WATER RELATIONS AND GROWTH OF TOMATO FRUIT PERICARP TISSUE

The water relations of young tomato fruit pericarp tissue were examine d and related to tissue expansion, The relationship between bulk turgo r pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing f ruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol, The bulk turgor of this tissue was low (abou t 0.2 MPa), even in fruit from plants that were otherwise fully turgid , whether measured psychrometrically or by length change in osmotic so lutions, The rate of tissue growth at maximum turgor was less than tha t at moderate turgor unless calcium was added to the incubation medium , However, added calcium also decreased the rate of growth at lower tu rgor pressures, Yield turgor was < 0.1 MPa, but it was increased by th e addition of calcium ions, Electrolyte leakage from tissue was greate st at maximum turgor pressure but was decreased by the addition of cal cium ions or osmoticum, Tissue growth was unaffected by a range of pla nt growth regulators (IAA, abscisic acid, benzyladenine and GA(3)) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed, Thus, fruit tissue may be able to mai ntain optimal expansion rates only at moderate turgor and low calcium concentration.