Sodium in the leaf apoplast does not affect growth of maize (Zea mays L.) under saline field conditions

Studies dealing with leaf apoplastic Na+ concentration of monocots, such as maize, under actual saline soils are scarce. Therefore, the current study was aimed to investigate the growth, total ions and leaf apoplastic Na+ concentration of salt sensitive maize plants growing in saline soils. Plants were subjected to salt stress with an electrical conductivity (EC) of 3, 8 10 and 14 dS m-1 using completely randomized design (CRD) for 3 weeks. Shoot fresh weight, plant height, leaf area and leaf length of maize plants drastically decreased when plants were exposed to increasing salt stress. We found that maize could display a steep increase in Na+ concentration in the total shoot biomass with maximum 82.3 μmol g-1 FW, when plants were subjected to highest soil salinity at 14 dS m-1. As expected, other cations i.e., K+, Ca2+ and Mg2+ decreased with increasing EC of the soil compared to Na+. Surprisingly, a maximum of 17 mM Na+ were found in the leaf apoplast of maize grown under very high soil salinity at EC 14 dS m-1. Considering this lower leaf apoplastic Na+ concentration at such a high EC level in maize plants, current study does not corroborate that surplus sodium in the leaf apoplast can result in dehydration and cell death under salt stress.