The common plant hormones are: auxins, giberellins and cytokinins.
Hormones are growth regulatory substances produced endogenously in plant. Generally their site of biosynthesis and site of action are different.
Common plant hormones are auxins, gibberellins and cytokinines. These have specific physiological role in plant growth.
Auxins are mainly concerned with cell enlargement. These also play role in Photo-tropic and geo-tropic movements in plants. These also contribute to initiation of lateral roots.
Gibberellins cause stem elongation. These play crucial role in flowering of plants. The photoperiodic responses in flowering are mediated through production of endogenous gibberellins under specific photoperiod.
Cytokinins play role in cell division. These along with auxins play crucial role in the process of differentiation. The callus, undifferentiated mass of cells, develops into shoot alone if concentration of cytokinins is more as compared to that of auxins and develops into roots only if concentration of auxins is more as compared to that of cytokinins.
The balanced amount of auxins and cytokinins in the culture medium leads to development of callus into both shoot and root tissue.