Heterogeneous population of mitochondrial DNA molecules in higher plants

Abstract

THE physicochemical properties of mitochondrial (mt)-DNA of higher plants have been reported^1–4. mt-DNAs occur as closed circles with molecular weights of (60–70) × 10⁶ and it is likely that each mitochondria contains several of these circles. mt-DNAs isolated from different higher plants exhibit similar physicochemical parameters: all mt-DNAs so far analysed^1–5 in higher plants band at a unique buoyant density of 1.706 g cm⁻³ in neutral CsCl gradients and the few published melting points and reassociation kinetics are not significantly different^2–4. Not enough values have been reported to state on possible differences in the contour length measured by electron microscopy. Thus, mt-DNAs isolated from different higher plants cannot be specifically identified by conventional physicochemical techniques. We have recently reported that the analysis of restriction nuclease digests by gel electrophoresis provides a very sensitive test to identify specifically chloroplastic (cp)-DNAs isolated from different plant genera and species⁶. We show here that this technique also allows the characterisation and the specific identification of mt-DNAs isolated from various higher plants. We used EcoRI specific cleavage to evidence the general occurrence of heterogeneous population of mt-DNA molecules within an higher plant and to detect clear differences between mt-DNAs extracted from normal and cytoplasmic male-sterile wheat.