A NEGATIVE HYDRAULIC MESSAGE FROM OXYGEN-DEFICIENT ROOTS OF TOMATO PLANTS - INFLUENCE OF SOIL FLOODING ON LEAF WATER POTENTIAL, LED EXPANSION, AND SYNCHRONY BETWEEN STOMATAL CONDUCTANCE AND ROOT HYDRAULIC CONDUCTIVITY

Four to 10 h of soil flooding delayed and suppressed the normal daily increase in root hydraulic conductance (L(p)) in tomato (Lycopersicon esculentum Mill. cv Ailsa Craig) plants. The resulting shortterm loss of synchrony between L(p) and stomatal conductance decreased leaf wate r potential (psi(L)) relative to well-drained plants within 2 h. A dec rease in psi(L) persisted for 8 h and was mirrored by decreased leaf t hickness measured using linear displacement transducers. After 10 h of flooding, further closing of stomata and re-convergence of L(p) in fl ooded and well-drained roots returned psi(L) to control values. In the second photoperiod, L(p) in flooded plants exceeded that in well-drai ned plants in association with much increased L(p) and decreased stoma tal conductance. Pneumatic balancing pressure applied to roots of inta ct flooded plants to prevent temporary loss of psi(L) in the 1st d did not modify the patterns of stomatal closure or leaf expansion. Thus, the magnitude of the early negative hydraulic message was neither suff icient nor necessary to promote stomatal closure and inhibit leaf grow th in flooded tomato plants. Chemical messages are presumed to be resp onsible for these early responses to soil flooding.