Embolized conduits of rice (Oryza sativa, Poaceae) refill despite negative xylem pressure

Stiller, Volker; Sperry, John S. and Lafitte, Renee. 2005. Embolized conduits of rice (Oryza sativa, Poaceae) refill despite negative xylem pressure. American J of Botany, Volume 92 no. 12 p. 1970-1974

Embolism reversal in rice plants was studied by testing the plant's ability to refill embolized conduits while xylem pressures were substantially negative. Intact, potted plants were water‐stressed to a xylem pressure of −1.88 ± 0.1 MPa and a 66.3 ± 3.8% loss of xylem conductivity (PLC) by cavitation. Stressed plants were carefully rewatered, allowing xylem pressure to rise, but not above the theoretical threshold of c. −0.15 MPa for embolism collapse. Despite xylem pressures being more negative than this threshold, the PLC fell significantly (28.5 ± 5.6%), indicating the refilling of vessels. Above c. −1.0 MPa, almost all plants regained their maximum hydraulic conductivity. Dye uptake experiments showed the same pattern of embolism refilling despite negative pressure. Refilling was prevented in plants that were light‐starved for 5 d, suggesting the unknown mechanism is dependent on metabolic energy. Results are among the first showing that herbaceous plants can reverse embolism without bulk xylem pressures rising near or above atmospheric.