Photosynthetic acclimation of wheat (<i>Triticum aestivum</i>) to winter

Overwintering performance limits the distribution range and yield of winter wheat (Triticum aestivum). Systematic research on the overwintering strategies of wheat is lacking. We conducted a detailed analysis of structural, physiological, and metabolic changes in the wheat leaves of plants growing at coordinates 36°11'N, 117°7'E from autumn to the following spring. Light-heat resources and multiple stresses, including cold, bright light, and repeated freeze-thaw cycles, coexist in winter. Wheat leaves retained a complete photosynthetic apparatus, induced sustained nonphotochemical quenching (NPQ) during the cold period in winter, and relaxed NPQ rapidly during the warm period. Thus, the photosynthetic apparatus of wheat switched quickly between photosynthetic carbon assimilation and the photoprotective state during the winter. This response is different from that of evergreen conifers, which cease growth and photosynthetic carbon assimilation and are in a photoprotective state throughout the winter. The unique overwintering strategy of wheat allows it to effectively use light-heat resources in winter but leads to oxidative damage to the biomembrane and an imbalanced cellular redox, despite increased levels of the secondary metabolites phenylpropanoid and antioxidant flavonoids, restricting the expansion of winter wheat to colder regions.