Plastid And Mitochondrial DNA Amount Variationduring Potato Tuber Greening Under Light

The growth and development of plant require coordination of three DNA-containing compartments including nucleus,plastid and mitochondria. There are currently debates on whether in green tissues plastid DNA(pt DNA) and mitochondrial DNA(mtDNA) were damaged to fragments by light and whether the cellular energy ATP produced by chloroplast phosphorylation can partly reduce the demand of mitochondrial respiration. Most studies are on leaves.It’s unclear whether it’s similar in other organs about the stability of DNA.In the present research, tubers of two potato(Solanum tuberosum L.) cultivars Favorita and Shepody were used as donors. To found out the difference of Organelle DNA content in tubers with different weight, there are two gruop of Favorita tubers( 38 g and 102 g) in the greening experiment.Total DNA of tuber peels was analyzed using real-time quantitative polymerase-chain-reaction(real-time PCR) and long PCR in comparison between tubers in the dark and tubers under light in both cultivars.1. The reference primers B20B22 nuclear DNA region was used as unique sequence reference control of the nuclear genome because the region was found to be unique single copy region(Dr. Xiu-Qing Li et al. will be published elsewhere). The ptDNA primers C5C6( acc D gene,acetyl-Co A carboxylase beta subunit) and the mtDNA primers C13C16(ATPase 6) and C15C16(COX I) were designed according to the Solanum tuberosum isolate RH89-039-16 reference chloroplast genome(JF772171) and the mitochondrial genome(version 3) of the some clone. The ratio between ptDNA and nuclear DNA(nuDNA) showed little decrease during greening when the weight of tubers are similar, but the mtDNA/nuDNA ratio significantly decreased during greening in both Cultivars. When the weight of tubers are different, the ptDNA/nuDNA ratio showed little increase, but the mt DNA/nu DNA ratio significantly increased in the weighter tubers. The result may suggest that the greening tubers reduce the demand of ATP which produced by mitochondrial respiration, and the weighter tubers increase the demand of ATP.2. To test the stability of ptDNA of greening tubers, we designed a couple of primers based on the Solanum tuberosum isolate RH89-039-16 chloroplast complete genome(JF772171.1) and the estimate amplification size is 8,033 bp(7261-15293). In the result, we amplified the target sequence successfully, and did not find evidence of DNA fragmentation.These results of little reduction of ptDNA but significant reduction of mtDNA in greening tubers(compared with the tubers that were not exposed to light) suggests reduced requirement of mitochondrial respiration in greening tissues of these two cultivars. As the weight of tubers increase the Organelle DNA content increased. Two hypotheses, one for the ptDNA amount stability and one for the mtDNA changes, were postulated.