Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars during Grain Filling: Impact of Invertase Activity on Carbon Metabolism during Kernel Development

Developmental changes in the starch and soluble sugars content of flag leaves and grains and the activities enzymes of sucrose metabolism in drought-tolerant (Triticum aestivumL. cv. Zagros) and drought-sensitive with high yielding potential under favorable conditions (cv. Marvdasht) wheat genotypes investigated under controlled water deficit during grain filling. Cultivars were grown in pots and treated with either well-watered (WW) or water-stressed (WS) from anthesis to maturity. WS caused a marked reduction in glucose, fructose and sucrose content of flag leaves and grains of sensitive cultivar. These changes were paralleled by sharp decline in the activity of cell wall invertase and soluble invertase at the both flag leaves and grains of sensitive cultivar. Whereas a transient surge in the activity invertases of flag leaves was found in tolerant cultivar. As the surge in invertase activity faded, in leaves and grains of tolerant cultivar it was replaced by a substantial increase in sucrose synthase activity as seed development proceeds. Notwithstanding increase in sucrose synthase activity in leaves and grains of sensitive cultivar, however this little raises could not be sufficiently active to compensate for decreased levels of invertases and might restrict sucrose export, and together with a concomitant repression in young ovaries, may limit sucrose transport and use and result in partial zygote abortion that led to dramatically reduction in number of kernel and subsequent grain yield under WS treatment in Marvdasht.