Actin in Xenopus Development: Indirect Immunofluorescence Study of Actin Localization

Actin was studied in Xenopus unfertilized eggs and early developmental stages. Immunochemical proof is given of structural differences between Xenopus laevis muscle actin and nonmuscle cell actin. Actin localization and changes of actin aggregation during Xenopus development were observed using indirect immunofluorescence. We have also tried to explain the presence of an actin shell around the yolk platelets that appeared in our experiments.     

Two closely linked tomato HKT coding genes are positional candidates for the major tomato QTL involved in Na+/K+ homeostasis

The location of major quantitative trait loci (QTL) contributing to stem and leaf [Na⁺] and [K⁺] was previously reported in chromosome 7 using two connected populations of recombinant inbred lines (RILs) of tomato. HKT1;1 and HKT1;2, two tomato Na⁺‐selective class I‐HKT transporters, were found to be closely linked, where the maximum logarithm of odds (LOD) score for these QTLs located. When a chromosome 7 linkage map based on 278 single‐nucleotide polymorphisms (SNPs) was used, the maximum LOD score position was only 35 kb from HKT1;1 and HKT1;2. Their expression patterns and phenotypic effects were further investigated in two near‐isogenic lines (NILs): 157‐14 (double homozygote for the cheesmaniae alleles) and 157‐17 (double homozygote for the lycopersicum alleles). The expression pattern for the HKT1;1 and HKT1;2 alleles was complex, possibly because of differences in their promoter sequences. High salinity had very little effect on root dry and fresh weight and consequently on the plant dry weight of NIL 157‐14 in comparison with 157‐17. A significant difference between NILs was also found for [K⁺] and the [Na⁺]/[K⁺] ratio in leaf and stem but not for [Na⁺] arising a disagreement with the corresponding RIL population. Their association with leaf [Na⁺] and salt tolerance in tomato is also discussed.     

Cross‐amplification of 10 new isolated polymorphic microsatellite loci for red mullet (Mullus barbatus) in striped red mullet (Mullus surmuletus)

Ten polymorphic dinucleotide microsatellite loci were isolated and characterized for the red mullet (Mullus barbatus). Allele variability was tested on both the red mullet and its congener the striped red mullet (Mullus surmuletus). Characterization of 30 individuals of both species from the western Mediterranean showed moderate to high allelic diversity ranging from two to 26 alleles per locus (mean 10.9). Three loci showed departures from Hardy–Weinberg proportions. No evidence of significant association between genotypes at pairs of loci was observed. These polymorphic loci could be suitable for population genetic assessments of both species.     

Effects of altered α‐ and β‐branch carotenoid biosynthesis on photoprotection and whole‐plant acclimation of Arabidopsis to photo‐oxidative stress

Functions of α‐ and β‐branch carotenoids in whole‐plant acclimation to photo‐oxidative stress were studied in Arabidopsis thaliana wild‐type (wt) and carotenoid mutants, lut ein deficient (lut2, lut5), n on‐p hotochemical q uenching1 (npq1) and s uppressor of z eaxanthin‐l ess1 (szl1) npq1 double mutant. Photo‐oxidative stress was applied by exposing plants to sunflecks. The sunflecks caused reduction of chlorophyll content in all plants, but more severely in those having high α‐ to β‐branch carotenoid composition (α/β‐ratio) (lut5, szl1npq1). While this did not alter carotenoid composition in wt or lut2, which accumulates only β‐branch carotenoids, increased xanthophyll levels were found in the mutants with high α/β‐ratios (lut5, szl1npq1) or without xanthophyll‐cycle operation (npq1, szl1npq1). The PsbS protein content increased in all sunfleck plants but lut2. These changes were accompanied by no change (npq1, szl1npq1) or enhanced capacity (wt, lut5) of NPQ. Leaf mass per area increased in lut2, but decreased in wt and lut5 that showed increased NPQ. The sunflecks decelerated primary root growth in wt and npq1 having normal α/β‐ratios, but suppressed lateral root formation in lut5 and szl1npq1 having high α/β‐ratios. The results highlight the importance of proper regulation of the α‐ and β‐branch carotenoid pathways for whole‐plant acclimation, not only leaf photoprotection, under photo‐oxidative stress.     

Life in harsh environments: carabid and spider trait types and functional diversity on a debris‐covered glacier and along its foreland

1. Patterns of species richness and species assemblage composition of ground‐dwelling arthropods in primary successions along glacier forelands are traditionally described using a taxonomic approach. On the other hand, the functional trait approach could ensure a better characterisation of their colonisation strategies in these types of habitat. 2. The functional trait approach was applied to investigate patterns of functional diversity and life‐history traits of ground beetles and spiders on an alpine debris‐covered glacier and along its forefield in order to describe their colonisation strategies. 3. Ground beetles and spiders were sampled at different successional stages, representing five stages of deglaciation. 4. The results show that the studied glacier hosts ground beetle and spider assemblages that are mainly characterised by the following traits: walking colonisers, ground hunters and small‐sized species. These traits are typical of species living in cold, wet, and gravelly habitats. The diversity of functional traits in spiders increased along the succession, and in both carabids and spiders, life‐history traits follow the ‘addition and persistence model’. Accordingly, there is no turnover but there is an addition of new traits and a variation in their proportion within each species assemblage along the succession. The distribution of ground beetles and spiders along the glacier foreland and on the glacier seems to be driven by dispersal ability and foraging strategy. 5. The proposed functional approach improves knowledge of the adaptive strategies of ground‐dwelling arthropods colonising glacier surfaces and recently deglaciated terrains, which represent landforms quickly changing due to global warming.     

