What are phyto-ho

Plants need light, water, oxygen and nutrition to grow and develop. All these qualify as extrinsic factors. While extrinsic factors are important, did you know that plant growth depends on intrinsic factors too? They can be intracellular genes or intercellular chemicals. These chemicals are called Plant Growth Regulators or plant hormones or phyto-hormones.

Phyto-hormones are defined as small, simple chemicals produced naturally by plants to regulate their growth and development.

Plant Growth Regulators can be of a diverse chemical composition such as gases (ethylene), terpenes (gibberellic acid) or carotenoid derivates (abscisic acid). Based on their action, they are broadly classified as follows:

• Plant Growth Promoters – They promote cell division, cell enlargement, flowering, fruiting and seed formation. Examples are auxins, gibberellins and cytokinins.

• Plant Growth Inhibitors – These chemicals inhibit growth and promote dormancy and abscission in plants. An example is an abscisic acid.

Note: Ethylene can be a promoter or an inhibitor, but is largely a Plant Growth Inhibitor.

All plant growth regulators were discovered accidentally

For example:

Auxin- This hormone is present in the seed embryo, young leaves, and apical buds' meristem.

Functions of Auxins

a) Stimulation of cell elongation, cell division in cambium, differentiation of phloem and xylem, root initiation on stem cuttings, lateral root development in tissue culture

b) Delaying leaf senescence

c) Suppression of lateral bud growth when supplied from apical buds

d) Inhibition or promotion of fruit and leaf abscission through ethylene stimulation

Cytokinin- They are synthesized in roots and then transported to other parts of the plant.

Functions of Cytokinins

a) Stimulation of cell division, growth of lateral buds, and apical dominance

b) Stimulation of shoot initiation and bud formation in tissue culture

c) Leaf cell enlargement that stimulates leaf expansion

d) Enhancement of stomatal opening in some plant species