Changes in H2O2 content and antioxidant enzyme gene expression during the somatic embryogenesis of Larix leptolepis

Abstract

Hydrogen peroxide (H2O2) content and transcript levels of genes encoding superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) antioxidant enzymes were investigated during different stages of somatic embryogenesis in Larix leptolepis. H2O2 content was lowest on day 0 when embryogenic callus was incubated on Murashige and Skoog (MS) medium supplemented with polyethylene glycol (PEG). This content began to increase when callus was transferred to the same medium but containing abscisic acid (ABA), and reached a peak at day 3 following incubation. The level of H2O2 dropped from day 7 to day 10, peaked at day 21, then dropped again at day 24 and day 35, but increased when somatic embryos reached maturity at day 45. Transcript levels of SOD, CAT, and APX were lowest when somatic embryos were cultured on callus induction medium without ABA. When calli were transferred onto somatic embryo maturation medium, expression patterns of SOD, CAT, and APX varied, and transcript levels at all stages were higher than those at d 0. SOD expression was highest at day 3. Whereas, CAT expression levels were low during early stages of somatic embryogenesis, but increased at day 21, declined at days 24 and 35, and then began to increase again at day 45. APX gene expression patterns were highest at days 3, 21, and 45. These results suggested that ABA was essential for promoting somatic embryogenesis of L. leptolepis. Moreover, ABA induced production of H2O2 and other active oxygen species (AOS), and mediated CAT, SOD, and APX gene expression in somatic embryogenesis of L. leptolepis.