- I'm a plant ecophysiologist with a main interest in photosynthesis and UV stress. I'm using non-destructive techniques to measure plant performance also in the field.edit
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Research Interests: Chemistry, Fluorescence, Polyphenols, Chlorophyll, Postharvest biology, and 15 moreChlorophyll Fluorescence, Blue Light, Estimation, Pigments, Pigment, Human health, Phenolic compound, Malus, Cross Section, Flavonoid, Absorbance, Polyphenol, Anthocyanin, Horticultural production, and Malus domestica
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Summary Plant submergence stress is a growing problem for global agriculture. During desubmergence, rising O2 concentrations meet a highly reduced mitochondrial electron transport chain (mETC) in the cells. This combination favors the... more
Summary Plant submergence stress is a growing problem for global agriculture. During desubmergence, rising O2 concentrations meet a highly reduced mitochondrial electron transport chain (mETC) in the cells. This combination favors the generation of reactive oxygen species (ROS) by the mitochondria, which at excess can cause damage. The cellular mechanisms underpinning the management of reoxygenation stress are not fully understood. We investigated the role of alternative NADH dehydrogenases (NDs), as components of the alternative mETC in Arabidopsis, in anoxia–reoxygenation stress management. Simultaneous loss of the matrix‐facing NDs, NDA1 and NDA2, decreased seedling survival after reoxygenation, while overexpression increased survival. The absence of NDAs led to reduced maximum potential quantum efficiency of photosystem II linking the alternative mETC to photosynthetic function in the chloroplast. NDA1 and NDA2 were induced upon reoxygenation, and transcriptional activation of NDA1 was controlled by the transcription factors ANAC016 and ANAC017 that bind to the mitochondrial dysfunction motif (MDM) in the NDA1 promoter. The absence of NDA1 and NDA2 did not alter recovery of cytosolic ATP levels and NADH : NAD+ ratio at reoxygenation. Rather, the absence of NDAs led to elevated ROS production, while their overexpression limited ROS. Our observations indicate that the control of ROS formation by the alternative mETC is important for photosynthetic recovery and for seedling survival of anoxia–reoxygenation stress.
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Photosynthetic electron flow, driven by photosystem I and II, provides chemical energy for carbon fixation. In addition to a linear mode a second cyclic route exists, which only involves photosystem I. The exact contributions of linear... more
Photosynthetic electron flow, driven by photosystem I and II, provides chemical energy for carbon fixation. In addition to a linear mode a second cyclic route exists, which only involves photosystem I. The exact contributions of linear and cyclic transport are still a matter of debate. Here, we describe the development of a method that allows quantification of electron flow in absolute terms through photosystem I in a photosynthetic organism for the first time. Specific in-vivo protocols allowed to discern the redox states of plastocyanin, P700 and the FeS-clusters including ferredoxin at the acceptor site of PSI in the cyanobacterium Synechocystis sp. PCC 6803 with the near-infrared spectrometer Dual-KLAS/NIR. P700 absorbance changes determined with the Dual-KLAS/NIR correlated linearly with direct determinations of PSI concentrations using EPR. Dark-interval relaxation kinetics measurements (DIRKPSI) were applied to determine electron flow through PSI. Counting electrons from hydrogen oxidation as electron donor to photosystem I in parallel to DIRKPSI measurements confirmed the validity of the method. Electron flow determination by classical PSI yield measurements overestimates electron flow at low light intensities and saturates earlier compared to DIRKPSI. Combination of DIRKPSI with oxygen evolution measurements yielded a proportion of 35 % of surplus electrons passing PSI compared to PSII. We attribute these electrons to cyclic electron transport, which is twice as high as assumed for plants. Counting electrons flowing through the photosystems allowed determination of the number of quanta required for photosynthesis to 11 per oxygen produced, which is close to published values.
