Uptake of auxins into membrane vesicles isolated from pea stems: an in vitro auxin transport system

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:6942494

Slone, J H

The objective of this research was to test the applicability of the chemiosmotic theory of auxin transport to a subcellular system. Membrane vesicles were isolated from the basal portion of the third internode of etiolated pea plants (Pisum sativum L. var. Alaska) by differential centrifugation. Uptake of auxin was determined by adding /sup 14/C-labeled indoleacetic acid (IAA) to vesicles. Nigericin, a monovalent cation ionophore, and the electrogenic protonophore, carbonyl-cyanide m-chlorophenylhydrazone (CCCP), at micromolar concentrations abolished saturable uptake. Bursting vesicles by sonication, osmotic shock and freeze/thawing also eliminated saturable uptake. As the temperature increased from 0 to 30/sup 0/C, saturable uptake decreased markedly. Nonsaturable auxin uptake was less affected by these treatments. The pH gradient-dependent uptake of auxin appeared to be a transmembrane uptake of auxin into the vesicles rather than surface binding. Unlabeled IAA, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-naphthaleneacetic acid (NAA) at low concentrations reduced the saturable accumulation of (/sup 14/C)IAA in vesicles, while phenylacetic acid, benzoic acid, and 1-NAA were effective only at high concentrations. Kinetic analysis revealed two types of sites: a high affinity site with an uptake capacity of 25 to 40 pmoles/g tissue, and a low affinity site with an uptake capacity of 260 to 600 pmole/g tissue, fresh wt. In conclusion, several principal elements of an auxin transport system, as specific by the chemiosmotic theory of polar auxin transport, were present in membrane vesicles isolated from relatively mature pea stem tissue. However, one important aspect of the theory was not demonstrated in this in vitro system - a TIBA/NPA-sensitive auxin efflux. The kinetics and specificity of auxin uptake strongly suggested that this system was physiologically significant.

• Research Organization: Montana Univ., Missoula (USA)
• OSTI ID: 6942494
• Country of Publication: United States
• Language: English

Related Subjects

550301* -- Cytology-- Tracer Techniques
553006 -- Agriculture & Food Technology-- Other Agricultural Applications-- (1987-)
59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
AROMATICS
AUXINS
AZAARENES
AZOLES
BIOCHEMICAL REACTION KINETICS
CARBON 14 COMPOUNDS
CELL CONSTITUENTS
CELL MEMBRANES
FOOD
HETEROCYCLIC COMPOUNDS
IN VITRO
INDOLES
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MEMBRANE TRANSPORT
MEMBRANES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PEAS
PLANT GROWTH REGULATORS
PLANTS
PYRROLES
REACTION KINETICS
SEDIMENTATION
TRACER TECHNIQUES
UPTAKE
VEGETABLES