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In the present study, the effect of ascorbic acid (5 mM) on some physiological parameters and three hormones (auxin, abscisic acid, salicylic acid) was determined under heat stress (40 °C) in maize tolerant cv. (MAY 69) and sensitive cv. SHEMAL (SH) at 0 h, 4 h and 8 h. Heat stress reduced total chlorophyll content (CHL), relative water content (RWC) and stomatal conductance (gs) in SH but did not lead to changes in MAY 69 at 4 h and 8 h. However, pretreatment with ascorbic acid increased (CHL), (RWC) and (gs) in SH under heat stress while it reduced MDA content significantly in both cv. We also observed that heat stress led to a reduction in SA level but increased ABA and IAA levels in SH, whereas it increased SA and IAA levels but did not change ABA level in MAY 69 at 4 h. Furthermore, in SH, ASC application under heat stress increased SA level and decreased IAA and ABA levels at 4 h, but it had no effect on SA and ABA at 8 h.

The purpose of this study was to illuminate the effects of fulvic acid in plants’ stress signaling pathway. 2.0 mg/l fulvic acid was sprayed on soybean leaves for 3 days at 12 h intervals, followed by treatment of 150 mM NaCl or exposed to heat stress at 35°C for 2 h over 2 days. Pre-treatment with fulvic acid increased the relative water content (RWC), antioxidant enzyme, isoenzyme activities (SOD, APX, GST), as well as alleviated the stress-induced oxidative damage by decreasing the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). In addition, the application of fulvic acid under salt stress induced rubisco expression only at 12 h, while it induced the expression of cytochrome c oxidase at 6 h and 12 h. On the other hand, fulvic acid under heat stress induced significant expression of both rubisco and cytochrome c oxidase at 6 h and 12 h. However, under high salinity conditions, fulvic acid suppressed the transcript levels of Hsp70, while it induced increases in Hsp70 levels under heat treatment at 6 h. As a result, in this study, fulvic acid played the role of a regulator and stimulant in stress response of soybean leaves.

The present study was conducted to present the responses of drought-sensitive ‘Shemal’ and drought-tolerant ‘71MAY69’ maize cultivars under drought condition (20% Polyethylene glycol, -0.40 MPa) and three different copper concentrations (0.5 mM, 1 mM, 1.5 mM CuSO4.5H2O) for 5 days to determine the enzymatic responses of copper treatment in maize leaves.Copper treatments alone did not change stomatal conductance, relative water content, malondialdehyde, proline, hydrogen peroxide content and abscisic acid level according to control groups. Combined treatment (drought and copper) alleviated the damage of PEG- induced drought stress in maize leaves. Superoxide dismutase (SOD), catalase (CAT), glutatione reductase (GR) activity increased and glutathione -S transferase (GST) activity decreased, while ascorbate peroxidase (APX) activity didnot change under drought stress in the tolerant cultivar. SOD, CAT and APX were decreased and GST activities were increased while GR did not change in ‘Shemal’. Also SOD, APX and CAT activity increased by copper treatment alone in both cultivars. Otherwise combined treatment increased SOD, APX and CAT activity at all concentrations, but GR and GST activity increased only by (PEG+1.5 mM) treatment when compared with PEG treatment alone in sensitive ones. As a result, exogenous copper alleviated drought stress, while it induced an oxidative damage by increasing antioxidant enzyme activities differently from drought tolerance. Copper tolerance in maize is not a common response of its defense mechanism because of different response to copper and drought in the same cultivar.