Changes in superoxide-dismutase (SOD) activity in auxin treated Prunus sp. softwood cuttings under oxidative stress

Abstract

Oxidative metabolism of normal cells and different stress situations generate highly reactive oxygen species (ROS). The ROS have been implicated in a number of physiological disorders in plants. Such factors as certain mechanical injuries are known to induce ROS formation in most aerobic organisms. Antioxidant defence systems have co-evolved with aerobic metabolism to counteract oxidative damage from ROS. This includes antioxidant enzymes such as superoxide-dismutase (SOD; EC 1.15.1.1). SOD is of the greatest importance since it catalyzes the dismutation of the superoxide radical (O2.-) to O2 and H2O. Thus, the aim of this study was to measure the intensity of SOD in the leaves of six cherry rootstock selections in order to investigate the effect of exogenously applied auxins on the mechanical injury induced oxidative stress during the process of rooting of softwood cuttings. The experiment was carried out in the plastic house under a fogging system with 95-99% average relative humidity. The 15-20 cm long terminal cuttings were treated with the mix of auxins (IBA, 0.5% and α-NAA, 0.8%) powder prior to insertion into the white sphagnum and perlite substrate mixture. Leaves of six promising rootstock selections of Prunus cerasus L., P. mahaleb L. and P. fruticosa Pall., and one standard rootstock PHL-A were sampled on the 1st, 3rd and 7th day after inserting softwood cuttings into the rooting substrate. The SOD activity was measured by monitoring the inhibition of nitroblue-tetrazolium (NBT) reduction at 560 nm. Results showed that generation of ROS occurred in all investigated genotypes, but they greatly differed in susceptibility towards oxidative stress induces by mechanical injury. Application of auxins on standard vegetative rootstock PHL-A, as well as P. mahaleb selection M6 showed positive effect on lowering SOD activity after the 3rd and 7th collecting day compared to control. On the other hand, selections of P. cerasus OV22 and P. fruticosa SV2 expressed high SOD activity during all collecting days which was from 3.6-54.9% higher compared to control. Enhanced SOD activity in leaves of softwood cuttings indicates induction of the enzymatic antioxidant system in both auxin treated and untreated cutting. According to these results SOD activity could be used as one of the biochemical parameters in further rootstock selection for sweet and sour cherries.