Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a severe leaf disease in wheat (Triticum aestivum). To elucidate the effect of powdery mildew on cell redox homeostasis in grains, three wheat cultivars with different resistance, Xi'nong 979 (susceptible), Zhengmai 379 (moderately susceptible), and Zhengmai 103 (resistant), were inoculated with Bgt in the field, and the changes in gene transcription and activity of the antioxidant enzymes in developing grains were analysed. The results showed that the gene expression patterns and enzyme activity changes of guaiacol peroxidase (POD), catalase (CAT), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and 1‐Cys peroxiredoxin (1‐Cys Prx) were similar under powdery mildew conditions. They increased significantly at 10–20 days after anthesis (DAA) in susceptible cultivars and at 20–30 DAA in the resistant cultivar. However, they showed a significant decrease in susceptible cultivars at 20–30 DAA. The gene expression and enzyme activity of ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) increased continuously during grain development, especially in susceptible cultivars. The results demonstrated that the antioxidant systems were induced under mild powdery mildew conditions, which was conducive to the synchronous regulation of reactive oxygen species (ROS). However, under severe powdery mildew conditions, the antioxidant systems were inhibited and the regulation of ROS was restricted, resulting in the breakdown of cell redox homeostasis. It is speculated that powdery mildew infection can inhibit the activity of some metabolic proteins (transcription factors or enzymes), change the carbon and nitrogen metabolism of grain cells, and further change the quality of wheat grains.

The effects of powdery mildew on gene expressions and activities of carbon (C) metabolism enzymes in Zhengmai 103 (resistant) and Xi'nong 979 (susceptible) are studied. Under severe powdery mildew, expressions and activities of sucrose synthase, uridine‐diphosphate glucose pyrophosphorylase, glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), and cytosolic α‐1,4‐glucan phosphorylase decrease at 20 or 25–30 days after anthesis, and total soluble sugars content also decreases. It indicates that the first part of C metabolism (sucrose degradation) changes and total C flux reduces. Meanwhile, decreases in expressions and activities of adenosine‐diphosphate glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS), starch‐branching enzyme I and II (SBEI and SBEII), and plastidic α‐1,4‐glucan phosphorylase coincide with decreases in amylopectin content, whereas increases in granule‐bound starch synthase I (GBSSI) expression and activity coincide with increases in amylose content. It shows that the second part of C metabolism (starch synthesis) changes. Therefore, powdery mildew alters C metabolism. In addition, it also induces defense responses in grains, such as the up‐regulation of a defense‐related protein endogenous α‐amylase/subtilisin inhibitor. Since GAPDH, AGPase, SSS, SBEII, and GBSSI are regulated by redox, changes of C metabolism are mainly regulated by cellular redox status.