Cloning of superoxide dismutase from post-harvest Hami melon and quantitative expression analysis before and after disease.
Two cDNA clones encoding mitochondrial manganese superoxide dismutases (MnSODs) from peach (Prunus persica [L.] Batsch) were identified, which show homologies to several plant MnSODs. The amino acid sequence predicted from one full-length clone (MnSOD1) showed the highest homology to an MnSOD from Nicotiana plumbaginifolia (94%) and included a 24-amino acid transit peptide typical of those used to target proteins to the mitochondria. A second, partial clone (MnSOD2) showed divergence from MnSOD1 in the 3′ untranslated region. It could therefore derive from a second gene or from an allele of MnSOD1. Southern hybridisation analysis suggests the existence of two MnSOD genes in peach. SOD isoenzyme profiles, MnSOD1 expression and protein levels were studied in aerial vegetative tissues derived from plants of different ages and in adult plants during the seasonal cycle. Zymograms revealed at least two isoforms of MnSODs in pre-shooting vegetative buds and in developing fruits. Levels of MnSODs were lower in leaves derived from apical shoots of adult plants than in leaves derived from seedlings, basal shoots or in vitro propagated juvenile plants, which are considered as juvenile-like structures. The MnSOD1 transcript and protein followed the same pattern. The results suggest that the steady-state levels of MnSOD1 mRNA in leaves vary with both the ontogenetic stage and the growth rate of the tissues examined.