Applicability of the chemiosmotic polar diffusion theory to the transport of indol-3yl-acetic acid in the intact pea (Pisum sativumL.)

✍ Scribed by Claire F. Johnson; D. A. Morris

• Publisher: Springer-Verlag
• Year: 1989
• Tongue: English
• Weight: 726 KB
• Volume: 178
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00393200

✦ Synopsis

The transport of exogenous indol-3ylacetic acid (IAA) from the apical tissues of intact, light-grown pea (Pisum sativum L. cv. Alderman) shoots exhibited properties identical to those associated with polar transport in isolated shoot segments. Transport in the stem of apically applied [1-14C] -or [5-3H]IAA occurred at velocities (approx. 8-15 ram. h-~) characteristic of polar transport. Following pulse-labelling, IAA drained from distal tissues after passage of a pulse and the rate characteristics of a pulse were not affected by chases of unlabelled IAA. However, transport of [I-14C]IAA was inhibited through a localised region of the stem pretreated with a high concentration of unlabelled IAA or with the synthetic auxins 1-napthaleneacetic acid and 2,4-dichlorophenoxyacetic acid, and label accumulated in more distal tissues. Transport of [1-14C]IAA was also completely prevented through regions of the intact stem treated with N-l-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid.

Export of IAA from the apical bud into the stem increased with total concentration of IAA applied (labelled+unlabelled) but approached saturation at high concentrations (834 mmol.m-3). Transport velocity increased with concentration up to 83 mmol. m-3 IAA but fell again with further increase in concentration.

Stem segments (2 mm) cut from intact plants transporting apically applied [1-~4C]IAA effluxed 93% of their initial radioactivity into buffer (pH 7.0) in 90 min. The half-time for efflux increased from 32.5 to 103.9 min when 3 mmol.m -3