Plant Growth and Development Test - 32

Cytokinins are a group of hormones. These hormones promote cell division in plant roots and shoots and they promote the growth of buds. Today there are about 200 different natural and synthetic cytokinins known to botanists. Most cytokinins are produced in the meristem of the roots. Cytokinins increase the cell division by stimulating the production of proteins needed for mitosis.

Kinetin is a type of cytokinin, a class of plant hormone that promotes cell division. Kinetin was originally isolated by Miller and Skoog et al, as a compound from autoclaved herring sperm DNA that had cell division-promoting activity. It was given the name kinetin because of its ability to induce cell division, provided that auxin was present in the medium. Kinetin is often used in plant tissue culture for inducing formation of callus and ti regenerate shoot tissues from callus.

NAA is a synthetic plant hormone in the auxin family and is an ingredient in many commercial plant rooting horticultural products; it is a rooting agent and used for the vegetative propagation of plants from stem and leaf cutting. It is also used for plant tissue culture. The hormone NAA does not occur naturally and like all auxins is toxic to plants at high concentrations. 2,4-D is also called as 2,4-dichlorophenoxy acetic acid which is also a synthetic auxin which can act as herbicide. it was used as defoliating agent as 'agent orange' during Vietnam war.

Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence. It was first recognized in 1926 by a Japanese scientist, Elichi Kurosawa, studying 'bakane', the 'foolish seedling' disease in rice. It was first isolated in 1935 by Teijiro Yabuta and Sumuki, from fungal strains (Gibberella fujikori) provided by Kurosawa. Yabuta named the isolate as gibberellin.

2,4-D is 2,4-Dichlorophenoxyacetic acid which is a synthetic auxin. It was used as 'Agent orange' - used in wide defoliation of leaves in Vietnam war. It is often used in laboratories for plant research and as a supplement in cell culture media such as MS medium. AMO 1618, Phosphan D are used to induce flowering in horticultural crops. Maleic hydrazide prevents potato and onion sprouting.

Fusarium moniliforme is also called as Gibberella fujikori. It is a most prevalent fungi associated with basic human and animal dietary samples such as corn. It is a fungal plant pathogen. It causes bakane disease in rice seedlings, by overloading them with phytohormone gibberellin as its own metabolic byproduct.

Solution

Correct answer is option C.

Explanation for correct option:

NAA is a synthetic plant hormone in the auxin family and is an ingredient in many commercial plants rooting horticultural products; it is a rooting agent and used for the vegetative propagation of plants from stem and leaf cutting. It is also used for plant tissue culture.

Cytokinins are the plant hormones which has manifold effects on plants. It includes delaying of senescence, active cell division and so on. Cytokinins increase cell division by stimulating proteins needed for mitosis. Mitosis is non-sexual cell division that occurs in all living things producing additional cells for body growth. The active principle responsible for inducing cell division was isolated first from the extracts of yeasts. Such a substance was called kientin, later the name was changed and called as cytokinin.

Correct answer: (B)

Explanation for correct option: (B)

The process of root initiation is the main function of auxin in the callus. Synthetic auxin hormones like 2,4 Dichlorophenoxy (2,4-D) acetic acid induces the process of root initiation in the callus.

Explanation for incorrect options:

(A) The excised plant part used for callus formation is explant.

(C) Embryo produced from a vegetative cell is a somatic embryo.

(D) Anther culture produces haploid plants only as there is no sexual reproduction.