Urs Feller - Academia.edu (original) (raw)

Papers by Urs Feller

Lemnaceen sind unter Photosynthesebedingungen in der Lage, sowohl Ammonium als auch Nitrat als St... more Lemnaceen sind unter Photosynthesebedingungen in der Lage, sowohl Ammonium als auch Nitrat als Stickstoffquelle zu verwenden. Die beiden Quellen sind jedoch nicht gleichwertig. Ferguson (1969) wies neben morphologischen Veranderungen auch Differenzen im Gesamtstickstoffgehalt und den Mengen der freien Aminosauren nach. Die beiden Ionen stellen somit nicht nur mogliche Stickstoffquellen, sondern auch Effektoren fur den Stoffwechsel dar.

Rubisco activase catalyzes the ATP-dependent activation of rubisco (1). At moderately elevated te... more Rubisco activase catalyzes the ATP-dependent activation of rubisco (1). At moderately elevated temperature (for wheat above 30°C), rubisco activase becomes reversibly inactivated in leaf segments (2). A further increase of the temperature (for wheat above 40°C) causes partial insolubilization and the formation of aggregates in less than 30 minutes (2).

Cotyledons from dwarf beans (Phaseolus vulgaris.L., var. "Saxa") were extracted at two ... more Cotyledons from dwarf beans (Phaseolus vulgaris.L., var. "Saxa") were extracted at two different stages of germination. Extract from ungerminated seeds (low endopeptidase activity) contained high leucine aminopeptidase activity, which was stable for several hours at pH 5.5 and 30 °C. A rapid inactivation was initiated by adding purified papain or extract from cotyledons of seeds germinated for 8 days (high endopeptidase and low aminopeptidase activities). Leucine aminopeptidase was protected in the presence of sucrose, glucose, fructose, glycine, alanine or serine. Added proteins or polypeptides (competitive substrates for the added endopeptidases) also delayed the inactivation. Only a minor stabilization was measured after adding potassium chloride or lysine, while the inactivation was even accelerated in the presence of magnesium _sulfate or magnesium chloride. The inhibiting effect of magnesium ions was not necessarily linked to the proteolytic inactivation. Our results...

Wahrend zehn Jahren wurden nach dem Reaktor- Unfall von Tschernobyl im Jahr 1986 Versuche zum bes... more Wahrend zehn Jahren wurden nach dem Reaktor- Unfall von Tschernobyl im Jahr 1986 Versuche zum besseren Verstandnis der Aufnahme der radioaktiven Isotope Casium-134 und Strontium-85 durch die Blatter von Pflanzen, deren Verteilung in den Pflanzen sowie der Abgabe an den Boden durchgefuhrt. Untersuchungen an Erdbeeren und Reben haben gezeigt, dass Strontium schlecht von den Blattern aufgenommen und in den Pflanzen praktisch nicht transportiert wird. Im Gegensatz dazu wird Casium von den Blattern schnell aufgenommen, in der ganzen Pflanze verteilt und teilweise durch die Wurzeln wieder ausgeschieden. Die Hohe dieser Abgabe wird durch die Kaliumversorgung der Pflanzen beeinflusst.

Acta Physiologiae Plantarum, 2007

Introduction: Drought is one of the most significant factors that limit plant productivity. Oxida... more Introduction: Drought is one of the most significant factors that limit plant productivity. Oxidative stress is a secondary event in many unfavorable environmental conditions. Intracellular proteases have a role in the metabolism reorganisation and nutrient remobilization under stress. In order to under stand the relative significance of oxidative stress and proteolysis in the yield reduction under drought, four varieties of Triticum aestivum L. with different field drought resistance were examined. Methods: A two-year field experiment was conducted. Analyses were performed on the upper most leaf of control plants and plants under water deficitat the stages most critical for yield reduction under drought (from jointing till milk ripeness). Leaf water deficit and electrolyte leakage, malondyaldehyde level, activities and isoenzymes of superoxide dismutase, catalase and peroxidase, leaf protein content and proteolytic activity were studied. Yield components were analyzed. Results: A g...