Stem CO2 efflux in six co‐occurring tree species: underlying factors and ecological implications

Stem respiration plays a role in species coexistence and forest dynamics. Here we examined the intra‐ and inter‐specific variability of stem CO₂ efflux (E) in dominant and suppressed trees of six deciduous species in a mixed forest stand: Fagus sylvatica L., Quercus petraea [Matt.] Liebl, Quercus pyrenaica Willd., Prunus avium L., Sorbus aucuparia L. and Crataegus monogyna Jacq. We conducted measurements in late autumn. Within species, dominants had higher E per unit stem surface area (E_s) mainly because sapwood depth was higher than in suppressed trees. Across species, however, differences in E_s corresponded with differences in the proportion of living parenchyma in sapwood and concentration of non‐structural carbohydrates (NSC). Across species, E_s was strongly and NSC marginally positively related with an index of drought tolerance, suggesting that slow growth of drought‐tolerant trees is related to higher NSC concentration and E_s. We conclude that, during the leafless period, E is indicative of maintenance respiration and is related with some ecological characteristics of the species, such as drought resistance; that sapwood depth is the main factor explaining variability in E_s within species; and that the proportion of NSC in the sapwood is the main factor behind variability in E_s among species.     

Pliensbachian gastropods from Venetian Southern Alps (Italy) and their palaeobiogeographical significance

Abstract: The Pliensbachian gastropods described by De Toni in 1912, coming from an isolated boulder at the foot of Mt Vedana (eastern margin of Trento Platform, Venetian Southern Alps, Italy) are revised. The fauna consists of 13 species representing nine families and eight superfamilies. Despite the low number of species, the assemblage represents the most diverse Early Jurassic gastropod fauna known for the Venetian Southern Alps. The boulder yielding the material was thought to derive from the upper part of the Early Jurassic Calcari Grigi Group, a carbonate platform unit extensively cropping out in the Mt Vedana area. The sedimentological analysis indicates a prevalently bioclastic wackstone‐floatstone, reflecting a lime‐muddy deposit undergone to an early consolidation. This and the high content of ammonoids, which is unusual for the Calcari Grigi Group, are typical aspects of a condensed pelagic sediment, presumably a fissure filling at the top of the carbonate platform succession. Palaeobiogeographical comparisons show that the fauna is composed of species occurring exclusively in pelagic limestones of the western Tethys. By contrast, it shows no relationships with the coeval faunas of the adjacent Trento platform and of the other western Tethyan carbonate platforms. These lines of evidence and the facies analysis would testify to the Pliensbachian drowning of the eastern margin of the Trento platform. In the wider context of the palaeobiogeographical history of Early Jurassic western Tethyan gastropods, the species from Vedana belong to a faunal stock which is typical for pelagic, mainly postdrowning sediments. Thus, appearance and diffusion in space and time of this stock were probably regulated by the direction, rate and pattern of the Neotethyan rifting. A new subgenus, Proarcirsa (Schafbergia) subgen. nov., and three new species, namely Ataphrus (Ataphrus) cordevolensis sp. nov., Guidonia pseudorotula sp. nov. and Proarcirsa (Schafbergia) zirettoensis sp. nov. are erected.     

Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

In this study we examined ecosystem respiration (R_ECO) data from 104 sites belonging to FLUXNET, the global network of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability of R_ECO: temporally and between sites as affected by climate, vegetation structure and plant functional type (PFT) (evergreen needleleaf, grasslands, etc.). We demonstrated that a model using only climate drivers as predictors of R_ECO failed to describe part of the temporal variability in the data and that the dependency on gross primary production (GPP) needed to be included as an additional driver of R_ECO. The maximum seasonal leaf area index (LAI_MAX) had an additional effect that explained the spatial variability of reference respiration (the respiration at reference temperature T_ref=15 °C, without stimulation introduced by photosynthetic activity and without water limitations), with a statistically significant linear relationship (r²=0.52, P<0.001, n=104) even within each PFT. Besides LAI_MAX, we found that reference respiration may be explained partially by total soil carbon content (SoilC). For undisturbed temperate and boreal forests a negative control of total nitrogen deposition (N_depo) on reference respiration was also identified. We developed a new semiempirical model incorporating abiotic factors (climate), recent productivity (daily GPP), general site productivity and canopy structure (LAI_MAX) which performed well in predicting the spatio‐temporal variability of R_ECO, explaining >70% of the variance for most vegetation types. Exceptions include tropical and Mediterranean broadleaf forests and deciduous broadleaf forests. Part of the variability in respiration that could not be described by our model may be attributed to a series of factors, including phenology in deciduous broadleaf forests and management practices in grasslands and croplands.