Oppositely-directed water flows in roots with respect to the plant integral hydrodynamic system

Abstract

Experiments with root segments of 5 to 6-day-old Zea mays L. seedlings demonstrated that the segments maintain the capacity to exude not only from their basal end (ascending water flow), but also from their apical end (descending water flow). Exudation from the basal end of segments resembled bleeding, whereas exudation from the apical end differed in its rate, temperature coefficient Q10, exudate osmotic pressure, exudation pattern in individual root zones, and sensitivity to biomediators (noradrenaline and acetylcholine). The chemical composition and pH values of all exudates were similar. One may conclude that both descending and ascending water flows occur along the xylem. This system of oppositely-directed water flows in root segments is discussed with respect to the plant’s integral hydrodynamic system and the participation of living cells in root pressure production.