THE SAP OF PLANT CELLS.

Recent advances in the understanding of the functional relevance of sap of mature plant cells are reviewed. The emphasis is placed on roles of vacuoles played in the temporary storage of saccharides and organic acids, in the accumulation of water soluble products of secondary metabolism and in the intracellular digestion of protein. Contents Summary 1 I. Introduction 1 II. Functions of vacuoles 2 III. Vacuoles as pools of saccharides 3 IV. Organic acids 7 V. (Potentially) toxic cell saps 9 VI. Pools of protein 14 VII. Digestive cell saps 15 VIII. Tonoplast, cell sap and cytoplasm 18 IX. Cellular homeostasis 19 Acknowledgement 20 References 20.