Salicylic Acid Induced Photosynthetic Adaptability of Raphanus sativus to Salt Stress is Associated with Antioxidant Capacity

Despite the plethora of published reports on ameliorative effects of exogenously applied salicylic acid (SA) to plants under salt stress, a critical role of SA in redox balance, photosynthetic and electron transport in mediating salt tolerance in plants is still ignored. The present study was aimed to assess the beneficial effects of SA on photosynthetic electron transport in five radish cultivars during salt stress which may translate into protection from salt-induced oxidative damage. Seeds of five radish cultivars (Red Neck Purple, Early Long White, Minnu Radish, Radish 40-day and Gong Swang Radish) were allowed to germinate for five days after which seedlings were sprayed with different concentrations of SA (0, 2 and 5 mM). After 48 h of SA treatment, seedlings were subjected to salt stress (0, 100, and 200 mM NaCl). Salt stress cause reduction in biomass, chlorophyll contents and PSII photochemistry in all five radish cultivars. However, salt stress causes an increase in proline content, lipid peroxidation, ROS content and antioxidant enzymatic activity. Foliar spray of SA downregulated the absorption, trapping and photosynthetic electron transport fluxes while it increased dissipation flux consequently improving photochemistry of most of the radish cultivars under salt stress. This Improved photochemistry and enhanced antioxidant enzymes activity of radish cultivars by SA application resulted in lower ROS generation and membrane damage. Greater accumulation of compatible solutes due to foliar spray of SA might have additional protective effects on photosynthetic machinery by lowering oxidative stress. Moreover, ameliorative effects of SA were cultivar specific. The study suggested that SA could mitigate the detrimental effects of salt stress by regulating physiological and biochemical mechanisms in radish plant.