Exogenous silicon alleviates salinity stress in fenugreek (Trigonella foenum-graecum L.) by enhancing photosystem activities, biological nitrogen fixation and antioxidant defence system

Abstract

Silicon (Si) application has emerged as a promising solution to improve plant growth under stressful conditions. However, the mechanisms by which Si alleviated salt damage, especially on photosynthetic machinery and symbiosis establishment in legume plants are not fully understood. Thus, this research was designed to investigate the beneficial effects of Si-treatment on salt stress tolerance in fenugreek (Trigonella foenum graecum L.). Fenugreek plants were exposed to 150 mM NaCl with or without 3 mM Si, to evaluate the effects of Si on photosynthetic traits, biological nitrogen fixation (BNF), membrane stability and oxidative stress metabolism. Results indicated that salinity significantly decreased plant growth in terms of plant biomass and high, relative water content and photosynthetic traits, including chlorophyll content and photosystems (PSI and PSII) functions, whereas the treatment of salt-stressed fenugreek with exogenous Si remarkably improved the same traits. As compared to salt-stressed control, the fenugreek-rhizobia symbiosis was also improved under salt stress in response to Si supplementation, reflected by higher nodule number and nitrogen content. On the other hand, Si supplementation to salt-stressed fenugreek plants lead to a significant decline in malonyldialdehyde and hydrogen peroxide in both shoot and root, indicating the protective effect of Si on membrane stability. This was shown to be related to the ability of Si to boost the activities of superoxide dismutase, catalase and guaiacol peroxidase. This research suggests the protective role of Si on salt-stressed fenugreek by enhancing photosynthesis, BNF and oxidative stress metabolism.