Physiological and Proteomic Analyses Indicate Delayed Sowing Improves Photosynthetic Capacity in Wheat Flag Leaves Under Heat Stress

Abstract

Background and aims: Climate warming has become an indisputable fact, and wheat is among the most heat-sensitive cereal crops. Heat stress during grain filling threatens global wheat production and food security. Here, we analyzed the physiological and proteomic changes by delayed sowing on the photosynthetic capacity of winter wheat leaves under heat stress. Our aim is to provide a new cultivation way for the heat stress resistance in wheat.

Methods: Through 2 years field experiment and an open warming simulation system, we compared the changes in wheat grain weight, yield, photosynthetic rate, and chlorophyll fluorescence parameters under heat stress at late grain-filling stage during normal sowing and delayed sowing. At the same time, based on the iTRAQ proteomics, we compared the changes of differentially expressed proteins (DEPs) during the two sowing periods under high temperature stress.

Key results: In our study, compared with normal sowing, delayed sowing resulted in a significantly higher photosynthetic rate during the grain-filling stage under heat stress, as well as significantly increased grain weight and yield at maturity. The chlorophyll a fluorescence transient (OJIP) analysis showed that delayed sowing significantly reduced the J-step and I-step. Moreover, OJIP parameters, including RC/CSm, TRo/CSm, ETo/CSm, DIo/CSm and ΦPo, ψo, ΦEo, were significantly increased; DIo/CSm and ΦDo, were significantly reduced. GO biological process and KEGG pathway enrichment analyses showed that, among DEPs, proteins involved in photosynthetic electron transport were significantly increased and among photosynthetic metabolic pathways, we have observed upregulated proteins, such as PsbH, PsbR, and PetB.

Conclusion: Physiological and proteomic analyses indicate delaying the sowing date of winter wheat reduced heat dissipation by enhancing the scavenging capacity of reactive oxygen species (ROS) in flag leaves, and ensuring energy transmission along the photosynthetic electron transport chain; this increased the distribution ratio of available energy in photochemical reactions and maintained a high photosynthetic system assimilation capacity, which supported a high photosynthetic rate. Hence, delayed sowing may represent a new cultivation strategy for promoting heat stress tolerance in winter wheat.

Keywords: delayed sowing; heat stress; photosynthetic capacity; proteomics; wheat.

FIGURE 1

The average temperature of the air at the flag leaf layer between delayed sowing and normal sowing during heat stress (19–21 DAA). (A,B) Are delayed sowing and normal sowing in the 2017–2018 growing seasons, respectively. (C,D) Are delayed sowing and normal sowing in the 2018–2019 growing seasons, respectively. NT, Natural temperature; HT, Temperature under heat stress.

FIGURE 2

Effect of delayed sowing on grain number, grain weight, and grain yield of wheat under heat stress at late grain–filling stage. Values are means of three replicates per treatment. Vertical bars indicate standard error. Different letters denote statistical differences by LSD test (P < 0.05) between treatments for each parameter in the same year.

FIGURE 3

Effect of delayed sowing on photosynthetic rate of wheat flag leaves under heat stress at late grain–filling stage. With a gray area from 19 to 21 DAA. Values are means of three replicates per treatment. Vertical bars indicate standard error.

FIGURE 4

Effect of delayed sowing on antioxidant enzymes activity and MDA content of wheat flag leaves under heat stress at late grain-filling stage.

FIGURE 5

JIP-test curve of relative variable fluorescence intensity before heat stress. (A,C) Are JIP-test curve of relatively variable fluorescence on the third day before heat stress in the 2017–2018 and 2018–2019 growing seasons, respectively. (B,D) Are JIP-test curve of relatively variable fluorescence on the third day after heat stress in the 2017–2018 and 2018–2019 growing seasons, respectively.

FIGURE 6

Enrichment analysis of differential protein. (A) GO biological process analysis. (B) KEGG pathway analysis. The bars represent –log10(P) where P represents the Fisher’ exact test P-values.

FIGURE 7

DEPs involvement photosynthetic were mapped in the metabolic pathway by KEGG analysis (red represents upregulated protein).