Variability in Superoxide Dismutase Isoforms in Tall and Dwarf Cultivars of Coconut (Cocos nucifera L.) Leaves

Abstract

Superoxide dismutases (SODs) are ubiquitous metallo-enzymes that constitute the first line of defense against reactive oxygen species (ROS). They constitute one of the major enzymatic components of detoxi?cation of superoxide radicals generated in biological system by catalyzing its dismutation to H2O2 and finally to H2O and O2. Most plant species contain numerous SOD isoforms differing in their active site metal ions. In the present investigation, we have attempted to identify variability in superoxide dismutase (EC 1.15.1.1) isoform pattern of 13 coconut genotypes comprising six talls, five dwarfs along with two reciprocal hybrids of WCT (Tall) with COD (Dwarf). Among the genotypes studied, a significant variation was observed in SOD enzyme activity as well as in SOD isoforms pattern. A total of eight to fourteen SOD isoforms were detected in different coconut cultivars. The variation was observed only in Mn-SOD isoforms while Fe-SOD (two) and Cu/Zn-SOD (five) isoforms were similar in all the analyzed cultivars. Mn-SOD isoforms varied from one to five in numbers. Among the tall cultivars, WCT, FMST and WCT X COD showed highest number (five) of Mn-SOD isoforms as well as highest enzymatic activity followed by LCT while TPT, PHOT and ADOT showed only single isoform for Mn-SOD. All dwarfs studied were found to have similar SOD isozyme profile for all SODs i.e. one Mn-SOD, five Cu/Zn-SOD and two Fe-SOD isoforms. It was also observed that Mn-SOD does not follow the Mendelian pattern of inheritance i.e. reciprocal crosses showed Mn-SOD isoform pattern similar to their mother palm. SOD activity and isoform pattern can be utilized as a biochemical marker for varietal identification and for abiotic stress/drought tolerance breeding.