Overview

Auxins, cytokinins, polyamines, ethylene, … are plant growth regulators also call plant hormones or phytohormones.

They are involved in all the stages of plant life from pollinisation – inducing the fecondation and the zygotic embryo development, all the way through its development into an adult plant – to flowering, development of the fruit and senecence control.

The same phytohormones not only control the growth and development processes: for that, they are crucially involved in specific processes of division, elongation and cellular differentiation, but are also necesary in the primary and secondary metabolisms.

Auxins are produced in the apical part of the plant, in buds,   favour the rhizogenesis (development of roots) and prevent the development of the axillary buds.

Cytokinins, as for them, are produced, mainly, in the roots and favour the development of the axillary buds.

The growth regulators are very important in control of in vitro cells, tissues, organs or whole plants cultures, according to the orientation chosen: keeping in live, growing, initiation of specific organogenesis (production of organs like stems with leaves, roots, somatic embryos*), organ or shoot multiplication, etc… they are also widely used for the control of the production of secondary metabolites of various interest.

With large concentrations of cytokinins and low concentrations of auxins, the development of axillary or adventitious buds can be obtained and in this way the shoots are multiplied.

With large concentrations of auxins and low concentrations of cytokinins or no cytokinins, the rooting of the shoots can be arrived at.

With equal concentrations of the two hormones, a callus is obtained. The callus is the result of the anarchic proliferation of cells which are more or less differentiated but which cannot organise them and form tissues and distinct organs.

If the knowledge of the quantity of hormones introduced (or sometimes secreted by the plants) in the culture medium is often of great usefulness, it’s principally the nature and the quantity of the phytohormones (and the report between their concentration) naturally metabolised by the plants that are important for a fondamental approach of the phenomenons. That permits the checking and modification of their endogenous content.