Browsing by Subject "Physiology"

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Interplay between nutrition, senescence and cytosine methylation in Arabidopsis thaliana
(2023) Vatov, Emil; Ludewig, Uwe
In monocarpic plants, senescence is the last stage of leaf development and usually leads to the death of the organism. Systematic degradation of leaf components provides nutrients for the newly developing flowers and seeds. The physiology and transcriptional changes that occur in A. thaliana during this process are very well documented. However, the involvement of epigenic mechanisms remains to be established. In this study, the role of cytosine methylation in the regulation of monocarpic leaf senescence was examined in A. thaliana. Hypomethylated ddc (drm1/2 cmt3) and hypermethylated ros1 mutants showed consistent senescence-specific phenotypes. Disrupted de-novo methylation resulted in delayed, while disrupted demethylation resulted in earlier flowering and appearance of first symptoms of senescence. Both genotypes executed the senescence program faster than Col-0, with lower leaf:seed and higher C:N ratios. During nitrogen, or phosphorus withdrawal and resupply, nutrient remobilization was not inhibited in the two mutants. However, the plant’s response in terms of changes in shoot and root growth was delayed, or non existent. Furthermore, the impact of N withdrawal on delay of the flowering time was inhibited in the two mutants. These results support involvement of cytosine methylation in stress response signaling and downstream effects on organ development and flowering times. The stress response and senescence specific phenotypes of ddc could be partially due to disrupted WRKY signaling, as loss of methylation in W-box binding sites was prevalent, specifically near the transcription start sites of ORFs, and WRKY18, 25 and 53 appeared to be sensitive towards cytosine methylation. Overall decrease in cytosine methylation levels was observed, as early as the opening of the first flowers, together with a decrease in chlorophyll concentrations and an increase in H2O2 and glucose levels in the wild type Col-0. Inhibition in maintenance methylation in the early stages of reproductive growth is consistent with these observations. A complex interaction between four cytokinins was present as early as flower induction, followed by a mass turnover of bound auxin (IAA) at flower opening, that resulted in near doubling of free IAA at seed development. Plant defense responses were induced thereafter, as an increase in salicylic acid (SA) and camalexin occurred, followed by an increase in jasmonic acid (JA) and abscisic acid (ABA). Active RNA-dependent DNA methylation (RdDM) was indicated by a moderate overrepresentation of hypermethylated CHG and CHH loci, together with partial recovery of total methylation levels at the latest stages during seed maturation. Considering the delayed senescence phenotype of ddc, de-novo methylation via RdDM appears to be involved in initiation and execution of the senescence program. Furthermore, hypomethylation at ROS1 gene regulatory region was related to down regulation of gene expression. As an antagonist of RdDM, together with the early senescence phenotype of ros1, these results strengthen the importance of de-novo methylation for senescence, while active demethylation gets down regulated. Overall, methylation changes were little related to known gene expression changes that are associated with senescence. Limited targeting of WRKY and bZIP binding sites hinders conclusions about senescence specific effects of cytosine methylation in signal transduction networks. Altogether, the present work shines light on the importance of proper maintenance of cytosine methylation for flowering time, nutrient remobilization and senescence, and identifies defined cytosine methylation changes during senescence in a comprehensive physiological framework.
Physiological mechanisms and growth responses of sweet potato subjected to salinity
(2023) Mondal, Shimul; Asch, Folkard
For the development of salt-tolerant sweet potato varieties, either through breeding or biotechnology, an appropriate salinity screening tool is necessary for the identification of tolerant or sensitive genotype. Our overall objectives for this study were to develop a suitable, reliable and rapid salinity screening tool in view of salt tolerance mechanism in sweet potato under salinity. To better understand the tolerance mechanisms; leaf level ion uptake and distribution patterns by transpirational water loss and leaf level ROS scavenging antioxidant enzyme activities were evaluated under salinity. Additionally, different ion extraction methods were tested which will contribute to the development of reliable salinity screening tool in sweet potato genotypes. All the experiments were conducted in the greenhouse and VPD (vapor pressure deficit) chambers of the Hans-Rutenberg Institute of Tropical Agricultural Sciences, University of Hohenheim, Germany, in a hydroponic system. Twelve genotypes of sweet potato were collected from Bangladesh Agricultural Research Institute (BARI) and used to evaluate salt thresholds with salt tolerance mechanisms for a wide range of salinity levels (0, 50, 100, and 150 mM NaCl). First, genotypic thresholds were determined for 12 sweet potato genotypes exposed to salinity, whereupon it was found that 75 mM root zone salinity (NaCl) was the threshold for sweet potato. The genotypic threshold was estimated from the dry matter accumulation that began to decrease under the influence of salinity. It was found that genotypic thresholds were negatively linearly correlated with the difference between tissue K content at 75 mM NaCl and tissue K content at controlled salinity in the root zone. This information is very important for identifying the salt tolerant and sensitive genotype of sweet potato. Second, the uptake and distribution of Na, K, and