Heat Inactivation of Starch Synthase in Wheat Endosperm Tissue

Abstract

ABSTRACIThe effect of temperature on accumulation of starch was studied in grain slices of wheat (Titicum aestivum cv SUN9E), taken 15 days after anthesis. As compared with pretreatment of such slices at 25°C, pretreatment at 30 or 35C reduced the subsequent conversion of sucrose to starch. In contrast to rice (Oryza sativa cv Calrose), pretreatment of wheat soluble starch synthase in vitro at 30°C or higher temperatures reduced its activity. In zymograms using nondenaturing polyacrylamide gel electrophoresis followed by activity staining, the slowest mirating band represented the most temperature sensitive isozyme. Although preincubation of a soluble enzyme sample in vitro at 25°C did not result in loss of starch synthase activity, it did result in a gradual shift of zymogram banding pattern toward faster migrating species. Pretreatment of isolated starch granules at 40°C increased their bound starch synthase activity. Both soluble and bound enzymes in the grains of whole wheat plants lost activity when the plants were held above 30°C for 30 minutes or longer. Both activities lost from the grains after a 1 hour treatment at 37°C were restored in 1 to 2 days by a return to 21°C. In slices, inactivation of the soluble starch synthase was increased by incubation with 2,4-dinitrophenol. It is tentatively suggested that in vivo heat inactivation of soluble starch synthase may be a direct effect of heat on the enzyme protein and that of bound enzyme an indirect effect involving metabolic factors.In wheat the optimum temperature, of plant culture for dry weight per grain at maturity occurs at a day/night temperature of 15°C/10°C (4). Increasing the temperature of the ear independent of the rest of the plant from 15 to 20°C and 25C has resulted in an increased growth rate of the ear but this was accompanied by earlier senescence and a shorter duration of growth (6). Ear warming at 33°C/25°C (day/night) in comparison with 2 1C/16°C, resulted in a reduction ofgrain growth rate after the 6 d warming period (1). From these data, it would be expected that at a suitably high temperature such a reduction in rate could be observed earlier and analyzed more directly. Also it has been suggested that for maize kernels grown in vitro, the adverse effects of high temperature on starch synthesis during the grain-fill period were due to deficiencies in the synthetic process rather than in the supply of substrate (8)

Environmental Stability and Correlation of Soybean Seed Starch with Protein and Oil Contents

“…These results are in line with previous reports (Piper and Boote 1999;Thomas et al 2003) in which the starch and soluble sugar contents in soybean seeds were found to decrease with rise in temperature. Similar correlations have been observed in other crops such as rice (Ahmed et al 2015) and wheat (Rijven 1986;Zhao et al 2006;Yan et al 2008;Liu et al 2011). The reasons for this phenomenon were supposedly the lower activities of starch synthase, ADP-glucose pyrophosphorylase, starch phosphorylase, and soluble starch synthase enzymes involved in sucrose to starch conversion at higher temperatures (Rijven 1986).…”

Effect of High Temperature at Ripening Stage on the Reserve Accumulation in Seed in Some Rice Cultivars

“…such as insensitive response of starch synthase in rice endosperm to high temperature compared with wheat endosperm (Rijven, 1986) or possible role of debranching enzymes in starch degradation (Nakamura et al, 1996) have been reported, ADP -glucose pyrophosphorylase and soluble starch synthase seem to be one of key enzymes under high-temperature stress. Further studies on the behavior of these enzymes are needed.…”

Heat Tolerance in Wheat - A Key Strategy to Combat Climate Change through Molecular Markers

“…Canopy temperature (Reynolds et al, 1994) Photosynthetic rate (Rijven, 1986) Chlorophyll content (Al-Khatib and Paulsen, 1984) Chlorophyll fluorescence (Azam et al, 2015) Stomata conductance (Reynolds et al, 1994) Stem reserve (Mohammadi et al, 2009) Membrane thermostability (Shanahan et al, 1990).…”