HYDRAULIC SIGNALS

Hydraulic signals are ubiquitous in plants. They can pass throughout the hydraulic continuum of the plant very quickly, especially in the xylem. They may permit integration of whole-plant responses. Their effect on stomata could be important; change in the environment (and water potential) of one leaf will be transmitted hydraulically and will affect the aperture of stomata throughout the shoot, by a hydropassive mechanism. Wound-induced hydraulic signals are a special case. The basipetal mass flows associated with these signals can sweep elicitors from wound sites to the remainder of the plant at rates of about 10 mm s-1. This could be the mechanism by which rapid, whole-plant defence responses to localized attack are coordinated.