High Temperature Affects the Activity of Enzymes in the Committed Pathway of Starch Synthesis in Developing Wheat Endosperm

Abstract

Ears of wheat were exposed for up to 10 days during the grain-filling stage to high temperature (35�C) and activities of five enzymes in the sucrose to starch pathway were compared to those in ears maintained at lower temperature (21�C day/16�C night). Two cultivars of wheat known to differ in their post-anthesis tolerance of high temperature were compared. On a per grain basis, the activity of sucrose synthase and of ADPglucose pyrophosphorylase in ears maintained at 21/16�C throughout did not change greatly between days 16 and 32 after anthesis, whereas UDPglucose pyrophosphorylase and soluble starch synthase activities declined with advancing development. Soluble starch synthase activity in grains of heated ears was decreased within 1 day to about one- half of the value in unheated grains, and 3 days' additional heating did not reduce the activity much further. Insoluble starch synthase activity was not significantly reduced by heating. Compared to soluble starch synthase, ADPglucose pyrophosphorylase activity was more slowly affected and decreased to a lesser extent by heat. Sucrose synthase and UDPglucose pyrophosphorylase activities were either not affected or only slightly reduced; part of this reduction could be due to advanced development at the higher temperature. In recovery experiments ears were heated for brief periods and then returned to 21/16�C for a few days. ADPglucose pyrophosphorylase and soluble starch synthase activities recovered in the cooler conditions but the other two enzymes generally only maintained or lost further activity. From a comparison of the activities of these enzymes with the rate of starch deposition, and by taking into account the effects of heating, it is proposed that the influence of heating on final grain dry weight is attributable to the observed reductions of soluble starch synthase activity.

Physicochemical characterization of starch from hexaploid triticale (X TriticosecaleWittmack) genotypes

“…duration of starch accumulation (Hawker & Jenner, 1993;Keeling et al, 1993) as well as the expression of gene encoding enzymes for starch biosynthesis (Hurkman et al, 2003). Differences in starch content between the triticale genotypes might also be due to the existence of null alleles on the short arms of chromosomes 7A (Wx-A1) and 7D (Wx-D1) and the long arm of chromosome 4A (Wx-B1), all derived from wheat, which code for the synthesis and expression of starch synthase (Fujita et al, 1996;Yamamori, Nakamura, Endo, & Nagamine, 1994).…”

Impacts of Heat Stress on Wheat: A Critical Review

“…Short-term exposure to heat stress (1 d at 35°C in wheat) results in decreased activity of soluble starch synthase, but further increase in stress duration did not impose any additional impacts [86].…”

Influence of Low/High Temperature on Water Status in Developing and Maturing Rice Grains

“…High temperature restricted the grain growth in rice (Inaba and Sato, 1976), wheat (Hawker and Jenner, 1993) and barley (Wallwork et al, 1998). They apprehended that these high temperature injuries were due to disappearance of enzyme activity relating to starch synthesis of the grains.…”