SHORT-TERM DRYING OF HALF THE ROOT-SYSTEM REDUCES GROWTH BUT NOT WATER STATUS OR PHOTOSYNTHESIS IN LEAVES OF PASSIONFRUIT (PASSIFLORA SP)

The impact of soil water deficits and non-hydraulic root signals on th e expansion, functioning and water status of leaves and the opening of flowers of passionfruit was studied in a series of pot experiments. H ydraulic and non-hydraulic signals were separated by withholding water from half the root system. The leaves of well-watered plants expanded in a sigmoid pattern to about 65 cm(2) over 15 to 18 days. Drying the whole root system stopped leaf expansion after 6 days, but did not ch ange the pattern of leaf growth. Growth resumed after rewatering but t he final leaf size was halved. As leaf growth slowed, the net photosyn thesis, P-n, of mature leaves fell from 11 +/- 1 mu mol CO2 m(-2) s(-1 ) to less than zero as the leaves wilted. Leaf water potential, psi(1) , of mature leaves at midday ranged from -0.9 MPa in well-watered plan ts to -3.1 to -3.7 MPa in wilted plants. After rewatering, psi(1) retu rned to -0.9 MPa within 1 day, but P-n took 3 days to return to contro l levels. A midday psi(1) of -1.5 MPa was associated with a 50% reduct ion in relative leaf expansion and net photosynthesis. Drying half of the root system reduced leaf expansion by 26%, compared with well-wate red plants, and water use by 21 to 27%, without influencing psi(1) or P-n. Plants with half the root system dry for 13 days flowered earlier than well-watered plants but had the same number of open flowers 1 mo nth after treatments ended, Non-hydraulic root signals affect leaf exp ansion and flowering in passionfruit.