Plant Physiology (Rockville) 111(2 Suppl. ), Apr 2, 1996

Drought strongly influences root activities in crop plants and weeds. This paper is focused on th... more Drought strongly influences root activities in crop plants and weeds. This paper is focused on the performance of the heavy metal accumulator Solanum nigrum, a plant which might be helpful for phytoremediation. The water potential in a split root system was decreased by the addition of polyethylene glycol (PEG 6000). Rubidium, strontium and radionuclides of heavy metals were used as markers to investigate the uptake into roots, the release to the shoot via the xylem, and finally the basipetal transport via the phloem to unlabeled roots. The uptake into the roots (total contents in the plant) was for most makers more severely decreased than the transport to the shoot or the export from the shoot to the unlabeled roots via the phloem. Regardless of the water potential in the labeling solution, 63 Ni and 65 Zn were selectively redistributed within the plant. From autoradiographs, it became evident that 65 Zn accumulated in root tips, in the apical shoot meristem and in axillary buds, while 63 Ni accumulated in young expanded leaves and roots but not in the meristems. Since both radionuclides are mobile in the phloem and are, therefore, well redistributed within the plant, the unequal transfer to shoot and root apical meristems is most likely caused by differences in the cell-to-cell transport in differentiation zones without functional phloem (immature sieve tubes).

More frequent and more severe extreme events (e.g. flooding, drought, heat waves) were predicted ... more More frequent and more severe extreme events (e.g. flooding, drought, heat waves) were predicted from climate models for the next decades. Impacts of such events are relevant for crop productivity. Effects on a whole-plant level are the focus of this study. The influence of an extended drought period on solute allocation via the phloem was compared in two Bulgarian wheat varieties differing in drought susceptibility: “Sadovo” (drought-sensitive) and “Katya” (drought-tolerant). Young plants grown hydroponically on standard nutrient solution were transferred at the beginning of the experiment to fresh medium (controls) or to medium with polyethylene glycol 6000 (artificial drought). Radiolabelled solution (57Co, 109Cd, 134Cs) was introduced via a flap into the lamina of the third or fourth leaf of young plants (youngest fully expanded leaf before stress treatment). Export and allocation of the radiolabel were monitored by gamma spectrometry. 57Co, 109Cd and 134Cs are suitable radionuc...

Water availability in soil is a key aspect in the context of global change. More frequent and mor... more Water availability in soil is a key aspect in the context of global change. More frequent and more severe extreme events including droughts, flooding and heat waves must be expected for the next decades in some regions. Since a high percentage of the area used for agriculture is covered by grasslands, the response of grass and legume species to severe drought is important for the evaluation of drought impacts. Differences between the species considered (Lolium perenne L., Dactylis glomerata L., Phleum pratense L., Trifolium repens L., Trifolium pratense L.) in their response to a low water potential in the root medium were evident. In general the number of photosynthetically active leaves per plant decreased under drought. This decrease was partially due to a smaller number of new leaves produced and partially to senescence of the oldest leaves. The strongest reduction in the number of active leaves was observed in Trifolium repens, while Trifolium pratense was less susceptible. The grasses were even less affected than the clover species. Temperature of sun-exposed leaves was increased in drought-stressed plants as a consequence of decreased transpiration. The elevated temperature may cause additional effects on leaf metabolism (e.g. inactivation of Rubisco activase). Modifications in leaf senescence and leaf emergence under drought stress are species-specific and influence plant performance during the stress and the subsequent recovery phase.

Plants, 2019

Heavy metal redistribution is relevant for the quality of edible crops and the suitability of hyp... more Heavy metal redistribution is relevant for the quality of edible crops and the suitability of hyperaccumulators for bioremediation. Root-to-shoot transfer via the xylem and redistribution in the aerial parts via the phloem differ between various heavy metals. In general, cadmium is more slowly released to the shoot than zinc (e.g., in wheat, bean, and lupin). However, rapid cadmium transport to the shoot was detected in the hyperaccumulator Solanum nigrum L. This is a key aspect in this article and might be important for bioremediation. The radionuclides 109Cd and 65Zn were used to investigate the respective influence of elevated cadmium or zinc in the root medium on the dynamics of the two heavy metals in S. nigrum. Although transport via the xylem to the leaves was similar for 109Cd and 65Zn, the further redistribution from older leaves to younger leaves, flowers, and fruits via the phloem was far less efficient for 109Cd than for 65Zn. Furthermore, the redistribution of 109Cd wit...

