BIOL 266 MT2 - Cytokinins

Third of the hormones from the list of five

“Cytokinins”, a hormone that promotes cell division (hence the name). Promotes tissue culture.

Plant Tissue Culture and Cytokinins

Used to identify the nature of cytokinins. They started with a small amount of plant tissue (very little) and over time, the plants would grow from nothing.

Two main methods: Callus Culture & Suspension Culture.

Callus used small chunks of plant tissues on an agar plate.

Suspension culture used much more smaller (microscopic level) chunks of plant tissue on a liquid medium, looking as if droplets suspended on clear liquid.

Cytokinin Research

Coconut milk was used to conduct cytokinin research. The mediums used to research cytokinin were inorganic salts, auxin, sugars, and coconut milk. Coconut milk was shown to have promoted cell division. As for other non-coconut milk products, old yeast extract had very active microbiology processes and demonstrated rapid cell division.

This lead to the reasoning that purine (adenine and guanine) or DNA was cytokinin. For instance, herring sperms, when its compounds were isolated, was shown to promote cell-division activities. These cell-breakdown/division activities were DNA breakdown products.

Herring sperms have an active ingredient named kinetin which regulated plant growth. It is however not a plant hormone,

Kinetin

A plant growth regulator but not a plant hormone (meaning not produced by plants).

Cytokinins in plants

Are synthesized in roots and in sites of cell division (aka vascular cambium, responsible for iincreasing and elongating plant tissue.) Especially important in apical dominance (controlling where the shoot grows). Applying cytokinins to the axillary bud makes the bud grow.

High auxin : Cytokinin ratio - Supresses axillary bud growth. (remember: auxin inhibits budding).

Low auxin : Cytokinin ratio - Axillary buds grow.

Organogenesis

Organogenesis is done through manipulating Auxin:CK ratios.

Low auxin:CK ratios causes root formation or embryogenesis.

High auxin:CK ratios causes shoot formation.

Cytokinin, Auxins, and bacterial production (Plant Gall Disease)

Cytokinins and Auxins can also be produced by bacteria. When a bacterium infects a plant cell, the plasmid is incorporated into the plant DNA. This causes the plasmid to produce hormones that utilize hormones present in the plant DNA (parasitizing it, almost, using the hosts’ resources to make the parasite’s needs).

This causes the plasmid to code for carbon/nitrogen compounds that serve as food source for the bacterium.

Bacterium Plasmid and Plant Transformation

Scientists have been able to successfully disarm the plasmid so that it no longer codes for Opine (a food resource the plasmid generates for the bacterium). The site is then restricted, and then a desire plant gene is inserted into the T-DNA (restricted region) of the plasmid. This gene, inside the plasmid, will now function as the “resource" that the bacterium will generate inside a plant cell. This bacterium is introduced into the cells of plants where they can transform a variety of plant species.