Unexpected efficiency of non-C(2) -symmetric bis(hydroxyamide)-based zinc-chelate catalysts

Asymmetric bis(hydroxyamide)-based zinc-chelate catalysts are able to promote the enantioselective addition of diethylzinc to benzaldehyde in the absence of titanium with yields and ees comparable, or inclusively superior, to their C(2) -symmetric analogues. This unexpected fact demonstrates that the previously established assumption on the necessity of using C(2) -symmetric bis(hydrdoxyamides) to generate C(2) -symmetric zinc-chelate catalysts can be discarded, which expand the possibilities for designing new ligands based on the interesting hydroxyl-amide functional grouping.     

Elevated CO2 stimulates grassland soil respiration by increasing carbon inputs rather than by enhancing soil moisture

It is not clear whether the consistent positive effect of elevated CO₂ on soil respiration (soil carbon flux, SCF) results from increased plant and microbial activity due to (i) greater C availability through CO₂‐induced increases in C inputs or (ii) enhanced soil moisture via CO₂‐induced declines in stomatal conductance and plant water use. Global changes such as biodiversity loss or nitrogen (N) deposition may also affect these drivers, interacting with CO₂ to affect SCF. To determine the effects of these factors on SCF and elucidate the mechanism(s) behind the effect of elevated CO₂ on SCF, we measured SCF and soil moisture throughout a growing season in the Biodiversity, CO₂, and N (BioCON) experiment. Increasing diversity and N caused small declines in soil moisture. Diversity had inconsistent small effects on SCF through its effects on abiotic conditions, while N had a small positive effect that was unrelated to soil moisture. Elevated CO₂ had large consistent effects, increasing soil moisture by 26% and SCF by 45%. However, CO₂‐induced changes in soil moisture were weak drivers of SCF: CO₂ effects on SCF and soil moisture were uncorrelated, CO₂ effect size did not change with soil moisture, within‐day CO₂ effects via soil moisture were neutral or weakly negative, and the estimated effect of increased C availability was 14 times larger than that of increased soil moisture. Combined with previous BioCON results indicating elevated CO₂ increases C availability to plants and microbes, our results suggest that increased SCF is driven by CO₂‐induced increases in substrate availability. Our results provide further support for increased rates of belowground C cycling at elevated CO₂ and evidence that, unlike the response of productivity to elevated CO₂ in BioCON, the response of SCF is not strongly N limited. Thus, N limited grasslands are unlikely to act as a N sink under elevated CO₂.     

Long-range organization of a satellite DNA family flanking the beet cyst nematode resistance locus (Hs1) on chromosome-1 of B. patellaris and B. procumbens

New members of a satellite DNA family (Sat 121), specific for wild beets of the section Procumbentes of the genus Beta, were isolated. Sequence analysis showed that the members of Sat-121 fall into two distinct classes. The organization of Sat-121 in the vicinity of a beet cyst nematode (Heterodera schachtii Schm.) resistance locus (Hs1) in B. patellaris and B. procumbens was investigated by pulsed-field gel electrophoresis (PFGE) using DNA from a series of resistant monosomic fragment additions, each containing an extra chromosome fragment of B. patellaris chromosome-1 (pat-1) in B. vulgaris. In this way several clusters of Sat-121 flanking the Hs1 ^pat-1 locus were identified. In nematode resistant diploid introgressions (2n=18), which contain small segments of B. procumbens chromosome-1 (pro-1) in B. vulgaris, only two major Sat-121 clusters were detected near the Hs1 ^pro-1 locus.     

Patterns of root activity and responses of species to nutrients in vegetation of fertile alluvial soil

Temporal pattern of growth, time and depth of root activity, and responses to N, P and K enrichment were measured for the three most abundant species in species-poor vegetation on fertile alluvial soil to examine whether differences in these characteristics could account for their co-existence. The responses of these co-existing species to nutrients were tested in a factorial experiment of N, P and K additions. In the control plots, repeated harvests and injections of Sr at different depths in the soil were used to test differences among species in temporal and spatial pattern of root activity. Root activities were assessed from the Sr concentrations in the aboveground biomass. Differences in temporal pattern of growth and root activity, but not differences in spatial root activity between species, could account for the co-existence of species, since Conium, the most abundant species, was the earliest grown and the deepest-rooted species and it died back when the other two species started to maximize their growth and root activity. In comparison with the second most abundant species Lactuca, Conium had higher N but lower P tissue concentrations. Addition of N favoured Conium and almost eliminated Lactuca, while P and/or K additions increased the abundance of Lactuca and restricted that of Conium. These results provide indications that the differential responses of species to nutrients could be explained by species co-existence also in fertile soils. The changes in vegetation composition after nutrient enrichment could merely be predicted by the species' tissue concentrations of nutrients. The addition of a particular nutrient tended to favor the species with the highest tissue concentration of this nutrient.     

