Auxins are produced by plant apices, i.e. root apex and shoot apex.They bring about cell elongation resulting in growth.They are diffusible substances which effect growth when in very small amounts.
Roots require lower concentrations than shoots.Auxins also exert other effects on plant growth and development. Among the effects of Auxin hormone in root and shoot are as discussed bellow;-
1. Apical Dominance: Auxins inhibit the growth of side branches.This is referred to as apical dominance.If the terminal bud is removed, side branches develop from the lateral buds.This knowledge is applied in pruning. Pruning the terminal bud removes the main sources of auxin, thus allowing side branches to sprout.
2. Growth of adventitious roots: Adventitious roots develop from the stem.Auxins stimulate the growth of such roots.
3. Parthenocarpy: This refers to the formation of fruits without fertilisation.This can be induced by treating unpollinated flowers with auxin. This phenomenon is applied in the development of seedless fruit varieties.
4. Auxins, together with other plant hormones, are involved in secondary growth, falling of leaves and ripening of fruits.