Effect of terminal heat stress on osmolyte accumulation and gene expression during grain filling in bread wheat (Triticum aestivumL.)

Abstract

AbstractThe grain‐filling stage inTriticum aestivum(wheat) is highly vulnerable to increasing temperature as terminal heat stress diminishes grain quality and yield. To examine the mechanism of terminal heat tolerance, we performed the biochemical and gene expression analyses using two heat‐tolerant (WH730 and WH1218) and two heat‐sensitive (WH711 and WH157) wheat genotypes. We observed a significant increase in total soluble sugar (25%–47%), proline (7%–15%), and glycine betaine (GB) (22%–34%) contents in flag leaf, whereas a decrease in grain‐filling duration, 1000‐kernel weight (8%–25%), and grain yield per plant (11%–23%) was observed under the late‐sown compared to the timely sown. The maximum content of osmolytes, including total soluble sugar, proline, and GB, was observed in heat‐tolerant genotypes compared to heat‐sensitive genotypes. The expression of 10 heat‐responsive genes associated with heat shock proteins (sHsp‐1,Hsp17, andHsfA4), flavonoid biosynthesis (F3′‐1andPAL), β‐glucan synthesis (CslF6andCslH), and xyloglucan metabolism (XTH1,XTH2, andXTH5) was studied in flag leaf exposed to different heat treatments (34, 36, 38, and 40°C) at 15 days after anthesis by quantitative real‐time polymerase chain reaction. A significant increase in the relative fold expression of these genes with increasing temperature indicated their involvement in providing heat‐stress tolerance. The high differential expression of most of the genes in heat‐tolerant genotype “WH730” followed by “WH1218” indicates the high adaptability of these genotypes to heat stress compared to heat‐sensitive wheat genotypes. Based on the previous results, “WH730” performed better in terms of maximum osmolyte accumulation, grain yield, and gene expression under heat stress.