The capitate and peltate glandular trichomes of Lavandula pinnata L. (Lamiaceae): histochemistry, ultrastructure, and secretion¹

Abstract

The morphology, histochemistry, and ultrastructural aspects of the secretion of Lavandula pinnata L. (Lamiaceae) glandular trichomes were studied in order to prepare for work on calcium distribution in normal and heat stressed plants. The secretory process was observed in both light and dark-grown plants. The secretion of the capitate glandular trichomes consists of both lipophilic and polysaccharidic substances (mainly the latter), while peltate glandular trichomes only secrete lipophilic substances. Our ultrastructural results are consistent with the finding that plastids are the main organelle that synthesizes the lipophilic substances, especially terpenes, while dictyosomes synthesize polysaccharides. The essential oil is most likely transported directly by the RER, while the polysaccharides reach the plasma membrane via Golgi-derived vesicles. Exocytosis is the main way that secretory products move from the cell to the subcuticular space. There are no differences in gland development or secretion between the light and dark-grown plants.