Import and unloading of 14C assimilate into nonphotosynthetic portions of variegated Coleus blumei leaves

Abstract

Variegated leaves of Coleus blumei Benth. were exposed for 4 h to 1.85 MBq 14CO2 to study the movement of 14C assimilate from green to albino portions of the lamina. Autoradiographs showed considerable 14C activity in both veins and mesophyll of the central albino regions, whether the lamina was left intact or various parts of it were severed or removed prior to 14CO2 exposure. However, when all of the photosynthetic tissue was removed, virtually no label appeared in the albino tissue. Autoradiographs of chromatographed extracts of albino regions from intact leaves showed that sucrose was the most abundant labeled compound and that imported assimilate was unloaded and metabolized into a number of other compounds. The albino region is therefore a genuine sink. No label was imported into any part of mature leaves when lower leaves were fed 14CO2, and young developing leaves ceased to import in the tip-to-base progression typical of dicotyledonous leaves.