SPOROBOLUS VIRGINICUS LEAF SALT-GLANDS - MORPHOLOGY AND ULTRASTRUCTURE

The leaves of the halophytic, C-4 grass, Sporobolus virginicus, posses s bicellular salt glands that are more abundant on the adaxial surface . Each gland is composed of a voluminous, flask-shaped basal cell, emb edded in the leaf and a smaller, dome-shaped cap cell that protrudes b eyond the epidermis. An ornamented, porose cuticle overlies the protru ding gland. The dense cytoplasm of the basal cell is partitioned into channels by a system of paired membranes which originate from invagina tions of the plasma membrane, adjacent to the common wall between basa l and cap cells. Closely associated with the partitioning membranes ar e numerous mitochondria, microtubules and endoplasmic reticulum. The b asal cell is intimately connected to adjacent cap, epidermal and mesop hyll cells by numerous plasmodesmata. The dense cytoplasm of the cap c ell lacks partitioning membranes, but contains numerous small vacuoles and a concentration of organelles in close proximity to the outer sur face. The basal cell appears to be suitably located and designed to ac cess and direct ions from surrounding mesophyll and epidermal cells in to the channels formed by the partitioning membranes. Subsequent ion m ovement is probably symplastic via the cytoplasm and plasmodesmata to the cap cell. The abundant mitochondria, which are closely associated with the partitioning membranes, are probably important in ion transpo rt through the cytoplasm of the basal cell. The ions appear to be comp artmentalised and transported across the cap cell in small vacuoles an d accumulate in the cuticular cavity prior to elimination via cuticula r pores or through rupture of the cuticle.