caused a significant reduction of maximum quantum yield of PSII. The net photosynthesis rate was inhibited by both salinity and UV stress following reduced stomatal conductance. Leaf osmotic and water potential were decreased by salinity but not UV radiation. Activity of antioxidant enzymes increased under both salinity and UV radiation stress, however, membrane damage was occurred only under UV stress. Our data implied that, high salinity sensitivity in this species was mainly attributable to the salt-induced disturbance in water relations and reduced assimilation rate rather than to other factors such as damage to PSII, oxidative stress or membrane damage. However, PSII photoinhibition, membrane damage and significant reduction of net assimilation rate were not able to affect negatively plants performance under UV stress implying involvement of other factors in high UV stress tolerance in Phlomis tuberosa

Benefit of iodine soil application for alleviating detrimental effects of salinity stress in strawberry

Since the photochemical mechanisms of iodine-mediated adaptation to salt stress is not yet clear, the present study was performed to address this issue. Strawberry (Fragaria × ananassa Duch.) plants were grown under controlled conditions, and soils of iodine treatment were fertilized with potassium iodate (KIO 3 ) (5 and 50 mg/kg soil) before filling the pots. Salt stress (50 mM) negatively affected protein synthesis and photochemical reactions of strawberry, as evaluated by a decrease in performance index (PI abs ) as well as higher levels of hydrogen peroxide (H 2 O 2 ) and malondialdehyde, whereas application of KIO 3 (at both 5 and 50 mg/kg) alleviated the detrimental effect of sodium chloride (NaCl) stress. Plants treated with 50 mg/kg showed an increase in the soluble sugars content with respect to no KIO 3 supply under salinity stress. In salt-stressed plants, the OJIP chlorophyll fluorescence curve showed a quicker fluorescence decrease in the I-P phase. Notably, I-P phase in plants treated with KIO 3 was increased. These results indicated that KIO 3 application could protect the photosystem II from damage under salinity stress. Additionally, application of KIO 3 raised free radical scavenging activities of strawberry leaf because of an enhancement of catalase activity. These data provided the first evidence that the root-applied KIO 3 pretreatment alleviated salt stress in strawberry by decreasing reactive oxygen species production, resulting in better photochemical functioning under salt stress

Exogenous silicon leads to increased antioxidant capacity in freezing-stressed pistachio leaves

<p> </p><p> </p><p style="margin: 0cm 0cm 0pt; line-height: normal;"><span style="font-family: 'Verdana','sans-serif'; font-size: 8.5pt; mso-ansi-language: DE-AT;" lang="DE-AT">Freezing stress limits photosynthesis and growth of plants. This may be attributed to the enhancement of freezing-associated oxidative damage. In this study, we followed precisely changes in the extent of lipid peroxidation and oxidative damage in leaves of pistachio (<em>Pistacia vera</em> ‘Ahmadaghaii’) plants exposed to foliar-applied silicon (Si) under freezing stress. The foliar-applied Si<strong> </strong>decreased significantly damaging effects of cold on relative water content (RWC), accompanied by an increase in shoot fresh mass (SFM). In addition, pre-Si treatment caused a significant reduction of the leaf area lost by freezing. There was a remarkable increase in phenylalanine ammonia-lyase (PAL) activity during recovery. Since leaf phenolic content was not affected by supplementary Si, the possibility that exogenously applied Si directly influences the activity of PAL seems thin. In the present work, freezing stress caused great membrane damage, as assessed by lipid peroxidation, but Si application significantly reduced the membrane damage because of an efficient scavenging by superoxide dismutase (SOD) and peroxidase (POD). Under freezing, despite the increasing POD activity, Si-supplied plants accumulated the highest levels of hydrogen peroxide (H₂O₂) may act as a signal for recovery ability from freezing injury. A positive correlation was found between the concentration of malondialdehyde (MDA) and the percentage of necrotic leaf area. This study suggests that the possible mechanisms for Si enhanced freezing resistance may be attributed to the higher antioxidant defense activity and lower lipid peroxidation through leaf water retention, in addition to its role as a mere physical barrier.</span></p><p> </p

Contrastive response of Brassica napus L. to exogenous salicylic acid, selenium and silicon supplementation under water stress

The present research was designed to determine the effects of exogenous salicylic acid (SA), selenium (Se) and silicon (Si) on the resistance of canola (Brassica napus L. cv Okapi) seedlings to salt stress. Foliar application of SA (0.1 mM) in canola plants under drought stress for 25 days exhibited a significantly positive effect on shoot dry mass and raised the levels of total chlorophyll as well as boosting the activity of superoxide dismutase (SOD) and catalase (CAT). In addition, soil application of silicon (0.35 g Na2SiO3/kg soil) had ameliorative effects on canola root growth under drought. It is concluded that SA and Si enhanced the salt tolerance of canola by protecting the cell membrane against lipid peroxidation. However, the foliar application of Se (10 mg/l) had no ameliorative effects on canola growth and antioxidant capacity under drought stress, as could be judged by accumulation of malondialdehyde (MDA)