Separation and localization of two classes of auxin binding sites in corn coleoptile membranes

Abstract

Further evidence is presented for the discrete nature of the two classes of high affinity auxin binding sites in corn (Zea mays L.) coleoptile membranes, site 1 and site 2. Fractions can be obtained by differential centrifugation that exhibit binding kinetics characteristic of site 2, but not site 1. Membrane preparations containing both binding sites may be resolved on sucrose gradients into a light and a heavy band, whose binding kinetics and analogue binding specificities correspond to those deduced for site 1 and site 2 respectively in unfractionated membranes. Evidence from enzymic and chemical assays and from electron microscopy suggests that site 2, the auxin-specific binding site, is located in fractions enriched in plasma membrane, whereas site 1 is associated with Golgi membranes and/or endoplasmic reticulum.

Molecular cloning and structural analysis of a gene from Zea mays (L) coding for a putative receptor for the plant hormone auxin

“…control of elongation growth, cambial activity and fruit development (Davies, 1987). Both natural and synthetic auxins have been found to bind to membrane-associated binding sites of Zea mays with relative affinities correlated with their ability to produce shoot elongation in the same tissue (Batt and Venis, 1976;Ray, 1977). These sites are concentrated in microsomes of maize coleoptiles and primary leaves which respond strongly to auxin by elongation, while their concentration is reduced in roots or completely absent in tissues from the coleoptile internode.…”

“…The level of expression is low in roots, stems and leaves; however, in comparison to the roots the expression is elevated in the style and in the ears, by -6-and 9-fold respectively. (Venis, 1985), particularly in fractions believed to be derived from the tonoplast , the plasmalemma (Batt and Venis, 1976;Dohrmann et al, 1978) and the ER Ray et al, 1977), the molecular structure and function of these binding sites was not known up to now. However, as these auxin-binding sites are mainly expressed in auxin-sensitive tissues (Venis, 1985;Davies, 1987) it is likely that they are involved in the primary auxinspecific physiological response(s).…”

Demonstration of Auxin Binding to Strawberry Fruit Membranes

“…The pH optimum for the 120 K membrane fraction is 4.0 (Fig. 2), while the pH optima for vegetative tissues range from 5.0 in zucchini (12) and tobacco pith callus (32), 5.5 in com (1,23), to 8.0 in mung bean (13,33). The physiological relevance ofthis low pH optimum is unknown, but fruits in general appear to have a low pH optimum for auxin binding as evidenced by pH optima of 3.75 for cucumber fruit and 3.5 for bean and tomato fruit CM fraction (16,18).…”

Localization of the Ethylene-synthesizing System in Apple Tissue

“…It is now apparent that plasma membrane and cell wall may share proteins and glycoproteins (13,25,27,29,33,34) and hormone-binding receptors or components (4,12,20,28); also the involvement of plant hormones, viz. IAA, gibberellins, cytokinins, and ABA with ethylene production has been pointed out (8,14,15).…”