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With the aim to contribute to elucidation of the role of phytohormones in plant responses to stresses the endogenous contents of abscisic acid (ABA) and cytokinins (CK) were followed in French bean, maize, sugar beet, and tobacco during water stress and subsequent rehydration. The effects of pre-treatments with exogenous ABA or benzyladenine (BA) before imposition of water stress were also evaluated. The content of ABA increased by water stress, and with the exception of bean plants increased content of ABA remained also after rehydration. In all plant species the ABA content was further increased by ABA pre-treatment, but in bean and maize it decreased by BA pre-treatment. The highest total content of CK was observed in bean and the lowest in maize during water stress. In their spectrum, the storage CK were dominant in bean, and inactive CK in tobacco while in sugar beet and maize all groups were present in comparable amounts. In all plant species, the contents of CK increased during water stress and with exception of bean they decreased back after rehydration. ABA pre-treatment further increased contents of CK in water-stressed bean and tobacco. BA pre-treatment increased contents of CK in sugar beet and tobacco after rehydration.  相似文献
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Species composition and interactions, biomass dominance, geographic distribution and driving variables were investigated for two key elements of the pelagic food web of Alpine lakes, the phytoplankton and the zooplankton, based on a single sampling campaign during summer 2000. Altogether, 70 lakes were surveyed, 49 of which located in three different lake districts of the west and eastern Italian Alps and 21 in the central Austrian Alps (within the uppermost Danube catchment). In addition to the analysis of environmental variables affecting distribution and species structure of the two planktonic compartments, a brief review of the main research lines and hypotheses adopted in the past for the study of phytoplankton and zooplankton in high Alpine lakes is given. The lakes, investigated partly within the European project EMERGE (EVK1-CT-1999-00032) and partly within a regional project in the eastern Alps, comprise a wide range of morphological, chemical and trophic conditions. The phytoplankton communities were found to be diverse and mostly dominated by flagellates (chrysophytes, cryptophytes and dinoflagellates), and only to a lesser extent by non-motile green algae, desmids and centric diatoms. The zooplankton communities were mainly dominated by Alpine cladocerans and copepod species, while rotifers were abundant within one group of Italian lakes (sampled in early summer). The multivariate statistical analyses (CCA) showed that catchment features (i.e. percentage of vegetation cover and geochemical composition) and nitrate concentration are essential drivers for the phytoplankton, whereas for zooplankton also trophic status of the lakes and phytoplankton structure are important. The combined variance analysis of the lake clusters outlined by the multivariate analyses on phytoplankton and zooplankton data, respectively, allowed the identification of four principal lake types (three located on siliceous and one on carbonaceous bedrock), each one characterised by a certain combination of habitat features, which in their turn influence trophic state, and phytoplankton and zooplankton species composition and functionality.  相似文献
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Interpretation of light trap catches of moths is complicated by daily variation in weather that alters flight activity and numbers caught. Light trap efficiency is also modified by wind and fog, and daily weather may effect absolute abundance (numbers actually present). However, actograph experiments and other sampling methods suggest that changes in daily activity are large by comparison to changes in absolute abundance. Daily variation in weather (other than wind and fog) is therefore a form of sampling error in absolute abundance estimates. We investigated the extent of this sampling bias in 26 years of population dynamics from 133 moth species. In a subset of 20 noctuid and geometrid species, daily numbers caught were positively correlated with temperature in 14 species, and negatively correlated with rainfall in 11 species. The strength of correlations varied between species, making it difficult to standardize catches to constant conditions. We overcame this by establishing how weather variation changed with time and duration of the flight period. Species flying later in the summer and for shorter periods experienced more variable temperatures, making sampling error greater for these species. Of the 133 moth species, those with shorter flight periods had greater population variability and more showed significant temporal density dependence. However, these effects were weak, which is encouraging because it suggests that population analyses of light trap data largely reflect factors other than sampling error.  相似文献
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The contact between the SH2 domain and the C-terminal tail of c-Src inhibits its kinase activity via a complex network of interactions, including the SH3 domain. We examined the role of the SH3 domain in v-Src, where the C-terminal tail is mutated and unbound. We used the v-Src variants Prague C (PRC) and Schmidt-Ruppin A (SRA), which are of low and high kinase activities, respectively, to measure phosphorylation in vitro by immunoprecipitated kinases produced in Saccharomyces cerevisiae. Swapping the regulatory domains between SRA and PRC revealed that N117D, I96T, and V124L mutations in the n-src- and RT-loops of the SH3 domain of PRC are responsible for the low kinase activity of PRC. Moreover, introducing D117N, R95W, T96I, and L124V into activated c-Src(Y527F) caused a 2.5-fold increase in its activity. The mutations in the CD linker KP249,250DG and L255A, which were shown to activate c-Src, had no effect on the activity of the "SH2-activated" Src kinases. Together our data suggest that in the "SH2-activated" forms of Src, the SH3 domain continues to influence the kinase activity via the direct contacts of the n-src- and RT-loops with the kinase N-terminal lobe.  相似文献
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Phlebotomus sergenti populations from different areas of the Mediterranean basin are known to exhibit high intraspecific variability. Previous studies of ITS2 revealed the presence of two branches that may represent sibling species. To corroborate this finding by other tools, two colonies of P. sergenti originating from Turkey and Israel, each belonging to a different ITS2 branch, were compared by three different methods: geometric morphometric analysis of wing shape, RAPD (random amplified polymorphic DNA), and cross-mating study. For geometric morphometric analysis, two-dimensional Cartesian coordinates of 16 landmarks from the wings were digitized and analyzed. Significant shape differences were found between colonies but not between sexes within each colony. RAPD results formed two distinctive clades corresponding to the origin of the colony but also showed heterogenity among members of both colonies. In cross-mating studies, viable hybrid F1 and F2 progeny were obtained when both Turkish males/Israeli females and Israeli males/Turkish females were crossed. F1 progeny was included in RAPD analysis and these hybrids formed a distinctive clade with an intermediate position between the two parental clades. No significant differences were found in egg production of crossed sand flies. The cross-mating study showed that there is no reproductive barrier between P. sergenti from different geographical areas. On the other hand, RAPD and geometric morphometric analysis revealed a significant difference between colonies and confirmed the suitability of previous ITS2 analysis for discrimination among sand fly populations. Further development of molecular markers should resolve a possible existence of sibling species within Phlebotomus sergenti.  相似文献
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