Phylogeography and genetic effects of habitat fragmentation on endangered Taxus yunnanensis in southwest China as revealed by microsatellite data.

It is not known how the profoundly complex topography and habitat heterogeneity generated by the uplift of the Qinghai-Tibetan Plateau (QTP) during the late Tertiary affected population genetic structure of endangered Taxus yunnanensis. In addition, the effects of habitat fragmentation due to anthropogenic disturbance on genetic diversity and population differentiation of this species have not been studied. T. yunnanensis is an ancient tree/shrub mainly distributed in southwest China. Recently, the species has suffered a sharp decline due to excessive logging for its famous anticancer metabolite taxol, resulting in smaller and more isolated populations. To understand the phylogeography and genetic consequences of habitat fragmentation of this endangered species, using 11 polymorphic microsatellites, we genotyped 288 individuals from 14 populations from a range-wide sampling in China. Our results suggest that two different population groups that were once isolated have persisted in situ during glacial periods in both areas, and have not merged since. Habitat fragmentation has led to significant genetic bottlenecks, high inbreeding and population divergence in this species. The two different population groups of T. yunnanensis could be attributed to restricted gene flow caused through isolation by geographical barriers and by habitat heterogeneity during uplift of the QTP, or the existence of two separate glacial refugia during the Pleistocene. In situ and ex situ conservation of the two Evolutionarily Significant Units (ESUs), artificial gene flow between populations and a comprehensive understanding of the pollination system in this endangered species are suggested from this study.

K+ channels inhibited by hydrogen peroxide mediate abscisic acid signaling in Vicia guard cells.

A number of studies show that environmental stress conditions increase abscisic acid (ABA) and hydrogen peroxide (H2O2) levels in plant cells. Despite this central role of ABA in altering stomatal aperture by regulating guard cell ion transport, little is known concerning the relationship between ABA and H2O2 in signal transduction leading to stomatal movement. Epidermal strip bioassay illustrated that ABA-inhibited stomatal opening and ABA-induced stomatal closure were abolished partly by externally added catalase (CAT) or diphenylene iodonium (DPI), which are a H2O2 scavenger and a NADPH oxidase inhibitor respectively. In contrast, internally added CAT or DPI nearly completely or partly reversed ABA-induced closure in half-stoma. Consistent with these results, whole-cell patch-clamp analysis showed that intracellular application of CAT or DPI partly abolished ABA-inhibited inward K+ current across the plasma membrane of guard cells. H2O2 mimicked ABA to inhibit inward K+ current, an effect which was reversed by the addition of ascorbic acid (Vc) in patch clamping micropipettes. These results suggested that H2O2 mediated ABA-induced stomatal movement by targeting inward K+ channels at plasma membrane.

Affinity chromatographic separation of alpha-fetoprotein variants: development of a mini-column procedure, and application to cancer patients.

This is an affinity chromatographic procedure for separating variants of alpha-fetoprotein in 0.1 mL of serum on a disposable mini-column containing 0.9 mL of concanavalin A-Sepharose, at pH 6.4 and with a flow rate of 5 mL/h. The binding capacity of the column is 52 micrograms. Analytical recovery was 90%. Between-run CVs varied from 2.0% for samples with a high percentage of concanavalin A nonreactive fraction to 13% for samples with a low percentage. The mean proportion of nonreactive alpha-fetoprotein was 13.4% for patients with hepatocellular carcinoma, 62.2% for testicular carcinoma, and 8.9% for nonmalignant liver diseases. This suggests that the alpha-fetoprotein variants could be used to distinguish hepatocellular carcinoma from other carcinomas. Serial determination of the concanavalin A nonreactive fraction in such patients showed a relatively constant percentage. This indicates that monitoring variants in patients with hepatocellular carcinoma throughout their clinical course may not provide useful information additional to that provided by the values for total serum alpha-fetoprotein.