Some Aspects of Carbon Metabolism and Translocation in Onions

Abstract

SUMMARYIn the first six leaves of plants of Allitim cepa L. cv. Creamgold grown from seed, the carbohydrate content per unit fresh weight within the leaf is highest in the leaf base and lowest at the tip. Soluble protein content is highest at the leaf tip and decreases down the leaf. The activity of ribulose bisphosphate carboxylase per unit fresh weight is constant in the upper leaf but is lower in the leaf sheath.During growth, ribulose bisphosphate carboxylase activity reaches a maximum when leaves are at about 50 "^o of final size. Thereafter activity decreases even though leaf growth continues. After short exposures to ^^COa, 80 % of ^^C in the leaf is recovered in sucrose. Carbon is rapidly translocated from the upper leaf to the leaf base and to a lesser extent to roots and unemerged leaves. The rapid carbon translocation is consistent with the absence of non-structural polysaccharide pools in the upper leaf segments.