Physiological and biochemical response of AtEXPA1 transgenic tobacco plants to salinity stress

Salinity is an environmental factor that adversely impacts seed germination, growth, and productivity by causing osmotic and ionic imbalances in plants. Expansins, which are non-enzymatic proteins, play important role in response to abiotic stress. In this study, three transgenic lines of Nicotiana tabacum cultivar. Samsun overexpressing AtEXPA1 were investigated for physiological and biochemical traits at four different NaCl concentration: 0, 100, 200, and 300 mM. The study was designed based on a factorial experiment in a completely randomized design with four replications. The results indicated that higher levels of salinity stress reduced relative water content and chlorophyll content in leaf, while increasing the electrolyte leakage index, malondialdehyde, and proline content. Lines 4 and 2 exhibited higher Na+ and K+ content, as well as an improved K+/Na+ ratio in the leaves, compared to line 7 and the non-transgenic wild-type plants. Enzymatic antioxidants, such as catalase, ascorbate peroxidase, and polyphenol oxidase, demonstrated high activity, especially in lines 4 and 2 under 200 mM salinity. However, guaiacol peroxidase activity did not significantly differ between wild-type and transgenic lines under severe salt stress. Principal component analysis and clustering identified lines 4 and 2 as salt-tolerant, while line 7 was non-tolerant. These findings suggest that lines 4 and 2 hold promise for use in advanced plant breeding programs aimed at improving salinity tolerance.