Journal of Plant Physiology, 2016

Global change is characterized by increased CO2 concentration in the atmosphere, increasing avera... more Global change is characterized by increased CO2 concentration in the atmosphere, increasing average temperature and more frequent extreme events including drought periods, heat waves and flooding. Especially the impacts of drought and of elevated temperature on carbon assimilation are considered in this review. Effects of extreme events on the subcellular level as well as on the whole plant level may be reversible, partially reversible or irreversible. The photosynthetically active biomass depends on the number and the size of mature leaves and the photosynthetic activity in this biomass during stress and subsequent recovery phases. The total area of active leaves is determined by leaf expansion and senescence, while net photosynthesis per leaf area is primarily influenced by stomatal opening (stomatal conductance), mesophyll conductance, activity of the photosynthetic apparatus (light absorption and electron transport, activity of the Calvin cycle) and CO2 release by decarboxylation reactions (photorespiration, dark respiration). Water status, stomatal opening and leaf temperature represent a "magic triangle" of three strongly interacting parameters. The response of stomata to altered environmental conditions is important for stomatal limitations. Rubisco protein is quite thermotolerant, but the enzyme becomes at elevated temperature more rapidly inactivated (decarbamylation, reversible effect) and must be reactivated by Rubisco activase (carbamylation of a lysine residue). Rubisco activase is present under two forms (encoded by separate genes or products of alternative splicing of the pre-mRNA from one gene) and is very thermosensitive. Rubisco activase was identified as a key protein for photosynthesis at elevated temperature (non-stomatal limitation). During a moderate heat stress Rubisco activase is reversibly inactivated, but during a more severe stress (higher temperature and/or longer exposure) the protein is irreversibly inactivated, insolubilized and finally degraded. On the level of the leaf, this loss of photosynthetic activity may still be reversible when new Rubisco activase is produced by protein synthesis. Rubisco activase as well as enzymes involved in the detoxification of reactive oxygen species or in osmoregulation are considered as important targets for breeding crop plants which are still productive under drought and/or at elevated leaf temperature in a changing climate.

Agriculture, 2016

Selection and breeding of genotypes with improved drought/heat tolerance become key issues in the... more Selection and breeding of genotypes with improved drought/heat tolerance become key issues in the course of global change with predicted increased frequency of droughts or heat waves. Several morphological and physiological plant traits must be considered. Rooting depth, root branching, nutrient acquisition, mycorrhization, nodulation in legumes and the release of nutrients, assimilates or phytohormones to the shoot are relevant in root systems. Xylem embolism and its repair after a drought, development of axillary buds and solute channeling via xylem (acropetal) and phloem (basipetal and acropetal) are key processes in the stem. The photosynthetically active biomass depends on leaf expansion and senescence. Cuticle thickness and properties, epicuticular waxes, stomatal regulation including responses to phytohormones, stomatal plugs and mesophyll resistance are involved in optimizing leaf water relations. Aquaporins, dehydrins, enzymes involved in the metabolism of compatible solutes (e.g., proline) and Rubisco activase are examples for proteins involved in heat or drought susceptibility. Assimilate redistribution from leaves to maturing fruits via the phloem influences yield quantity and quality. Proteomic analyses allow a deeper insight into the network of stress responses and may serve as a basis to identify suitable genotypes, although improved stress tolerance will have its price (often lowered productivity under optimal conditions).

