Overexpression of SsCHLAPXs confers protection against oxidative stress induced by high light in transgenic Arabidopsis thaliana

To evaluate the physiological importance of chloroplastic ascorbate peroxidase (CHLAPX) in the reactive oxygen species (ROS)-scavenging system of a euhalophyte, we cloned the CHLAPX of Suaeda salsa (SsCHLAPX) encoding stromal APX (sAPX) and thylakoid-bound APX. The stromal APX of S. salsa (Ss. sAPX) cDNA consists of 1726 nucleotides including an 1137-bp open reading frame (ORF) and encodes 378 amino acids. The thylakoid-bound APX of S. salsa (Ss.tAPX) cDNA consists of 1561 nucleotides, including a 1284-bp ORF, and encodes 427 amino acids. The N-terminal 378 amino acids of Ss. sAPX are identical with those of Ss.tAPX, whereas the C-terminal 49 amino acids differ. Arabidopsis thaliana lines overexpressing Ss.sAPX and Ss.tAPX were constructed using Agrobacterium tumefaciens transformation methods. Under high light (1000 mu mol m(-2) s(-1)), malondialdehyde (MDA) content was lower in transgenic plants than in the wild type. Under high light, Fv/Fm and chlorophyll contents of both overexpressing lines and the wild type declined but were significantly higher in the overexpressing lines than in the wild type. The activities of APX (EC 1.11.1.11), catalase (CAT 1.11.1.6) and superoxide dismutase (SOD EC 1.15.1.1) were higher in the overexpressing lines than in the wild type. The transgenic plants showed increased tolerance to oxidative stress caused by high light. These results suggest that SsCHLAPX plays an important role in scavenging ROS in chloroplasts under stress conditions such as high light.