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The tropical fig Ficus microcarpa L. f. cv. Golden Leaves lacks heat-stable dehydroascorbate reductase activity

Yamasaki, H., Takahashi, S., Heshiki, R.
Plant & cell physiology 1999 v.40 no.6 pp. 640-646
Ficus, leaves, color, protein composition, dehydroascorbic acid, metabolism, glutathione, oxidation, oxidoreductases, enzyme activity, heat stability, chemical reactions, biochemical pathways, antioxidants
Dehydroascorbate reductase (DHAR) is an enzyme which mediates a regeneration of ascorbate from dehydroascorbate using GSH as the electron donor. Here we report a tropical fig lacking a heat-stable DHAR activity in leaves. The leaves of Ficus microcarpa L. f. cv. Golden Leaves are normally green under dim light but are yellow under full sunlight in the field. We compared DHAR activity from the leaves of Golden Leaves to that of the wild type using two distinct assay methods. Total leaf DHAR activity of Golden Leaves, determined in the presence of 2-mercaptoethanol and EDTA, was 0.3 micromoles min-1 (mg protein)-1 which was comparable to that of the wild type or spinach leaves. This activity was completely eliminated by heat treatment at 80 degrees C, whereas 40% of the activity was resistant to this treatment in the wild type leaves. Similar results were obtained with another assay method employing dithiothreitol and gel filtration. We conclude that the absence of heat-stable DHAR activity is a significant biochemical marker that distinguishes Golden Leaves from the wild type. A physiological role for DHAR in adaptation to high light stress is proposed.