Exocysteine application mitigates salt stress in chickpea (Cicer arietinum L.)

Environmental factors such as salt stress inhibit the growth of plants and agricultural productivity. Exogenous amino acid application has been shown to benefit plants. However, the effect of cysteine application on salt stress reduction in chickpea (Cicer arietinum L.) is unknown. This study examined how exogenous cysteine could reduce salt stress in 2 chickpea cultivars with different salt tolerances. Salt-resistant Gökçe and salt-sensitive Küsmen cultivars were subjected to 100 mM NaCl stress with or without a 100 μM Cys pretreatment. Without Cys pretreatment, salt stress caused the sensitive Küsmen variety to lose 1.49 times its dry weight and 1.35 times its relative water content compared to the mock (control) group. These characteristics were not significantly affected in the resistant Gökçe variety. Salt stress increased malondialdehyde (MDA), a marker for lipid peroxidation, by 1.55 times in Küsmen but remained steady in Gökçe compared to the mock group. In Küsmen, cysteine with salt (Cys + NaCl) treatment increased dry weight and decreased MDA 1.2 times compared to salt alone. Cysteine treatment increased putrescine levels in Küsmen 1.34 times against NaCl alone. Increased putrescine levels and upregulation of delta-1-pyrroline-5-carboxylate synthase (2.75 times) and trehalose-6- phosphate synthase (1.34 times) in the Cys + NaCl group showed that osmotic regulation was involved in salt stress recovery. Cys + NaCl enhanced arginine decarboxylase expression 1.68 times in Gökçe but not in Küsmen compared to NaCl. During salt stress, cysteine increased trehalose-6-phosphate synthase expression 1.34 times in Küsmen but not in Gökçe. The Cys + NaCl treatment reduced the expression of the catalase gene in both varieties compared to NaCl, indicating a complex regulation, while the CAT enzyme activity increased in Gökçe. This study showed that exogenous cysteine protected chickpeas against salt stress. The benefit was larger in Küsmen, the salt-sensitive cultivar. In salt-stressed plants, cysteine increased antioxidant defense and osmotic management, maintaining membrane integrity and improving growth. These findings suggest that cysteine could increase crop resistance in salt-affected areas.