Carbohydrates Accumulation and Remobilization in Wheat Plants as Influenced by Combined Waterlogging and Shading Stress During Grain Filling

Wheat plants were subjected to combined waterlogging and shading stress (WS) at 07, 815, 1623 and 2431 days after anthesis (DAA), respectively. Compared to the non-stressed plants, WS significantly decreased the final grain yield. Grain number was dramatically lowered by WS imposed at 07 DAA but hardly affected by other WS treatments; while the thousand-kernel-weight was unaffected by WS imposed at 07 DAA and lowered by other WS treatments. Photosynthate accumulation in the stem was decreased by WS imposed at 07 and 815 DAA, but was unaffected by WS imposed at later stages. Grain-filling rate was decreased, although the apparent remobilization of carbohydrate reserves from stem to grain was stimulated under WS. The carbohydrate reserves stored in the lower stem internodes were activated earlier and remobilized much more than those in the upper internodes; however, the proportion of the apparent remobilized reserves among the different stem internodes was consistent for all treatments. WS decreased contents of fructans, fructose and sucrose in the stem, which coincided with increased activity of fructan exohydrolase and decreased activities of sucrose-1-fructosyltransferase and fructan-1-fructosyltransferse. The results indicate that post-anthesis WS stimulated carbohydrate reserves remobilization by modifying the activities of the fructans-catalysing enzymes in the stem.