英文论文作业.doc

英文论文写作课作业 The production and scavenging of ROS Abstract Production of ROS by these sources is enhanced in plants by conditions limiting CO 2 fixation, such as drought, salt and temperature stress, as well as by the combination of these conditions with high-light stress.It is well known that abscisic acid (ABA) promotes reactive oxygen species (ROS) production through plasma membrane–associated NADPH oxidases during ABA signaling.It is possible that the use of ROS as versatile signaling molecules originated from their proposed use to sense stress. Most forms of biotic or abiotic stress disrupt the metabolic balance of cells, resulting in enhanced production of ROS.Glutathione peroxidases (GPXs) are a group of enzymes that protect cells against oxidative damage generated by reactive oxygen species (ROS). The presence of GPXs in plants has been reported by several groups, but the roles of individual members of this family in a single plant species have not been studied.?A family of seven related proteins named AtGPX1- AtGPX7 in Arabidopsis was identified, and the genomic organization of this family was reported.Major ROS-scavenging enzymes of plants include superoxide dismutase (SOD), ascorbate peroxidase (APX),catalase (CAT), glutathione peroxidase (GPX) and perox-iredoxin (PrxR). Key words Reactive Oxygen Species Glutathione peroxidases Introduction Organelles with a highly oxidizing metabolic activity or with an intense rate of electron flow, such as chloroplasts,mitochondria and microbodies, are a major source of ROS production in plant cells. Together with an extensive battery of oxidases, the plant cell is well armed for bountiful yet flexible ROS production. In chloroplasts, the primary sources of ROS production are the Mehler reaction and the antenna pigments.Ever since the introduction of molecular oxygen (O2 ) into our atmosphere by O2-evolving photosynthetic organisms w2.7 billion years ago, reactive oxygen species (ROS) have been the unwelcome compa