Comparative analysis of salinity tolerance mechanisms in two maize genotypes: growth performance, ion regulation, and antioxidant responses

Abstract

This study investigates the differential responses of two maize genotypes, SC180 and SC168, to salt stress, aiming to elucidate the mechanisms underlying salinity tolerance and identify traits associated with improved stress resilience. Salinity stress, imposed by 150 mM NaCl, adversely affected various growth parameters in both genotypes. SC180 exhibited a more pronounced reduction in shoot length (13.6%) and root length (13.6%) compared to SC168, which showed minimal reductions (3.0% and 2.3%, respectively). Additionally, dry weight losses in SC180's leaves, stems, and roots were significantly greater than those in SC168. Under salinity stress, both genotypes accumulated Na⁺ in all organs, with SC168 showing higher Na + concentrations. However, K⁺ levels decreased more significantly in SC180's leaves than in SC168's. The study also assessed physiological responses, noting that SC180 experienced a substantial reduction in relative water content (RWC) in leaves (22.7%), while SC168's RWC remained relatively stable (5.15%). Proline accumulation, a marker for osmotic adjustment, increased 2.3-fold in SC168 compared onefold in SC180. Oxidative stress indicators, such as electrolyte leakage and hydrogen peroxide levels, were elevated in both genotypes under salt stress, with SC180 showing higher increases (48.5% and 48.7%, respectively) than SC168 (35.25% and 22.0%). Moreover, antioxidant enzymes (APX, CAT, POD, SOD, GR) activities were significantly enhanced in SC168 under salinity stress, whereas SC180 showed no significant changes in these activities. Stress indices, used to quantify and compare salinity tolerance, consistently ranked SC168 as more tolerant (average rank = 1.08) compared to SC180 (average rank = 1.92). Correlation analyses further confirmed that SC168's superior tolerance was associated with better Na + regulation, maintenance of K⁺ levels, and a robust antioxidant defense system. In conclusion, SC168 demonstrated greater resilience to salinity stress, attributed to its efficient ion regulation, stable water status, enhanced osmotic adjustment, and strong antioxidant response. These findings provide valuable insights for breeding and developing salinity-tolerant maize varieties.