Role of melatonin in improving leaf mineral content and growth of sweet corn seedlings under different soil salinity levels

Melatonin (MEL) hormone regulates plant growth and development and increases plant resistance against stress conditions. In the present this study, effects of external melatonin treatments (0, 50 mu M, 100 mu M and 200 mu M) under different soil salinity levels (0.27 dSm(-1), 2.50 dSm(-1), 5.0 dSm(-1) and 8.0 dSm(-1)) on seedling growth parameters, stomatal conductance (g(s)), chlorophyll content (SPAD value) and leaf mineral contents (Na+, K+, Ca2+, Cu2+, Mn2+ and Zn2+) of sweet corn were investigated. The study was carried out in pots under rain-shelter conditions considering a randomized complete block design with three replicates. The results showed that soil salinity stress significantly decreased the plant height, root length, above-ground fresh and dry biomass, root fresh and dry weights, stem diameter, number of leaves, stomatal conductance, and SPAD values. However, melatonin-pretreated seeds demonstrated higher increases in these parameters than untreated melatonin seeds under soil salinity levels depending on the treated dose. Additionally, the melatonin-priming treatment increased the leaf K+, Ca+, K+/Na+ and Ca2+/Na+ ratios under saline soil conditions. Notably, a significant increase in seedling growth ability and nutrient uptake was recorded in sweet corn seeds up to 100 mu M melatonin dose. With increasing melatonin dose from 0 mu M to 100 mu M, above-ground fresh biomass increased by about 17.15% at 0.27 dSm(-1) soil salinity condition, while about 35.42% at 8.0 dSm(-1) soil salinity condition. In conclusion, present findings revealed that sweet corn plants were found to be very sensitive against soil salinity at the seedling stage, and seed priming with 100 mu M MEL dose increased plant resistance against negative effects of soil salinity.