INDOLE-3-ACETIC-ACID UPTAKE IN ISOLATED PROTOPLASTS OF THE MOSS FUNARIA-HYGROMETRICA

Protoplasts of the moss Funaria hygrometrica Hedw. were used to study the mechanism of Indole-3-acetic acid (IAA) accumulation. Three main components appeared to be involved. 1. The pH gradient between plasma and outer medium is the basis for an anion trap. The protonophores carbonylcyanide m-chlorophenylhydrazone (CCCP) and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) reduce IAA accumulation by destruction of the pH gradient. 2. An intact efflux carrier could be demonstrated by an increase of IAA accumulation with the efflux inhibitors 2,3,5-triiodo-benzoic acid (TIBA) and 1-naphthylphthalamic acid (NPA). In efflux experiments, reduction of IAA efflux by the two inhibitors was directly demonstrated. 3. The existence of an influx carrier was concluded from the strong stimulation of IAA accumulation by calcium in calcium-deprived protoplasts. It is postulated that this carrier system transports IAA anions, protons and Ca2+. A computer simulation of the accumulation process with the three components, including internal IAA concentration determined by enzyme-linked immunosorbent assay (ELISA), gave a highly accurate description of the data measured in the different experiments.