Hormonal control of nitrogen acquisition: roles of auxin, abscisic acid, and cytokinin

Nitrogen is the mineral nutrient that often limits plant growth and development. In response to changes in nitrogen supply, plants display elaborate responses at both physiological and morphological levels to adjust their growth and development. Because higher plants consist of multiple organs with different functions and nutritional requirements, they rely on local and long-distance signalling pathways to coordinate the responses at the whole-plant level. Phytohormones have been considered as signalling substances of such pathways. Amongst phytohormones, abscisic acid, auxin, and cytokinins have been closely linked to nitrogen signalling. Recent evidence has provided some insights into how nitrogen and the phytohormone signals are integrated to bring about changes in physiology and morphology. In this review, the evidence is summarized, mostly focusing on examples related to nitrogen acquisition.