Cell migration: integrating signals from front to back

Cell migration is a highly integrated multistep process that orchestrates embryonic morphogenesis; contributes to tissue repair and regeneration; and drives disease progression in cancer, mental retardation, atherosclerosis, and arthritis. The migrating cell is highly polarized with complex regulatory pathways that spatially and temporally integrate its component processes. This review describes the mechanisms underlying the major steps of migration and the signaling pathways that regulate them, and outlines recent advances investigating the nature of polarity in migrating cells and the pathways that establish it.     

Impact of number of stems per stool on mechanical harvesting of a Eucalyptus globulus coppiced plantation in south-west Western Australia

Coppice regeneration of eucalypt plantations is increasingly being used in Australia to reduce re-establishment costs. However, little is known about the impact of early coppice reduction regimes on harvester performance during clearfelling. The trial compared the productivity, time consumption, cost and fuel use of a single-grip harvester (Hyundai 210LC-9 base and SP 591LX harvesting head) clearfelling a 10.5-year-old, second-rotation coppiced Eucalyptus globulus stand in south-west Western Australia for chip logs. Coppice stems had been reduced to one stem or two stems per stool or left untreated. Time and piece counts were used to determine harvester productivity. Harvester cycle and elemental times and the number of logs and harvester head passes per stem were obtained from video recordings. Harvester fuel use was determined by refilling the fuel tank to the same point each day. Stem size was the major factor influencing harvester productivity (20.8 m3 per productive machine hour without delays [PMH₀], 11.8 m³ PMH₀^?1 and 8.6 m³ PMH₀^?1 in the single-stem (mean stem volume [MSV] 0.21 m³), two-stem (MSV 0.09 m³) and untreated trial areas (MSV 0.06 m³), respectively. Estimated harvester cost (AU$ m^–3) was considerably greater for the two-stem and untreated trial areas, which reflected the lower harvester productivity in these areas. Processing time represented over 60% of the total cycle time for all trial areas. Coppice characteristics resulted in significantly different moving/positioning times between trial areas. However, this difference had no impact on cycle times. Number of logs per stem was a significant variable in cycle and processing time regressions for all trial areas and felling time for the single-stem trial area. Number of harvester head passes was a significant variable in cycle and processing time regressions for the single-stem trial area and processing times for the two-stem trial area, although its effect was less than that of the number of logs per stem. Fuel consumption (L PMH₀^?1) was relatively constant between the trial areas, hence harvester energy intensity (L m^?3) reflected the harvester productivity in each trial area.     

Grassland soil organic carbon and the effects of irrigated cropping in Alberta,Canada

High heterogeneity in the spatial distribution of soil organic carbon (SOC) in grasslands causes uncertainty in estimating its content and storage. In this study, we investigated the spatial distribution of SOC content and storage in the prairies of southern Alberta, Canada, and how it is affected by land use such as irrigated cropping and other environmental conditions such as cattle grazing, slope landscape position and dominant plant species. The mean SOC content was determined to be 11.5 g kg^–1 (range: 8.9 to 22.4 g kg^–1) in the 0–10 cm layer and 6.8 g kg^–1 (range: 4.0 to 13.3 g kg^–1) in the 10–30 cm layer; mean SOC storage was 1.59 kg C m^–2 (range: 1.23 to 2.78 kg C m^–2) in the 0–10 cm layer and 2.07 kg C m^–2 (range: 1.21 to 3.62 kg C m^–2) in the 10–30 cm layer. The SOC content was significantly affected by slope position in both the 0–10 and 10–30 cm layers, in the following order: bottom >middle > top position. Moreover, SOC storage was higher in sites dominated by shrubs than graminoid/forb communities. Thus, SOC content and storage had distinctly clustered spatial patterns throughout the study area and were significant differences between the 0–10 and 10–30 cm soil layers. Prior land-use change from arid grassland to irrigated cropland increased SOC content and storage in bulk soils.