Nodulation ofTrifolium subterraneum byRhizobium leguminosarum

Summary Four cultivars ofTrifolium subterraneum were nodulated by five strains ofRhizobium leguminosarum; all combinations except one gave 100% nodulation. Rates of nodule formation and total nodule numbers were similar to those with an effectiveR. trifolii strain. The nodules were more commonly associated with lateral roots and were ineffective in nitrogen fixation.     

Detection and quantification of triazine herbicides using algal cell fluorescence

Summary A continuous-flow system is described which, by measuring fluorescence of the unicellular alga Chlorella, is capable of measuring concentrations of the triazine herbicide, simazine, as low as 60nM (approx 12g l^-1) within 5 minutes. Further developments are suggested to achieve the desired detection limit of 0.5nM. The use of such an instrument in environmental analysis is discussed.     

Long-term culture of human aortas

Summary Segments of human thoracic aorta were maintained in long-term explant culture for 18 weeks in serum-supplemented medium. The aortas were grossly normal in appearance, and random samples fixed for light microscopy prior to culture revealed a normal morphology. The intima contained no more than five layers of smooth muscle cells. After 7 days in culture, the intima was noticeably thicker than the uncultured segments. The increased thickness was due to proliferating smooth muscle cells and production of extracellular material. After several months in culture, extracellular material consisting of collagen and flocculent material was present in areas resembling atherosclerotic fibrous plaques. A peripheral growth, which formed around the explant, was composed of fibroblastlike cells and added to the overall thickness of the intima. However, aortic segment maintained for up to 2 months in serum-free culture medium showed no cellular proliferation. This study demonstrates that changes resembling early stages of atherosclerosis occur in human aortas maintained in explant culture using routine culture procedures. Supported in part by the Pangborn Fund and the Graduate School of the University of Maryland. This is publication 443 from the Cellular Pathobiology Laboratory.     

Cyclin D1 and cyclin D3 show divergent responses to distinct mitogenic stimulation

D‐type cyclins predominantly regulate progression through the cell cycle by their interactions with cyclin‐dependent kinases (cdks). Here, we show that stimulating mitogenesis of Swiss 3T3 cells with phorbol esters or forskolin can induce divergent responses in the expression levels, localization and activation state of cyclin D1 and cyclin D3. Phorbol ester‐mediated protein kinase C stimulation induces S phase entry which is dependent on MAPK activation and increases the levels and activation of cyclin D1, whereas forskolin‐mediated cAMP‐dependent protein kinase A stimulation induces mitogenesis that is independent of MAPK, but dependent upon mTor and specifically increases the level and activation of cyclin D3. These findings uncover additional levels of complexity in the regulation of the cell cycle at the level of the D‐type cyclins and thus may have important therapeutic implications in cancers where specific D‐cyclins are overexpressed. J. Cell. Physiol. 225: 638–645, 2010. © 2010 Wiley‐Liss, Inc.     

Amazonia trees have limited capacity to acclimate plant hydraulic properties in response to long‐term drought

The fate of tropical forests under future climate change is dependent on the capacity of their trees to adjust to drier conditions. The capacity of trees to withstand drought is likely to be determined by traits associated with their hydraulic systems. However, data on whether tropical trees can adjust hydraulic traits when experiencing drought remain rare. We measured plant hydraulic traits (e.g. hydraulic conductivity and embolism resistance) and plant hydraulic system status (e.g. leaf water potential, native embolism and safety margin) on >150 trees from 12 genera (36 species) and spanning a stem size range from 14 to 68 cm diameter at breast height at the world's only long‐running tropical forest drought experiment. Hydraulic traits showed no adjustment following 15 years of experimentally imposed moisture deficit. This failure to adjust resulted in these drought‐stressed trees experiencing significantly lower leaf water potentials, and higher, but variable, levels of native embolism in the branches. This result suggests that hydraulic damage caused by elevated levels of embolism is likely to be one of the key drivers of drought‐induced mortality following long‐term soil moisture deficit. We demonstrate that some hydraulic traits changed with tree size, however, the direction and magnitude of the change was controlled by taxonomic identity. Our results suggest that Amazonian trees, both small and large, have limited capacity to acclimate their hydraulic systems to future droughts, potentially making them more at risk of drought‐induced mortality.     

Inconsistent detection of extinction debts using different methods

The extinction debt, delayed species extinctions following landscape degradation, is a widely discussed concept. But a consensus about the prevalence of extinctions debts is hindered by a multiplicity of methods and a lack of comparisons among habitats. We applied three contrasting species–area relationship methods to test for plant community extinction debts in three habitats which had different degradation histories over the last century: calcareous grassland, heathland and woodland. These methods differ in their data requirements, with the first two using information on past and current habitat area alongside current species richness, whilst the last method also requires data on past species richness. The most data‐intensive, and hence arguably most reliable method, identified extinction debts across all habitats for specialist species, whilst the other methods did not. All methods detected an extinction debt in calcareous grassland, which had undergone the most severe degradation. We conclude that some methods failed to detect an extinction debt, particularly in habitats that have undergone moderate degradation. Data on past species numbers are required for the most reliable method; as such data are rare, extinction debts may be under‐reported.