Dynamic responses of accumulation and remobilization of water soluble carbohydrates in wheat stem to drought stress

Remobilization of stem water soluble carbohydrates (WSC) can supply crucial carbon resources for grain filling against drought stress. Here, spatiotemporal variations in post-anthesis WSC levels and compensatory effects for grain weight from different internodes of the main stem were investigated, when exposed two wheat genotypes with contrasting drought tolerance to drought-stressed and well-watered conditions. Analysis of variance revealed that stem WSC levels were predominantly affected by days after anthesis, water stress and their interactions. Compared with well-watered conditions, the peak time of WSC levels was curtailed by 7-14 days in drought-stressed plants. Drought stress highly promoted WSC levels (ca. 20-30%) in upper internodes during the early period of grain filling, but significantly reduced WSC levels (ca. 40-90%) in all internodes during the late period. The drought-tolerant genotype LJ196 was more superior in WSC partitioning than the drought-prone genotype XD18, due to its stronger capacity for stem WSC remobilization, especially for pre-anthesis reserves under drought stress. This was associated with a better grain filling and compensation to the loss of grain weight. The WSC levels induced by drought stress formed a high-to-low concentration gradient from the lower to the upper internodes. Presumably, it might favorably drive WSC flux from stem to developing kernels, indicative of higher WSC remobilization efficiency generally in lower internodes than in upper ones. These findings provide the well-understanding of the spatiotemporal pattern of post-anthesis WSC accumulation and remobilization along stem internodes and their roles in the wheat grain-filling process under drought stress.