Introduction

The term ‘vacuolar compartment’ is used advisedly. In the green plant cell, one can speak of the vacuole as a distinct entity, since it can routinely occupy c. 90% of the volume of the cell. The size of the vacuole can be such – as is the case in large algal coenocytes such as Chara and Nitella – that the vacuolar sap can be withdrawn readily for analysis (Hope & Walker, 1975). Further, the large size of the vacuole relative to the cytoplasm in green plant cells means that the vacuole makes a significant contribution to the cell osmotic potential. Study of the flux of radiotracers into and out of the above coenocytes has allowed the fluxes of the major ions across the vacuolar membrane (tonoplast) to be determined. Since the cytoplasmic and vacuolar concentrations of these ions can be determined readily and the potential difference across the tonoplast determined without too much difficulty, by insertion of an electrode into the vacuole, the driving force on any particular major ion can be determined. The literature on green plant vacuoles has been reviewed relatively recently (Marin, 1986; Raven, 1987).

In fungi, it is not often that there is a single vacuole. Certainly, there does not appear to be a single vacuole in actively growing hyphae, indeed on the basis of the different responses of vacuoles to stains there may be more than one type of vacuole (Clipson et al., 1989).