Losemann, Emely Kristin ORCID: 0000-0001-8990-971X (2024). Impact of evolution of C4 photosynthesis on N nutrition. PhD thesis, Universität zu Köln.
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Abstract
The evolution of C4 photosynthesis led to increased photosynthetic efficiency compared to C3 relatives particularly in warm and dry conditions, offering great potential to improve crop performance under increasingly arid conditions brought on by climate change. C4 plants achieve this improved photosynthetic efficiency by employing a CO2-concentrating mechanism which minimizes the oxygenation reaction of RuBisCO. This mechanism depends on spatial separation of primary CO2 fixation by PEP carboxylase (PEPC) in mesophyll (MS) cells, transfer of the C4 acid intermediates to bundle sheath (BS) cells for decarboxylation, and the assimilation of the CO2 by RuBisCO. Through this compartmentalization the N balance between MS and BS cells is disrupted, nitrate reduction is specifically localized in MS, and C4 plants possess a higher nitrogen use efficiency. However, so far it is not sufficiently understood how N uptake and assimilation adapted in the course of C4 photosynthesis evolution. Identifying these alterations in the N assimilation pathway will be necessary to support efforts of engineering the more efficient C4 photosynthesis mechanism in C3 staple crops like rice or wheat. This thesis characterizes and compares mineral nutrition traits of C3, C3-C4 and C4 species from the Brassicales order to determine metabolic differences dependent on photosynthesis type and how they are conserved among species of the same type. The analyses revealed a higher N deficiency tolerance in the C4 species, which is achieved through a higher uptake ability and accumulation of NO3- and amino acids in leaves, which might serve as a N reserve for production of photosynthetic enzymes to upkeep photosynthesis rates under low N conditions. In contrast, intermediate species did not show an increase in N deficiency tolerance implying that improved N deficiency tolerance is dependent on a complete transition to C4 photosynthesis. Metabolite profiling further revealed significant differences in accumulation patterns of sugars, amino acids and TCA intermediates between the C3 and C4 species under N deficiency conditions suggesting a differential regulation of N deficiency responses in C3 and C4 species. 15N uptake and gene expression analysis revealed clear differences in the regulation of the uptake and assimilation of NO3- and NH4+ between the C3 and C4 Cleome species. The higher sensitivity to NH4+ as their sole N source in C4 plants was shown to be linked to a lower uptake capacity for NH4+. Overall the results suggest a differential regulation of N assimilation and deficiency responses in C3, C3 C4 and C4 species from the Brassicales order and highlight the importance of understanding the metabolic fluxes to improve plant performance.
Item Type: | Thesis (PhD thesis) | ||||||||
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URN: | urn:nbn:de:hbz:38-743440 | ||||||||
Date: | 2024 | ||||||||
Language: | English | ||||||||
Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
Divisions: | Faculty of Mathematics and Natural Sciences > Department of Biology > Botanical Institute | ||||||||
Subjects: | Life sciences | ||||||||
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Date of oral exam: | 30 October 2024 | ||||||||
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Refereed: | Yes | ||||||||
URI: | http://kups.ub.uni-koeln.de/id/eprint/74344 |
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