Patrick L. Healey

Development, structure, and occurrence of secretory trichomes ofPharbitis

SummarySecretory trichomes develop from epidermal cells on the leaf primordia and stem ofPharbitis nil. Following an initial growth phase, trichomes begin active secretion of a protein-carbohydrate mucilage. This mucilage covers the shoot apex and developing leaves ofPharbitis.The secretory cells possess cellular organelles in forms usually associated with actively secreting cells: many mitochondria, an elaborate network of rough endoplasmic reticulum (RER), many free ribosomes, and numerous dictyosomes. The role of the dictyosomes is twofold: 1. dictyosome vesicles bud coated vesicles which transport materials from the cell and, 2. dictyosome vesicles coalesce, forming large storage vesicles. The storage vesicles are surrounded by, and often in contact with, poculiform RER. The RER forms an interconnected network throughout the cytoplasm, extending from the nuclear envelope to the plasmalemma. Distended profiles of RER are frequently in direct contact with the plasmalemma. Thus, inPharbitis secretory trichomes, it is the coated vesicles and RER which are active in secretion export. These findings imply a secretory pathway which deviates from the usual pattern in glandular cells.

Development and histochemistry of nuclear crystals in the secretory trichome of Pharbitis nil

Trichomes of Pharbitis nil develop nuclear crystals at the onset of secretion. Mature crystals may reach 7 μ m in length and occupy up to 40% of the cross-sectional area of the nucleus. Concomitant with crystal growth, nucleoli undergo a 50% decrease in cross-sectional area. Crystal development is discussed in relation to nucleolar size, and to the secretion of a protein-carbohydrate product by the glandular trichome.