PHYSIOLOGICAL-BASIS OF SALINITY TOLERANCE OF SORGHUM SEEDS DURING GERMINATION

Effects of salinity on the isozyme activities of alpha-amylase in germinating sorghum seeds were studied under laboratory conditions. Seeds were imbibed in NaCl solutions at concentrations ranging from 0-500 nM (osmotic pressure: 0-2.28 MPa) for 0-24h and the isozymes activities were estimated after disc-gel electrophoresis. Seed germination of sorghum was not affected by NaCl concentrations less than 100 nM (0.46 MPa). Germination was reduced by 50% at 300 nM NaCl (1.31 MPa), and completely inhibited at 500 nM (2.28 MPa). The alpha-amylase activity in the treated seeds followed a similar pattern to that of germination. At least five isozyme patterns of alpha-amylase were observed in germinating sorghum seeds. The activities of the respective isozymes were enhanced with increasing duration of imbibition in distilled water. When treated with 100 nM NaCl, the activities of isozymes 2 and 5 decreased, but this was compensated by the increased activity of isozyme 1. The sensitivity of isozymes to the salinity treatments varied where isozyme 1 was the most tolerant. The isozyme activities were completely inhibited by 500 nM NaCl. The results indicate that sorghum seeds could germinate well in saline environments up to 0.46 MPa. Higher osmotic pressure or saline concentrations could be detrimental to the seed germination of sorghum. The salinity tolerance could be attributable to the compensation of loss of activities of certain isozymes of alpha-amylase by the other types.