Journal of Plant Nutrition, 2015

ABSTRACT Investigations were focused on light effects on allocation of root-borne macronutrients ... more ABSTRACT Investigations were focused on light effects on allocation of root-borne macronutrients (calcium, magnesium and potassium) and micronutrients (iron, manganese, zinc and copper) in roots, shoots and harvested grains of wheat (Triticum aestivum L.). Plants were exposed to low (100 μmol photons m−2 s−1) or high light (380 μmol photons m−2 s−1). High light stimulated both root and shoot growth. While the total contents per plant of some nutrients were markedly higher (calcium and potassium) or lower (copper) under high light, no major differences were observed for other nutrients. The distribution of nutrients and the further redistribution within the shoot were influenced by the light intensity in an element-specific manner. Nutrients were selectively directed to the leaves of the main shoot (low light) or to the tillers (high light). The quality of the harvested grains was also affected by the light intensity.

Photosynthesis: from Light to Biosphere, 1995

Archives of Microbiology, 2002

The genes encoding the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Methylococc... more The genes encoding the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Methylococcus capsulatus (Bath) were localised to an 8.3-kb EcoRI fragment of the genome. Genes encoding the large subunit ( cbbL), small subunit ( cbbS) and putative regulatory gene ( cbbQ) were shown to be located on one cluster. Surprisingly, cbbO, a second putative regulatory gene, was not located in the remaining 1.2-kb downstream (3') of cbbQ. However, probing of the M. capsulatus (Bath) genome with cbbO from Nitrosomonas europaea demonstrated that a cbbO homologue was contained within a separate 3.0-kb EcoRI fragment. Instead of a cbbR ORF being located upstream (5') of cbbL, there was a moxR-like ORF that was transcribed in the opposite direction to cbbL. There were three additional ORFs within the large 8.3-kb EcoRI fragment: a pyrE-like ORF, an rnr-like ORF and an incomplete ORF with no sequence similarity to any known protein. Phylogenetic analysis of cbbL from M. capsulatus (Bath) placed it within clade A of the green-type Form 1 Rubisco. cbbL was expressed in M. capsulatus (Bath) when grown with methane as a sole carbon and energy source under both copper-replete and copper-limited conditions. M. capsulatus (Bath) was capable of autotrophic growth on solid medium but not in liquid medium. Preliminarily investigations suggested that other methanotrophs may also be capable of autotrophic growth. Rubisco genes were also identified, by PCR, in Methylococcus-like strains and Methylocaldum species; however, no Rubisco genes were found in Methylomicrobium album BG8, Methylomonas methanica S1, Methylomonas rubra, Methylosinus trichosporium OB3b or Methylocystis parvus OBBP.

Higher plants play an important role in closed ecological life support systems as oxygen pro-duce... more Higher plants play an important role in closed ecological life support systems as oxygen pro-ducers, carbon dioxide and water recyclers, and as a food source. For an integration of higher plant chambers into the MELiSSA (Micro Ecological Life Support System Alternative) loop, a detailed characterization and optimization of the full food production and preparation chain is needed. This implies the prediction and control of the nutritional quality of the final products consumed by the crew, the prediction of the wastes ...

Agronomy, 2015

Copper, zinc, manganese, iron, nickel and molybdenum are essential micronutrients for plants. How... more Copper, zinc, manganese, iron, nickel and molybdenum are essential micronutrients for plants. However, when present in excess they may damage the plant or decrease the quality of harvested plant products. Some other heavy metals such as cadmium, lead or mercury are not needed by plants and represent pollutants. The uptake into the roots, the loading into the xylem, the acropetal transport to the shoot with the transpiration stream and the further redistribution in the phloem are crucial for the distribution in aerial plant parts. This review is focused on long-distance transport of heavy metals via xylem and phloem and on interactions between the two transport systems. Phloem transport is the basis for the redistribution within the shoot and for the accumulation in fruits and seeds. Solutes may be transferred from the xylem to the phloem (e.g., in the small bundles in stems of cereals, in minor leaf veins). Nickel is highly phloem-mobile and directed to expanding plant parts. Zinc and to a lesser degree also cadmium are also mobile in the phloem and accumulate in meristems (root tips, shoot apex, axillary buds). Iron and manganese are characterized by poor phloem mobility and are retained in older leaves.

