Gum Duct Development in Almond Fruit, Prunus dulcis (Mill.) D. A. Webb

Abstract

Gum ducts form schizolysigenously in the vascular bundles of almond mesocarp tissue just prior to endocarp lignification. The first indication of gum duct initiation is the differentiation of densely cytoplasmic secretory cells in the mesocarp vascular parenchyma. The secretory cells are characterized by their abundance of dictyosomes and dictyosome vesicles, mitochondria, and rough endoplasmic reticulum. Duct formation is initiated by the schizogenous separation of parallel rows of secretory cells. During duct initiation and growth, the duct lumen is completely lined by the gum-secreting cells. In the later stages of duct development, the cytoplasm of the secretory cells degenerates as gum accumulates in the space between the plasmalemma and cell wall. Finally, the cell walls and remaining cytoplasm disintegrate. The mature duct is surrounded mainly by vascular parenchyma cells after lysis of the secretory cells. Gum is primarily a secretory product of the specialized secretory cells, but disintegrating ...