Ants accelerate succession from mountain grassland towards spruce forest

Question: What is the role of mound‐building ants (Lasius flavus) in successional changes of a grassland ecosystem towards a spruce forest? Location: Slovenské Rudohorie Mountains, Slovakia; ca. 950 m a.s.l. near the Obrubovanec point (1020 m a.s.l.; 48°41′N, 19°39′E). Methods: Both chronosequence data along a successional gradient and temporal data from long‐term permanent plots were collected on ants, spruce establishment, and vegetation structure, together with additional data on spruce growth. Results: There are more spruce seedlings on ant mounds (4.72 m^?2) than in the surrounding vegetation (0.81 m^?2). Spruce seedlings grow faster on these mounds compared to surrounding areas. The first colonization wave of seedlings was rapid and probably occurred when grazing prevailed over mowing. Ant colony presence, mound volume, and plant species composition change along the successional gradient. Mounds become bigger when partly shaded but shrink in closed forest, when ant colonies disappear. Shade‐tolerant acidophylic species replace grassland plants both on the mounds and in surrounding areas. Conclusions: The massive occurrence of Lasius flavus anthills contributes to a runaway feedback process that accelerates succession towards forest. The effect of ants as ecosystem engineers is scale‐dependent: although they stabilize the system at the scale of an individual mound, they may destabilize the whole grassland system over a longer time scale if combined with changes in mowing regime.     

Approaches for enhancement of N2 fixation efficiency of chickpea (Cicer arietinum L.) under limiting nitrogen conditions

Chickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N₂ inside the root nodules, are of particular importance for chickpea's productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C‐15, Ch‐191 and CP‐36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar ‘Bivanij’ as well as studied the mechanism underlying the improvement of N₂ fixation efficiency. Our data revealed that C‐15 strain manifested the most efficient N₂ fixation in comparison with Ch‐191 or CP‐36. This finding was supported by higher plant productivity and expression levels of the nifHDK genes in C‐15 nodules. Nodule specific activity was significantly higher in C‐15 combination, partially as a result of higher electron allocation to N₂ versus H⁺. Interestingly, a striking difference in nodule carbon and nitrogen composition was observed. Sucrose cleavage enzymes displayed comparatively lower activity in nodules established by either Ch‐191 or CP‐36. Organic acid formation, particularly that of malate, was remarkably higher in nodules induced by C‐15 strain. As a result, the best symbiotic efficiency observed with C‐15‐induced nodules was reflected in a higher concentration of the total and several major amino metabolites, namely asparagine, glutamine, glutamate and aspartate. Collectively, our findings demonstrated that the improved efficiency in chickpea symbiotic system, established with C‐15, was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes connected to the nodule carbon and nitrogen metabolism.     

Platinum(II) complexes with steroidal esters of L-methionine and L-histidine: synthesis, characterization and cytotoxic activity

Twelve steroidal platinum(II) complexes were synthesized by reaction of potassium tetrachloroplatinate with steroidal esters of L-methionine and L-histidine. The steroidal esters coordinated as bidentate ligands via S and N donor atoms of L-methionine and via two N donor atoms of L-histidine. Cholesterol, cholestanol, diosgenine, pregnenolone, dehydroepiandrosterone, testosterone, estrone, and estradiol were used as the steroidal compounds. The esters and complexes prepared were characterized by infrared, mass, and (1)H NMR spectroscopy and elemental analysis. Platinum complexes were tested for in vitro cytotoxicity against several cancer cell lines: T-lymphoblastic leukemia CEM, breast carcinoma MCF-7, lung carcinoma A-549, multiple myeloma RPMI 8226, and one normal cell line human fibroblast BJ.     

Interaction between embryogenic cultures of Scots pine and ectomycorrhizal fungi

 Embryogenic cell masses of three Scots pine (Pinus sylvestris) cell lines K779, K884 and K1009 were cultivated with the ectomycorrhizal (ECM) fungi Laccaria bicolor, L. proxima, Pisolithus tinctorius, Paxillus involutus and two strains of Suillus variegatus. The average growth ratio of the slowly proliferating cell line K1009 was improved by L. proxima and S. variegatus strain H, while of the rapidly proliferating lines K779 and K884 the non-mycorrhizal controls grew best. The fungi caused two distinct reactions in embryogenic cultures. In the positive reaction, the shape and light yellow colour of the cultures resembled the controls, while in the negative reaction the embryogenic cells became brown and necrotic and the fungi grew aggressively over them. These reactions to the fungi did not correlate completely with effects on the growth ratio. All the cell lines enhanced the radial growth of S. variegatus H and of P. tinctorius, while the Laccaria species and S. variegatus strain 1 thrived better alone. This study shows that early-stage embryogenic cells of Scots pine and ECM fungi are able to interact. As some fungi produced a positive reaction or even increased proliferation, they could be used to enhance somatic embryogenesis of Scots pine. Specific fungi might be used to induce the growth of slowly proliferating cell lines, and knowledge of positive cell line-fungus interactions could be useful in work with later stages of somatic embryogenesis, such as rooting. Accepted: 16 July 1998     

