Intact plant cytokinins

Cloning. Asexual propagation (cloning) of plants ordinarily occurs by virture of the ability of embryonic meristematic tissue to differentiate into roots and shoots. If isolated phloem cells or other more differentiated cells are cultured, the result is often the formation of a callus, a dedifferentiated mass of cells somewhat reminiscent of embryonic cells. Under proper conditions, e.g., in a coconut milk culture and in the presence of the correct auxin-to-cytokinin ratio, some carrot root phloem cells revert to embyronic cells and develop into intact plants.99 This experiment provided proof that the differentiated carrot phloem cells... 

Although considerable data now implicate particular hormones in the control of senescence, data which demonstrate and integrate the specific hormonal control systems that function in intact plants are limited. A model for hormonal control of monocarpic senescence proposed by Woolhouse will not be considered here, because it is mostly incorrect and it is discussed elsewhere [19]. The hormonal regulation of leaf senescence as a component of monocarpic senescence in soybean is a case where we can begin to relate specific hormones to the correlative controls. At this time, the role of cytokinins (Section 2) and the nature of the senescence signal (Section 3) warrant special consideration. 

Various data indicate that phytohormones modulate protein phosphorylation in plant cell nuclei. For example, 2,4-D-pretreatment of soybean hypocotyls activated in vitro protein phosphorylation in isolated nuclei, and this was consistent with an in vivo increase of RNA synthesis [12]. Other phytohormones also alter nuclear protein phosphorylation in plants, and these include ABA [23], GA3 [25] and cytokinins [15]. However, in all these experiments phytohormones were applied to intact plants or to isolated plant organs. Therefore, the hormonal modulation of nuclear protein phosphorylation could be an indirect result of earlier cell response to the phytohormone. 

This chapter is intended to provide an overview of the functions of the five major plant growth hormones in the intact plant auxin (lAA), gibberellins (GA), cytokinins (K), ethylene, and abscisic acid (ABA). The effects of these hormones have been described in detail on numerous occasions over the last 10 years (see general references at the end of this chapter). This review utilizes these previous reviews as well as including a survey of the literature published between January 1977 and January 1980. The most recent and surely the most detailed treatment of the subject is to be found in Phytohormones and Related Compounds A Comprehensive Treatise. D.S. Letham et al., Volumes 1 and 2, 1978. The intent of the present review is to provide a more general overview and to consider overall patterns of regulatory controls by hormones in the whole plant. 

In earlier work, [ H]-[9R]Z was supplied to the transpiration stream of both de-rooted and intact blue lupin (Lupinusangustifolius L.) plants [2]. Features of this work included (1) the very low proportion of [9R]Z which moved to the seed, although [9R]Z reached the pod walls in significant amounts and tended to be conserved therein (2) the direct lateral movement of [9R]Z and/or related cytokinins from xylem to bark (all tissues outside secondary xylem) (3) the detection of a metabolite, or closely related metabolites, of unknown nucleotide-like structure in pod walls, stem bark and developing lateral shoots. For convenience, the metabolites were all designated U-NT (meaning unknown nucleotides), because all... 

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