EPIDERMAL PEELS OF AVICENNIA-GERMINANS (L) STEARN - A USEFUL SYSTEM TO STUDY THE FUNCTION OF SALT-GLANDS

Adaxial peels were made from fully expanded leaves of Avicennia germinans (L). Stearn. The peels consisted of the epidermis, epidermal salt glands, and underlying hypodermal cells. Electron microscopic examinations showed that the structural integrity (except for the innermost hypodermal cells) of all cell types was not altered in making the peels. When the peels were floated on salt solutions, the glands were shown to be functionally competent in secretion. Secretion also occurred when the peels were floated on distilled water, presumably from salts stored in the hypodermis. Secretion occurred in the dark and since all cell types in the peels lacked chloroplasts, glandular function could not be directly coupled energetically to photosynthesis. However, secretion was shown to be temperature dependent and inhibited by azide and dinitrophenol, which indicates that the energy cost underlying secretion is mitochondrial and most likely coming from the mitochondria-enriched gland cells. Inhibitors known to affect membrane H+ATPase activity and membrane transport also inhibited secretion, indicating that membrane transport is probably the primary mechanism underlying secretion. Lanthanum, a membrane calcium antagonist, also inhibited secretion. © 1992 Annals of Botany Company.