POLLEN AND TAPETUM DEVELOPMENT IN MALE FERTILE ROSMARINUS-OFFICINALISL (LAMIACEAE)

The development of microspores/pollen grains and tapetum was studied i n fertile Rosmarinus officinalis L. (Lamiaceae). Most parts of the cel l walls of the secretory anther tapetum undergo modifications before a nd during meiosis: the inner tangential and radial cell walls, and oft en also the outer tangential and radial wall, acquire a fibrous appear ance; these walls become later transformed into a thin polysaccharidic film, which is finally dissolved after microspore mitosis. Electron o paque granules found within the fibrous/lamellated tapetal walls consi st of sporopollenin-like material, but cannot be interpreted as Ubisch bodies. The middle lamella and the primary wall of the outer tangenti al and radial tapetal walls remain unmodified, but get covered by an e lectron opaque, sporopollenin-like layer. Pollenkitt is formed only by lipid droplets from the ground plasma and/or ER profiles, the plastid s do not form pollenkitt precursor lipids. Tapetum maturation (''degen eration'') does not take place before late vacuolate stage. The apertu res are determined during meiosis by vesicles or membrane stacks on th e surface of the plasma membrane. The procolumellae are conical, but a t maturity the columellae are more cylindrical in shape. The columella r bases often fuse, but a genuine foot layer is lacking. The formation of the endexine starts with sporopollenin-accumulating white lines ad jacent to the columellar bases. Later, the endexine grows more irregul arly by the accumulation of sporopollenin globules. In mature pollen t he intine is clearly bilayered. Generative cells (GCs) and sperm cells contain a comparatively large amount of cytoplasm, and organelles lik e mitochondria, dictyosomes, ER, and multi-vesicular bodies, but no pl astids; GCs and sperms are separated from the vegetative cell only by two plasma membranes.