title: Determination of malate levels during the swelling of vacuoles isolated from guard-cell protoplasts.
abstract: A method for the preparation of vacuoles from guard cells ofVicia faba L. is described. Vacuoles were released from guard-cell protoplasts by osmotic shock and purified on a Ficoll gradient. Contamination of the vacuoles was examined by assaying marker enzymes, such as fumarase, glucose-6-phosphate dehydrogenase, phosphofructokinase, acid phosphatase and mannosidase. Potassium ions in the incubation medium caused increases in the volume of the vacuoles by a factor of about 2.6, while the malate level remained unchanged. In contrast, malate synthesis was stimulated during the swelling phase when complete guard-cell protoplasts were exposed to K(+). The possible role of K(+) as an efficient osmotic effector is discussed.
authors.affiliation: Institut für Botanik der Technischen Universität, Arcisstrasse 21, D-8000, München 2, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Schnabl
authors.forename: C
authors.initials: C
authors.lastname: Kottmeier