Lemnaceen sind unter Photosynthesebedingungen in der Lage, sowohl Ammonium als auch Nitrat als St... more Lemnaceen sind unter Photosynthesebedingungen in der Lage, sowohl Ammonium als auch Nitrat als Stickstoffquelle zu verwenden. Die beiden Quellen sind jedoch nicht gleichwertig. Ferguson (1969) wies neben morphologischen Veranderungen auch Differenzen im Gesamtstickstoffgehalt und den Mengen der freien Aminosauren nach. Die beiden Ionen stellen somit nicht nur mogliche Stickstoffquellen, sondern auch Effektoren fur den Stoffwechsel dar.

Rubisco activase catalyzes the ATP-dependent activation of rubisco (1). At moderately elevated te... more Rubisco activase catalyzes the ATP-dependent activation of rubisco (1). At moderately elevated temperature (for wheat above 30°C), rubisco activase becomes reversibly inactivated in leaf segments (2). A further increase of the temperature (for wheat above 40°C) causes partial insolubilization and the formation of aggregates in less than 30 minutes (2).

Cotyledons from dwarf beans (Phaseolus vulgaris.L., var. "Saxa") were extracted at two ... more Cotyledons from dwarf beans (Phaseolus vulgaris.L., var. "Saxa") were extracted at two different stages of germination. Extract from ungerminated seeds (low endopeptidase activity) contained high leucine aminopeptidase activity, which was stable for several hours at pH 5.5 and 30 °C. A rapid inactivation was initiated by adding purified papain or extract from cotyledons of seeds germinated for 8 days (high endopeptidase and low aminopeptidase activities). Leucine aminopeptidase was protected in the presence of sucrose, glucose, fructose, glycine, alanine or serine. Added proteins or polypeptides (competitive substrates for the added endopeptidases) also delayed the inactivation. Only a minor stabilization was measured after adding potassium chloride or lysine, while the inactivation was even accelerated in the presence of magnesium _sulfate or magnesium chloride. The inhibiting effect of magnesium ions was not necessarily linked to the proteolytic inactivation. Our results...

Wahrend zehn Jahren wurden nach dem Reaktor- Unfall von Tschernobyl im Jahr 1986 Versuche zum bes... more Wahrend zehn Jahren wurden nach dem Reaktor- Unfall von Tschernobyl im Jahr 1986 Versuche zum besseren Verstandnis der Aufnahme der radioaktiven Isotope Casium-134 und Strontium-85 durch die Blatter von Pflanzen, deren Verteilung in den Pflanzen sowie der Abgabe an den Boden durchgefuhrt. Untersuchungen an Erdbeeren und Reben haben gezeigt, dass Strontium schlecht von den Blattern aufgenommen und in den Pflanzen praktisch nicht transportiert wird. Im Gegensatz dazu wird Casium von den Blattern schnell aufgenommen, in der ganzen Pflanze verteilt und teilweise durch die Wurzeln wieder ausgeschieden. Die Hohe dieser Abgabe wird durch die Kaliumversorgung der Pflanzen beeinflusst.

Acta Physiologiae Plantarum, 2007

Introduction: Drought is one of the most significant factors that limit plant productivity. Oxida... more Introduction: Drought is one of the most significant factors that limit plant productivity. Oxidative stress is a secondary event in many unfavorable environmental conditions. Intracellular proteases have a role in the metabolism reorganisation and nutrient remobilization under stress. In order to under stand the relative significance of oxidative stress and proteolysis in the yield reduction under drought, four varieties of Triticum aestivum L. with different field drought resistance were examined. Methods: A two-year field experiment was conducted. Analyses were performed on the upper most leaf of control plants and plants under water deficitat the stages most critical for yield reduction under drought (from jointing till milk ripeness). Leaf water deficit and electrolyte leakage, malondyaldehyde level, activities and isoenzymes of superoxide dismutase, catalase and peroxidase, leaf protein content and proteolytic activity were studied. Yield components were analyzed. Results: A g...

