Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties

Photosynthesis and carbohydrate content of flag leaves were measured during the post-anthesis period of three spring wheat (Triticum aestivum L.) varieties grown with two levels of nitrogen supply, with ears either left intact or with the upper halves removed at anthesis. With low nitrogen supply, removing the upper half of the ear increased photosynthesis in the varieties Shasta and Anza, but not in Yecora. With high nitrogen, removing half ears inhibited photosynthesis in Yecora but had no effect on the other two varieties. Early in grain growth, halving ears decreased the contents of glucose, fructose (hexose), fructans and starch in leaves of Shasta and Anza, and increased those of Yecora, grown with low nitrogen level. The treatment of the ear increased hexose content of leaves of the three varieties supplied with high nitrogen level but had no effect on fructan and starch contents. Neither with high nor with low nitrogen level was leaf sucrose content affected by the treatment of the ear. There were significant correlations among levels of carbohydrates, the level of hexoses being most closely related to that of fructans. The rate of photosynthesis showed a significant negative regression over hexose levels