Cytokinin |
Occurrence: Cytokinins are found both in free and as constituents of tRNA of higher plants, algae, yeasts, bacteria and mosses. The root tips, shoot tips, developing fruits, xylem sap, germinating seeds and tumour tissues of higher plants are the good sources of cytokinins. The root tip contains more cytokinin than other tissues of the root. It is synthesized in root tips and moves upward through xylem cells. The cytokinin concentration increases before flowering and decreases during senescence of plant organs. Its concentration also lowers in resting buds than the active one.
Biosynthesis: The roots (tips) and developing seeds (embryos) are the major sites of cytokinin synthesis in the plants. The biosynthesis of cytokinins is not completely known however cytokinins may biosynthesize by hydrolysis of tRNA to mononucleotides. Some scientists suggested that biosynthesis path of cytokinins is similar to that of isopentenyle adenosin-5-phosphate (isopentenyle AMP) and Adenine. The modification of adenine produces the cytokinins. The cytokinins mainly degrade by the enzyme cytokinin oxidase.
Antagonists: The compounds like 4-cyclopentylamino-2-methylthiopyrrolo pyrimidine, N-benzyl-N, phenylurea and N-benzyl-N-3-4-diphenylurea show anticytokinins activity. The RNA and protein synthesis inhibitors also inhibit cytokinins action.