Cytokinins
or CKs are a group of chemicals that influence cell division and shoot
formation. They were called kinins in the past when the first cytokinins
were isolated from yeast cells. They also help delay senescence
of tissues, are responsible for mediating auxin transport throughout
the plant, and affect internodal length and leaf growth. They have a
highly synergistic effect in concert with auxins, and the ratios of
these two groups of plant hormones affect most major growth periods
during a plant's lifetime. Cytokinins counter the apical dominance
induced by auxins; they in conjunction with ethylene promote abscission
of leaves, flower parts, and fruits.The correlation of auxins and cytokinins in the plants is a constant (A/C = const.).