Seed priming with cypress leaf extract enhances photosynthesis and antioxidative defense in zucchini seedlings under salt stress

Exogenous ameliorants hold a great potential to strengthen endogenous plant defence under various environmental stresses, including salinity. The effects of Cypress Leaf Extract (CLE, as a biostimulant) and salicylic acid (SA) on growth, physio-biochemical and molecular responses of zucchini (Cucurbita pepo L. cv. Kavili) seedlings under salt stress were investigated. Salt stress resulted in decreased photosynthesis activity and increased oxidative stress. However, CLE- and SA-pretreatment of salt-stressed seedlings enhanced their growth, photosynthetic capacity, antioxidant enzyme (SOD, CAT, APX, GPX, GR, and DHAR) activities and the contents of ascorbate, glutathione and proline as compared to the salt-stressed untreated seedlings. CLE- and SA-pretreatment also alleviated the salt stress-induced negative effects on CO2 assimilation and significantly increased the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Furthermore, CLE pretreatment also upregulated the expression of stress-inducible antioxidation-related genes (CuZnSOD2, CAT1, APX, GR, DHAR and PrxQ) in salt-stressed seedlings. Interestingly, CLE was found to outperform SA in augmenting these processes under both stress and stress-free conditions. Our study reveals that CLE-mediated enhancement of photosynthesis and antioxidative defence mechanisms plays a crucial role in the alleviation of salt stress, and thereby increasing salt tolerance and growth of zucchini plants.