Browsing by Subject "Seed"

Now showing 1 - 3 of 3

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.
Nutrient seed treatments to improve abiotic stress tolerance in Brassica napus L.
(2020) Mahmood, Asim; Neumann, Günter
Poor germination and limitations during early plant growth are widespread constraints for oilseed rape (OSR; Brassica napus L.) with increasing importance due to a rising frequency of weather extremes related with global climate change. In this study, efforts have been made to improve health and stress resistance of OSR by exploring perspectives of cost-effective application techniques for micronutrients with stress- protective functions to cover increased demands of these nutrients under stress conditions. After preliminary screening experiments, special emphasis was placed on zinc (Zn) seed treatments including seed priming (SP) and seed dressing (SD). Effects on seedling performance during early growth were recorded at optimal conditions for plant growth in terms of temperature, nutrient and water supply and also under drought stress for winter OSR and under low root zone temperature (RZT) stress in spring OSR. Accordingly, both, ZnSP and ZnSD may offer practical, economically low-cost application methods to improve early seedling establishment particularly under challenging environmental conditions, to improve the perspectives for conversion into higher economic yields and could be equally attractive for small-scale on-farm use and rape seed industry.