Isolated plant protoplasts are 'naked' cells that have had their cell wall removed either by mechanical action or by enzymic digestion. As a result of wall removal the only barrier that exists between the cell protoplasm and the external environment is the plasma membrane. The removal of the cell wall has drastic osmotic consequences for the isolated cell. Rather like animal cells, the isolated protoplasts must be maintained in an osmotically balanced (isotonic) nutrient medium or they will burst. As will be seen later, the isolation of plant protoplasts is not a particularly new event; as...