Synthesis Of Wall Material Research Articles

Determinants of Vascular Structure

The development of the vasculature is a complex process, the end result of which enables the cardiovascular system to supply each tissue with the required amount of blood at the correct pressure. The mechanisms controlling this development are poorly understood, and this article seeks to review briefly some of the mechanisms that may be involved. At the capillary level, it appears that capillary proliferation is closely related to tissue metabolism. The lumen diameter of the feeding arterioles and arteries then develops (through a mechanism that appears to be dependent on endothelial factors) to accommodate the new flow requirements. In studies of the development of esophageal varices, it seems that the increased lumen diameter resulting from increased flow is due to the rapid synthesis of wall material. Within the walls of the feeding arterioles and arteries, the smooth muscle develops to insure a constant loading of the individual smooth muscle cells. This development is not necessarily associated with alterations in the amount of smooth muscle, but can be due to "remodeling," i.e., the rearrangement of existing smooth muscle cells to allow them to perform their function more effectively. Clearly, if we assume that antihypertensive therapy should seek not only to reduce blood pressure but also to normalize vascular structure, a better understanding of the mechanisms controlling vascular development is needed.

Pollen-pistil interactions inGrevillea banksii

Abstract Morphology and ultrastructure of stigma, transmitting tissue and pollen were examined in Grevillea banksii R. Br. (Proteaceae), a bird-pollinated shrub with stylar presentation of pollen. Stigmatic cells are not cuticularised and secrete copious lipidic exudate. Intercellular material of the thick primary walls of transmitting tissue cells stains positively for protein. The pollen exine is cavate and foveolate, but labile protein could be detected only in the thickened intine below germ pores. Self and non-self pollen of G. banksii, germinated on the stigma, both show normal protein mobilisation and synthesis of wall material. Ectexine of germinated grains consistently appears saccate. Intra- and interspecific pollinations using five other species of Grevillea and one of Persoonia as ‘foreign’ pollen sources, showed no pollen rejection at the stigma or in the upper transmitting tissue. Sporophytic control in compatibility regulation, believed most usual with stylar presentation, is inferred to be...