Development and Ultrastructure of Primary Secretory Ducts in the Stem of Semecarpus Anacardium (Anacardiaceae)

Abstract

Development and ultrastructure of primary phloem secretory ducts in the stem of Semecarpus anacardium are described. Ducts are formed schizolysigenously in the phloic procambium of the young stem just below the shoot apex. The cytoplasm of the epithelial cells is rich in osmiophilic material (resin), plastids, rough endoplasmic reticulum (RER), free ribosomes, polysomes, mitochondria with swollen cristae and golgi bodies. The plastids are of varying shapes, have an electron dense matrix and a poorly developed internal membrane system. They are highly contorted and invariably surrounded by a sheath of RER. Osmiophilic material is frequently observed in the plastid stroma. Epithelial cell cytoplasm and its plastids are the plausible sites of resin formation. The gum component of the secretion may be derived from the inner tangential wall (ITW). The secretory substances reach the apoplast principally by granulocrine and eccrine secretion. Epithelial cells are linked with each other and with the neighbouring cells by numerous plasmodesmatal connections. Some epithelial cells undergo lysis while others retain their secretory function.