title: Potent hydroxyl radical-scavenging activity of drought-induced type-2 metallothionein in wild watermelon.
abstract: 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 x 10(11) 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.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara 630-0101, Japan. akashi@bs.naist.jp
authors.forename: Kinya
authors.initials: K
authors.lastname: Akashi
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nishimura
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ishida
authors.forename: Akiho
authors.initials: A
authors.lastname: Yokota
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D029773:Citrullus; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004190:Disasters; D004305:Dose-Response Relationship, Drug; D020869:Gene Expression Profiling; D017665:Hydroxyl Radical / Q000737:chemistry; D008668:Metallothionein / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D018384:Oxidative Stress; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry; D012313:RNA / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; C100789:MT2A protein, Arabidopsis; D010940:Plant Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D017665:Hydroxyl Radical; D012313:RNA; D004247:DNA; D008668:Metallothionein