Effect of Drought on Metabolism and Partitioning of Carbon in Two Wheat Varieties Differing in Drought-tolerance

Abstract

A model was constructed to describe the partitioning of carbon on the third and seventh day from anthesis for well-watered and droughted plants of two wheat varieties (Triticum aestivum L. cv. Warigal and Condor). The glasshouse-grown plants were detillered so that a simplified model could be derived for the main stem. The 9-d drought treatment, imposed just after anthesis during the period of cell division in the grains, reduced grain yield by 18 per cent in Warigal and 30 per cent in Condor. Net carbon fixation was up to 60 per cent higher in Warigal than Condor towards the end of the drought period and this correlated with better osmotic adjustment in the flag leaf. Carbon partitioning between plant organs responded to water deficit more rapidly than net carbon fixation. On day 3, carbon allocation to the roots of droughted plants was maintained in Condor and increased by 14 per cent in Warigal, whereas carbon allocation to the ear decreased in both varieties. However the roots did not compete well with the ear when the water deficit became more severe. Warigal accumulated 3 times more stem reserves than Condor under drought. In the roots, the pattern of carbon allocation between respiration and carbon accumulation changed soon after imposition of drought. Although total root respiration decreased under drought it became more energy efficient, particularly for Warigal, as less respiration took place via the alternative pathway. On day 3, the larger carbon allocation to the roots and the lower root respiration accounted for the 4-times larger sugar accumulation in droughted roots of Warigal compared with those of Condor. Osmotic adjustment in mature leaves and roots may be of importance for the maintenance of vital processes and for recovery after drought.