Monosomic additions in beet (Beta vulgaris) carrying extra chromosomes of Beta procumbens

Summary Eleven isozyme systems were used to identify the extra chromosomes, originating from Beta procumbens, in progenies of 33 monosomic additions in beet (B. vulgaris). Nine groups of monosomic additions could be distinguished, representing the nine different chromosome types of B. procumbens.     

A full set of monosomic addition lines in Beta vulgaris from Beta webbiana: morphology and isozyme markers

Summary Nine different monosomic additions in Beta vulgaris from Beta webbiana were characterized through morphological characters and isozyme markers. The effect of the alien chromosome on the morphology of the recipient species is chromosome specific, and nine morphotypes could be distinguished. The added chromosome caused a growth reduction in the recipient plants. Eleven isozyme systems were used as marker systems. A 6PGDH band was found as a marker for chromosome 7, which contains a resistance gene for the beet cyst nematode in monosomic additions from Beta procumbens and Beta webbiana. A difference in the 6PGDH zymogram pattern between the two species with respect to this chromosome has been noted.     

Isolation of DNA markers linked to a beet cyst nematode resistance locus in Beta patellaris and Beta procumbens.

Summary In cultivated beet no useful level of resistance of the beet cyst nematode (BCN) Heterodera schachtii Schm. has been found, unlike the situation in wild species of the section Procumbentes. Stable introgression of resistance genes from the wild species into Beta vulgaris has not been achieved, but resistant monosomic additions (2n =18 + 1), diploids of B. vulgaris with an extra alien chromosome carrying the resistance locus, have been obtained. Here we describe a new series of resistant monosomic fragment addition material of B. patellaris chromosome 1 (pat-1). We further describe the cloning of a single-copy DNA marker that specifically hybridizes with a monosomic addition fragment of approximately 8 Mb (AN5-90) carrying the BCN resistance locus. This marker and another fragment-specific, single-copy DNA marker probably flank the BCN locus on the addition fragment present in the AN5-203 material, which is approximately 19 Mb in size. Furthermore, several specific repetitive DNA markers have been isolated, one of which hybridizes to AN5-90 and also to DNA from a smaller DNA segment of Beta procumbens, present in line B883, carrying a BCN resistance locus introgressed into the B. vulgaris genome. This suggests that the specific repetitive marker is closely linked to the BCN locus.     

Isolation and characterization of RAPD-based markers linked to the beet cyst nematode resistance locus (Hs1 pat-1) on chromosome 1 of B. patellaris

A beet cyst nematode (BCN)-resistant telosomic addition of B. patellaris chromosome 1 in B. vulgaris was used to isolate 6 RAPD markers linked to the BCN resistance locus Hs1 ^pat-1. Southern analysis showed that the analyzed RAPD products contain either low-, middle or high-repetitive DNA. The relative positions of the random amplified polymorphic DNA (RAPD) markers and of the restriction fragment length polymorphism (RFLP) loci corresponding to the low-repetitive RAPD products were determined by deletion mapping using a panel of seven nematode-resistant B. patellaris chromosome-1 fragment additions. One RAPD marker, OPB11₈₀₀, was found to be present in two copies on the long arm telosome of B. patellaris chromosome 1. These copies are closely linked to the BCN resistance gene and flank the gene on both sides. On the basis of the nucleotide sequence of OPB11₈₀₀, sequence-tagged site (STS) primers were developed that amplify specific fragments derived from the two OPB11₈₀₀ loci. These STS markers can be used in the map-based cloning of the BCN gene, as they define start and finishing points of a chromosomal walk towards the Hs1 ^pat-1 locus. Two copies of the middle-repetitive OPX2₁₁₀₀ marker were mapped in the same interval of the deletion mapping panel as the resistance gene locus and thereby belong to the nearest markers as yet found for the BCN gene in B. patellaris.