Effects of silicon on antioxidant enzymes, CO2, proline and biological activity of in vitro grown cape gooseberry under salinity stress

Abstract

Cape gooseberry (Physalis peruviana L.) cannot tolerate high levels of salinity. Salt stress is one of the most damaging abiotic stresses that affects plant development. However, there are some evidences that silicon (Si) can act as a mitigating agent of environmental stresses. Towards understanding the stress using tissue culture, we investigated the effect of in vitro NaCl-induced salt stress in cape gooseberry and the potential mitigating effect provided by Si. Nodal segments were inoculated in MS medium with different combinations of NaCl concentrations (0.5 and 1.0% NaCl) and silicic acid (0.0, 0.5, and 1.0 g L-1). The experimental design was completely randomized, in a factorial design with a control treatment [(2x3) + 1], totalizing 7 treatments. The control treatment consisted of an additional treatment without the addition of any of the factors. Isoenzyme activity, proline content, CO2 level and biological activity were assessed after 30 d. We found an increase in all antioxidant enzymes (SOD, CAT and POD) activities when salt stress was imposed, indicating that the plant has an efficient system to protect itself against stress. Among these enzymes, Si played a mitigating role only in POD activity. In relation to other evaluated enzymes, NaCl enhanced the EST and MDH activities, followed by a subsequent decrease in MDH. Si showed different performances according to the concentration of NaCl. Electrophoretic analysis represented by bands illustrated these behaviors. Proline content increased as salinity increased, and Si effect was observed by increasing the levels of this amino acid. High CO2 level was found at the concentration of 1.0% NaCl, and Si contributed to decrease this variable to normal levels. The reduction in the respiratory rates may contribute to the allocation of carbon to other chemical reactions such as the synthesis of new tissues. Salt stress also increased the biological activity of leaves and there was no effect of Si for this variable. We conclude that salt stress causes a great damage to in vitro-grown cape gooseberry plants and the addition of 1.0 g L-1 Si can ameliorate that damage for some characteristics. However, more studies are necessary since the physiological changes played by Si have been poorly understood for dicots.