Data integration gets 'Sloppy'.
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Biology↗
Biomedical subjects
Andreas Bohn
Publications and source records attributed to Andreas Bohn.
Cellulose: fascinating biopolymer and sustainable raw material.
As the most important skeletal component in plants, the polysaccharide cellulose is an almost inexhaustible polymeric raw material with fascinating structure and properties. Formed by the repeated connection of D-glucose building blocks, the highly functionalized, linear stiff-chain homopolymer is characterized by its hydrophilicity, chirality, biodegradability, broad chemical modifying capacity, and its formation of versatile semicrystalline fiber morphologies. In view of the considerable increase in interdisciplinary cellulose research and product development over the past decade worldwide, this paper assembles the current knowledge in the structure and chemistry of cellulose, and in the development of innovative cellulose esters and ethers for coatings, films, membranes, building materials, drilling techniques, pharmaceuticals, and foodstuffs. New frontiers, including environmentally friendly cellulose fiber technologies, bacterial cellulose biomaterials, and in-vitro syntheses of cellulose are highlighted together with future aims, strategies, and perspectives of cellulose research and its applications.
Bacteria↗
Perturbations of malate accumulation and the endogenous rhythms of gas exchange in the Crassulacean acid metabolism plant Kalanchoë daigremontiana: testing the tonoplast-as-oscillator model.
In continuous light, leaves of the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier exhibit a circadian rhythm of CO2 uptake, stomatal conductance and leaf-internal CO2 pressure. According to a current quantitative model of CAM, the pacemaking mechanism involves periodic turgor-related tension and relaxation of the tonoplast, which determines the direction of the net flux of malate between the vacuole and the cytoplasm. Cytoplasmic malate, in turn, through its inhibitory effect on phospho enolpyruvate carboxylase, controls the rate of CO2 uptake. According to this mechanism, when the accumulation of malate is disrupted by removing CO2 from the ambient air, the induction of a phase delay with respect to an unperturbed control plant is expected. First, using the mathematical model, such phase delays were observed in numerical simulations of three scenarios of CO2 removal: (i) starting at a trough of CO2 uptake, lasting for about half a cycle (ca. 12 h in vivo); (ii) with the identical starting phase, but lasting for 1.5 cycles (ca. 36 h); and (iii) starting while CO2 increases, lasting for half a cycle again. Applying the same protocols to leaves of K. daigremontiana in vivo did not induce the predicted phase shifts, i.e. after the end of the CO2 removal the perturbed rhythm adopted nearly the same phase as that of the control plant. Second, when leaves were exposed to a nitrogen atmosphere for three nights prior to onset of continuous light to prevent malate accumulation, a small, 4-h phase advance was observed instead of a delay, again contrary to the model-based expectations. Hence, vacuolar malic acid accumulation is ruled out as the central pacemaking process. This observation is in line with our earlier suggestion [T.P. Wyka, U. Lüttge (2003) J Exp Bot 54:1471-1479] that in extended continuous light, CO2 uptake switches gradually from a CAM-like to a C3-like mechanism, with oscillations of the two CO2 uptake systems being tightly coordinated. It appears that the circadian rhythm of gas exchange in this CAM plant emerges from one or several devices that are capable of generating temporal information in a robust manner, i.e. they are protected from even severe metabolic perturbations.
Carbon Dioxide↗
Identification of rhythmic subsystems in the circadian cycle of crassulacean acid metabolism under thermoperiodic perturbations.
Leaves of the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie show overt circadian rhythms in net CO2 uptake, leaf conductance to water and intercellular CO2 concentration, which are entrained by periodic temperature cycles. To probe their sensitivity to thermoperiodic perturbations, intact leaves were exposed to continuous light intensity and temperature cycles with a period of 16 h, applying a set of different baseline temperatures and thermodriver amplitudes. All three overt rhythms were analyzed with respect to their frequency spectra and their phase relations with the thermodriver. For most stimulation protocols, stomatal conductance and net CO2 change were fully or partially entrained by the temperature pulses, while the internal CO2 concentration remained dominated by oscillations in the circadian range. Prolonged time series recorded for up to 22 d in continuous light underline the robustness of these circadian oscillations. This suggests that the overt circadian rhythm of net CO2 uptake in CAM results from the interaction of two coupled original systems: (i) an endogenous cycle of CO2 fixation in the mesophyll, showing very robust periodic activity, and (ii) stomatal movements that respond to environmental stimuli independently of rhythmic processes in the mesophyll, and thus modulate the gas exchange amplitude.
Carbon Dioxide↗