PRODUCTION OF AUXINS AND THEIR EFFECTS ON PLANT GROWTH
- 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.
- The effect of auxins on the growth of roots and shoots has already been discussed.
- Auxins also exert other effects on plant growth and development.
- There are various other chemical substances which have been shown to influence plant growth and development.
Effects of Auxin on Plant Growth
- 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.
- As long as the main stem is allowed to remain intact, the development of side branches is suppressed.
- Pruning the terminal bud removes the main sources of auxin, thus allowing side branches to sprout.
Growth of adventitious roots
- Adventitious roots develop from the stem.
- Auxins stimulate the growth of such roots.
- 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.
- Auxins, together with other plant hormones, are involved in secondary growth, falling of leaves and ripening of fruits.