Reproductive organs regulate leaf nitrogen metabolism mediated by cytokinin signal.

The metabolism of vegetative organs in plants changes during the development of the reproductive organs. The regulation of this metabolism is important in the control of crop productivity. However, the complexity of the regulatory systems makes it difficult to elucidate their mechanisms. To examine these mechanisms, we constructed model experiments using Arabidopsis to analyze metabolic and gene expression changes during leaf-stage progression and after removal of the reproductive organs. Leaf gene expression levels and content of major amino acids, both of which decreased during leaf-stage progression, increased after removal of the reproductive organs. In particular, the levels of expression of cytokinin biosynthesis genes and cytokinin-responsive genes and the cytokinin content increased after removal of the reproductive organs. Analysis of plants with knockout of a cytokinin-biosynthetic gene (AtIPT3) and a cytokinin receptor gene (AHK3) indicated that glutamate dehydrogenase genes (GDH3) were regulated by cytokinin signaling. These data suggest that cytokinins regulate communication between reproductive and vegetative organs, and that GDH3 is one target of the cytokinin-mediated regulation of nitrogen metabolism.