The discovery of cytokinins and its physiological function

Cytokinins are a class of plant hormones with adenine ring structure. The common feature is in the sixth position of adenine ring has a specific substituent. Their physiological functions prominently performance in promoting cell division and induce bud formation.

In 1948 U.S. Skog and China Cui Cheng found adenine in tobacco tissue cultures can induce tobacco pith tissue differentiation and budding. In 1955 Miller in the degradation product of yeast DNA and herring sperm’s DNA purified from a substance can promote cell division, known as kinetin, its chemical structure is furan methyl adenine, also known as furfuryl gland purine. In 1963 Latham from the 11-16 days fertilized corn seeds isolated the first one natural cytokinin exist in the higher plants, and named zeatin. Currently had been get several adenine derivatives from the higher plants, such as dihydro zeatin, zeatin riboside and isopentenyl adenine. Now there are a variety of synthetic similarly materials, such as benzyl adenine, tetrahydropyranyl benzyl adenine. They are known as cytokinin.

Root meristem (apical) synthesize cytokinin is the most active, long-range transport through the xylem from the root to the stem. Leaves, buds, young fruit and developing seeds can be formed cytokinin, zeatin is the first obtained from the maize immature seeds. Cytokinin can produce by transfer RNA cleavage, also can through medroxyprogesterone valerate and adenine as a precursor synthesis.

As a plant growth regulator, cytokinin has a variety of physiological effects. Its physiological effects were as follows: firstly, promote cell division, cytokinins main physiological function is to promote cell division. Auxins, gibberellins and cytokinins have the effect of promoting cell division, but each of them has different role. Auxin is only promoting nuclear division, which has nothing to do with the division of the cytoplasm. The cytokinin was mainly worked on the cytoplasmic division. Second, promote buds division. Promote bud differentiation is one of the important physiological effects of cytokinin, some emperor detached leaves treated with cytokinin, the leaf margins basal veins can produce buds. Third, promote cell expansion. Cytokinins can promote some of dicotyledonous plants such as beans, radish expanding cotyledon or leaf discs, mainly because such expansion promotes cell lateral thickening. Fourth, promote lateral bud developing, eliminating the top edge. Cells can release the apical dominance caused by growth hormone, promote lateral bud growth and development. Such as pea sprouts dropped cytokinin solution in leaf axils part, buds can grow and develop. Fifth, delay leaf aging. If partially coated with cytokinin in detached leaves, the remaining parts of the leaves yellowing and aging, smear kinetin parts remain bright green. Due to the cytokinin have the effect of remaining green and anti-aging, so it can be used to deal with fresh fruit and flowers to remain fresh and green, prevent fruit drop. For example, with cytokinin to treat young citrus fruit can significantly prevent fruit drop, and overstriking stems, dark green fruit, compared with the control group, the fruit also significantly increased. Break seed dormancy. Need light seeds, such as lettuce and tobacco could not germinate in the dark, use cytokinin can instead of light to break the dormancy of this seed, promote germinating.

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