Element localization in ultrathin cryosections of high-pressure frozen ectomycorrhizal spruce roots

We present, for the first time, elemental mapping of ultra-thin cryosections from high-pressure frozen ectomycorrhizal roots of Picea abies–Hebeloma crustuliniforme. The maps provide interpretable information on the relationship between elements and the structure of inhomogeneous objects. Cryoultramicrotomy together with energy dispersive X-ray microanalysis (EDX) offers the potential to study the subcellular localization of specific ions and ecologically important tracers (Cs and Sr) in ectomycorrhizal roots under conditions resembling the natural slate as closely as possible. Structural changes of the ectomycorrhizal roots, in particular the absence of a Hartig net at high NH₄⁺ levels in the nutrient solution, were accompanied by elemental modification of Ca in cortical cell walls, where markedly higher concentrations of Ca were found. Cs and Sr applied to the nutrient solution were localized in root and fungal cells of the Hartig net. Cs accumulated mainly in the vacuoles of the Hartig net hyphae and its distribution was very similar to the distribution of K. In contrast to Cs, Sr was found to occur mainly in electron-opaque and P-rich granules. From this study, (here is no indication that Ca is the only ion accompanying P in the P-rich granules. Several elements including Ca, K, Cl, S, Cs and Sr, with highest concentrations for S, can occur together with P in these granules. The occurrence of the P-rich electron-opaque deposits in fungal cells might be the first evidence of polyphosphate granules in the native state, since our specimen preparation technique did not include chemical fixation.     

Sex ratio, reproductive mode and genetic diversity in Triops cancriformis

1. Aquatic invertebrates display a wide array of alternative reproductive modes from apomixis to hermaphroditism and cyclical parthenogenesis. These have important effects on genetic diversity and population structure. Populations of the 'living fossil' Triops cancriformis display a range of sex ratios, and various reproductive modes are thought to underlie this variation. Using sex ratio information and histological analyses European populations have been inferred to be gonochoric (with separate males and females), selfing hermaphroditic and androdioecious, a rare reproductive mode in which selfing hermaphrodites coexist with variable proportions of males. In addition, some populations have been described as meiotic parthenogens.
2. Here we use population genetic analysis using microsatellite loci in populations with a range of sex ratios including a gonochoric population, and marker segregation patterns in heterozygote individuals reared in isolation, to clarify the reproductive mode in this species.
3. Our data show that populations in general have very low levels of genetic diversity. Non-gonochoric populations show lower genetic diversity, more heterozygote deficiencies, higher inbreeding coefficients and stronger linkage disequilibria than the gonochoric population. The maintenance of some heterozygosity in populations is consistent with some male influence in T. cancriformis populations, as would be expected from an androdioecious reproductive system. Results of marker segregation in eggs produced in isolation from non-gonochoric populations indicate that meiosis occurs and are consistent with two reproductive modes: selfing hermaphroditism and a type of ameiotic parthenogenesis.
4. Overall, our data indicate that androdioecy and selfing hermaphroditism are the most likely reproductive modes of non-gonochoric European Triops populations. Triops populations are strongly structured, suggesting high genetic drift and low levels of gene flow.