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Research Interests: Botany, Plant Biology, Biology, Flora, Lichen, and 5 moreChlorophyll Fluorescence, Desiccation, Photoinhibition, Thallus, and Dew
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Background To stimulate how to move the field of plant-UV research forward, and create a coherent framework to highlight valuable future directions in plant UV research we had a group discussion of the most prescient questions and how to... more
Background To stimulate how to move the field of plant-UV research forward, and create a coherent framework to highlight valuable future directions in plant UV research we had a group discussion of the most prescient questions and how to address them. The following sections are broken-down into those from the molecular, biochemical and physiological discussions followed by those from the ecological and plant production discussions. In each case, first basic research questions are considered and then applications and methodological considerations put forward. Finally, some common ground bringing together the two perspectives is proposed, aimed at solving scaling problems and ways in which the UV4Plants network might be put to good use.
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Melting mountainous snowfields are populated by extremophilic microorganisms. An alga causing orange snow above timberline in the High Tatra Mountains (Poland) was characterised using multiple methods examining its ultrastructure,... more
Melting mountainous snowfields are populated by extremophilic microorganisms. An alga causing orange snow above timberline in the High Tatra Mountains (Poland) was characterised using multiple methods examining its ultrastructure, genetics, life cycle, photosynthesis and ecophysiology. Based on light and electron microscopy and ITS2 rDNA, the species was identified as Chloromonas krienitzii (Chlorophyceae). Recently, the taxon was described from Japan. However, cellular adaptations to its harsh environment and details about the life cycle were so far unknown. In this study, the snow surface population consisted of egg-shaped cysts containing large numbers of lipid bodies filled presumably with the secondary carotenoid astaxanthin. The outer, spiked cell wall was shed during cell maturation. Before this developmental step, the cysts resembled a different snow alga, Chloromonas brevispina. The remaining, long-lasting smooth cell wall showed a striking UV-induced blue autofluorescence,...
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ABSTRACT
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Pfanz H, Vollrath B, Lomsky B, et al. Life expectancy of spruce needles from trees growing under extremely high air pollution. Trees, Sttruct. Funct. 1994;8:213-222
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Main conclusion In accordance with a key role of WHIRLY1 in light-acclimation mechanisms, typical features of acclimation to high light, including photosynthesis and leaf morphology, are compromised in WHIRLY1 deficient plants. Abstract... more
Main conclusion In accordance with a key role of WHIRLY1 in light-acclimation mechanisms, typical features of acclimation to high light, including photosynthesis and leaf morphology, are compromised in WHIRLY1 deficient plants. Abstract Acclimation to the environment requires efficient communication between chloroplasts and the nucleus. Previous studies indicated that the plastid-nucleus located WHIRLY1 protein is required for the communication between plastids and the nucleus in situations of high light exposure. To investigate the consequences of WHIRLY1 deficiency on the light acclimation of photosynthesis and leaf anatomy, transgenic barley plants with an RNAi-mediated knockdown of HvWHIRLY1 were compared to wild-type plants when growing at low and high irradiance. While wild-type plants showed the typical light acclimation responses, i.e. higher photosynthetic capacity and thicker leaves, the WHIRLY1 deficient plants were not able to respond to differences in irradiance. The re...
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Research Interests: Chemistry, Photosynthesis, Plant Biology, Biology, Cell Biology, and 3 moreMedicine, Chloroplast, and Planta
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Chlorophyll fluorescence parameters (Fv/Fm, F0, and Fm) for all species and treatments.
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A newly developed fluorescence measuring system is employed for the recording of chlorophyll fluorescence induction kinetics (Kautsky-effect) and for the continuous determination of the photochemical and non-photochemical components of... more
A newly developed fluorescence measuring system is employed for the recording of chlorophyll fluorescence induction kinetics (Kautsky-effect) and for the continuous determination of the photochemical and non-photochemical components of fluorescence quenching. The measuring system, which is based on a pulse modulation principle, selectively monitors the fluorescence yield of a weak measuring beam and is not affected even by extremely high intensities of actinic light. By repetitive application of short light pulses of saturating intensity, the fluorescence yield at complete suppression of photochemical quenching is repetitively recorded, allowing the determination of continuous plots of photochemical quenching and non-photochemical quenching. Such plots are compared with the time courses of variable fluorescence at different intensities of actinic illumination. The differences between the observed kinetics are discussed. It is shown that the modulation fluorometer, in combination with the application of saturating light pulses, provides essential information beyond that obtained with conventional chlorophyll fluorometers.
