ISSN:
1573-5087
Keywords:
auxin binding isotherm
;
auxin receptor
;
dose response curve
;
H+-ATPase
;
iIndole-3-acetic acid
;
Oryza sativa
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract An auxin receptor protein, isolated from the soluble fractionsof rice shoots and roots, was characterised in terms of the affinity andspecificity for IAA and the modulating effect onH+-ATPase of plant plasma membrane. The receptor proteingives a biphasic binding isotherm for IAA, indicating the existence ofthe primary and secondary binding sites. The predominant isoform of thereceptor in roots shows much higher affinity to IAA compared with thatin shoots. Being monomeric protein with about the same molecular mass(57–58 kDa) and showing a similar chromatographic behaviour, bothisoforms mediate IAA-induced modulation of the plasma membraneH+-ATPase in the respective IAA concentration rangesseparated by ca. 3 orders of magnitudes(10-10–10-7 M vs.10-7–10-4 M). Analysis of kinetic data ofthe H+-ATPase activity revealed that the receptor perse functions as an effector of the enzyme, causing a decrease inKm and an increase in Vmax through protein-proteininteraction at a 1:1 ratio. Further, it appeared that, while IAAdoes not affect by itself the kinetic parameters of theH+-ATPase, the auxin exerts its effect via thereceptor, biphasically regulating the efficiency of the effectormolecule probably by inducing two-phase conformational changes thatinvolve IAA binding to two separate binding sites. It was also foundthat other active auxins examined, such as indole-3-propionic acid,1-naphthalene acetic acid and 2,4-dichlorophenoxyacetic acid, do notwork together with the receptor to elicit the same response of theH+-ATPase as seen with IAA.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1010745310101
