Activities of key enzymes in sucrose-to-starch conversion in wheat grains subjected to water deficit during grain filling

Abstract

This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodging-resistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grain-filling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.

Figure 1.

Changes of leaf water potentials of wheat during the first 22 d after withholding water. The treatments are NN + WW (•), NN + WD (○), HN + WW (▪), and HN + WD (□). Measurements were made on the flag leaves at predawn (6 am, dashed lines) and at midday (11:30 am, solid lines). Vertical bars represent ±se of the mean (n = 12) where these exceed the size of the symbol.

Figure 2.

Changes of ¹⁴C partitioning in the stems (A) and grains (B) of wheat. The ¹⁴C was fed to the flag leaves at the booting stage. The treatments are NN + WW (•), NN + WD (○), HN + WW (▪), and HN + WD (□). Arrows in the figure indicate the start of withholding water. Vertical bars represent ±se of the mean (n = 12) where these exceed the size of the symbol.

Figure 3.

Starch accumulation process (A) and SAR (B) of wheat grains. The treatments are NN + WW (•), NN + WD (○), HN + WW (▪), and HN + WD (□). SAR was calculated according to Richards' (1959) equation. Arrows in the figure indicate the start of withholding water. Vertical bars in A represent ±se of the mean (n = 6) where these exceed the size of the symbol.

Figure 4.

Changes in activities of SuSase (A), soluble AI (B), and insoluble AI (C) in wheat grains. The treatments are NN + WW (•), NN + WD (○), HN + WW (▪), and HN + WD (□). Arrows in the figure indicate the start of withholding water. Vertical bars represent ±se of the mean (n = 6) where these exceed the size of the symbol.

Figure 5.

Changes in activities of AGPase (A), SSS (B), GBSS (C), and SBE (D) in wheat grains. The treatments are NN + WW (•), NN + WD (○), HN + WW (▪), and HN + WD (□). Arrows in the figure indicate the start of withholding water. Vertical bars represent ±se of the mean (n = 6) where these exceed the size of the symbol.

Figure 6.

Changes in ABA content in wheat grains. The treatments are NN + WW (•), NN + WD (○), HN + WW (▪), and HN + WD (□). Arrow in the figure indicates the start of withholding water. Vertical bars represent ±se of the mean (n = 6) where these exceed the size of the symbol.