Transport in Giant Plant Cells Freshwater Cells

Abstract

Fresh water giant algal cells have long provided favoured experimental material for studies of processes of ion transport in plant cells. Characean cells played a major role in the early development of the subject, in the classic work of Osterhout et al., in the period 1920–40, and after a period of relative neglect they have been much used in more modern studies. They have been used in their own right, with the aim of understanding the processes involved in maintaining the internal ionic composition of a single plant cell, and its intracellular organelles, but have also been studied as potential models for the behaviour of more typical cells in higher plants, where the small cell size, the heterogeneity of cells and the complexities of tissue organisation make it difficult to study well-defined membrane processes. While it is clear that not all the transport and metabolic processes involved in the activities of higher plant cells are reproduced in the simpler algae, there are reasonable indications that the ion transport processes identified in giant algal cells can be observed also in higher plant cells under suitable experimental conditions, and are likely to form a part of the range of normal activities of such cells. The problems faced by any plant cell, in acquiring its complement of osmotic solutes for growth, largely to be sequestered in the central vacuole, and in maintaining ionic environments in its cytoplasm and various constituent organelles that are suitable for their respective ranges of metabolic activities, are basically similar. Understanding of membrane activities in cells in which such processes are accessible to well-defined experiment must certainly throw light on more complex systems, and may be directly transferable. Freshwater conditions are more nearly comparable to the ionic environment sampled by cells in most parts of normal terrestrial plants, with relatively low external ion concentrations (in soil or in the free space supplied by the transpiration stream) than are marine conditions; it is probably only in halophytes growing in extreme saline conditions that higher plant cells face conditions similar to those of the marine giant cells. The evidence available bears this out, and the transport activities of higher plant cells and of fresh water giant algal cells do seem to have much in common.