Proton extrusion in leaves of Olea europaea L. cv. Frantoio and evidence for an ATP-driven H⁺ pump. A study carried out under different chemical, physical, and electrophysiological conditions

• Published in: Advances in horticultural science 1999-01, Vol.13 (3), p.113-124
• Main Authors: Rinaldelli, E., Bandinelli, R.
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatases; Auxins; Cell membranes; Leaves; Plant cells; Plants; Proton pumps; Protons; Vanadates
• ISSN: 0394-6169; 1592-1573

Measurements of H⁺ extrusion in leaves of Olea europeaea L. cv. Frantoio, under different experimental conditions, were carried out for the fírst time. The results obtained lead to the following conclusions: a) The cuticle constitutes an obstacle to the diffusion of protons from the apoplast toward the exterior. In order to remove this barrier a specifîc technique was devised which does not damage the cells of surrounding tissues, b) Proton extrusion is blocked, or greatly reduced, by hypoxia, low temperature and orthovanadate while it is stimulated by K⁺ , isobutyric acid and light. IAA did not show, in mature leaves, notable effects, c) pH values around 6,1-6,2 represent the equilibrium threshold below wich H + extrusion is inhibited and above which it is stimulated, d) The amount of H⁺ extrusion varies as a function of leaf age. Extrusion in growing leaves is more than triple that of mature leaves, e) A H⁺ extrusion gradient exists which depends on the position of the leaf on the shoot. Proton extrusion increases progressively from proximal to distal leaves, f) Cell transmembrane electrochemical potentials (Em) of distal, median and proximal leaves indirectly confirm the findings from H⁺ extrusion trials. The results of this study support the existence of a proton pump at the cell membrane level which corresponds to plasmalemma H⁺-ATPase.