Time-course changes in organic metabolites and mineral nutrients in germinating maize seeds under salt (NaCl) stress

The kernels of maize (cv Sultan) were incubated for seven days in solution culture containing 0, 40, 80 or 120 mol m(-3) NaCl. Data for seed germinati on and fresh and dry weights of plumule, radicle and germinating seed were recorded daily after the inception of germination. Fresh weights of seeds d ecreased significantly with increase in NaCl concentration of the growth me dium whereas seed dry weights remained almost unaffected. However, fresh an d dry weights of both shoot axis and radicle increased consistently with ti me but this increase was considerably higher in non-saline conditions than that in saline substrate. Na+ concentrations in the germinating seeds incre ased with time in all salt treatments except the control treatment and the marked effect of time was observed at the highest salt regime (120 mol NaCl m(-3)). The same pattern of Na+ transport was observed in the shoot axis w hereas the reverse was true for radicle in which Na+ concentrations decreas ed considerably with One. Saline medium caused a significant increase in Cl - concentration of the seeds, plumule and radicle and the time-course incre ase in Cl- was also significant in these plant parts. K+ concentrations in the germinating seeds and shoot axis decreased with time and a significant reduction in K+ level was observed on day 7 of germination in all treatment s. Saline growth medium had no effect on K+ concentrations of radicles but in contrast, there was a significant time-course reduction in radicle K+ co ncentration regardless of NaCl treatment. Similar effect of salt and time w as observed on Ca2+ concentration of the germinating seeds. No significant effect of salt or time was observed on Ca2+ concentrations in the radicles but in contrast, the time-course decrease in shoot axis Ca2+ was observed o nly at the highest salt level. Soluble proteins of seeds, plumule and radic le decreased significantly with increase in time or external salt regimes w hereas no effect of salt or time was observed on free amino acids of the ge rminating seeds. However, a slight time-course decrease in these biochemica ls was found in both plumule and radicle. in contrast, a time-course increa se in soluble sugars of seeds, plumule and radicle was significant. Total l ipids decreased significantly in the germinating seeds with time but this d ecrease was more pronounced in the control treatment than that in the salin e conditions. The time-course change in lipid content was negligible at the highest salt level. The salt sensitivity of maize at the germination stage was found to be associated with high transport of Na+ and Cl- to the growi ng shoot axis and time-course decrease in K+ and Ca2+ concentration in the embryonic tissues. In addition, the adverse effect of salt on seed germinat ion is partly due to impairment in breakdown of seed lipids so as to supply soluble sugars to the respiratory metabolism of the growing embryo.