Source-Sink Modifications Affect Leaf Senescence and Grain Mass in Wheat

Abstract

A field experiment was performed in wheat to investigate the responses of flag leaf and grain to sink/source manipulations. The results showed that half-degraining delayed but defoliation (only flag leaf left) enhanced the leaf senescence. Sink/source manipulations influenced the content of reactive oxygen species of flag leaf and the content of phytohormones including cytokinins, indoleacetic 3-acid, gibberellin 3, salicylic acid and jasmonic acid in the defoliated flag leaf (DL) and grain (DG), half-degrained flag leaf (HL) and grain (HG). An iTRAQ based quantitative proteomic analysis indicated that at 16 days after manipulation a total of 97 and 59 differentially expressed proteins (DEPs) from various functional categories were observed in HL and DL groups, respectively, compared with control and 115 and 121 DEPs were observed in HG and DG groups, respectively. GO annotation terms of DEPs mainly included carbon fixation, hydrogen peroxide catabolic process, chloroplast and cytoplasm, oxidoreductase activity and glutamate synthase activity in flag leaf of manipulated plants; organonitrogen compound metabolic process, cytoplasm, vacuolar membrane, CoA carboxylase activity, starch synthase activity and nutrient reservoir activity in grain of manipulated plants. KEGG pathway enrichment analysis revealed that photosynthesis, carbon, nitrogen and pyruvate metabolisms and glycolysis/gluconeogenesis were the most remarkable processes for sink/source manipulations. Sink/source manipulations affected the activities of - and {beta}- amylases and proteinases. Ultimately, manipulations changed the mass per grain. In conclusion, manipulations to change the sink/source ratio affect the levels of hormones, activities of hydrolytic enzymes, metabolisms of carbon, nitrogen and other main compounds, stress resistance, the leaf senescence, and ultimately influence the grain mass.