Chapter 21 Cytokinins:

a diffusible and water-soluble regulators of cell division

autoclaved herring sperm DNA immature endosperm of corn (banana)

Common structure: N6-substituted aminopurines,

the structural requirements for activity

No kinetin-induced cell division occurs without auxin in the culture medium.

Cytokinins definition:

have biological activities similar to those of trans-zeatin, including

¤ induce cell division in callus cells in the presence of an auxin

¤ promote bud and root formation from callus cultures when in the

appropriate molar ratios to auxin

¤ delay senescence of leaves

¤ promote expansion of dicot cotyledons

¤ cell proliferation

¤ chloroplast differentiation

¤ nutrient mobilization

Callus: grow as a mass of disorganized, relatively undifferentiated cells

wounding inducible

de-differentiated

Crown gall: a specific type of callus, the wounding site of plants was

invaded by Agrobacterium tumefaciens, it cause the neoplastic

(tumor-forming) disease.

Sources:

yeast extract, tomato juice, banana extract, coconut milk,

transfer-RNA— hypermodified bases

Conjugated cytokinins:

¤ N3, N7, N9 with sugars

riboside: N9 attach sugar ribotide: ribose sugar moiety contains a phosphate group glycoside: even the oxygen of zeatin.

¤ is inactive form

¤ glucosidase remove the

conjugation at the side chain

¤ Dormant seeds:

high levels of cytokinin glucosides

Witches’ broom on balsam fir,

Induced by Corynebacterium fascians

Some plant pathogenic bacteria, insects, and nematodes secrete free cytokinins

Isopentenyl transferase

Dimethylally diphosphate1-hydroxy-2-methyl-2-butenyl 4-diphosphate

古森本

The sites of cytokinins biosynthesis:

root apical meristems: root-derived cytokinin in shoot development, in general

young maize embryos, young developing leaves, young fruits

the difference of physiological significance

The transported form: zeatin ribosides in the xylem exudate

The degradation of cytokinins: cytokinin oxidase

but not for O-glucoside derivatives