Abstract

SDH1-1 is the gene encoding the subunit 1 (flavoprotein) of the mitochondrial respiratory complex II: Succinate Dehydrogenase (SDH) in Arabidopsis thaliana. We have previously shown that a null mutation of SDH1-1 is gametophytic, i.e. no homozygous mutant plants can be obtained. Interestingly, a mild reduction of SDH activity in heterozygous mutant plants (SDH1-1/sdh1-1) results in better growth and higher CO2 assimilation rates, which correlate with increased stomatal density and aperture. Furthermore, while no decreases in chlorophyll or protein content were observed, metabolome analysis revealed decreases in key aminoacids suggesting higher fluxes to N containing macromolecules and higher Nitrogen efficiency to support increased growth. To investigate if these plants actually use N more efficiently, theywere grown on media containing differents concentrations of KNO3. Interestingly, mutants exhibited increased shoot and root growth than their wild type counterparts when grown on low N-containing media. Moreover, transcripts of nitrate transporters (NRT2.1 and NRT1.1) and nitrate reductase (NIA1 and NIA2) showed increased levels in roots of SDH1-1/sdh1-1 plants. 1 5N-nitrate uptake was also evaluated and mutant plants exhibited higher 1 5N-uptake than wild type plants. Altogether, our results suggest that plants with a mild deficiency in SDH activity have ahigher photosynthetic performance due to improved CO2 uptake through stomata and that this leads to better nitrogen assimilation to maintain the C/N balance and support increased biosynthesis of macromolecules and growth