Protein accumulation and composition in wheat grains: Effects of mineral nutrients and high temperature

Effects of mineral nutrition and temperature on accumulation and composition of protein in wheat grains and on baking quality were studied under controlled environments. Under a moderate temperature regimen of 24 °C days and 17 °C nights (24/17 °C), post-anthesis N:P:K 20:20:20 (NPK) supplied by continuous drip irrigation increased the rate of protein accumulation, doubled flour protein percentage and slightly increased final single kernel weight. In contrast, post-anthesis NPK had almost no effect on rate or duration of protein accumulation or flour protein percentage under a high temperature regimen of 37 °C days and 28 °C nights (37/28 °C). The 37/28 °C regimen shortened and compressed the stages of grain fill, reduced the duration of dry matter accumulation, and reduced single kernel weight by 50%. Rate and duration of protein accumulation in thermal time and total protein per grain at 37/28 °C with or without NPK were similar to that at 24/17 °C in the absence of post-anthesis NPK. Protein percentage was higher for flour from grain produced at 37/28 °C with or without NPK than at 24/17 °C in the presence of post-anthesis NPK. Transcript and protein profiling studies confirmed that the 37/28 °C regimen compressed development without disrupting coordinate synthesis of gliadins and glutenin subunits, although some specific effects of NPK and temperature on relative amounts of individual gliadins and glutenins were observed. Transcript levels for ω-gliadins, α-gliadins and high molecular weight glutenin subunits (HMW-GS) declined at 24/17 °C in the absence of post-anthesis NPK, whereas transcript levels for low molecular weight glutenin subunits (LMW-GS) and γ-gliadins showed little change. Two-dimensional gel electrophoresis (2DE) demonstrated that relative spot volumes for several ω-gliadins, α-gliadins and HMW-GS were lower at 24/17 °C in the absence than in the presence of post-anthesis NPK, whereas the relative spot volume for a major LMW-GS was lower in the presence of NPK. Effects of temperature on relative spot volume were generally smaller than effects of NPK. Compared to the 24/17 °C regimen in the absence of post-anthesis NPK, relative spot volume for some α-gliadins and HMW-GS were higher at 37/28 °C, with or without NPK, and relative spot volume for a major LMW-GS decreased at 37/28 °C. Loaf volume was correlated with flour protein percentage regardless of temperature regimen but mixing tolerance was highest for flour from grain produced under the 24/17 °C regimens with NPK.