Barley [Hordeum distichum (L.) Lam.] seedlings were infected with uredmiospores of rust, Puccinia hordei Otth., 10 d after germination and the Zimmermann micro-pressure probe was used to measure the turgor potential of individual epidermal and palisade cells, during disease development. Turgor potential was measured as a function of time and as a function of distance from the centre of the rust colony. When the centre of a rust colony was within 300 μm of probed cells, palisade cell turgor declined significantly on days 6, 7 and 9 after infection in comparison to control leaf palisade cells.
Control leaf palisade cell turgor remained constant with time. On day 4 after infection, epidermal cell turgor of control and infected leaves did not differ. However, by day 6 when the uredinium was visible and approaching sporulation, epidermal cell turgor of infected leaves declined. The reduction was dependent upon the distance from the centre of the colony, thereby creating a gradient of turgor such that the lowest turgors were recorded at the centre of the colony and the highest at the colony boundary. By day 9 after infection, when ‘green island’ development had begun, this gradient was reversed. However, turgors of all epidermal cells in colony areas were significantly less than those in control leaves. These results are discussed in relation to die impact of rust infection upon leaf water relations in barley.