Refine
Document Type
- Article (2)
- Postprint (2)
- Bachelor Thesis (1)
Keywords
- fatty acid (5) (remove)
Institute
Leaf senescence is a key process in plants that culminates in the degradation of cellular constituents and massive reprogramming of metabolism for the recovery of nutrients from aged leaves for their reuse in newly developing sinks. We used molecular-biological and metabolomics approaches to identify NAC transcription factor (TF) RD26 as an important regulator of metabolic reprogramming in Arabidopsis thaliana. RD26 directly activates CHLOROPLAST VESICULATION (CV), encoding a protein crucial for chloroplast protein degradation, concomitant with an enhanced protein loss in RD26 over-expressors during senescence, but a reduced decline of protein in rd26 knockout mutants. RD26 also directly activates LKR/SDH involved in lysine catabolism, and PES1 important for phytol degradation. Metabolic profiling revealed reduced c-aminobutyric acid (GABA) in RD26 overexpressors, accompanied by the induction of respective catabolic genes. Degradation of lysine, phytol and GABA is instrumental for maintaining mitochondrial respiration in carbon-limiting conditions during senescence. RD26 also supports the degradation of starch and the accumulation of mono-and disaccharides during senescence by directly enhancing the expression of AMY1, SFP1 and SWEET15 involved in carbohydrate metabolism and transport. Collectively, during senescence RD26 acts by controlling the expression of genes across the entire spectrum of the cellular degradation hierarchy.
Erucasäure ist eine einfach ungesättigte Fettsäure, die sich in großer Menge im Samen von Raps und anderen Kreuzblütlern findet. Ernährungsphysiologisch gilt sie als problematisch, da sie eine nachweislich schädliche Wirkung auf die Herzmuskulatur hat. Daher wurde sie im Laufe des 20. Jahrhunderts zum größten Teil aus dem Deutschen Winterraps durch Züchtung fast vollständig eliminiert. In einigen Zweigen der Industrie ist sie jedoch weiterhin ein bedeutender Rohstoff. In dieser Arbeit wird die Papierchromatographie als kostengünstige Methode zur Trennung von Fettsäuren vorgestellt, welche auch im Schulunterricht angewendet werden kann. Diese veraltete Methode wurde reaktiviert und für die vorliegenden Zwecke optimiert. Mit Hilfe der hier beschriebenen Papierchromatographie lassen sich sowohl Rapssamen auf ihren qualitativen Gehalt an Erucasäure untersuchen, als auch eine Vielzahl von ungesättigten Fettsäuren in Raps- und auch Leinsamen qualitativ nachweisen. Es ist so möglich erucasäurefreie und erucasäurehaltige Rapssamen auf dem Papier zu unterscheiden. Der Gehalt an Erucasäure, welcher von nur zwei additiv wirkenden Genen gesteuert wird, kann im Schulunterricht z.B. im Themenbereich „Errungenschaften der Pflanzenzüchtung“ als praktisches Beispiels herangezogen werden. Durch die hier beschriebene Methode können die Mendelschen Regeln anhand dieses phänotypischen Merkmals erarbeitet oder vertieft werden. Zudem ermöglicht die praktische Untersuchung von Erucasäure themenübergreifendes Arbeiten im Biologieunterricht, da sie klassische Genetik mit moderner Pflanzenzüchtung verbindet.
It has been proposed that growth and reproduction of animals is frequently limited by multiple nutrients simultaneously. To improve our understanding of the consequences of multiple nutrient limitations (i.e. co-limitation) for the performance of animals, we conducted standardized population growth experiments using an important aquatic consumer, the rotifer Brachionus calyciflorus. We compared nutrient profiles (sterols, fatty acids and amino acids) of rotifers and their diets to reveal consumerdiet imbalances and thus potentially limiting nutrients. In concomitant growth experiments, we directly supplemented potentially limiting substances (sterols, fatty acids, amino acids) to a nutrient-deficient diet, the cyanobacterium Synechococcus elongatus, and recorded population growth rates. The results from the supplementation experiments corroborated the nutrient limitations predicted by assessing consumerdiet imbalances, but provided more detailed information on co-limiting nutrients. While the fatty acid deficiency of the cyanobacterium appeared to be of minor importance, the addition of both cholesterol and certain amino acids (leucine and isoleucine) improved population growth rates of rotifers, indicating a simultaneous limitation by sterols and amino acids. Our results add to growing evidence that consumers frequently face multiple nutrient limitations and suggest that the concept of co-limitation has to be considered in studies assessing nutrient-limited growth responses of consumers.
Significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the hypothesis that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells which are deficient in polyunsaturated fatty acids (PUFAs), and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the postmetamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha lead to irreversible effects for postmetamorphic animals, and is related to inferior competitive abilities.
The factors that determine the efficiency of energy transfer in aquatic food webs have been investigated for many decades. The plant-animal interface is the most variable and least predictable of all levels in the food web. In order to study determinants of food quality in a large lake and to test the recently proposed central importance of the long-chained eicosapentaenoic acid (EPA) at the pelagic producer-grazer interface, we tested the importance of polyunsaturated fatty acids (PUFAs) at the pelagic producerconsumer interface by correlating sestonic food parameters with somatic growth rates of a clone of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments spanning one season with Daphnia feeding on natural seston from Lake Constance, a large pre-alpine lake. Somatic growth rates were fitted to sestonic parameters by using a saturation function. A moderate amount of variation was explained when the model included the elemental parameters carbon (r2 = 0.6) and nitrogen (r2 = 0.71). A tighter fit was obtained when sestonic phosphorus was incorporated (r2 = 0.86). The nonlinear regression with EPA was relatively weak (r2 = 0.77), whereas the highest degree of variance was explained by three C18-PUFAs. The best (r2 = 0.95), and only significant, correlation of Daphnia's growth was found with the C18-PUFA α-linolenic acid (α-LA; C18:3n-3). This correlation was weakest in late August when C:P values increased to 300, suggesting that mineral and PUFA-limitation of Daphnia's growth changed seasonally. Sestonic phosphorus and some PUFAs showed not only tight correlations with growth, but also with sestonic α-LA content. We computed Monte Carlo simulations to test whether the observed effects of α-LA on growth could be accounted for by EPA, phosphorus, or one of the two C18-PUFAs, stearidonic acid (C18:4n-3) and linoleic acid (C18:2n-6). With >99 % probability, the correlation of growth with α-LA could not be explained by any of these parameters. In order to test for EPA limitation of Daphnia's growth, in parallel with experiments on pure seston, growth was determined on seston supplemented with chemostat-grown, P-limited Stephanodiscus hantzschii, which is rich in EPA. Although supplementation increased the EPA content 80-800x, no significant changes in the nonlinear regression of the growth rates with α-LA were found, indicating that growth of Daphnia on pure seston was not EPA limited. This indicates that the two fatty acids, EPA and α-LA, were not mutually substitutable biochemical resources and points to different physiological functions of these two PUFAs. These results support the PUFA-limitation hypothesis for sestonic C:P < 300 but are contrary to the hypothesis of a general importance of EPA, since no evidence for EPA limitation was found. It is suggested that the resource ratios of EPA and α-LA rather than the absolute concentrations determine which of the two resources is limiting growth.