GLAND DEVELOPMENT ON LEAF SURFACES OF NEPETA-RACEMOSA

Trichomes present on the leaf surface of catmint (Nepeta racemosa L.) were examined using both scanning and transmission electron microscopy. Three types of trichomes were observed: (a) multicellular, uniseriate, nonglandular hairs, (b) small capitate glands with two cells in the head, and (c) large, peltate glands with four secretory/head cells. Secretory cells of capitate glands exhibited typical transfer cell morphology, with an abundance of RER and Golgi bodies, indicative of secretion of mainly hydrophilic substances. Mature peltate glands exhibited a distended cuticle and large subcuticular cavity, presumably containing the essential oils. Morphologically well-developed peltate glands were observed on young leaf primordia, with development occurring earlier at the leaf apex and along the midvein than at the leaf margins or base. Four major stages in the development of the peltate gland secretory cells were identified. The first stage was marked by highly vacuolated cytoplasm and normal distribution of subcellular organelles. The second stage, during which there was substantial accumulation of material in the subcuticular cavity, was marked by an abundance of tubular endomembrane elements in proximity to plastids with little internal differentiation. Retraction from the cell wall and an unusual scalloped appearance to the plasmalemma characterized a third stage. Presence of a large subcuticular cavity, an exaggerated retraction of the plasmalemma, and a band of peripheral mitochondria were typical of a fourth, presumably mature stage.