Effect of abscisic acid and sodium chloride on germination, storage protein degradation and protein synthesis of Sinapis alba and Raphanus sativus

The degradation of storage protein and the synthesis of new protein processes were compared under the influence of ABA as a growth inhibitor and NaCI as a salt stress to determine their inhibitory effect on seed germination and protein degradation. Seeds of two plant species of the family Brassicaceae were selected for the present work. The selected species are Sinapis alba and Raphanus sativus. The effect of NaCI was put in relation to the effect of mannitol with the same osmotic pressure on inhibition of protein degradation and stimulation of osmotic-stress proteins. Results showed that both treatments inhibited seed germination and retarded the increase in seedling length and fresh weight in both species. The retardation increased with increase in concentration, while the development of the dry weight remained unchanged. It was found that ABA has a stronger effect on seed germination than NaCl in Sinapis alba and Raphanus sativus. During the same time, ABA an d NaCl retarded storage protein degradation in both investigated species depending on the concentration. Cruciferin B, which was the most stable storage protein in untreated seeds, was also the most retarded protein in the ABA or NaCl-treated seeds of both species. Inhibition of the newly formed proteins was also observed with 7.5 muM ABA treatment in both species. From the two types of new proteins, which appear at different times during germination of the untreated samples, only the first one was detected in the ABA-treated seeds while the second one did not appear. By 170 mM NaCl treatment it was found that synthesis of new proteins was inhibited in the two investigated species. NaCl or mannitol solution, with the same osmotic pressure, stimulated some protein bands. These bands have molecular weights of about 10 & 40 KD in Sinapis alba and about 12 & 40 KD in Raphanus sativus. These proteins were not detected with control or ABA.