Cl ions by transpiration, across different-aged leaves, were studied to better understand the mechanisms of salt tolerance in sweet potato. Two different sweet potato genotypes were subjected to salt stress of 0 and 50 mM NaCl in artificially dry (VPD 2.27 kPa) and humid (VPD 0.76 kPa) chambers. We found that cumulative water loss per unit leaf area was twice as high at a VPD of 2.27 kPa, but Na uptake remained the same. No relationship was observed between water loss from individual leaves and Na or Cl uptake. About 30% more Na was distributed in the petioles of salt tolerant genotype compared to leaf blades, while the opposite was observed in salt sensitive sweet potato genotype and VPD had no effect on Na distribution. Third, the activities of ROS scavenging antioxidant enzymes were evaluated with respect to different leaf age, in two different genotypes of sweet potato under 100 mM salinity. In general, antioxidant enzymes in sweet potato do not respond to salt stress but are altered by the effects of leaf position, leaf age, duration of stress, and genotype. No effect of Na on antioxidant enzyme activities was found under salt stress in sweet potato leaves. However, the significant positive correlation between K concentration and the level of SOD (super oxide dismutase) in older leaves suggests that SOD contributes to the maintenance of a high K concentration to protect photosynthetic activity. In summary, this study shows that sweet potato responds differently to salinity depending on the genotype, and that the threshold beyond which yield decreases is 75 mM NaCl. Genotypic threshold strongly linked to high tissue K content under increasing salinity that suggests a salt tolerance mechanisms in sweet potato. Salt-tolerant sweet potatoes distribute significant amounts of Na and K in their petioles. Young leaves of the tolerant genotype contain more K under salt stress. GR and positive relationship between K concentration and SOD in salt tolerant genotypes indicate some tolerance mechanisms. So, a screening tool is proposed for sweet potato based on the genotypic ability to maintain high tissue K levels under increasing salinity level.
Physiologische und genetische Einflüsse auf die Qualität von Schweinefleisch aus baden-württembergischen Gebrauchskreuzungen
(2012) Fecke, Anna; Weiler, Ulrike
What genotypes, basing on the genetic lines supplied by German Genetic, guarantees both a high-value carcass and excellent pork quality and high eating quality and also how the criteria of fertility, weight development and yield at slaughter, relate to the criteria of pork quality. 10 genotypes were studied. Therefore the sows crossbred represent typically genotypes in Baden-Württemberg as well as the Leicoma hybrid sows. These sows were bred at the LSZ Boxberg with Pietrain and Duroc boars. The sows of the LW*(LC*DL) had the highest fertility rate. The boar lines showed no influence on either the birth weight or fertility parameters. The boar line, however, did reflect a highly significant influence on the daily gain in all further production periods (Duroc vs. Pietrain: suckling +8%; rearing +3,8%; fattening +6,5%).The offspring from the sows LW*(LC*DL) had the greatest daily gain in the suckling period and had a higher weaning weight (+6%, p<0.05) than the offspring from the LW*(SH*DL), which achieved the lowest overall weaning weight. On analyzing the relationship between the development weights in the various production periods and the birth weight, it was obvious that the birth weight provides a significant positive influence on the performance in every production period, except for rearing. Indeed, in the rearing period the animals with a high birth weight tended to show low daily gains, whereas the piglets with a low birth weight were able to partially compensate for the early growth deficit during this period. The Pietrain offspring had more lean meat content than the Duroc offspring. The dissection in Trial #2 shows that the Pietrain offspring had 3.3% more ham content and 4.0% more of the valuable cuts. The Duroc offspring had less lean meat content in the belly (-4.2%, Gruber Formula), more back fat (+13.7%), more leaf fat (+14.6%), and 12.5% more corrected fat area than the Pietrain offspring. The offspring of the sows LC*LW had a significantly shorter carcass than the offspring of the other sows. The offspring from the 50% Leicoma sows showed the greatest corrected fat area. The offspring from the sows LW*(LC*DL) had 17.1% less corrected fat area. The correlation analysis resulted in the established relationships. Especially of a practical interest, is the close relationship between lean meat content (FOM) and the pork underbelly (Gruber Formula) (r=0.92; n=240; p<0.001). For nearly every parameter the results of the pork quality grading under practical conditions (Trial #1) tended toward improved values for the pigs with Duroc genes, which showed a significantly lower drip loss. The influence of the sows on pork quality parameters was negligible. Besides these parameters, some carcasses were also characterized with PSE qualities (pH1<5.8; conductivity 24hr p.m.