Journal of Plant Process and Function

Abstract Thioredoxins are invoved in redox regulation of many cellular processes. In this study the role of NADP+-Thioredoxin reductase C (NTRC) in the control of leaf senescence was investigated by biochemical characterization of Arabidopsis ntrc mutants. Forty days old wild type and two ntrc mutant lines were incubated either under normal dark-light or continous darkness regimes for 6 days as control and senescence treatment, respectively. Growth parameters, the contents of carbohydrates, pigments and the activity of some antioxidant enzymes were compared between wild type and ntrc mutant lines during dark induced senescence. Darkness led to decreased fresh and dry weights, chlorophylls and carotenoides, starch and protein contents in both wild type and mutant plants and there were no significant differences in the interactions of genotypes and treatments regarding to theses parameters. Darkness also induced the accumulation of anthocyanins, total and non-reducing sugars however, the accumulation of the carbohydrates in mutant lines was more pronounciated than wild type plants and again there were no significant differences in response of wild type and mutants to dark treatment. The activities of catalase, peroxidase and polyphenol oxidase of mutant lines were significantly greater than wild type plants. While darkness decreased the activities of ascorbate peroxidase and catalase it led to increased activities of peroxidase and polyphenol oxidase especially in the mutant lines. There were significant differences in the activities of all four enzymes between mutant and wild type plants in response to darkness. Thus, it appears that defects in NTRC mainly affects the activities of antioxidant enzymes rather than the other studied biochemical parameters of plants during the senescence process. This study might be useful in future breeding programs for controlling senecence process to achieve better performance of crop plants.

Drought stress stimulates the production of reactive oxygen species (ROS) in chloroplasts. ROS laed to lipid peroxidation and damage to the cell membrane. In the current study, the effect of different concentrations of silicon were examined on oxidative stress caused by drought in fennel plant. The experimental design was a split plot based on RCBD with three replications in which irrigation regimes includingirrigation at 100%, 70% and 40% of field capacity were assigned as main plots and five levels of silicon foliar sprays (0, 2.5, 5, 7.5 and 10 mM) were allocated to sub plots. The experiment was conducted in 2009 at the Zabol University research farm, Zabol, Iran. The results showed that drought stress significantly decreased chlorophyll a, chlorophyll b, carotenoids, leaf relative water content and catalase activity. In drought conditions, malondialdehyde levels and electrolyte leakage showed a 2 -fold increase over the control. Silicon treatment (7.5 mM) accompanied by drought, increased the activity of peroxidase and ascorbate peroxidase, proline and soluble sugars by 18, 25, 14 and 28%, respectively and decreased malondialdehyde and electrolyte leakage by 30 and 28%, respectively over the control, suggesting that silicon spraying (5 and 7.5 mM) could increase the ability of plants in response to drought stress by strengthening the antioxidant system of the plant and increasing osmolytes, and have protective effect against lipid peroxidation, induced by stress.

This greenhouse experiment, consisted of a completely randomized factorial design, was conducted to investigate the changes in antioxidant enzyme activities of lettuce plants cv. Syahoo inoculated with Piriformospora indica fungus under different levels of zinc (0, 2.5, 5 and 10 mg l^-1) in the research laboratory of Maragheh university in spring 2016. Fungal treatment was added at two leaf stage of seedling on the lettuce roots in the sandy substrate. The plant samples, at 35 days after sowing, were measured for dry and fresh weights of shoot, total soluble protein, malondialdehyde (MDA) concentration and activities of antioxidant enzymes superoxide dismutase (SOD), guaiacol peroxidase (GPOX), and catalase (CAT). The results revealed that the effect of P. indica and zinc application on dry and fresh weights of shoot, total soluble protein and activity of SOD were significant at P≤0.01. The main effect of zinc on MDA concentration, activity of GPOX and CAT was significant at P≤0.01. Highest amount of dry and fresh weights and total soluble protein, and maximum activity of SOD were obtained in presence of P. indica under 10 mg L^-1 Zn. Maximum activity of CAT, GPOX, and MDA concentration were observed in treatments without zinc application. Results from our research showed that inoculation by P. indica and zinc application (especially at 10 mg L^-1) have an important role in enhancing the growth parameters and modulating the activities of antioxidant enzymes in lettuce.