Detecting phenology change in the mayfly Ephemera danica: responses to spatial and temporal water temperature variations

1. Rising water temperatures under climate change are expected to affect the phenology of aquatic insects, including the mayfly Ephemera danica Müller which is widespread throughout Europe. 2. To assess temporal and spatial variability in mayfly emergence, E. danica were monitored at two thermally contrasting reaches in the River Dove, English Peak District over the period 2007–2013. Inter‐annual variations in growing degree days (GDDs) were modelled for an upstream site with intermittent spring flow supplementing main channel flow (Beresford Dale) and downstream site dominated by near constant discharges of cool groundwater (Dovedale). 3. A strong association exists between the emergence cycle of E. danica and GDDs at each site. Beresford Dale accumulated on average 374 more GDDs than Dovedale. After warm summers E. danica emerged after only 1 year in Beresford Dale but began to revert to a bi‐annual cycle after the particularly wet/cool year of 2012. In Dovedale, E. danica maintained a 2‐year cycle throughout the monitoring period in spite of the phenology changes observed 8 km upstream. 4. Data from the present study suggest that habitats near cool groundwater may provide important refugia for populations of insects, potentially delaying permanent shifts in phenology under climate change. However, an ability to detect changes in the thermal triggers and phenological response may be hindered by conventional spot sampling protocols.     

Electron-probe Microanalysis Studies of Silicon in the Elongating Basal Internodes of Avena sativa (L.), Hordeum sativum (Jess.) and Triticum aestivum (L.)

Silicon deposits in the elongating basal internodes of almostmature, field grown specimens of Avena sativa, Hordeum sativumand Triticum aestivum were investigated using electron-probemicroanalysis. In A. sativa and H. sativum silicon was foundto be confined to the cells in the endodermal layer, being presentwithin the inner tangential and radial walls, and occasionallyin the outer tangential wall. In T. aestivum some silicon wasalso located in walls of cells surrounding the vascular bundles. The anatomy of the internodal tissues is discussed for the threespecies from light micrographs. The endodermal layer is discontinuousin A. sativa and H. sativum, in the former species it partlyextends around individual vascular bundles. In T. aestivum itforms a complete cylinder around the stelar region and alsoshows considerably more thickening of the inner tangential wallthan in the other species. The results are discussed in relation to the anatomy of theinternodal tissues and the possible function of silicon in theendodermis. Avena sativa L., Hordeum sativum Jess, Triticum aestivum L., oat, barley, wheat, silicon deposition, electron-probe microanalysis     

The expression of resistance to powdery mildew infection in winter wheat cultivars. I. Seedling resistance

Detached seedling leaf tests were used to assign 18 winter wheat cultivars to three wheat mildew resistance (WMR) groups on the basis of identified race-specific resistance characters. The same cultivars were exposed in mobile seedling nurseries from 1976 to 1979. Infection by mildew populations containing matching pathogenicity characters was used to recognise background seedling resistance in three cultivars: Maris Freeman, Maris Huntsman and Sentry. The value of background seedling resistance is discussed.     

rDNA Sites in Mitotic and Polytene Chromosomes of Vigna unguiculata (L.) Walp. and Phaseolus coccineus L. Revealed by in situ Hybridization

Root tip mitotic and tapetal polytene cells ofVigna unguiculataandPhaseolus coccineus were hybridized with a ribosomal DNA(rDNA) probe. While the number of rDNA sites were as expectedforP. coccineus, it was surprisingly higher inV. unguiculatawhere ten rDNA sites were found in both tissues. A sequentialbanding technique on mitotic chromosomes ofV. unguiculata wasused to map the positions of the rDNA sites more accurately.In mitotic cells eight of the rDNA hybridization sites weresimilar in size while the remaining sites were smaller. In contrast,the hybridization sites were more variable in size in polytenecells with no more than six sites being relatively large. Thedifferences in size of the hybridization sites between the twotissues suggest differential amplification of the rDNA sequences.InP. coccineus six hybridization sites were found in both tissuetypes. The relative sizes of the sites were similar in bothtissue. The presence of speckled signal surrounding four ofthe six sites suggested that at least four of the rDNA siteswere transcribed. rDNA; in situ ; Vigna ; Phaseolus ; polytene; tapetal; Leguminosae     

Genome downsizing in polyploid plants

All else being equal, polyploids are expected to have larger C-values (amount of DNA in the unreplicated gametic nucleus) than their diploid progenitors, increasing in direct proportion with ploidy. This expectation is observed in some polyploid series, especially those newly formed, but there are examples suggesting that C-values in particular polyploids are less than expected. The availability of the Angiosperm DNA C-values database ( http://www.rbgkew.org.uk/cval/homepage.html ) has allowed this question to be addressed across a broad range of angiosperms and has revealed striking results deviating from expectation: (i) mean 1C DNA amount did not increase in direct proportion with ploidy, and (ii) mean DNA amount per basic genome (calculated by dividing the 2C value by ploidy) tended to decrease with increasing ploidy. These results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance. Recent advances in our understanding of the molecular events that take place following polyploid formation together with new data on how DNA amounts can both increase and decrease provide some insights into how genome downsizing may take place. The nature of the evolutionary forces that may be driving DNA loss are also discussed.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 651–663.