Starch synthesis in the kernel of wheat under high temperature conditions [review]. [Workshop paper].
1994
Jenner C.F.
As temperature rises above 18-22 deg. C, the observed decrease in the duration of deposition of dry matter in the kernel is not accompanied by a compensating increase in the rate of grain filling with the result that grain weight (and yield) is diminished at high temperature. Reduced starch content accounts for most of the reduction in grain dry matter at high temperature. Variation amongst cultivars of wheat in tolerance of high temperature is evident in the low temperature range. At temperatures above 30 deg. C (in the high temperature range (HTR) between 30 and 40 deg. C), even for short periods, the rate of starch deposition is slower than that observed at lower temperatures, an effect which is carried over after transfer from high to lower temperatures. This response is attributable to a reduction in the activity, possibly due to thermal denaturation, of soluble starch synthase (SSS). Several forms of SSS are found in cereal endosperm, and some forms may be more tolerant of high temperature than others. Loss of enzyme activity at high temperature is swift, but is partially restored after cooling. There appear to be 2 distinct mechanisms of response to elevated temperature, both resulting in a reduced grain weight through reduced starch deposition, but 1 of them is important only in the range of temperature above 30 deg. C.
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