压力室测定根系导水率方法探讨

用压力室连续测定了玉米根系升压和降压过程的导水率。结果表明 ,降压过程测得的根系导水率显著大于用升压过程的 ,并且前者的相关系数大于后者。这种差异是由于这两个过程中质外体途径细胞壁空间充水量不同造成的。开始升压时 ,由于细胞壁空间含水量低 ,质外体途径阻力大 ,导致非结构阻力 ;随着压力的升高 ,细胞壁空间含水量增大 ,质外体途径导度增大 ,减小甚至可以消除非结构阻力。降压法可以使根系快速复水 ,消除传统方法因长时间复水所致根结构的改变。建议用降压法测定根系导水率

Osmoregulatory actions of growth hormone in juvenile tilapia (Oreochromis niloticus)

Growth hormone (GH) effectively promotes seawater (SW) adaptation in salmonids, but little is known of its effect in tilapias. Experiments were performed to investigate the effects of recombinant eel GH (reGH) on osmoregulatory actions and ultrastructural features of gill chloride cells in juvenile tilapia, Oreochromis niloticus. Tilapia showed a markedly improved SW survival, when directly transferred from freshwater (FW) to 62.5% SW 24h after a single reGH injection (0.25 or 2.5 mu g g(-1)) or 3 reGH injections (0.25 mu g g(-1) every other day). Plasma Na+ and Mg2+ levels were significantly reduced by reGH (0.25 and 2.5 mu g g(-1)) compared with saline injections; Ca2+ concentrations were reduced significantly by high dose of reGH (2.5 mu g g(-1)) after SW transfer. However, fish failed to survive more than 24h when directly transferred to 70 % SW, although the fish treated with reGH could survive longer than the controls. When examined by electron microscopy, the chloride cells were identified as mitochondrion-rich and an extensive tubular system was induced by GH treatment. The results of the present study suggest that, similar to its effect on salmonids, GH also exerts acute osmoregulatory actions and enhances SW adaptation in juvenile tilapia. GH also stimulates the differentiation of chloride cells toward SW adaptation.

Laurencia nanhaiense sp nov., a new species of the genus Laurencia(Rhodomelaceae, Rhodophyta) from China

Laurencia nanhaiense sp. nov. (Rhodomelaceae, Rhodophyta) is described from Hainan and Guangdong Provinces, China. The new species clearly displays one of the defining features of the genus, viz. four periaxial cells per vegetative axial segment. It differs from other closely related species in having a combination of features such as terete axes from a basal system composed of a primary, discoid holdfast and a secondary attachment to give rise to many short rhizoids, branching oppositely and alternately, irregularly tristichous or subverticillately polystichous, having more curve branches with very sparse, adventitious ultimate branchlets, non-projecting superficial cortical cells at the apices of ultimate branchlets, presence of longitudinally oriented secondary pit-connections between contiguous superficial cortical cells, absence of lenticular thickenings in the walls of medullary cells, parallel arrangement of tetrasporangia along the axis of stichidia, and presence of intercellular spaces between medullary cells.