Pathways of ROS homeostasis regulation in Mesembryanthemum crystallinum L. calli exhibiting differences in rhizogenesis

A comparison of the hydrogen peroxide (H2O2) content, proline and betacyanin concentration and activities of some antioxidant enzymes (catalase, superoxide dismutase, guaiacol and ascorbate peroxidases) was made in Mesembryanthemum crystallinum L. calli differing in rhizogenic potential. Callus was induced from hypocotyls of 10-day-old seedlings on a medium containing 1 mg l−1 2,4-dichlorophenoxyacetic acid and 0.2 mg l−1 kinetin, which was either supplemented with 40 mM NaCl (CIM-NaCl medium) or did not contain any salt (CIM medium). The callus obtained on CIM-NaCl was rhizogenic, whereas the callus induced on the medium without salt was non-rhizogenic throughout the culture. The rhizogenic callus differed from the non-rhizogenic callus in lower betacyanin and H2O2 content, but the rhizogenic callus displayed a higher proline level. The activity of H2O2 scavenging enzymes, such as catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (POD), was markedly higher in the rhizogenic callus than in the non-rhizogenic callus, but the total activity of superoxide dismutase (SOD) was higher in the non-rhizogenic callus than in the rhizogenic callus. Aminotriazole (CAT inhibitor) and diethyldithiocarbamate (SOD inhibitor) were added solely to the CIM and CIM-NaCl media to manipulate the concentration of reactive oxygen species (ROS) in the cultured tissues. Both CAT and SOD inhibitors brought about an increase in H2O2 content in calli cultured on CIM-NaCl and the loss of rhizogenic potential. Conversely, the addition of inhibitors to the medium without salt led to a decrease in H2O2 content. This corresponded with a significant decrease in the endogenous concentration of betacyanins, but did not change the lack of rhizogenic ability.