Export, Mobilization, and Respiration of Assimilates in Uniculm Barley during Light and Darkness

Abstract

The respiratory losses and the pattern of carbon supply from a leaf of unicuim barley were examined during a complete diurnal period using a steady state ¹⁴C-labelling technique. After a delay of c. 1 h a portion of the ¹⁴C exported from a continuously assimilating leaf was lost in respiration in the light. This respiratory loss amounted to c. 20% of the total ¹⁴C fixed. A further 28% of the total ¹⁴C fixed was respired during the dark period. In the light, carbon was fixed at a rate of c. 8·9 mg C dm^−2h−1 and exported from the leaf at ^c. 5·3 mg C dm^−2h−1. Dark export averaged ^c. 31% of the day-time rate. Carbohydrate was stored in the leaf during the day and was almost completely remobilized during the dark. Sucrose, the major reserve carbohydrate, was exported first whilst the starch level remained constant. After some 9 h of darkness, sucrose declined to a low level and starch remobilization began.