Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Effects of exogenous ABA on photosynthesis and stomatal conductance of cut twigs from oak. | 406s Ann. Sci. For. 1989 46 suppl. 406S-41ŨS Forest Tree Physiology E. Dreyer ef al. eds. Elsevier INRA Effects of exogenous ABA on photosynthesis and stomatai conductance of cut twigs from oak seedlings E. Dreyer and I. Scuiller Laboratoire de Bioclimatologie et d Ecophysiologie Forestiere INRA Nancy Champenoux F-54280 Seichamps France Introduction Abscisic acid ABA plays a major role in plant-water relations. It has been shown to promote stomatai closure in many species including trees Johnson 1987 and there is growing evidence that it could be a root-produced effector for water stress reactions Zhang et al. 1987 . These assertions are based on studies with cut twigs supplied with exogenous ABA and on measured increases of ABA concentrations in xylem sap. However many questions remain open to discussion are the concentrations of exogenous ABA necessary to promote a sensible reaction of the same magnitude as those of free ABA measured in the xylem during water stress Is the rapid stomatai closure promoted by exogenous ABA the direct cause of the observed decline in net photosynthesis Downton etal. 1988 or is there some direct effect of ABA on mesophyll photosynthesis Raschke and Hedrich 1985 Do forest trees display the same responses to ABA as other species We have therefore as a preliminary to a detailed survey of the role of ABA in reactions of oak species to water deficits test ed the reactions of cut twig photosynthesis to exogenous ABA. The effects of shoot removal on gas exchange were assessed prior to use of this technique with ABA. Materials and Methods Plant material 3 yr old seedlings grown on a sand-peat soil 50 50 v v in 8 I pots were transferred into a climate chamber February to accelerate bud break prior to measurements conducted during March and April 1988. Species Quercus robur Fig. . Q. petraea L. seeds collected near Nancy and Q. pubescens L. Avignon . Gas exchange measurements These were made in an open flow chamber. Twig transpiration was .
