High night temperature induced changes in grain starch metabolism alters starch, protein and lipid accumulation in winter wheat.
Unlike sporadic day-time heat spikes, a consistent increase in night-time temperatures can potentially derail the genetic gains being achieved. Ten winter wheat genotypes were exposed to six different night-time temperatures (15°C to 27°C) during flowering and grain-filling stages in controlled environment chambers. We identified night-time temperature of 23o C as the critical threshold beyond which a consistent decline in yield and quality was observed. Confocal laser scanning micrographs of central endosperm, bran and germ tissue displayed differential accumulation of protein, lipid and starch with increasing night-time temperatures. KS07077M-1 recorded a decrease in starch and increase in protein and lipid in central endosperm with increasing night-time temperatures, while the same was significantly lower in SY Monument. Expression analysis of genes encoding 21 enzymes (including isoforms) involved in grain-starch metabolism in developing grains, revealed high night-time temperature (HNT) induced reduction in transcript levels of ADP-glucose pyrophosphorylase small subunit involved in starch synthesis and a ≥ 2-fold increase in starch degrading enzymes isoamylase III, alpha- and beta-amylase. The identified critical threshold, grain compositional changes and the key enzymes in grain starch metabolism that lead to poor starch accumulation in grains establish the foundational knowledge for enhancing HNT tolerance in wheat.