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 peroxid ase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reducta se (DHAR) and glutathione reductase (GR) and SOD were studied in cell organ elles of the cultivated tomato Lycopersicon esculentum (M82) and its wild s alt-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 on e order of magnitude Lower than that of MDHAR. Based on these results, it i s suggested that in the organelles of both tomato species, ascorbate is reg enerated mainly by MDHAR. In both tomato species, GR activity, and to a les ser extent DHAR activity, was found to reside in the soluble fraction of al l leaf and root cell organelles, while APX and MDHAR activities were distri buted between the membrane and soluble fractions. A higher SOD to APX activ ity ratio in all Lpa organelles was the major difference between the two to mato species. It is possible that this higher ratio contributes to the inhe rently better protection of Lpa from salt stress, as was previously reporte d.