STARCH METABOLISM IN SALT-TOLERANT AND SALT-SENSITIVE SHAMOUTI CALLUS

Starch content and metabolism, related to salt tolerance, were studied in citrus calli from Shamouti ovules (Citrus sinensis Osbeck.), comparing a salt tolerant line (R-10) and a salt sensitive line (L-5). The salt sensitive callus contained 2-3 fold more starch than the stilt tolerant callus when grown in control medium, and as much as five fold more starch when grown in the presence of 0.1 M NaCl. Analysis of the starch biosynthetic enzymes, revealed five fold and three fold higher activity of ADPglucose pyrophosphorylase and starch synthase, respectively, in salt sensitive cells as compared to salt tolerant cells. The activity of starch degrading enzymes, amylase and maltase, showed no major differences between salt sensitive and salt tolerant calli. It is suggested that adaptation to salt in citrus calli is characterized by reduced starch biosynthesis, leading to lower starch accumulation as compared to the salt sensitive callus. ADPglucose pyrophosphorylase seems to be the key enzyme determining starch content in citrus cells.