Question

Name four plant hormones?

Answer 1

Hint: Plant hormones are the small, organic substances of different chemical composition. The plant hormones involved in the promotion, inhibition and modification of the plant. Plant hormones are also known as plant growth regulators or phytohormones.

Complete answer:
There are many plant hormones which are present in the plants:
> Auxins: Auxins was the first hormone to be discovered. It was first isolated from human urine samples. Auxins were also isolated from the tips of coleoptiles of oat seedlings by F.W. Went. Auxins stimulate the root formation on stem cuttings. Auxins such as IAA and IBA in diluted form are used to produce Parthenocarpic or seedless fruits, e.g., tomatoes. The auxins are widely used in agricultural and horticultural practices. Tryptophan (amino acid) is the precursor of Auxin.
> Gibberellins: The precursor of this hormone is Acetyl-CoA. This hormone stimulates stem elongation and other aerial parts. Gibberellins stimulate the synthesis of various types of hydrolytic enzymes such as amylases and proteases.
> Cytokinins: The first natural cytokinins were isolated from the unripe maize grains or kernels. This hormone helps in the production of new leaves and chloroplast in leaves. It also stimulates the lateral shoot growth and adventitious shoot formation. Cytokinins delay the ageing of leaves and other organs by controlling protein synthesis. Cytokinins are important for cytokinesis (division of cytoplasm).
> Abscisic acid (ABA): The precursor of ABA is violaxanthin. ABA promotes abscission of flowers and fruits. ABA acts as a growth inhibitor and induces dormancy of buds and seeds. ABA inhibits the protein and RNA synthesis.

Note: Plant hormones are classified into two groups on the basis of functions performed in the plant body: Plant growth promoters (Auxin, gibberellins and cytokinins) and plant growth inhibitors (ABA). Ethylene is the only gaseous plant hormone and it is synthesized in almost all plant parts like roots, leaves, flowers and fruits etc.