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Measurement of nanomolar diphenols by substrate recycling coupled to a pH- sensitive electrode
(1995)
Potentiometric enzyme electrodes based on substrate recycling and mediatorless bioelectrocatalysis
(1995)
Biosensor based on an enzyme modified electrode for highly - sensitive measurement of polyphenols
(1995)
Microtubule-associated movement of mitochondria and small particles in Acanthamoeba castellanii.
(1995)
Enzyme - based electrodes
(1995)
Localization of carbonic-anhydrase in the salivary-glands of the cockroach, Periplaneta americana
(1994)
Oxime ether analogs of sex pheromone components of turnip moth (Agrotis segetum SCHIFFERMÜLLER)
(1994)
Conformational states and substates of cytochrome P450cam - insight in protein dynamics and folding
(1994)
Three-dimensional organization of endoplasmatic reticulum in the ventral photoreceptors of Limulus
(1994)
Recently crops encounter an increased number of individual and combined abiotic and biotic stress, which severely affect their growth and yield. Plants are associated with a large number of microorganisms including beneficial as well as pathogenic microorganisms. The interaction of plants with beneficial microorganisms can exert a substantial impact on plant growth and health and their potential can be utilized in sustainable plant production systems. Currently, climate change will increase the impact of stress on crops which will more likely be exposed to combined abiotic and biotic stress. At present, knowledge on how abiotic and biotic stress and the combination of both stresses affect the plant performance and the microbiome is limited. Soil-borne pathogens are responsible for relevant economic losses and are difficult to control. The root bacterial endophytes have shown potential in alleviating stress on plants and improving crop yield and quality. This raises the question how individual abiotic stress like salinity (ionic) and drought (osmotic) and the combination with biotic stress (Verticillium dahliae or Fusarium oxysporum) affects the root microbiota and thus the performance of the plant. Therefore, the goal of this thesis was to improve the understanding of the impact of individual and combined biotic and abiotic stress especially the endophytic root microbiota and thus plant performance. The work is focused on the economically important horticultural crop tomato. The bacterial rootendophytes of tomato plants exposed to individual and combined abiotic and biotic stress was studied with culture-independent and culture-dependent methods. Bacterial root endophytes obtained from tomato roots exposed to individual and combined stress were characterized for their traits that are beneficial to plant growth and health in in vitro and in vivo assays. Finally, the efficacy of selected endophytes in alleviating individual and combined abiotic and biotic stress in tomato plants was assessed. Furthermore, stress conditions can alter the composition of root exudates and volatiles, which may in turn affect the root microbiota assembly. Therefore, the volatile profiles of healthy and pathogen (F. oxysporum) infected tomato roots grown in soil was investigated. A soil olfactometer was established to study the impact of root volatiles of healthy and infected tomato on migration of applied beneficial bacteria. The results of tomato characteristics (plant growth, photosynthesis rate) confirmed the negative effect of individual abiotic and biotic stress reported in other studies. However, the response of combined abiotic stress with biotic stress on plant growth varied depending on the type of combined stress.. For instance, a significant higher negative impact on plant growth was observed when tomato plants were cultivated under ionic stress and infected with F. oxysporum. No additional negative effect on plant growth was observed when tomato was infected with V. dahliae. Both culture-dependent and cultureindependent analyses of the root microbiota revealed that individual and combined abiotic and biotic stress alter the root microbiota structure and diversity of tomato. A significantly lower number of cultivable root endophytes was obtained from roots exposed to ionic stress. 16S rRNA amplicon analysis revealed a stronger impact on the diversity of root-associated bacteria in comparison to biotic stress. The endophytes were characterized as member of the phyla Proteobacteria, Actinobacteria and Firmicutes, and members of Bacteriodetes were only detected by culture-independent approach. A total of 683 cultivable bacterial endophytes were characterized using various in vitro and in vivo plant growth-promoting (PGP) assays. As expected, the highest number of root endophytes with tolerance to ionic stress were obtained from tomato roots exposed to ionic stress. Comparably, a high percentage of root endophytes isolated from roots exposed to osmotic were tolerant to osmotic stress showing that the environment affects the selection of microorganisms by the plant. Interestingly, endopyhtes obtained from roots exposed to abiotic stress showed no traits related to plant growth promotion. Based on in vivo and in vitro traits, five selected endophytes were able to alleviate abiotic and biotic stress on plants. These endophytes were obtained from tomato roots infected with V. dahliae. The blend of root emitted volatiles also differed between healthy and F. oxysporum infected tomato plants. The olfactometer setup results highlighted that root volatiles were involved in attraction of bacteria to the plant roots and beneficial bacteria were observed to migrate towards both, diseased and healthy plants in comparable density. It is proposed that root volatiles from healthy and pathogen infected plants not only work as signals but are also used as an energy source for the rhizosphere bacteria. Concluding, the results of this study indicate that abiotic and biotic stress altered the bacterial rootendophytes and thus affects plant performance. The treatment of plants with beneficial microorganisms reduced the negative impact of stress conditions on plant performance. However, more studies using the selected isolates must be performed in the field for drawing inferences on the efficacy of the selected bacterial isolates in ameliorating the effect of abiotic and biotic stress in plants. The extensive isolate collection will serve as a basis for conducting investigations of root-associated bacteria on plant performance. This is important for the development of new plant protection strategies.
Bioelectrochemical investigation of E. coli TMAO reductase and R. capsulatus formate dehydrogenase
()
The European fire-bellied toad (Bombina bombina) is regarded as one of the most threatened species of amphibians in central Europe and is particularly affected by environmental perturbations. During the last decades population numbers in Germany have declined drastically due to pollution, eutrophication and habitat fragmentation. Illegal translocations resulted in an introgression from southern genotypes (probably Austrian) into three local Bombina populations (Northern Germany and Southern Sweden) belonging to the northern lineage of the species. Interestingly, these populations show high frequencies of allochthonous (non-local) alleles at multiple loci and outperform the autochthonous populations in terms of their body condition. Over a time period of ten years, I could show that the Southern lineage haplo- and genotypes are still present in the North and that frequencies of introgressed haplotypes in allochthonous populations did not increase over time. However, the introgression itself expanded towards adjacent populations while the overall haplotype diversity has decreased. In contrast, southern lineage genotypes for two candidate genes under selection, the (immunity) MHC class II gene, as well as the (temperature) stress response HSP70 kDa gene, either do not occur at all or only at low frequencies in northern populations. Furthermore, these alleles do not seem to follow the introgression pattern, as they are also present in non-introgressed populations. This thesis tested two possible outcomes of introgressive hybridization in Northern B. bombina populations: (1) local populations (autochthonous) of Bombina bombina are highly adapted to their environments so that introgression of alien genes causes outbreeding depression or (2) local populations of Bombina bombina potentially lack adaptive variation so that introgression of alien genes causes genetic rescue and promotes adaptive change. I found that this unintentional experiment, as a result of illegal translocations imitating introgression of alien genes coming from a southern population (potentially adapted to warmer climate) into a northern lineage (potentially adapted to local pathogens), has increased the genetic diversity and improved fitness in introgressed northern populations, without disrupting local adaptation in the threatened amphibian species B. bombina, favouring the genetic rescue hypothesis. These results and conclusions represent relevant information for future conservation plans, including supportive breeding programmes for fire-bellied toads in Northern Germany and Southern Sweden.