Gradual increase in NaCl concentration overcomes inhibition of seed germination due to salinity stress in Sorghum bicolor (L.)

Abstract

A gradual increase in NaCl concentration in the growth medium was used as a strategy to adapt sorghum plants (Sorghum bicolorL.) to relatively high concentrations of NaCl. over a period of 15 days, a low percentage (22.2%) of sorghum seeds germinated in 200 mM NaCl, but most of the seedlings obtained (85.8%) died. On the other hand, plants subjected to adaptation by a gradual increase in NaCl concentration in the growth medium became capable of growth in soil containing 300 mM NaCl. In general, salinization induced a highly significant decrease in fresh and dry masses, and in the pigment content of sorghum seedlings. The content of free amino acids and soluble carbohydrates increased with a rise in the salinization level, especially in the adapted sorghum plants. The adapted plants contained less Na+but more K+compared to the unadapted plants, especially when the plants were subjected to relatively high NaCl concentration. Plants adapted in soil showed a new peroxidase isoenzyme form (POX-4). The peroxidase band POX-1 was detected under salt stress in both adapted and unadapted plants. Under salt stress, indophenol oxidase and glutamate oxaloacetate transaminase expressed new isoenzyme forms, IPOX-3 and IPOX-5, and GOT-2 and GOT-3, respectively. The induction of salt tolerance by a gradual increase in NaCl concentration for three weeks was recommended to overcome the inhibition of seed germination in saline soil.