Bread wheat (Triticum aestivum) is less adaptable to high temperatures than other major cereals. Previous studies of the effects of high temperature on wheat focused on the reproductive stage. There are few reports on yield-related trait after high temperatures at other growth stages. Understanding growth-stage-specific responses to heat stress will contribute to the development of tolerant lines suited to high temperatures at various stages. We exposed wheat cultivar “Norin 61” to high temperature at three growth stages: seedling-tillering (GS1), tillering-flowering (GS2), and flowering-maturity (GS3). Our analysis based on any agronomical traits, seed maturity, and photosynthesis revealed that heat at GS2 reduced plant height and number of grains in plants; heat at GS3 shortened period of the grain formation and decreased grain weight. On the other hand, heat at GS1 prolonged period of grain formation by delaying senescence, resulting increased weight of each grain. In addition, the plants exposed to high temperature at all stages (GS1-3) was delayed senescence compared to that only after the flowering stage (GS3). To elucidate the metabolic mechanism behind the above phenomenon, metabolite analysis was conducted using flag leaves at 7 days after flowering. Beta-alanine, tryptophan, serotonin, proline and putrescine were identified as potential biomarkers for assessing senescence, as they showed a strong correlation with yield-related traits such as thousand kernel weight.

These data provide fundamental insights into the biochemical and molecular adaptation of bread wheat to high-temperature stress and have important implications for the development of wheat lines that can respond to high temperatures at different times of the year.