JXB Advance Access originally published online on August 28, 2007
Journal of Experimental Botany 2007 58(12):3183-3195; doi:10.1093/jxb/erm164
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Uptake and allocation of carbon and nitrogen in Vicia narbonensis plants with increased seed sink strength achieved by seed-specific expression of an amino acid permease
1Fachgebiet Pflanzenbau in den Tropen und Subtropen, Humboldt Universität zu Berlin, D-14195 Berlin, Germany
2Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), D-06466 Gatersleben, Germany
3Biology Department, Trent University, Peterborough, ON, K9J 7B8 Canada
4Universität Rostock, Medizinische Fakultät, Kinder- und Jugendklinik, D-18057 Rostock, Germany
* To whom correspondence should be addressed. E-mail: weber{at}ipk-gatersleben.de
Over-expressing an amino acid permease in Vicia narbonensis seeds increases sink strength for N that is evident from the higher seed protein content and seed weight. Here, the effect of increased seed sink strength of line AAP-12 on growth, development, and on whole plant carbon and nitrogen uptake and partitioning is analysed. AAP-12 plants have a prolonged growth period. Accumulation and partitioning of dry matter and N in leaves, stems, and pods are higher whereas remobilization to the seeds is delayed, indicating that the switch from growth to reserve allocation and remobilization is delayed. Measuring uptake and allocation of 15N-ammonia applied via the roots revealed a higher and longer label uptake period during maturation. Measuring whole plant carbon fixation and allocation after 13C labelling shows higher levels at maturation, particularly in seeds, indicating higher seed sink strength for C and increased allocation into maturing seeds. Levels of cytokinins were dramatically increased in AAP-12 seeds indicating its role in nitrogen-mediated growth stimulation. AAP-12 seeds have higher natural abundances for 13C indicating increased C fixation via PEP carboxylase in order to meet the higher demand of carbon acceptors for amino acid synthesis. In summary, increased seed sink strength for N in AAP-12 stimulates seed growth, but also that of vegetative organs, which finally leads to a higher ratio of vegetative to seed biomass at maturity and thus a lower harvest index. Therefore, the increased N uptake due to higher seed demand of AAP-12 is partly compensated by growth stimulation of vegetative organs.
Key words: Amino acid permease, C and N partitioning, cytokinin, harvest index, legume seed development, seed sink strength, transgenic plants
Received 28 March 2007; Revised 13 June 2007 Accepted 26 June 2007
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