The Strategy of Carbon Utilization in Uniculm Barley

Abstract

After a photoperiod of 8.25 h during which the youngest fully expanded leaf of uniculm barley plants was allowed to assimilate ¹⁴CO₂ for 30 min, groups of plants were transfered either to continuous light or to continuous dark. Plants were harvested over a 72 h period to examine the effect of the treatments (compared with control plants growing in normal light/dark cycles) on the transport of ¹⁴C from the exposed leaf, the distribution of ¹⁴C assimilates to the rest of the plant, and the chemical fate of assimilated ¹⁴C. In continuous light a substantial quantity (22% at 72 h) of the ¹⁴C assimilated by the leaf remained in that leaf in the form of starch and neutral sugars compared with only 4% in the control fed leaf. Also the total amount of ¹⁴C respired from plants maintained in continuous light was significantly less (c. 18% of the total originally fixed by 24 h) than that respired from control plants (c. 36%). The result was that approximately equal amounts of ¹⁴C were accumulated in the growing leaves and roots of plants given continuous light or normal light/dark cycles. In continuous dark the fate of ¹⁴C was similar to that of control plants. This is probably because the two treatments shared a common light/dark environment for the first 22 h, during which time almost complete distribution and utilization of ¹⁴C occurred.