Plant hormone binding site

Venis MA (1985) Hormone binding sites in plants. Longman, London... 

M. A. Venis, Hormone Binding Sites in Plants Longman, New York (1985). 

With the availability of labeled hormones of high specific activity and the application of the principles of affinity chromatography, researchers were able to isolate cellular proteins that bind to plant hormones in vitro. Such proteins have been referred to as receptor proteins, binding proteins, or acceptor proteins. Tacit in the concept of hormone receptor proteins is the stereo-specific interaction of the hormone and the receptor protein (19). The resulting hormone-protein complex participates in growth processes that depend on new or enhanced protein synthesis. Advances in molecular biology and related sciences have enabled many researchers to study the role of receptors in the control of nuclear functions or other activities and to determine the site of primary hormonal action. 

At physiological pH in plants, polyamines exist as proton-ated forms. These protonated forms bind to the negatively charged phospholipid head groups and other anionic sites in membranes and alter the stability and permeability characteristics of such membranes. Polyamines also stabilize chloro-plast thylakoid membranes and retard chlorophyll loss in senescing barley leaf tissue. Polyamines also influence membrane fluidity, affect membrane localized proton pumps, and alter plant hormone responses, perhaps by competing for... 

The characterization of receptors for plant hormones has just started, in spite of the description of different proteins or membrane fractions able to bind hormones [4]. For ABA only Hornberg and Weiler [6] have succeeded so far in such a receptor characterization. They used photoaffinity labeling to cross-link radio-labeled ABA to putative binding sites at the plasmalemma of Vicia faba guard cell protoplasts and obtained high-affinity (Kd = 3-4 nM) binding sites which were specific for those protoplasts. 

Binding sites for plant hormones are often located in membranes, although numerous cytoplasmic binding sites have been reported [26, 31]. The brassino-steroids, by analogy, possibly bind in the nucleus, although this has not been determined. What role the cytoplasmic binding sites might play is entirely obscure. 

Zbell B. and Walter, G. 1987. About the research of the molecular action of auxin binding sites on membrane localized rapid phosphoinositide metabolism in plant cells. In Plant Hormone Receptors. Ed. D. Klambt, Springer Verlag - Berlin, pp. 143-53. 

Most considerations of plant lectin function revolve around the carbohydrate binding activities of these proteins. Yet, as discussed in a previous section of this chapter, additional activities are associated with some of these lectins. These activities must also be taken into account in considering the possible roles of these proteins. For example, a major class of plant hormones, the cytokinins, are derivatives of adenine that bind with high affinity to the hydrophobic binding sites found on some of the legume seed lectins and at least one seed-like vegetative tissue lectin [20, 30]. It is of interest that the specificity of this site, when present, appears to have... 

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