Browsing by Subject "Samen"

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Comprehensive analyses of DNA methylation profile, regulation on flowering, and seed mineral accumulation in Arabidopsis thaliana in response to zinc deficiency
(2016) Chen, Xiaochao; Ludewig, Uwe
Zinc (Zn) is an essential micronutrient for plant growth and development, which plays important roles in DNA binding, metabolic, catalytic and transcriptional regulator activities. However, Zn deficiency is a worldwide problem due to its limited bioavailability in soils in many agricultural areas, often as a result of high CaCO3 content and high pH. In addition, phytic acid is able to strongly chelate cations, such as Zn2+, Fe2+, Ca2+ and Mg2+ to form the phytate salts. Phytate cannot be digested by human beings or other monogastric animals due to lack of phytase, an enzyme that can hydrolyze phytate. Therefore, Zn bioavailability in seeds (or grains) is restricted by phytate. Moreover, seed Zn concentration is also reduced by elevated CO2, especially in C3 plants, such as wheat, rice and soybean. Regarding to the crucial roles but limited bioavailability of Zn, here I present a comprehensive analysis on roots, leaves (and flowering) and seeds in response to Zn deficiency in the model plant Arabidopsis thaliana via three experiments. First, I investigated the transcriptional response and whole-genome DNA methylation profile upon Zn deficiency in roots using next-generation sequencing. Ionome analysis on shoots showed that Zn concentration was strongly reduced in Zn deficiency, whereas other nutrients were not affected. Microarray Analysis identified several known Zn-deficiency responsive genes, confirming the effectiveness of Zn deficiency in this work. However, bisulfite sequencing results revealed that DNA methylation was eliminated by Zn deficiency in transposable elements and slightly in gene bodies as well. The DNA demethylation response to nutrient stress was a novel finding, as reversed to previous reports about phosphate stress which accumulated methylation. Surprisingly, further analysis suggested that DNA methylation occurred independent of gene transcription. Nevertheless, non-CpG methylation has a potential impact on flower development in response to Zn deficiency. The second experiment investigated the relationship between rosette size and flowering, and how rosette size and flowering time were regulated by Zn deficiency. Using natural variation population (168 Arabidopsis accessions), I found that flowering time was positively correlated with rosette size in early-flowering accessions but not in late-flowering accessions. Intriguingly, the flowering time was delayed by Zn deficiency in these early-flowering plants and resulting in promotion of vegetative biomass. However, Zn-regulated flowering time was independent of previously reported flowering pathways. Then genome-wide association study identified the underlying candidate gene was FLOWERING LOCUS T (FT) which was strongly inhibited by Zn deficiency in all accessions. Detailed genetic analysis confirmed this result as well. Furthermore, the promotion of leaf size in Zn deficiency was found being contributed by cell proliferation (cell number) but not cell size. Lastly, in the third experiment I was interested in the natural genetic variation in seed Zn concentration, together with iron (Fe) and manganese (Mn), in response to Zn deficiency. Across around 100 accessions, average seed Zn concentration decreased from 47.4 µg g-1 to 31.3 µg g-1 due to Zn deficiency. To identify candidate genes affecting seed Zn, Fe and Mn concentrations, genome-wide association mapping was performed. A candidate gene, inositol 1,3,4-trisphosphate 5/6-kinase 3 gene (ITPK3), was associated which is involved in phytate synthesis pathways. However, loss of this gene in itpk3-1 did neither affect phytate seed levels nor seed Zn, Fe and Mn. Nevertheless, large natural variance of micronutrient seed levels was identified in the population and several accessions maintained high seed Zn despite growth in Zn-deficient conditions. Altogether, this study presents comprehensive analyses in how Arabidopsis adapts to Zn deficiency in regard of root transcription and DNA methylation, flowering and leaf regulation, and seed mineral accumulation. I provided new possibilities of correlation between DNA methylation and gene transcription, which is much more complex than previously reported. I also opened a novel insight into flowering regulation on leaf size, resulting in promotion of vegetative biomass in nutrient deficiency. Substantial natural variation of seed experiment indicated that the evolution process was involved in seed mineral accumulation in Arabidopsis, especially those accessions maintaining Zn concentration in Zn-deficient soils are valuable for further investigations. I believe these findings in Arabidopsis also provide precious knowledge for plant breeders and agronomists who work on crops.
