The Strategy of Carbon Utilization in Uniculm Barley I. THE CHEMICAL FATE OF PHOTOSYNTHETICALLY ASSIMILATED ¹⁴C

Abstract

Following exposure of the youngest mature leaf of uniculm barley to ¹⁴CO₂, groups of plants were harvested over a 72 h period to determine the fate of 14C in the photosynthesizing leaf and in growing leaves and roots. Initially, ¹⁴C was mainly present in sucrose with a little in starch and charged compounds; transport out of the fed leaf was rapid and, by 7 and 24 h, 56 and 93% respectively of the ¹⁴C had been translocated about equally to growing leaves and roots. Sucrose entering meristems was quickly metabolized to protein and structural carbohydrate (40 and 60% of the ¹⁴C in these organs at 7 and 24 h respectively), while the remainder was converted to short-term storage products or intermediary metabolites. By the end of the first day c. 35% of the 14C originally assimilated had been lost in respiration.

The metabolism of the leaf appeared to be organized on a diurnal basis, for it exported nearly all its carbon within 24 h of assimilation. In contrast, some of the assimilate imported into growing leaves and, to a lesser extent, roots was not immediately used for growth but persisted as temporary metabolites and was subsequently used for growth in the following days.