The Tropical Fig Ficus microcarpa L. f. cv. Golden Leaves Lacks Heat-Stable Dehydroascorbate Reductase Activity

Dehydroascorbate reductase (DHAR) is an enzyme which mediatesa regeneration of ascorbate from dehydroascorbate using GSHas the electron donor. Here we report a tropical fig lackinga heat-stable DHAR activity in leaves. The leaves of Ficus microcarpaL. f. cv. Golden Leaves are normally green under dim light butare yellow under full sunlight in the field. We compared DHARactivity from the leaves of Golden Leaves to that of the wildtype using two distinct assay methods. Total leaf DHAR activityof Golden Leaves, determined in the presence of 2-mercaptoethanoland EDTA, was 0.3 µmol min^–1 (mg protein)^–1which was comparable to that of the wild type or spinach leaves.This activity was completely eliminated by heat treatment at80°C, whereas 40% of the activity was resistant to thistreatment in the wild type leaves. Similar results were obtainedwith another assay method employing dithiothreitol and gel filtration.We conclude that the absence of heat-stable DHAR activity isa significant biochemical marker that distinguishes Golden Leavesfrom the wild type. A physiological role for DHAR in adaptationto high light stress is proposed. (Received December 4, 1998; Accepted April 15, 1999)