Developing cropping systems for the ancient grain chia (Salvia hispanica L.) in two contrasting environments in Egypt and Germany
(2020) Mack, Laura; Graeff-Hönninger, Simone
Chia (Salvia hispanica L.) seeds have been revived as functional “superfood” for human nourishment especially for vegan and vegetarian diets and are becoming increasingly widespread and present in new food products in Europe. The seeds are beneficial because of being gluten-free, containing antioxidants and a high concentration of α-linolenic acid, and having a high content of dietary fiber and high-quality protein. Chia is originally adapted to short-day conditions and grows naturally in tropical and subtropical environments. Nevertheless, it can survive under water stress and could, therefore, be cultivated in arid regions. Egypt has been classified as a water-scarce state. Due to its drought tolerance, chia might contribute to saving the scarce source “water” in Egypt and offer the chance to export these high value seeds, generating foreign exchange for reimporting e.g. wheat characterized by a higher water demand. Worldwide, the biggest problems and key challenges under climate change (CC) are water and food security in arid and semiarid regions. In the future, CC and water scarcity will significantly threaten agriculture and sustainable development. A rising population requires on the one hand an increase in food grain production, but also a change toward environmentally sound sustainable agriculture. Chia has been suggested as a favorably economic alternative for common field crops sustaining diversification and stabilization of the local agricultural economy. However, broad experience in growing chia in new environments is missing. The agronomic management has not been improved from formerly small-scale production systems. Most of the previous studies focused on seed characteristics. Information on fertilization, plant protection, and improved varieties is scarce, which are reasons for its low productivity in the countries of origin. Field experiments were conducted at the experimental station “Ihinger Hof” of the University of Hohenheim in southwestern Germany from 2015 to 2017 and in Egypt during the cropping season 2015 to 2016 at SEKEM’s experimental station located 50 km Northeast of Cairo. The present doctoral thesis was based on a project embedded in the graduate school Water-People-Agriculture (WPA) at the University of Hohenheim funded by the Anton-&-Petra-Ehrmann foundation that focuses on key water issues and water related challenges of todays society. On a final note, the main results of this thesis provide further information and expanded knowledge on chia cultivation in two contrasting environments (including a desert region) out of its center of origin. Overall, the current doctoral thesis presents a combined approach of experimental field research and crop modeling to support the optimization of farming practices of chia in new environments. A universal and nondestructive LA estimation model for chia was developed. Further, the CROPGRO model was adapted for chia to provide a preliminary model for a realistic simulation of crop growth variables. The approaches presented in this thesis may contribute to testing new environments for chia cultivation and to improving its production. Moreover, this study helped to develop further general model source codes to simulate the growth of tiny seeds. The adaptation to other Salvias should be much easier with this developed model. Future research requirements and issues requiring model improvement such as N-response and the development of code relationships that can simulate parameters of seed quality could improve the plant growth model for chia.
Genotypische Variation der Überdauerungsneigung von transgenem und konventionell gezüchtetem Raps und Möglichkeiten der Beeinflussung durch Bodenbearbeitung als Beitrag zur Sicherheitsforschung bei transgenen Kulturpflanzen
(2004) Gruber, Sabine; Claupein, Wilhelm
High losses during harvesting of oilseed rape in combination with secondary dormancy of the seeds can result in a large soil seed bank which may persist for several years. Volunteers emerging from this seed bank cannot be controlled completely, particularly when they develop in another rapeseed population. In addition to well known agricultural problems, the risk of temporal and spatial gene dispersal by persistent seeds and volunteers gets more significant. With regard to genetically modified (GM) cultivars, seed dormancy and persistence of oilseed rape volunteers have to be reconsidered. The aim of the current study was to investigate the chances for a reduction of seed persistence and gene dispersal by growing specific genotypes and by the implementation of appropriate tillage operations. Four publications describe and discuss experiments in the laboratory and the field on the aspects ?genotype? and ?soil tillage?. One central point was the characterisation of the genotypic variation of secondary dormancy and seed persistence in GM (herbicide tolerant) and conventionally bred oilseed rape. A gradual approach towards field conditions was performed by three experiments. The first experiment examined potential seed persistence by artificial induction of secondary dormancy in the laboratory. The second experiment was a burial of seeds in the soil for six months on a field. The third experiment examined persistence of seeds actually lost during harvest and exposed afterwards to different tillage operations in a field experiment. All three experiments showed a high genotypic variability in seed dormancy and persistence. In the laboratory the level of secondary dormancy of conventional cultivars was a total of 3?76% and of the GM cultivars 1?31%. The number of persistent seeds in the burial experiment was 7?90% in the conventional and 12?79% in the GM assortment. Seeds from the seed rain of the four conventionally bred cultivars in the field experiment persisted in the soil from 0?11% over six months. A significant, positive correlation was found between the laboratory results for cultivars from two crop years as well as between the results from laboratory and burial experiments. This is an indication for a genetic background of seed dormancy and persistence of oilseed rape. It has been demonstrated that a laboratory method for induction of secondary dormancy can describe differences of seed persistence in the field. This result gives a chance for screening new cultivars in the laboratory to identify desired, low persistent genotypes. The other focus of the study was the effect of various tillage treatments on seed persistence and seedling recruitment in the field. Four differently intensive tillage operations incorporated the seeds of two near-isogenic cultivars at different times and soil depths, or left the soil untilled. Winter wheat was sown as following crop in all treatments whereby no weed control was performed. The highest number of seeds generally entered the soil seed bank when seeds were incorporated into the soil by stubble tillage immediately. After six months 1?14% of the initial seed input was found again in the soil in these treatments, and in one isolated case about 28%. Delaying the stubble breaking, the soil seed bank was 0?3%. Leaving the seeds undisturbed on the soil surface until direct drilling resulted in a soil seed bank of 0?17%. Therefore, the first tillage operation after harvest of oilseed rape should be performed with some time delay to avoid large soil seed banks. Soil inversion by a mouldboard plough shifted the majority of seeds into deep soil horizons from where a successful germination was restricted. In contrast, primary tillage by a rigid tine cultivator or zero tillage mainly distributed the seeds within the upper soil layer. Thus the number of flowering volunteers in the first spring was highest in these treatments, with a maximum of one volunteer m-2. Gene dispersal from oilseed rape volunteers to other rape crops and feral relatives was possible because their flowering periods overlapped. The volunteers were able to produce viable seeds, despite high levels of damage by pests and diseases. Overall, a high genotypic variability was found for seed persistence of oilseed rape. Tillage operations, particularly the time of stubble tillage, can also influence seed persistence and the occurrence of volunteers. Combined with a thorough knowledge of the processes involved, the selection of low persistent genotypes and adequate tillage operations offer chances to limit or even to avoid undesired gene dispersal from oilseed rape volunteers, and to make gene dispersal a predictable factor.