>8.0mS/cm). In Trial #1, based on the pH-readings at the slaughterhouse, almost no carcasses (0.15%) were identified with PSE, whereas the conductivity measurements in ham, 5.79% of the carcasses were identified as PSE. In Trial #2, 15.0% of the animals were PSE based on pH1 or conductivity measurements in the loin and ham. There were 5 carcasses which have PSE after both measurements in loin and ham. In the histochemical analysis of the muscle fiber classification the only difference between the boar lines was found in the percentage of red fibers. The eating quality tests revealed an influence from the boar line. In general, all genotypes produced a high quality lean meat content according to the market requirements. As to expectation the improved pork quality of the Duroc breed was justified by the best eating quality, an improved water-holding capacity and a higher intramuscular fat content. An acceptable overall pork quality can be achieved by pairing the offspring from the Pietrain*LW*(LC*DL). The offspring with some Schwäbisch-Hall genes have an opportunity to establish a regional market. However, their performance was not convincing because in fertility, in daily gain, and even in pork quality they attained below average values. Nevertheless, an optimal pork quality can be achieved more efficiently with other genotypes. On establishing predicting criteria, the percentage of PSE of the pork carcasses is quite positive. The superiority of the 24hr p.m. conductivity value for the drip loss predict is evident here. The measurement of the conductivity subsume the effects of slaughtering and cooling and is more appropriate than the pH1 value, especially, for the incoming inspection in the deboning area as well as for quality assurance.
Reaktionen einer Weizen-Wildkraut Gemeinschaft auf erhöhtes CO2 im FACE Experiment: Proteomik, Physiologie und Bestandesentwicklung
(2006) Weber, Simone; Fangmeier, Andreas
The enhancement of the atmospheric carbon dioxide concentration in the last 150 years due to human activities is one of the main components of global change. For the future, different scenarios predict a steadily increase of carbon dioxide in our atmosphere. As carbon dioxide is the most important carbon source for plants, higher CO2 concentrations have the potential to cause direct effects on plant metabolism and vegetation development. Until now almost all of the studies concerning the effects of elevated CO2 on plants were carried out under controlled conditions, whereas the effects under natural conditions are in-vestigated at only 33 sites worldwide. The aims of this study were to investigate the effects of elevated carbon dioxide on a plant community under natural conditions with regard of (i) the plant proteome, (ii) the plant physiology, (iii) the vegetation development and (iv) the potential interactions between these criteria. Therefore a Mini-FACE system was used to expose a plant community composed of wheat and weeds to two different treatments: (a) Ambient (ambient CO2 concentration, circa 380 ppm) and (b) FACE (Ambient + 150 ppm CO2). The study mainly focussed on the bio-chemical and physiological reactions of spring wheat (Triticum aestivum cv. Triso) as a crop species and wild mustard (Sinapis arvensis L.) as a weed species on carbon dioxide enrich-ment. The SELDI-TOF-MS technology was applied for the first time in the topic of carbon dioxide impacts on plants. The technology provides the opportunity to quantitatively and qualitatively investigate low molecular weight proteins with low abundances, which has been difficult to realise with the standardized methodology in proteomics until now. In addition to the biochemical and physiological analysis, the vegetation development was investigated continuously during the vegetation period using non-destructive methods. This included the assessment of species phenology and species dominance. The results of the performed study show that the carbon dioxide enrichment affects the protein profiles of both species wheat and wild mustard. Interestingly, many alterations in the protein concentrations were found, but no protein could be detected to be exclusively ex-pressed under CO2 treatment. The degree of modification in both species was influenced by their developmental stage. Particularly the protein profile of wheat leaves was strongly in-fluenced during generative plant development, therefore the plants seems to be highly sensitive to environmental changes during this developmental stage. Altogether three proteins were identified which were affected by CO2 treatment. The first protein, the saccharose-H+-symporter protein, was detected in the grain of spring wheat and is associated with the plant?s primary metabolism. This protein plays an important role in controlling the import of saccharose in developing grain. Consequently, elevated CO2 seems to regulate the allocation of assimilates in an active way by influencing the saccharose-H+-symporter concentration in the grain of spring wheat. Furthermore, the remaining two proteins, the PR4 protein localized in the grains and the LRR-kinase protein accumulated in the leaves of spring wheat, are associated with the secondary plant metabolism and they also responded to the elevated CO2 concentrations. These proteins are linked with defense reactions of the plants against patho-gens. The elevated CO2 concentrations caused a decrease in defense recognition in the vege-tative tissue. If the plant is infected by pathogens this down-regulation could result in a ne-gative impact. The concentration of soluble proteins and of total nitrogen decreased in the leaves of spring wheat whereas the C/N ratio increased. Despite this the relative concentration of Chlorophyll a was not affected and therefore an accelerated growth of the plants due to the carbon dioxide enrichment can be excluded. Thus the detected pattern of responses suggests an enhanced nitrogen use efficiency under increased CO2 concentrations. The biomass of single spring wheat plants was unaltered during the vegetation period whereas other investi-gations in parallel showed an enhanced growth and a greater yield of spring wheat at the end of the vegetation period. Species dominance of wheat and weeds was neither influenced in the first nor the second year of investigation with regard to CO2 enrichment. The results indicate that annual crop systems under natural conditions indeed exhibit strong reactions concerning proteomics and physiology, but not concerning the plant development probably due to a relative short time of exposition. Based on long term considerations the detected reactions of the plant proteome may play an important role in the breeding of optimal adapted plants.
