ENDOMEMBRANES, CYTOSKELETON, AND CELL-WALLS - ASPECTS OF THE ULTRASTRUCTURE OF THE VASCULAR CAMBIUM OF TAPROOTS OF AESCULUS-HIPPOCASTANUM L(HIPPOCASTANACEAE)

The ultrastructure of ray and fusiform cells within the active vascula r cambial zone of taproots of Aesculus hippocastanum L. is described. Both cell types are uninucleate and highly vacuolate and contain perin uclear and parietal populations of plastids and mitochondria, abundant rough endoplasmic reticulum, numerous dictyosomes and associated smoo th vesicles, coated vesicles, numerous free ribosomes and polysomes, a xially oriented microfilament bundles, and randomly oriented cortical microtubules, and they bear unlignified primary cell walls. Oleosomes, microbodies, and amyloplasts are more common within ray cells than in the fusiform cells and provide the main ultrastructural difference be tween the two. Generally, the ultrastructure of root cambial tissue is similar to the shoot cambium of this species and to the shoot cambia of other hardwood species. On the basis of ultrastructure, it has not been possible to identify true cambial initials in this tissue. Aspect s of wall biosynthesis and chemistry were studied with light microscop y, conventional transmission electron microscopy, periodic acid-thioca rbohydrazide-silver proteinate staining (PATAg, Thiery reaction), and indirect immunolocalization, using the monoclonal antibodies JIM5 and JIM7 at the optical and ultrastructural levels. The presence of coated vesicles attached to a membranous structure is reported and discussed in relation to its identification as partially coated reticulum or tr ans-Golgi network. The results are discussed in relation to the endome mbrane system, cell walls, and cytoskeleton of this tissue.