Characterization of Chloroplast and Nuclear DNAs of Zea mays L.1

Abstract

Highly purified chloroplasts and nuclei were isolated from two hybrids of maize (Zea mays L.), ‘McNair X210N’ containing normal and ‘X210 cms T’ containing Texas‐type male‐sterile cytoplasm. Chloroplast and nuclear deoxyribonucleic acids were obtained from their respective organelles and purified by CsCl density gradient centrifugation. These DNAs were compared with respect to thermal denaturation temperature (Tm), buoyant density (ρ) and the guanine‐plus‐cytosine content (molar % GC).Nuclear DNA (nDNA) had a mean buoyant density in CsCl of 1.7019 g/cm3 and a Tm of 86.9 C. Mean molar GC was calculated to be 43.3%. In contrast, Chloroplast DNA (cDNA) had a lower buoyant density in CsCl (1.6998 g/cm3) and a lower Tm (85.9 C). Mean molar GC was determined to be 39.5%. Thus, cDNA was distinguishable from nDNA by its lower buoyant density, lower Tm, lower GC content, and the absence of 5‐methylcytosine, which was present in significant amounts (6.9%) in nDNA. GC content, Tm, and buoyant density values of cDNAs did not differ between normal and Texas cytoplasms, and therefore, cannot account for their cytoplasmic differences.