Auxin action and auxin‐binding proteins

Abstract

SUMMARY The plant growth regulator auxin mediates an enormous range of developmental and growth responses, some of which are manifest rapidly and others manifest only after considerable lag periods. The protein that perceives auxin, the auxin receptor, has been sought by many laboratories and the search has identified a good number of candidates. However, a receptor must not only bind auxin, but also transduce the auxin stimulus into the responses we recognize. Finding evidence for this second condition has always proved very demanding. A key requisite is a convenient assay for auxin activity and preferably one involving a rapid response because this is likely to be linked directly to the perception event. For one auxin‐binding protein (ABP1) there is growing evidence that it is a functional auxin receptor. The assays used in this work have been rapid auxin‐induced changes in protoplast electrophysiology. There are many other responses induced rapidly by auxin for which a link to ABP1 has yet to be established. We have reviewed the whole range of rapid auxin‐mediated responses and by doing so we hope to have provided a comprehensive picture of the many events to which a receptor (or receptors) must connect. Against this framework we match the known properties of all putative receptors, including ABP1. Not only have we tried to identify auxin‐binding proteins unlikely to be receptors, but we also highlight the remaining gaps in our understanding of the more likely receptor candidates.

Developmentally Regulated Expression of a Peptide:N-Glycanase during Germination of Rice Seeds (Oryza sativa) and Its Purification and Characterization

“…(b) When auxin, one of the plant hormones, activated a plant cell, the apoplast area was always acidified first (36,37), and this should be accompanied by K ϩ ion flux inward into the cytosol. The properties clarified for the purified PNGase Os in this study can be related to the physiology of the germinating rice seed.…”

Ca2+-Stimulated Exocytosis in Maize Coleoptile Cells

“…Assuming that the number of fusion sites on the plasma membrane is limited, it would be essential to increase the speed of the membrane fusion process to avoid a logjam of vesicles arriving at increased rates. Such a situation would occur during auxin-stimulated growth of coleoptiles when the rates of both vesicle and secretory cargo production as well as the presence of [Ca 2ϩ ] cyt all increase roughly within the same period of time (reviewed in Napier, 1995;Napier and Venis, 1995).…”

“…For cell elongation, new membranes, proteins, and polysaccharide compounds must be delivered to the plasma membrane-cell wall interface (reviewed in Napier and Venis, 1995). Comparative electron microscopic studies of elongating cells in the apex of grass coleoptiles have shown that growing cells have increased numbers of dictyosomes and secretory vesicles in the cytoplasm (Quaite et al, 1983).…”

Biochemical characterization of recombinant polypeptides correspondingto the predicted ²±± fold in Aux/IAA proteins

“…The plant hormone auxin, typified by the naturally prevalent indole-3-acetic acid, is a key regulator of plant growth and development [1,2]. Auxin transcriptionally activates a select set of immediate-early genes that are thought to mediate the various effects of auxin in plants [3,4].…”