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Chlorophyll contents in pendulous lichens, including chlorophyll methods.
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Main conclusionDesiccation-induced chlorophyll fluorescence quenching seems to be an indispensable part of desiccation resistance in the surveyed 28 green microalgal species.Lichens are desiccation tolerant meta-organisms. In the... more
Main conclusionDesiccation-induced chlorophyll fluorescence quenching seems to be an indispensable part of desiccation resistance in the surveyed 28 green microalgal species.Lichens are desiccation tolerant meta-organisms. In the desiccated state photosynthesis is inhibited rendering the photobionts potentially sensitive to photoinhibition. As a photoprotective mechanism, strong non-radiative dissipation of absorbed light leading to quenching of chlorophyll fluorescence has been proposed. Desiccation-induced quenching affects not only variable fluorescence, but also the so-called basal fluorescence, F0. This phenomenon is well-known for intact lichens and some free living aero-terrestrial algae, but it was often absent in isolated lichen algae. Therefore, a thorough screening for the appearance of desiccation-induced quenching was undertaken with 13 different aero-terrestrial microalgal species and lichen photobionts. They were compared with 15 aquatic green microalgal species, among them also three marine species. We asked the following questions: Do isolated lichen algae show desiccation-induced quenching? Are aero-terrestrial algae different in this respect to aquatic algae and is the potential for desiccation-induced quenching coupled to desiccation tolerance? How variable is desiccation-induced quenching among species? Most of the aero-terrestrial algae, including all lichen photobionts, showed desiccation-induced quenching, although highly variable in extent, whereas most of the aquatic algae did not. All algae displaying quenching were also desiccation tolerant, whereas all algae unable to perform desiccation-induced quenching were desiccation intolerant. Desiccation-induced fluorescence quenching seems to be an indispensable part of desiccation resistance in the investigated species.
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At temperate latitudes environmental factors such as irradiance, including ultraviolet-B radiation (UV-B, 280-315 nm), temperature and day length vary widely over the course of a year in a concerted way. In the present study physiological... more
At temperate latitudes environmental factors such as irradiance, including ultraviolet-B radiation (UV-B, 280-315 nm), temperature and day length vary widely over the course of a year in a concerted way. In the present study physiological acclimation of photoprotection, growth and development of the model organism Arabidopsis thaliana were correlated to these strongly but gradually changing conditions in a one year field study. Plants were sown in the field avoiding any manipulation (and abrupt change) during their life. Developmental rate was strongly dependent on prevailing temperature. Moderate signs of light stress in form of photoinhibition at photosystem II were significantly related to solar irradiances while amount of DNA damage was low and not correlated to UV-B irradiance. Although all the markers were hypothesized to primarily react to radiation, multiple regression analysis showed at least a similarly strong influence of temperature as that of light. Especially for the classical UV screening compounds a positive correlation to UV-B radiation during the course of the year was absent, whereas there was a significant negative correlation between temperature and quercetin content. The sum of violaxanthin cycle pigments was correlated to both, irradiance and temperature, but with opposite sign. Epidermal UV-B transmittance was also much better related to air temperature than to UV-B irradiance. The data show that under natural conditions temperature has at least a similar importance for photoprotective acclimation and partially also for photosensitivity as solar irradiance.
