Proline and glycine betaine: A dynamic duo for enhancing salt stress resilience in maize by regulating growth, Stomatal size, and Oxidative stress responses

• Salt stress significantly decreased maize seed germination and seedling growth. • Stomatal size and K + /Na + ratios were significantly decreased under salt stress. • Under salt stress, MDA and H 2 O 2 increased, whereas antioxidant enzymes decreased. • Proline and glycine-betaine increased germination, stomatal size, and K + /Na + ratios. • Proline and glycine-betaine reduced salt-induced H 2 O 2 and MDA by boosting antioxidants. Osmolytes proline (Pro) and glycine betaine (GB) have been reported to impart tolerance against salinity stress in many plants. However, there is no report available on the combined application of Pro and GB to mitigate salinity-induced growth inhibition in maize. Consequently, the goal of the current study is to assess Pro's and GB's potential as priming and exogenous agents in maize under salt stress. Therefore, the present study was conducted using a petri dish and hydroponic pot experiment to evaluate the morpho-physiological and biochemical characteristics of maize plants subjected to salt stress, with the addition of Pro and GB. The seeds of maize were germinated under 20 mM of each Pro or GB, with or without 120 mM salinity stress. The findings demonstrated that salt stress lessened the final germination percentage (FGP) (52.9 %), photosynthetic pigments (40.0 %), relative water content (RWC) (20.2 %), stomatal size (59.3 %), and leaf and root K + /Na + ratios of maize seedlings compared to control. In addition, compared to the control, higher levels of malondialdehyde (MDA) (24.2 %) and hydrogen peroxide (H 2 O 2 ) (25.7 %) were observed, whereas lower levels of catalase (CAT) (43.8 %) and peroxidase (POX) (30.4 %) were noted. The priming with Pro, GB, Pro+GB significantly increased FGP, germination index (GI), shoot-root biomass, seed vigor index (SVI), and reduced mean germination time (MGT) under salt stress. Foliar application of Pro, GB, or Pro+GB resulted in a significant increment in chlorophyll contents, RWC, K + absorption, and stomatal size under salt stress. Furthermore, supplementing with Pro, GB, or Pro+GB reduced the accumulation of H 2 O 2 (24.0, 23.3, and 31.1 %, respectively) and MDA (22.8, 17.2, and 32.1 %, respectively) caused by salt and augmented the levels of CAT (33.3, 22.8, and 45.2 %, respectively) and POX (36.4, 23.5, and 47.2 %, respectively) in the leaves. Taken together, the current study's findings indicate that combining Pro and GB is one of the most effective techniques for improving the salinity-tolerant seed germination and seedling traits of maize plants. Consequently, this study recommends that Pro and GB can be used as seed priming and exogenous agents to help maize grow faster in salt-stress situations.