Effect of chloroplastic overproduction of ascorbate peroxidase on photosynthesis and photoprotection in cotton leaves subjected to low temperature photoinhibition

The photosynthetic performance of leaf discs of transgenic cotton with fourfold elevated activity of ascorbate peroxidase in the chloroplast stroma (APX / plants) was compared to that of wild type (Gossypium hirsutum L. cv. Coker 312) during exposure to 10 8C and 500 mmol photons m 2 s . APX / leaves did not exhibit as large of an increase in cellular H2O2 that was evident in wildtype leaves shortly after the imposition of the chilling treatment. In addition, APX / leaves exhibited slightly, but significantly, less photosystem (PS)I and PSII photoinhibition. However, the greatest genotypic difference in H2O2 scavenging did not coincide with the greatest difference in PSI inactivation, and APX / leaves exhibited a greater quantum yield for PSII. Therefore, genotypic differences in H2O2 scavenging may not have been the sole mechanism enhancing PSI protection in APX / leaves. No evidence of competition for reduced ascorbate between ascorbate peroxidase and violaxanthin de-epoxidase was found. The dynamics of xanthophyll cycle carotenoid conversions, as well as the level of thermal dissipation, were similar for wildtype and transgenic plants throughout the chilling treatment and subsequent recovery. # 2003 Elsevier Ireland Ltd. All rights reserved.