Searching for gene flow from cultivated to wild strawberries in Central Europe

Background and Aims

Experimental crosses between the diploid woodland strawberry (Fragaria vesca L.) and the octoploid garden strawberry (F. × ananassa Duch.) can lead to the formation of viable hybrids. However, the extent of such hybrid formation under natural conditions is unknown, but is of fundamental interest and importance in the light of the potential future cultivation of transgenic strawberries. A hybrid survey was therefore conducted in the surroundings of ten farms in Switzerland and southern Germany, where strawberries have been cultivated for at least 10 years and where wild strawberries occur in the close vicinity.

Methods

In 2007 and 2008, 370 wild F. vesca plants were sampled at natural populations around farms and analysed with microsatellite markers. In 2010, natural populations were revisited and morphological traits of 3050 F. vesca plants were inspected. DNA contents of cell nuclei of morphologically deviating plants were estimated by flow cytometry to identify hybrids. As controls, 50 hybrid plants from interspecific hand-crosses were analysed using microsatellite analysis and DNA contents of cell nuclei were estimated by flow cytometry.

Key Results

None of the wild samples collected in 2007 and 2008 contained F. × ananassa microsatellite markers, while all hybrids from hand-crosses clearly contained markers of both parent species. Morphological inspection of wild populations carried out in 2010 and subsequent flow cytometry of ten morphologically deviating plants revealed no hybrids.

Conclusions

Hybrid formation or hybrid establishment in natural populations in the survey area is at best a rare event.     

Cadmium induces premature xylogenesis in barley roots

The effect of Cd on H₂O₂ production, peroxidase (POD) activity and root hair formation were analyzed in barley root. Cd causes a strong H₂O₂ burst in the root region 0–6 mm behind the root tip. POD activity was activated in root tip and raised toward the root base in Cd treated roots. In situ analyses showed that both elevated H₂O₂ production and POD activity are localized in the early metaxylem vascular bundles. Cd induces root hair formation in the region 2 to 4 mm behind the root tip that was not detected in control roots. These results suggest that Cd-induced root growth inhibition is at least partially the consequence of Cd-stimulated premature root development involving xylogenesis and root hair formation, which is correlated with shortening of root elongation zone and therefore with root growth reduction.     

Function of a Novel Cadmium-Induced YodA Protein in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Cells of Escherichia coli increase greatly the synthesis of a small primarily cytoplasmic protein as soon as the cell growth rate falls below the maximal growth rate supported by cadmium exposure, after which the mature product is exported to the periplasm. This protein was previously identified as the product of the E. coli yodA open reading frame. We now report the isolation of an E. coli mutant defective in YodA synthesis because of insertional inactivation of the corresponding gene. In experiments to test the ability of both the wild-type and yodA mutant E. coli cells to bind cadmium, we have used γ-labeled [¹⁰⁹Cd]. Whereas the wild-type E. coli strain was able to bind metal, the yodA mutant strain failed to do so. In addition, analysis of such a mutant demonstrated that it grows at a rate distinguishable from that of the isogenic parent in the presence of cadmium ions. However, challenging cells with hydrogen peroxide and additional metals such as zinc, copper, cobalt, and nickel did not significantly affect the growth rate of the mutant. This growth phenotype was found to be the result of the loss of its ability to bind cadmium. These results suggest that the role of YodA protein might be to decrease the concentration level of cadmium ions in E. coli cells during cadmium stress by its ability to bind heavy metal.     

β-Amylase fromBacillus megaterium

Bacillus megaterium strain B₆ producing extracellular β-amylase was isolated and grown in a medium supplemented with waste potato starch. It showed highest enzyme synthesis in the early stationary phase. The partially purified β-amylase had a temperature optimum at 60°C and a pH optimum at 6.9 and was not affected by Schardinger dextrins. These properties would allow its application in sugar industry.