A PEROXIREDOXIN ANTIOXIDANT IS ENCODED BY A DORMANCY-RELATED GENE, PER1, EXPRESSED DURING LATE DEVELOPMENT IN THE ALEURONE AND EMBRYO OF BARLEY GRAINS

Antioxidants can remove damaging reactive oxygen species produced as b y-products of desiccation and respiration during late embryogenesis, i mbibition of dormant seeds and germination. We have expressed a protei n, PER1, encoded by the Balem (barley aleurone and embryo) transcript previously called B15C, and show it to reduce oxidative damage in vitr o. PER1 shares high similarity to a novel group of thiol-requiring ant ioxidants, named peroxiredoxins, and represents a subgroup with only o ne conserved cysteine residue (l-Cys). PER1 is the first antioxidant b elonging to the l-Cys subgroup shown to be functionally active, and th e first peroxiredoxin of any kind to be functionally described in plan ts. The steady state level of the transcript, Per1, homologous to a do rmancy-related transcript (pBS128) from bromegrass (Bromus secalinus), increases considerably in imbibed embryos from dormant barley (Hordeu m vulgare L.) grains. Our investigations also indicate that Per1 trans cript levels are dormancy-related in the aleurone layer of whole grain s. In contrast to most seed-expressed antioxidants Per1 disappears in germinating embryos, and in the mature aleurone the transcript is down -regulated by the germinating embryo or by gibberellic acid (GA). Our data show that the barley seed peroxiredoxin is encoded by a single Pe r1 gene. Possible roles of the PER1 peroxiredoxin in barley grains dur ing desiccation, dormancy and imbibition are discussed.