Kinetics of proton secretion and growth in maize roots: action of various plant growth effectors

Abstract

The response of maize roots to several growth effectors was investigated. Relations between growth and H +-secretion could be determined since measurements of these parameters were carried out under constant pH conditions. FC stimulated growth and proton secretion in a proportional manner, whereas the drop of elongation rate induced by high concentrations (10 −8 — 10 −6 M) of auxin was accompanied by a rather small reduction of proton efflux. Evidence is presented that these discrepancies do not necessarily contradict the acid growth hypothesis but are caused by the fact that only the root tips show a large inhibition of proton excretion in response to auxin. An increase of growth or medium acidification by very low levels could not be demonstrated in our experiments, neither with nor without pretreatment with ethylene biosynthesis inhibitors. The effects of the anti-auxins 5,7-Cl 2-indole-3-acetic acid (5,7-Cl 2-IAA) and p-chloro-isobutyric acid (PCIB) were found to be similar to those induced by auxins, but higher concentrations were required to achieve the inhibition.