Antioxidant mechanisms in salt-stressed Maize (Zea mays L.) seedlings: comparative analysis of tolerant and susceptible genotypes

Abstract

Recent anthropogenic activities have spurred unparalleled environmental changes, among which elevated salinity levels emerge as a substantial threat to plant growth and development. This threat is characterized by oxidative stress, marked by the excessive generation of reactive oxygen species (ROS), proline accumulation, and lipid peroxidation. This study investigated the response of four maize (Zea mays L.) genotypes - two tolerant (9120 and Super Gold) and two susceptible (Pacific 984 and PS999) - to salinity-induced oxidative stress. Seedlings aged seven days were exposed to 12 dSm^− 1 salinity stress for five days, with various parameters including relative water content (RWC), ROS accumulation, proline levels, lipid peroxidation, lipoxigenase (LOX) activity, enzymatic and non-enzymatic antioxidants, and glyoxalases evaluated in fully expanded leaves. Susceptible genotypes exhibited higher RWC loss compared to tolerant genotypes, while proline accumulation was elevated in the latter. Enhanced ROS production (hydrogen peroxide and superoxide), melondialdehyde (MDA) levels, and LOX activity were observed in susceptible genotypes under salinity stress, along with increased oxidation of glutathione (GSH) and ascorbate (ASA) compared to tolerant genotypes. Enzymatic antioxidants such as superoxide dismutase (SOD), peroxidase (POD), glutathione peroxidase (GPX), and monodehydroascorbate reductase (MDHAR) displayed higher activity in tolerant genotypes, while catalase (CAT) activity was significantly different between tolerant and susceptible genotypes under salinity stress in maize. Conversely, elevated activities of ascorbate peroxidase (APX), glutathione S-transferase (GST), glutathione reductase (GR), and dehydroascorbate reductase (DHAR) were observed in both genotypes, indicating their crucial role in cellular protection against ROS and metabolites during salt stress. In short, plants have devised tactics to scavenge surplus Reactive Oxygen Species (ROS) and uphold cellular redox balance amidst oxidative stress. This study aims to offer basic knowledge regarding both enzymatic and nonenzymatic antioxidants, and the defense mechanisms they constitute against ROS detoxification upon salt stress conditions; furthermore, it also explores their interactions with cellular components.