Exogenous potassium differentially mitigates salt stress in tolerant and sensitive maize hybrids

A hydroponic experiment was conducted to investigate the role of potassium (K) in extenuating the injurious effect of salt stress on maize hybrids differing in salt tolerance. Two salt-sensitive viz., 33H25 and 8441 and two salt-tolerant viz. 26204 and Hysun-33 maize hybrids were grown for four weeks in half strength Hoagland’s solution. The nutrient solution was salinized by three salinity (0, 70 and 140 mM L-1 NaCl) levels and supplied with three levels of potassium (3, 6 and 9 mM L-1). Salt stress significantly reduced the plant growth as reflected by a decrease in the plant height, leaf area, shoot length, shoot fresh and dry weight, relative water content (RWC), membrane stability index (MSI), chlorophyll contents (chl), transpiration rate (E), photosynthetic rate (A), internal CO2 concentration (Ci), stomatal conductance (gs), K+/Na+ ratio and increased the activities of anti-oxidative enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) at 70 mM NaCl, but activities of SOD, POD and CAT declined at 140 mM NaCl for all four maize hybrids. Salinity induced diminution in all these attributes was significantly greater in salt sensitive maize hybrids as compared to salt tolerant maize hybrids. However, application of potassium counteracted the unsympathetic effects of salinity on the growth of salt tolerant maize hybrids, particularly at 9 mM L-1 level. Potassium enhanced growth of salt-stressed maize hybrids 26204 and Hysun- 33 was associated with increased CAT activity, higher photosynthetic capacity, and accumulation of K+ in the leaves. These results suggested that potassium application counteracted the unfavorable effects of salinity on growth of maize by civilizing photosynthetic capacity of maize plants against salinity-induced oxidative stress and maintaining ion homeostasis, however, these alleviating effects were cultivar specific