Seasonal Changes in the Ultrastructure of the Vascular Cambium in Shoots of Populus tomentosa

Wood is the product of cambial activity in trees, and the seasonal activity style of cambium directly influences wood biomass production, structures and properties. The seasonal changes in the ultrastructure of the vascular cambium activity of Populus tonientosa Carr. planted in Beijing area were examined in shoot tissues collected during 15 months by means of transmission electron microscopy. Before xylem mother cells reactivated completely, the dividing fusiform cells in cambium and new phloem cells had appeared at the same time. The initiation of cambial activity may be related to the bud sprouting and the young leaf growth in shoots. More details about the ultrastructural changes of cambial cells at the onset of cambial activity have been gained. When the large vacuole in active cambial cells divided into smaller ones during the dormant phase, proteinaceous material that disappeared in active cambial cells refilled many of these small vactioles. In addition, lipid droplets and starch granules had the same cycles as proteinaceous material. The plasmalemma invaginations of fusiform cells were observed not only in active phase but also in dormancy. The endomembrane system consisting of nuclear membrane, endoplasmic reticulum (ER), dictyosomes and their secretory vesicles, changed in form and distribution at different phases during a cycle and performed important roles at the onset of active cambium and during the wall formation process of secondary xylem cells. The tangential walls remained relatively thin throughout the year but the radial walls thickened markedly when the cambium was dormant. During the transition from dormancy to activity, a partial autolysis occurred in the radial walls of the cambial cells, especially at the cell wall junctions. A notable feature of the cells at the onset of cambial activity was the thinning of the radial walls.

ADAMTS-7 promotes vascular smooth muscle cells proliferation in vitro and in vivo

Vascular smooth muscle cell(VSMC) proliferation and migration are pivotal for the pathogenesis of atherosclerosis and post-angioplasty restenosis. We have recently reported that a disintegrin and metalloproteinase with thrombospondin motifs-7(ADAMTS-7), a novel metalloproteinase, contributes directly to neointima formation by mediating VSMC migration. However, whether ADAMTS-7 affects VSMC proliferation remains unclear. In this study, we found that luminal adenoviral delivery of ADAMTS-7 aggravated intimal hyperplasia 7 d after injury, paralleled by an increased percentage of PCNA-positive cells in both intima and media. In contrast, perivascular administration of ADAMTS-7 si RNA, but not scrambled si RNA to injured arteries attenuated intimal thickening at day 7, paralleled with reduced intimal VSMC replication, without alteration of VSMC proliferation in the media. In accordance, [3H]-thymidine incorporation assay in primary cultured rat VSMCs revealed an enhanced replication rate(by 61%) upon ADAMTS-7 overexpression and retarded proliferation(by 23%) upon ADAMTS-7 si RNA administration. Our data demonstrates that ADAMTS-7 promotes VSMC proliferation both in vitro and in vivo. ADAMTS-7 may therefore serve as a novel therapeutic target for atherosclerosis and post-angioplasty restenosis.