Plant Physiology (Rockville) 111(2 Suppl. ), Apr 2, 1996

Drought strongly influences root activities in crop plants and weeds. This paper is focused on th... more Drought strongly influences root activities in crop plants and weeds. This paper is focused on the performance of the heavy metal accumulator Solanum nigrum, a plant which might be helpful for phytoremediation. The water potential in a split root system was decreased by the addition of polyethylene glycol (PEG 6000). Rubidium, strontium and radionuclides of heavy metals were used as markers to investigate the uptake into roots, the release to the shoot via the xylem, and finally the basipetal transport via the phloem to unlabeled roots. The uptake into the roots (total contents in the plant) was for most makers more severely decreased than the transport to the shoot or the export from the shoot to the unlabeled roots via the phloem. Regardless of the water potential in the labeling solution, 63 Ni and 65 Zn were selectively redistributed within the plant. From autoradiographs, it became evident that 65 Zn accumulated in root tips, in the apical shoot meristem and in axillary buds, while 63 Ni accumulated in young expanded leaves and roots but not in the meristems. Since both radionuclides are mobile in the phloem and are, therefore, well redistributed within the plant, the unequal transfer to shoot and root apical meristems is most likely caused by differences in the cell-to-cell transport in differentiation zones without functional phloem (immature sieve tubes).

More frequent and more severe extreme events (e.g. flooding, drought, heat waves) were predicted ... more More frequent and more severe extreme events (e.g. flooding, drought, heat waves) were predicted from climate models for the next decades. Impacts of such events are relevant for crop productivity. Effects on a whole-plant level are the focus of this study. The influence of an extended drought period on solute allocation via the phloem was compared in two Bulgarian wheat varieties differing in drought susceptibility: “Sadovo” (drought-sensitive) and “Katya” (drought-tolerant). Young plants grown hydroponically on standard nutrient solution were transferred at the beginning of the experiment to fresh medium (controls) or to medium with polyethylene glycol 6000 (artificial drought). Radiolabelled solution (57Co, 109Cd, 134Cs) was introduced via a flap into the lamina of the third or fourth leaf of young plants (youngest fully expanded leaf before stress treatment). Export and allocation of the radiolabel were monitored by gamma spectrometry. 57Co, 109Cd and 134Cs are suitable radionuc...

Water availability in soil is a key aspect in the context of global change. More frequent and mor... more Water availability in soil is a key aspect in the context of global change. More frequent and more severe extreme events including droughts, flooding and heat waves must be expected for the next decades in some regions. Since a high percentage of the area used for agriculture is covered by grasslands, the response of grass and legume species to severe drought is important for the evaluation of drought impacts. Differences between the species considered (Lolium perenne L., Dactylis glomerata L., Phleum pratense L., Trifolium repens L., Trifolium pratense L.) in their response to a low water potential in the root medium were evident. In general the number of photosynthetically active leaves per plant decreased under drought. This decrease was partially due to a smaller number of new leaves produced and partially to senescence of the oldest leaves. The strongest reduction in the number of active leaves was observed in Trifolium repens, while Trifolium pratense was less susceptible. The grasses were even less affected than the clover species. Temperature of sun-exposed leaves was increased in drought-stressed plants as a consequence of decreased transpiration. The elevated temperature may cause additional effects on leaf metabolism (e.g. inactivation of Rubisco activase). Modifications in leaf senescence and leaf emergence under drought stress are species-specific and influence plant performance during the stress and the subsequent recovery phase.

Plants, 2019

Heavy metal redistribution is relevant for the quality of edible crops and the suitability of hyp... more Heavy metal redistribution is relevant for the quality of edible crops and the suitability of hyperaccumulators for bioremediation. Root-to-shoot transfer via the xylem and redistribution in the aerial parts via the phloem differ between various heavy metals. In general, cadmium is more slowly released to the shoot than zinc (e.g., in wheat, bean, and lupin). However, rapid cadmium transport to the shoot was detected in the hyperaccumulator Solanum nigrum L. This is a key aspect in this article and might be important for bioremediation. The radionuclides 109Cd and 65Zn were used to investigate the respective influence of elevated cadmium or zinc in the root medium on the dynamics of the two heavy metals in S. nigrum. Although transport via the xylem to the leaves was similar for 109Cd and 65Zn, the further redistribution from older leaves to younger leaves, flowers, and fruits via the phloem was far less efficient for 109Cd than for 65Zn. Furthermore, the redistribution of 109Cd wit...

