Influence of Cytokinin on Plastid Biogenesis in Rye Leaves

Abstract

Cytokinins are known to promote the multiplication and growth of higher plant cells (for review see Kende, 1971). Besides this general growth-promoting action they appear to exert some specific influence on the differentiation of chloroplasts, which has been the subject of our own research, as well as on the stability of chloroplasts during leaf senescence (for review see Parthier, 1979). The specific quality of the plant response to cytokinin is, however, not universally and exclusively determined by the hormone, but primarily depends on the physiological conditions, the specific stage of differentiation, and the genetic competence of the individual target tissue, so that even in different organs or tissues of the same plant cytokinin can be employed as a trigger to initiate the expression of quite opposing types of response. Thus, in the shoot organs of rye seedlings, the experimental system with which we have been working, cytokinins promote the growth of the leaves but, in complete contrast to their well-known senescence-retarding action in leaves, enhance the onset of senescence in the coleoptiles, including the degradation of nucleic acids and protein (de Boer and Feierabend, 1978; Sossinka and Feierabend, 1978). In order to respond to an exogenously applied hormone, the tissue must not only be genetically competent but must also have a deficiency of this hormone. While a kinetin treatment clearly stimulated the growth of rye leaves at 22°C, it had, for instance, no effect on their protein and enzyme formation at 2°C (Feierabend, 1970a).