The root tip, shoot apex, and immature seeds are all rich in them.
The endogenous concentration of these molecules is in the nanomolar range.
In most tissues, several types of cytokinins and their modified forms are present.
Cytokinins can act over great distances or near the cytokinin-producing cells (paracrine signaling).
Cytokinins may also affect the cell that made them (autocrine signaling).
Cytokinins are also made by cyanobacteria, plant pathogenic bacteria (such as Agrobacterium tumefaciens, Pseudomonas savastanoi, and Rhodococcus fascians), and the slime mold Dictyostelium discoideum.