Uptake and Transport of Fusicoccin in Higher Plant Tissues

Abstract

The uptake and release of 3H-labelled fusicoccin (FC) fed to pea internode segments and the transport of [3H]FC in whole plants and in excised parts of plants of pea, maize, and pumpkin have been investigated. FC uptake showed three phases apparently corresponding to the pene tration of FC: (1) into the free space; (2) into the cytoplasm; (3) into the vacuole. The first phase is a little thermosensitive and apparently includes adsorption binding to some free space component (cell surface?). The second and third phases are highly temperature sensitive and in part energy-dependent. However, no accumulation of FC against a concentration gradient is observed at high external FC concentration. Accumulation at low concentration seems due to the formation of a poorly exchangeable complex with some cell structure. The efflux of the FC penetrated within the cells is limited by some highly temperature sensitive process. A small fraction of the accumulated FC tends to be retained in the tissue, either because sequestered in some compartment or because bound to some cellular component. FC transport in whole plants as well as in isolated plant parts seems to depend mainly on simple diffusion and on transport by mass flow in the xylem. Long distance transport of the toxin in pumpkin plants mainly occurs in the xylem, while the slow movement in non-vascular tissues seems to depend on diffusion combined with mass flow in the free space, and does not seem heavily influenced by metabolic factors.