Fig. 10.

A proposed model depicting the role of cytokinin in C:N homeostasis. Cytokinin restores the C:N balance by down-regulating NO₃^– uptake in a C-status-dependent manner: when grazing or inorganic N application leads to a decrease in the C:N balance, cytokinin serves as a signal to mediate the down-regulation of NO₃^– uptake in roots and the up-regulation of NO₃^– assimilation in the re-growing shoots, thereby re-balancing the C and N resources at the whole-plant level.