Abstract
The effect of high temperature on starch accumulation, starch granule populations, and expression of genes encoding key enzymes for starch biosynthesis was examined during grain development in wheat ( Triticum aestivum L. cv. Butte 86). High temperature applied from anthesis to maturity reduced the duration of starch accumulation. Starch accumulation ceased approximately 6 days earlier for grain produced under a 37/17 °C (day/night) regimen and 21 days earlier under a 37/28 °C (day/night) regimen than for grain produced under a 24/17 °C (day/night) regimen. Compared to the 24/17 °C regimen, starch content was approximately 19% less for mature grain produced under the 37/17 °C regimen and 58% less under the 37/28 °C regimen. Based on relative volume, the smaller type B starch granules were the predominant class in mature grain produced under the 24/17 and 37/17 °C regimens, whereas the larger type A granules were predominant in grain produced under the 37/28 °C regimen. Under the 24/17 °C regimen, steady state transcript levels for ADP-glucose pyrophosphorylase, starch synthases I, II, and III, granule-bound starch synthase, and starch branching enzymes I and II were highest from 12–16 days post-anthesis (dpa). Under the 37/17 °C regimen, steady state levels of these transcripts followed the same temporal pattern, but were substantially lower. Under the 37/28 °C regimen, transcript levels peaked earlier, at 7 dpa. The high temperature regimens reduced the relative levels of transcripts for starch synthase more than the other starch biosynthetic enzymes.
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