Transport of 14 C-indoleacetic Acid in the Hepatic Marchantia polymorpha

Abstract

Tracer experiments using exogenous 14C-indoleacetic acid showed that its transport is localized in the midrib cells of Marchantia polymorpha vege- tative thalli. Transport occurs both acropetally and basipetally at approximately the same velocity, but basipetal transport is significantly greater in intensity. In- terference with energy-yielding metabolism due to anaerobic conditions, iodoacetic acid or sodium fluoride reduced basipetal transport by 40-50%. Disruption of cel- lular integrity via centrifugation or cytochalasin B reduced basipetal transport by 30-40%. IAA transport in M. polymorpha gametophytes is essentially the same as in vegetative axes of flowering plants with respect to all parameters compared. The presence of naturally occurring auxin in gametophytic tissue of Marchantia poly- morpha has been demonstrated by both chemical methods and bioassays. As early as 1956, an endogenous compound was isolated from thalli that gave positive results with the Avena curvature test (La Rue & Narayanaswami 1957). Schneider et al. (1967) isolated an Erlich and Salkowski-positive ethanol-soluble compound with an Rf corresponding to indoleacetic acid (IAA). La Rue and Narayanaswami (1957) also present evidence for the localized synthesis of auxin in the apical region of the thallus, and Maravolo (1976) dem- onstrated that IAA was the major transport form in Marchantia. Endogenous growth regulators exert correlative action over developmental processes in bryophytes analogous to their action in tracheophytes. Their correlative activity is dependent upon absolute concentrations, gradients, differential rates of synthesis, inacti- vation and the direction and intensity of transport. The polar distribution of auxin in Marchantia polymorpha assumes an important regulatory role in apical dominance, gem- mae-cup formation and rhizoid initiation through its influence on the balance between cell division and elongation (Maravolo & Voth 1966; Binns & Maravolo 1972; Davidonis & Munroe 1972; Rota & Maravolo 1975). Hebant (1970) and Scheirer (1977) demonstrated that some bryophytes possess spe- cialized cells within the midrib tissue with morphological characteristics of phloem sieve tube cells. Translocation of auxin in Marchantia is conducted in a similar transport system. This transport is strictly basipetal, and was adversely affected by triiodobenzoic acid, cinnamic acid and ethylene, all inhibitors of polar transport in tracheophytes (Maravolo 1976). The present investigation derives from the latter and investigates the nature of several aspects of the auxin transport mechanism in Marchantia.