GABA mitigates NaCl toxicity by enhancing photosynthesis, chloroplast structure, and redox balance in salt-tolerant and sensitive tomato varieties

Abstract

GABA serves as the major metabolite and signaling molecule for plant growth and development under fluctuating environmental conditions. In the present study, the effect of different concentrations of GABA (0, 0.25, 0.5, or 0.75 mM) as foliar spray or seed soaking treatment on K-21 and S-22 varieties of tomato (Solanum lycopersicum L.) under normal and NaCl stress (150 mM) was studied. At 40 days after transplantation (DAT), NaCl stress impaired the photosynthetic apparatus, elevated reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and reduced photosynthetic traits and related enzymes, and consequently compromised plant growth and development. However, among the different concentrations of GABA tested 0.5 mM of GABA applied through foliar mode proved best in improving growth, photosynthetic traits (like P_N of K-21 and S-22 varieties by 39.17% and 30.35%, gs by 40.11% and 32.37%; Ci by 39.48% and 33.67%; E by 37.98% and 30.08% respectively, compared to control group) and enzyme activities (Rubisco, succinate dehydrogenase, and fumarase activity) maintained organization of chloroplast in the leaves and also improved lycopene and β-carotene contents in fruits of tomato plants. Moreover, treatment of GABA (0.5 mM) reduced levels of ROS (such as decreased the contents of O₂^·− by 38.10% and 34.05%; and H₂O₂ by 35.95% and 30.36% respectively, in K-21 and S-22 varieties, as compared to their control) and cell death compared to non-treated tomato plants. Foliar application of GABA (0.5 mM) also was more effective than seed soaking to overcome the adverse effects of salt stress specifically in K-21 than S-22 variety. This study addresses this gap and uniquely investigates role of GABA in regulating photosynthetic (Rubisco), GABA shunt, and respiratory (fumarase, succinate dehydrogenase) enzyme activities under salt stress, offering new insights into its multifaceted stress-mitigating potential.