PRESSURE-VOLUME ANALYSIS OF A RANGE OF POIKILOHYDRIC PLANTS IMPLIES THE EXISTENCE OF NEGATIVE TURGOR IN VEGETATIVE CELLS

Pressure-volume (PV) isotherms were determined for a range of poikiloh ydric plants. The plants included a lichen, a filmy fern, three bryoph ytes and two angiosperms. Graphs of turgor potential (psi(p)) as a fun ction of relative water content (RWC) derived from the PV curves sugge sted that most of the cryptogams, but not the angiosperms, contained s ignificant amounts of intercellular water when fully hydrated. In seve ral species part of the PV curve fell below the extrapolated linear po rtion of graph, implying that over this range of RWCs the plant's cell s have negative turgor; values as low as -0.3 MPa were recorded. Negat ive turgor occurred in those species with a high bulk modulus of elast icity, implying that it develops only in plants that have cells with r igid walls. Plants that can display negative turgor will undergo cytor rhysis at lower RWCs than plants in which negative turgor does not occ ur. The significance of these findings for the water relations of poik ilohydric plants is discussed. (C) 1997 Annals of Botany Company.