Sequestration of plant toxins in milkweed bugs (Heteroptera: Lygaeinae) : physiological implications and mechanisms
(2023) Espinosa del Alba, Laura; Petschenka, Georg
Insect herbivores and plants together are a crucial component of terrestrial macro-biodiversity. Within the realm of plant-insect interactions, phytophagy by insects triggered an “arms-race” dynamic resulting in escalatory adaptation and counter-adaptation over time. This coevolution led to complex phenomena such as sequestration of plant toxins by specialized insects, with the main aim to deter predators. Although sequestration is an extensively reported phenomenon, many physiological aspects and underlying mechanisms remain largely unexplored. Milkweed bugs (Heteroptera: Lygaeinae) constitute a versatile model ideally suited for studying both areas due to their particular evolutionary history. They are primarily associated with plant species in the Apocynaceae which commonly produce cardenolides, but remarkably some milkweed bug species secondarily evolved novel associations with phylogenetically disparate plant families supplying new sources of chemically related or unrelated toxins. Using as model milkweed bugs the cardenolide specialist Oncopeltus fasciatus and Spilostethus saxatilis, a species that shifted to sequestration of the chemically unrelated colchicoids, the present thesis first aimed to develop a new artificial diet that allowed the incorporation of the desired types and amounts of toxins without impairing insect performance. Taking a simplified approach, an artificial diet presented in a pill form and made of 100% organic sunflower meal was established. Despite the fact that the new diet has remarkable energy and nutrient differences with sunflower seeds (the laboratory diet), no differences in terms of insect performance were found between the two diets in O. fasciatus and S. saxatilis. Moreover, the new diet presented an acceptable concentration accuracy and shelf-life for short-term toxin feeding assays. Once established, the new diet was used to investigate the effects of cardenolides and colchicoids on several life-history traits of S. saxatilis, and to compare them with the effect of cardenolides in O. fasciatus. Although both classes of toxins have different molecular targets (cardenolides: Na+/K+-ATPase; colchicoids: tubulin), S. saxatilis was able to sequester them at a cost-free level. In fact, an increased performance was observed in O. fasciatus and an according trend was found in S. saxatilis after dietary exposure to cardenolides and colchicoids, respectively. Among cardenolides, labriformin is especially toxic for milkweed-specialist Na+/K+-ATPases in vitro. Nevertheless, it was shown to have no costs in terms of growth and fertility at the whole organism level for O. fasciatus. This finding might be an example of reciprocal evolution between milkweed plants and its herbivores, where highly toxic cardenolides specifically targeted to insect specialists are counteracted by tolerance, detoxification, and sequestration strategies. To assess the role of sequestration beyond normal physiological conditions, O. fasciatus and S. saxatilis were orally infected with the bacterium Pseudomonas entomophila. Neither cardenolides nor colchicoids provided a higher resistance or tolerance. Regarding mechanisms of sequestration, the other overarching research topic of the present thesis, both in vivo (whole animal) and in vitro (isolated digestive tracts) approaches showed no reciprocal competition for the same transport mechanism between chemically related and unrelated toxins. Furthermore, the digestive tract of milkweed bugs did not seem to be a critical mediator as it is for other non-sequestering and sequestering species. The time course of sequestration for the model species was resolved from three days to one hour, and the higher levels of colchicoids detected in S. saxatilis compared to the level of cardenolides in O. fasciatus might indicate an early acquisition of defenses with the shift from cardenolide to colchicoid-containing plants. Finally, a hint to preadaptation mechanisms to resist novel toxins was documented in Spilostethus pandurus, a species that belongs to the same genus as S. saxatilis, thereby providing a basis for future investigations.