Purification and quantitative changes of mitochondrial DNA in etiolated cucumber seedlings

The mtDNA (mitochondrial DNA) extracted from etiolated seedlings of Cucumis sativus L. has been purified by a three-step procedure: RNase and pronase treatment, bio-gel filtration, analytical CsCl gradient centrifugation. This procedure appeared rapid, suitable for small quantities of DNA and gave highly reproducible results. It was used to follow the quantitative variation of the mtDNA in hypocotyls and cotyledons of dark-grown cucumber seedlings.The major feature occurring during the etiolation process appeared to be an important accumulation of the mtDNA in hypocotyls between 3 and 5 days of culture. The amount of the mtDNA per hypocotyl increased 5 times, the hypocotyl length and the total DNA increased 6 and 12 times respectively, between these two stages. It was demonstrated that at least during the first week of culture in the dark, endogeneous hormone-induced elongation in the cucumber hypocotyl (a non-dividing tissue) was associated to an important accumulation of mtDNA.