Journal of Plant Physiology, 2016

Global change is characterized by increased CO2 concentration in the atmosphere, increasing avera... more Global change is characterized by increased CO2 concentration in the atmosphere, increasing average temperature and more frequent extreme events including drought periods, heat waves and flooding. Especially the impacts of drought and of elevated temperature on carbon assimilation are considered in this review. Effects of extreme events on the subcellular level as well as on the whole plant level may be reversible, partially reversible or irreversible. The photosynthetically active biomass depends on the number and the size of mature leaves and the photosynthetic activity in this biomass during stress and subsequent recovery phases. The total area of active leaves is determined by leaf expansion and senescence, while net photosynthesis per leaf area is primarily influenced by stomatal opening (stomatal conductance), mesophyll conductance, activity of the photosynthetic apparatus (light absorption and electron transport, activity of the Calvin cycle) and CO2 release by decarboxylation reactions (photorespiration, dark respiration). Water status, stomatal opening and leaf temperature represent a "magic triangle" of three strongly interacting parameters. The response of stomata to altered environmental conditions is important for stomatal limitations. Rubisco protein is quite thermotolerant, but the enzyme becomes at elevated temperature more rapidly inactivated (decarbamylation, reversible effect) and must be reactivated by Rubisco activase (carbamylation of a lysine residue). Rubisco activase is present under two forms (encoded by separate genes or products of alternative splicing of the pre-mRNA from one gene) and is very thermosensitive. Rubisco activase was identified as a key protein for photosynthesis at elevated temperature (non-stomatal limitation). During a moderate heat stress Rubisco activase is reversibly inactivated, but during a more severe stress (higher temperature and/or longer exposure) the protein is irreversibly inactivated, insolubilized and finally degraded. On the level of the leaf, this loss of photosynthetic activity may still be reversible when new Rubisco activase is produced by protein synthesis. Rubisco activase as well as enzymes involved in the detoxification of reactive oxygen species or in osmoregulation are considered as important targets for breeding crop plants which are still productive under drought and/or at elevated leaf temperature in a changing climate.

Agriculture, 2016

Selection and breeding of genotypes with improved drought/heat tolerance become key issues in the... more Selection and breeding of genotypes with improved drought/heat tolerance become key issues in the course of global change with predicted increased frequency of droughts or heat waves. Several morphological and physiological plant traits must be considered. Rooting depth, root branching, nutrient acquisition, mycorrhization, nodulation in legumes and the release of nutrients, assimilates or phytohormones to the shoot are relevant in root systems. Xylem embolism and its repair after a drought, development of axillary buds and solute channeling via xylem (acropetal) and phloem (basipetal and acropetal) are key processes in the stem. The photosynthetically active biomass depends on leaf expansion and senescence. Cuticle thickness and properties, epicuticular waxes, stomatal regulation including responses to phytohormones, stomatal plugs and mesophyll resistance are involved in optimizing leaf water relations. Aquaporins, dehydrins, enzymes involved in the metabolism of compatible solutes (e.g., proline) and Rubisco activase are examples for proteins involved in heat or drought susceptibility. Assimilate redistribution from leaves to maturing fruits via the phloem influences yield quantity and quality. Proteomic analyses allow a deeper insight into the network of stress responses and may serve as a basis to identify suitable genotypes, although improved stress tolerance will have its price (often lowered productivity under optimal conditions).

