XVI International Botanical Congess

The relative importance of cell turgor versus hormonal signals from roots in controlling cell expansion in leaves of water-stressed plants was examined over a range of timescales. Large and transient effects on leaf elongation were induced by sudden changes in light, humidity, and soil salinity. The transient changes (lasting about 30 min) could be completely overcome if the shoot was kept fully turgid by pressurising the roots. Over the timescale of days, soil salinity and dryness reduced leaf elongation rates, even in pressurised plants. Pressurisation did raise the growth rate during the light period, but there was a subsequent decrease during the dark The result was no net effect on leaf growth over a 24 h period, indicating the overall importance of hormonal signals in determining leaf expansion rates during water stress.