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Effect of high temperature on gene expression for starch biosynthesis in developing wheat grains.
WILLIAM J. HURKMAN, Kent F. McCue, Anna Korn, Charlene K. Tanaka, Susan B. Altenbach, and
Frances M. DuPont. USDA, ARS, Western Regional Research Center, Albany, CA.
High temperatures during grain development reduce final grain weight
in wheat (Triticum aestivum) by decreasing starch deposition. The effect of high temperature on the
expression of genes for starch biosynthetic enzymes was examined in wheat plants (Butte 86). Plants were
grown in a climate-controlled greenhouse that had a maximum daytime temperature of 25°C and a nighttime
temperature of 16°C. At the onset of flowering, half of the plants were transferred to a second greenhouse
with identical growing conditions, except that daytime temperature was programmed for 38°C. Developing
grains 8 to 46 days post anthesis (dpa) were collected from control and heat-treated plants and total RNA
was isolated from embryos, endosperm, and pericarp/testa. Transcript levels for ADPglucose
phosphorylase, soluble starch synthase, granule bound starch synthase, and starch branching enzymes I and
II were analyzed during the developmental time course. Transcripts for these enzymes were detectable in
the endosperm, but not in embryos and pericarp/testa. All transcripts had the same pattern of developmental
regulation; steady state transcript levels were highest at 12 dpa and decreased gradually to very low levels
by 46 dpa. Steady state levels of all transcripts decreased substantially at 8 and 12 dpa in response to high
temperature. Despite this decrease in transcript levels, starch accumulated at a similar rate in the grains of
both the heat-treated plants and the control plants. However, starch accumulation ceased about six days
earlier in the heat-treated plants.
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