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The apparent diffusion constant, K, derived from profiles ofradioactivity during labelled sucrose translocation, is temperature-dependentwith a Q10 of 2.9 in Pteridium. This value is similar to thoseobtained by other authors for mass transfer rates. The behaviourof K with temperature supports a translocation mechanism ofthe activated-diffusion type and is consistentwith the Canny and Phillips translocation model which also suggestsa basis for the 25-30° C temperature optimum in translocation. 相似文献
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Translocation in Pteridium 总被引:2,自引:0,他引:2
The distributions of radioactivity with distance have been mappedin the rachis of Pteridium aquilinum at different times afterapplication of 14CO2 to a pinna. Profiles change in shape withtime, from wave to transition and then to diffusion. The apparentdiffusion constant of sucrose may be obtained from transitionand diffusion profiles. Values varied from 2.2 x 103to 3.6 x 102 cm2 sec1. These results are comparedwith those for various angiosperm species. 相似文献
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Abstract: Limopsis is one of the most speciose and widespread bivalve genera in the Southern Ocean at the present day. However, the fossil record of the genus is poorly known from the southern high latitudes. Here, we review the fossil record in this region to help understand the evolutionary origins of the genus. Limopsis infericola sp. nov. and additional specimens of a previously described species are added to the fossil record of Antarctica. The globally distributed limopsid clade had its earliest occurrences in the Early Cretaceous of Europe and New Zealand, then radiated during the Late Cretaceous (Maastrichtian, 70.6–65.5 Ma). Fossil evidence shows that the genus underwent a second, Cenozoic, radiation related to the isolation of Antarctica and the onset of cooling in the southern hemisphere. The genus has persisted in Antarctica for the last 50 myr, adapting to extreme changes in the environmental conditions, including surviving the last glacial maximum in marine refugia. 相似文献
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