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AbstractMain conclusionUp to 40% of incident light was screened in redBerberisleaves in vivo by anthocyanins, resulting also in up to 40% reduction of light-limited photosynthesis. The biological function of anthocyanins in leaves has... more
AbstractMain conclusionUp to 40% of incident light was screened in redBerberisleaves in vivo by anthocyanins, resulting also in up to 40% reduction of light-limited photosynthesis. The biological function of anthocyanins in leaves has been strongly discussed, but the hypothesis of a screening function is favored by most authors. For an evaluation of the function as photoprotective pigments, a quantification of their screening of the mesophyll is important. Here, chlorophyll fluorescence excitation of leaves of a red and a green variety of Berberis thunbergii was used to estimate the extent of screening by anthocyanins at 545 nm and over the whole photosynthetically active wavelength range. Growth at high light (430 µmol m−2 s−1) resulted in 90% screening at 545 nm corresponding to 40–50% screening over the whole wavelength range, depending on the light source. The concomitant reduction of photosynthetic quantum yield was of the same size as the calculated reduction of light reaching the chloroplasts. The induction of anthocyanins in the red variety also enhanced the epoxidation state of the violaxanthin cycle under growth conditions, indicating that red leaves were suffering less from excessive irradiance. Pool sizes of violaxanthin cycle carotenoids indicated a shade acclimation of the light harvesting complexes in red leaves. The observed reduction of internal light in anthocyanic leaves has by necessity a photoprotective effect.
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Despite the weak absorption of hydroxycinnamic acids in the UV-A region, we found evidence that these compounds protect against damage induced by UV-A radiation in sunflowers.
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In this article a novel mechanism of retrograde signaling by chloroplasts during stress is described. This mechanism involves the DNA/RNA binding protein WHIRLY1 as a regulator of microRNA levels. By virtue of its dual localization in... more
In this article a novel mechanism of retrograde signaling by chloroplasts during stress is described. This mechanism involves the DNA/RNA binding protein WHIRLY1 as a regulator of microRNA levels. By virtue of its dual localization in chloroplasts and the nucleus of the same cell, WHIRLY1 was proposed as an excellent candidate coordinator of chloroplast function and nuclear gene expression. Comparison of wild-type and transgenic plants with an RNAi-mediated knockdown of WHIRLY1 showed, that the transgenic plants were unable to cope with continuous high light conditions. They were impaired in production of several microRNAs mediating post-transcriptional responses during stress. The results support a central role of WHIRLY1 in retrograde signaling and also underpin a so far underestimated role of microRNAs in this process.
Research Interests: Genetics and RNA biology
WHIRLY1 in barley was isolated as a potential regulator of the senescence-associated gene HvS40. In order to investigate whether the plastid-nucleus-located DNA/RNA-binding protein WHIRLY1 plays a role in regulation of leaf senescence,... more
WHIRLY1 in barley was isolated as a potential regulator of the senescence-associated gene HvS40. In order to investigate whether the plastid-nucleus-located DNA/RNA-binding protein WHIRLY1 plays a role in regulation of leaf senescence, primary foliage leaves from transgenic barley plants with an RNAi-mediated knockdown of the WHIRLY1 gene were characterized by typical senescence parameters, namely pigment contents, function and composition of the photosynthetic apparatus, as well as expression of selected genes known to be either down- or up-regulated during leaf senescence. When the plants were grown at low light intensity, senescence progression was similar between wild-type and RNAi-W1 plants. Likewise, dark-induced senescence of detached leaves was not affected by reduction of WHIRLY1. When plants were grown at high light intensity, however, senescence was induced prematurely in wild-type plants but was delayed in RNAi-W1 plants. This result suggests that WHIRLY1 plays a role in...
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Stratospheric ozone depletion is most pro- nounced at high latitudes, and the concurring increased UV-B radiation might adversely affect plants from polar areas. However, vascular plants may protect themselves against UV-B radiation by... more
Stratospheric ozone depletion is most pro- nounced at high latitudes, and the concurring increased UV-B radiation might adversely affect plants from polar areas. However, vascular plants may protect themselves against UV-B radiation by UV-absorbing compounds located in the epidermis. In this 3-year study, epidermal UV-B (kmax 314 nm) and UV-A (kmax 366 nm) screening was assessed using a fluorescence method