Abstract

Developmental changes in the starch and soluble sugars content of grains and the activities of sucrose metabolism enzymes in drought-tolerant (Triticum aestivum L. cv. Zagros) and drought-sensitive with high yielding potential under favorable conditions (cv. Marvdasht) wheat genotypes were investigated under controlled water deficit during grain filling. The two cultivars were grown in pots under well-watered (WW) and water-stressed (WS) starting from anthesis until maturity. Water stress caused a marked reduction in glucose, fructose and sucrose content of grains of sensitive cultivar. These changes were paralleled by sharp decline in the activities of cell wall invertase and soluble invertase in the grains of sensitive cultivar. Whereas in tolerant cultivar as the surge in invertase activity faded; in grains it was replaced by a substantial increase in sucrose synthase activity as seed development proceeds. Notwithstanding the increase in sucrose synthase activity in grains of sensitive cultivar; however, this little raise could not be sufficient to compensate for decreased levels of invertases and might restrict transport efficiency of storage material, and together with insufficient photosynthate may be the main reasons for dramatical reduction in the number of kernel and subsequent grain yield under WS treatment in Marvdasht.

Key words: Invertase activity, sucrose metabolism, sucrose synthase, water stress, wheat (Triticum aestivum L.).