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 poikilohydric plants. The plants included a lichen, a filmy fern, three bryophytes and two angiosperms. Graphs of turgor potential (ψ p ) as a function of relative water content (RWC) derived from the PV curves suggested that most of the cryptogams, but not the angiosperms, contained significant amounts of intercellular water when fully hydrated. In several species part of the PV curve fell below the extrapolated linear portion of graph, implying that over this range of RWCs the plant's cells have negative turgor; values as low as -0.3 MPa were recorded. Negative turgor occurred in those species with a high bulk modulus of elasticity, implying that it develops only in plants that have cells with rigid walls. Plants that can display negative turgor will undergo cytorrhysis at lower RWCs than plants in which negative turgor does not occur. The significance of these findings for the water relations of poikilohydric plants is discussed.