Activities of SOD and the ascorbate-glutathione cycle enzymes in subcellular compartments in leaves and roots of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii

The activities of the ascorbate-glutathione cycle enzymes ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) and SOD were studied in cell organelles of the cultivated tomato Lycopersicon esculentum (M82) and its wild salt-tolerant related species Lycopersicon pennellii (Lpa). All four enzymes of the ascorbate-glutathione cycle were present in chloroplasts/plastids, mitochondria and peroxisomes of leaf and root cells of both tomato species. In all leaf and root organelles of both species, the activity of MDHAR was similar to, or higher than, that of APX, while the activity of DHAR was one order of magnitude lower than that of MDHAR. Based on these results, it is suggested that in the organelles of both tomato species, ascorbate is regenerated mainly by MDHAR. In both tomato species, GR activity, and to a lesser extent DHAR activity, was found to reside in the soluble fraction of all leaf and root cell organelles, while APX and MDHAR activities were distributed between the membrane and soluble fractions. A higher SOD to APX activity ratio in all Lpa organelles was the major difference between the two tomato species. It is possible that this higher ratio contributes to the inherently better protection of Lpa from salt stress, as was previously reported.