Accumulation of starch and quality of wheat (Triticum aestivum L.) grain grown under different shoot/root temperatures during maturation

High temperature is a major determinant of wheat (Triticum aestivum L.) development and growth and a major factor in the end-use properties of the grain. The impact of high temperatures on accumulation of starch, the major component of the wheat kernel, is usually attributed to direct effects of the stress on the enzymes involved. However, roots are extremely sensitive to temperatures that can be as high as those of the shoots, and their role in whole-plant responses has been ignored. The objectives of these studies were to identify the role of roots in regulating the conversion of assimilates to starch and assess the milling and flour quality of grain from plants grown under different shoot/root temperatures during maturation. Hard spring wheat (cv Len) was grown under uniform conditions until 10 d after anthesis, when shoot/root regimes of 15/15, 30/15, 15/30, and 30/30°C were imposed until ripeness.;Dry matter and N accumulation were affected more by root than by shoot temperatures. High whole-plant temperatures (30/30°C) accelerated linear grain growth but diminished the duration of assimilation, the contents of sucrose and starch, and the activities of the enzymes involved. The effects of high root temperature (15/30°C) resembled those of high whole-plant temperature, whereas low root temperature (30/15°C) tended to ameliorate them. Sucrose synthase and soluble starch synthase were affected more than the other enzymes by high shoot and/or root temperature; however, treatments that caused the lowest activities resulted in the fastest but briefest linear rates of grain growth.;Kernel characteristics were diminished more by high root than by high shoot temperature. Flour yield correlated positively with kernel weight and diameter, grain test weight, and the proportion of large kernels. However, flour yield was significantly decreased only by high shoot and root temperature in combination and correlated negatively with hardness index and proportion of small kernels.;Flour starch granule size had a bimodal distribution. The volume of B granules was reduced by high shoot temperature, and the size of A granules was decreased by all high temperature treatments. Amylose concentration was increased by high shoot and root temperatures, resulting in decreased pasting characteristics.;Flour protein concentration increased after all high temperature treatments, but high shoot temperature decreased the polymer/monomer ratio and the unextractable protein fraction. The concentration of the latter had a strong effect on the flour mixing time and breakdown.;We concluded that stress on roots directly affects processes in the grain and may have an important role in whole-plant responses to high temperature.