Molecular Cloning and Characterization of Fe-Superoxide Dismutase (Fe-SOD) from the Fern Ceratopteris thalictroides

Ferns are, evolutionarily, in a pivotal position between bryophytes and seed plants (Pryer et al., 2001). Fern gametophytes, like bryophytes, have no vascular system and live on substrate surfaces as small individual plants. However, fern sporophytes do have a vascular system enabling more vertical growth than the gametophytes, and resulting in a larger herbaceous plant form. The origins of plant vascular systems must have arisen during the evolution of primitive ferns (Kenrick , 2000). Ferns are historic plants and provide many facets of interest for researchers (Dyer, 1979; Raghavan, 1989). An especially important reason for choosing to study ferns is to gain insight into the evolution of higher plants . Homosporous ferns,such as Ceratopteris,is a genus of homosporous ferns found in most tropical and subtropical area of the world (Lloyd, 1974, 1993; Masuyama, 1992). Ceratopteris are vascular plants that exhibit a biphasic life cycle with independent autotrophic haploid and diploid generations. Thus, they offer unique opportunities for studying a wide variety of experimental approaches and a large body for literature has been producedうMiller, 1986; Dyer, 1979え. In contrast to most other ferns, Ceratopteris possesses a fast life cycle time of less than 120 d, can be cultured easily, and is readily amenable to genetic analyses (Hickok et al., 1987) Ceratopteris has been used as a model plant for many years in the study of genetics, biochemistry, cell biology, and molecular biology (Hickok et al., 1995; Chatterjee, 2000). Plants are continually exposed to environmental fluctuations that lead to oxidative stress. Part of the damage caused by conditions such as intense light, drought, temperature stress, air pollutants etc. is associated with oxidative stress is an increase in the production of reactive oxygen species (ROS) (Levine A., 1999). Reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), superoxide anion (O2-) and hydroxyl radical (OH-) are generated from normal metabolic process in all aerobic organisms. The damages from ROS include lipid peroxidation, cross-linking and inactivation of proteins, breaks in DNA and RNA, and cell death (Bestwick & Maffulli, 2004; Fridovich, 1995). Aquatic organisms are often subjected to enhanced “oxidative stress” by ROS due to chronic exposure to pollutants in their environments (Marikovsky et al., 2003; Geret et al., 2004). To limit the harmful effect of ROS production and prevent damage from oxidative stress, cells have evolved to use antioxidant systems as part of the innate immune defense to maintain reactive oxygen species at low basal levels and protect themselves from the constant oxidative challenge (Geret et al., 2004; Manduzio et al., 2004).