Cytochemical localization of chloride in the leaves of Ruppia maritima L

Abstract

Ruppia maritima L. is a submerged halophyte which occurs frequently in estuaries where sodium chloride is the dominant salt. Unlike terrestrial halophytes, R. maritima does not possess any specialized salt-secreting structures such as salt glands. Knowledge of salt tolerance mechanisms in this plant is important to our understanding of its biology. In the present study, the subcellular distribution of chloride ions in leaf blade epidermal cells of R. maritima was determined.Chloride ions in the cells were localized by precipitation with silver, resulting in the formation of silver chloride (AgCl2) deposits. Leaf samples were fixed in a mixture of osmium and silver acetate under red safe light conditions to prevent reduction of silver by light. The material was dehydrated and embedded in a chloride-free resin. Leaf samples fixed only in osmium were used as controls. Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) microanalysis using a Joel 6100 SEM with a Noran Voyager 2100 EDX microanalyser, were used to study AgCl2 distribution. Ultrathin sections for TEM were examined unstained. EDX microanalysis was performed on thick sections of resinembedded material mounted on glass slides.