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Potent hydroxyl radical-scavenging activity of drought-induced type-2 metallothionein in wild watermelon

2004; Elsevier BV; Volume: 323; Issue: 1 Linguagem: Inglês

10.1016/j.bbrc.2004.08.056

1090-2104

Kinya Akashi, Noriyuki Nishimura, Yoshinori Ishida, Akiho Yokota,

Plant Stress Responses and Tolerance

Wild watermelon (Citrullus lanatus sp.) has the ability to tolerate severe drought/high light stress conditions despite carrying out normal C3-type photosynthesis. Here, mRNA differential display was employed to isolate drought-responsive genes in the leaves of wild watermelon. One of the isolated genes, CLMT2, shared significant homology with type-2 metallothionein (MT) sequences from other plants. The second-order rate constant for the reaction between a recombinant CLMT2 protein and hydroxyl radicals was estimated to be 1.2 × 1011 M−1 s−1, demonstrating that CLMT2 had an extraordinary high activity for detoxifying hydroxyl radicals. Moreover, hydroxyl radical-catalyzed degradation of watermelon genomic DNA was effectively suppressed by CLMT2 in vitro. This is the first demonstration of a plant MT with antioxidant properties. The results suggest that CLMT2 induction contributes to the survival of wild watermelon under severe drought/high light stress conditions.