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.), compa ring 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 to lerant callus when grown in control medium, and as much as five fold m ore starch when grown in the presence of 0.1 M NaCl. Analysis of the s tarch biosynthetic enzymes, revealed five fold and three fold higher a ctivity of ADPglucose pyrophosphorylase and starch synthase, respectiv ely, in salt sensitive cells as compared to salt tolerant cells. The a ctivity of starch degrading enzymes, amylase and maltase, showed no ma jor 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 c ompared to the salt sensitive callus. ADPglucose pyrophosphorylase see ms to be the key enzyme determining starch content in citrus cells.