Structure and functioning of oil cavities in the shoot apex of Metrodorea nigra A. St.-Hil. (Rutaceae).

This study investigates the histology and subcellular features of secretory cavities during the development of the shoot apex of Metrodorea nigra A. St.-Hil. in order to better understand the functioning of these glands. This Rutaceae species is a very suitable model for studying secretory cavity life span, since the shoot apex exhibits both dormant and growth stages during its annual cycle. Shoot apices were collected during the dormant and growth stages from populations of M. nigra growing under natural conditions. Materials were processed using standard techniques for light and electron microscopy. The secretory cavities originate under the protodermis, and their initiation is restricted to the early developmental stage of shoot organs, which are protected by a hood-shaped structure. Secretory cavities have a multi-seriate epithelium surrounding a lumen that expands schizolysigenously. Oil production begins before lumen formation. When the shoot apex resumes development after the dormant stage, the glands remain active in oil secretion in the developing shoot apex and fully expanded leaves. The mature epithelial cells are flattened and exhibit very thin walls, large oil bodies, leucoplasts surrounded by endoplasmic reticulum, and mitochondria with unusual morphology. The tangential walls of the epithelial cells facing the lumen undergo continuous peeling. The vacuole extrusion appears to be the primary mode of release oil into the lumen, in an exocytotic way. The continuity of oil secretion is ensured by the replacement of the damaged inner epithelial cells by divisions in the parenchyma layer that surround the oil gland, likely a meristematic sheath.

Pollen morphology of the genus Skimmia (Rutaceae) and its taxonomic implications.

Pollen morphology of the genus Skimmia was studied. Of six species of the genus, five species were investigated by light microscopy and scanning electron microscopy. Pollen grains of Skimmia had striate to striate-reticulate sculpture and variable aperture number (3-7), and these characters differed from even the phylogenetically closest relatives such as Dictamnus and Casimiroa which have 3-colporate pollen grains with reticulate exine. In Skimmia laureola, pollen dimorphism is suggested in the aperture number in accordance with the floral system. Pollen grains of Skimmia japonica, a morphologically very variable species, were extensively surveyed covering its whole distribution area. The grains were also striate to striate-reticulate, and the exine sculpture was not different between varieties. However, the aperture number of S. japonica showed a geographical variation ranging from 4 to 6; in Sakhalin, Hokkaido, most part of Honshu and Taiwan, grains with 4-5 apertures were dominant, while in the southern part of Japan, including the Ryukyu Islands and the Izu Islands, those with 5-6 apertures were common.