WATER RELATIONS IN WALNUT DURING WINTER

Studies dealing with the water status of the xylem sap in branches of trees during the winter period show that variation in degree of embolism can occur as a consequence of the frost-thaw alternation. At present only two known mechanisms are proposed to explain a resorption of embolism: sap pressurisation or cambial growth. Results show that walnut hydraulic conductivity varies considerably during the winter period and with the water status of xylem (tension/pressure). In winter, water status can be either under tension (negative water potential) or under pressure (positive, above atmospheric pressure), depending on the air temperature. Positive sap pressures are related to high sugar content (stem pressure) These studies show also clearly that important relations exist between xylem water status and dynamics of the carbon reserves (see also Valentin et al., this issue). Sugar content in the vascular sap is controlled by contact cells or vessel-associated cells (VACs: see also Alves et al. this issue a and b). Refilling of embolisms is most active in spring before budbreak (root pressure) and during this period, sugars in the vascular sap are retrieved for growth of buds and the vascular cambium.

IV International Walnut Symposium

T. Améglio, A. Lacointe, H. Cochard, G. Alves, C. Bodet, M. Vandame, V. Valentin, B. Saint-Joanis, S. Ploquin, P. Cruiziat, J.L. Julien, A. Guilliot, G. Petel

embolism, root pressure, stem pressure, vessel-associated cell, plasma membrane H+-ATPase, sugar fluxes.

https://doi.org/10.17660/ActaHortic.2001.544.32