Journal of Plant Nutrition, 2015

ABSTRACT Investigations were focused on light effects on allocation of root-borne macronutrients ... more ABSTRACT Investigations were focused on light effects on allocation of root-borne macronutrients (calcium, magnesium and potassium) and micronutrients (iron, manganese, zinc and copper) in roots, shoots and harvested grains of wheat (Triticum aestivum L.). Plants were exposed to low (100 μmol photons m−2 s−1) or high light (380 μmol photons m−2 s−1). High light stimulated both root and shoot growth. While the total contents per plant of some nutrients were markedly higher (calcium and potassium) or lower (copper) under high light, no major differences were observed for other nutrients. The distribution of nutrients and the further redistribution within the shoot were influenced by the light intensity in an element-specific manner. Nutrients were selectively directed to the leaves of the main shoot (low light) or to the tillers (high light). The quality of the harvested grains was also affected by the light intensity.

Photosynthesis: from Light to Biosphere, 1995

Archives of Microbiology, 2002

The genes encoding the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Methylococc... more The genes encoding the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Methylococcus capsulatus (Bath) were localised to an 8.3-kb EcoRI fragment of the genome. Genes encoding the large subunit ( cbbL), small subunit ( cbbS) and putative regulatory gene ( cbbQ) were shown to be located on one cluster. Surprisingly, cbbO, a second putative regulatory gene, was not located in the remaining 1.2-kb downstream (3') of cbbQ. However, probing of the M. capsulatus (Bath) genome with cbbO from Nitrosomonas europaea demonstrated that a cbbO homologue was contained within a separate 3.0-kb EcoRI fragment. Instead of a cbbR ORF being located upstream (5') of cbbL, there was a moxR-like ORF that was transcribed in the opposite direction to cbbL. There were three additional ORFs within the large 8.3-kb EcoRI fragment: a pyrE-like ORF, an rnr-like ORF and an incomplete ORF with no sequence similarity to any known protein. Phylogenetic analysis of cbbL from M. capsulatus (Bath) placed it within clade A of the green-type Form 1 Rubisco. cbbL was expressed in M. capsulatus (Bath) when grown with methane as a sole carbon and energy source under both copper-replete and copper-limited conditions. M. capsulatus (Bath) was capable of autotrophic growth on solid medium but not in liquid medium. Preliminarily investigations suggested that other methanotrophs may also be capable of autotrophic growth. Rubisco genes were also identified, by PCR, in Methylococcus-like strains and Methylocaldum species; however, no Rubisco genes were found in Methylomicrobium album BG8, Methylomonas methanica S1, Methylomonas rubra, Methylosinus trichosporium OB3b or Methylocystis parvus OBBP.

Higher plants play an important role in closed ecological life support systems as oxygen pro-duce... more Higher plants play an important role in closed ecological life support systems as oxygen pro-ducers, carbon dioxide and water recyclers, and as a food source. For an integration of higher plant chambers into the MELiSSA (Micro Ecological Life Support System Alternative) loop, a detailed characterization and optimization of the full food production and preparation chain is needed. This implies the prediction and control of the nutritional quality of the final products consumed by the crew, the prediction of the wastes ...

Agronomy, 2015

Copper, zinc, manganese, iron, nickel and molybdenum are essential micronutrients for plants. How... more Copper, zinc, manganese, iron, nickel and molybdenum are essential micronutrients for plants. However, when present in excess they may damage the plant or decrease the quality of harvested plant products. Some other heavy metals such as cadmium, lead or mercury are not needed by plants and represent pollutants. The uptake into the roots, the loading into the xylem, the acropetal transport to the shoot with the transpiration stream and the further redistribution in the phloem are crucial for the distribution in aerial plant parts. This review is focused on long-distance transport of heavy metals via xylem and phloem and on interactions between the two transport systems. Phloem transport is the basis for the redistribution within the shoot and for the accumulation in fruits and seeds. Solutes may be transferred from the xylem to the phloem (e.g., in the small bundles in stems of cereals, in minor leaf veins). Nickel is highly phloem-mobile and directed to expanding plant parts. Zinc and to a lesser degree also cadmium are also mobile in the phloem and accumulate in meristems (root tips, shoot apex, axillary buds). Iron and manganese are characterized by poor phloem mobility and are retained in older leaves.