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.

Paclobutrazol (PBZ) enhances plant resistance to salt stress in two ways: directly, by straight clearance of reactive oxygen species; and indirectly by enhancing antioxidant enzyme activity, photosynthetic efficiency, and metabolite content, and by regulating transcription factors associated with stress. However, the regulatory effects of PBZ under salt stress in soybean are still not well explained and need further investigation. With this aim, the combination effect of salinity (250 mM NaCl) and three different doses of PBZ (5, 10 and 20 ppm) on physiological, biochemical and molecular traits of soybean (Glycine max L.) leaves were studied in soil experiments. Furthermore, physiological parameters (relative growth rate, relative water content), chlorophyll, malondialdehyde (MDA), hydrogen peroxide (H2O2) content and as well as enzymatic antioxidants (SOD, POX, APX, CAT and GST), ion content (Na, Cl) and soybean Na+/H+ antiporter GmNHX1 and chloride channel GmCLC1 gene expressions were investigated. The results showed that PBZ caused a reduction in salt-induced damages and an increase in biomass yield, water status, and chlorophyll. Moreover, PBZ regulated enzymatic antioxidants and alleviated the oxidative damages under salinity. In this study, for a first time it was determined that PBZ increased both GmNHX1 (ABA dependent or independent) and GmCLC1 (ABA independent) gene expressions and reduced Na and Cl concentrations in soybean under salinity. In conclusion, PBZ plays a role as a regulator and stimulant in salt stress response by mostly regulating ion balance in soybean leaves.

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Paclobutrazol (PBZ) is a member of the triazole family of plant growth regulators and is known to protect crops from environmental stresses such as salinity and drought. It plays a role in maintaining water balance, photosynthesis capacity and enhancing antioxidant enzyme activities. Despite the well-documented effects of PBZ on antioxidant defence in soybean plants, the changes in non-enzymatic antioxidants and endogenous polyamines in the PBZ-treated plants grown under salinity stress are still not studied. Herewith, the study aimed to clarify the effects of PBZ on these molecules. For this purpose, the combined effect of salt (250 mM NaCl) and three different concentrations of PBZ (5, 10 and 20 ppm) on soybean (Glycine max L.) plants were studied. Proline, hydroxyl radical (OH.) scavenging capacity, non-enzymatic antioxidants (anthocyanin, flavonoid, phenolic and free thiol-containing compounds) and polyamines spermine, spermidine, and putrescine were investigated in the treated plants. We found that the PBZ (10 ppm) treatment was the most effective concentration to counteract oxidative stress due to NaCl in soybean seedlings. It significantly increased hydroxyl radical scavenging activity, proline, total phenolics, flavonoids, and conjugated polyamine content compared to those found in salt-treated plants only. For the first time, our study showed that PBZ could induce the non-enzymatic antioxidant defence in soybean plants grown under salt stress conditions.

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