Plant Growth and Hormones

Cytokinins are plant hormones that specifically promote cell division (cytokinesis) and are involved in promoting root formation in tissue culture. They work in conjunction with auxins - high cytokinin to auxin ratio promotes shoot formation, while low ratio (more auxin) promotes root formation. However, cytokinins themselves are directly associated with promoting root initiation in tissue culture experiments. Options A, B, and D are not the primary functions of cytokinins.

Kinetin (6-furfurylaminopurine) is a synthetic cytokinin, a class of plant growth regulators that promote cell division. The structure consists of a purine base (adenine) with a furfuryl amino group attached at the 6-position. It was the first cytokinin discovered and is used extensively in tissue culture.

 Sprouting of dormant buds of a potato tuber can be induced by GA.

Cytokinins are concentrated in regions of active cell division: embryos (rapidly dividing), developing fruits (cell expansion and division), and root tips (apical meristems). This distribution reflects their primary role in promoting cytokinesis. While present in other tissues, the highest concentrations are found in these metabolically active regions.

Gibberellic acid (GA) is a plant hormone that stimulates the production of alpha-amylase enzyme in the aleurone layer of barley seeds during germination. This enzyme breaks down starch into sugars, providing energy for the growing embryo. Pectinase, cellulase, and protease are not induced by GA in this context.

Cytokinins are plant hormones that delay senescence (aging) by promoting cell division and preventing protein degradation. They act as anti-aging hormones in plants. Gibberellins promote elongation, auxins regulate growth, and ethylene promotes ripening and senescence.

Cytokinins (CK) are a class of plant growth substances (plant hormones) that promote cell division, or cytokinesis, in plant roots and shoots. These are primarily involved in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence.

Gibberellins were first isolated from the fungus Gibberella fujikuroi, which causes foolish rice disease (excessive elongation). They are plant hormones that promote growth.

Gibberellins were first discovered from the fungus Gibberella fujikuroi causing foolish seedling disease in rice. Kinetin (a cytokinin) was isolated from herring sperm DNA. Auxins occur naturally in plants, and 2,4-D is synthetic. Ethylene is a gaseous hormone produced by plants.

F.W. Went's classic Avena coleoptile experiment (1928) demonstrated that the curvature response was directly proportional to the concentration of auxin. By placing agar blocks containing different auxin concentrations on decapitated coleoptiles, he showed that higher concentrations produced greater curvature - establishing the quantitative relationship between auxin and tropic response.

Coumarin is a phenolic hormone.

It is a natural auxin known as auxin-b.

By adding auxin and sugar, continued growth of callus may be obtained and new shoots and even new plants can be produced from the callus.

Apical dominance is exhibited by auxins as their presence in the tip stimulates the growth of apical bud, but suppresses the growth of lateral buds.

Gibberellins function in both conversion of dwarf plants into normal plants and Parthenocarpic development of fruits.