Acclimation to Diverse Environmental Stresses Caused by a Suppression of Cytosolic Ascorbate Peroxidase in Tobacco BY-2 cells

Abstract

The active oxygen species (AOS) that arise from normal metabolic processes are kept under tight control by various antioxidant mechanisms. AOS are important signal molecules that regulate many physiological processes, including environmental stress responses. In this work, we have investigated the effect of lowered cytosolic ascorbate peroxidase (APX) activity in transgenic tobacco BY-2 cells, using two transformed BY-2 cell lines, cAPX-S2 and cAPX-S3, resulting from co-suppression by expression of Arabidopsis APX1 cDNA under the cauliflower mosaic virus (CaMV) 35S promoter. cAPX-S2 and cAPX-S3 possessed 50 and 75% lower cytosolic APX activity, respectively, compared with that in the untransformed cells. Chemical fluorescence analysis indicated that the AOS levels were markedly higher in the two APX-suppressed cell lines than in the wild-type cells. However, there were no substantial differences in the activity levels of the various other antioxidant enzymes. Interestingly, the APX-suppressed cells showed different responses and tolerances to environmental stresses, such as heat and salinity. Suppression subtractive hybridization revealed that several heat- and salt stress-inducible genes were up-regulated in cAPX-S3 cells. HSP70, DnaJ-like protein and purple acid phosphatase were among the constitutively induced genes. An in-gel kinase assay suggested that a mitogen-activated protein (MAP) kinase of approximately 46 kDa was predominantly active in the APX-suppressed cells, and transcript levels of both nicotiana protein kinase 1 (NPK1) and nucleoside diphosphate kinase 2 (NDPK2) were up-regulated. These data suggest the possibility that MAP kinase cascades are activated by subtle imbalances in the homeostasis of the cellular redox status caused by lowered cytosolic APX activity.

Galactinol and Raffinose Constitute a Novel Function to Protect Plants from Oxidative Damage

“…It has been reported that a wide range of environmental stresses cause the enhanced production of ROS in plant cells (Bowler et al, 1992;Foyer et al, 1994;Alscher et al, 1997;Shigeoka et al, 2002;Mittler et al, 2004;Ishikawa et al, 2005;Miller and Mittler, 2006;Al-Taweel et al, 2007). The overexpression of GolS1 or GolS2 also conferred tolerance to salinity or chilling stress ( Fig.…”

Recent Advances in Ascorbate Biosynthesis and the Physiological Significance of Ascorbate Peroxidase in Photosynthesizing Organisms

“…Cultured transgenic tobacco cells with lowered cAPX activity due to co-suppression showed greater tolerance to environmental stress, such as heat and salinity, than wild-type cells. 7) This tolerance was accompanied by activation of a specific protein kinase and upregulation of the expression of stress-responsive genes including HSP as well as increased cellular ROS accumulation. Pnueli et al 95) have also demonstrated that cAPX (APX1)-knockout Arabidopsis plants showed upregulation of the expression of various genes, including those for stressrelated proteins and transcription factors.…”

“…6) Meanwhile, convincing evidence of the involvement of APX in the regulation of redox signal transduction is also accumulating. 7,8) This review focuses on recent advances concerning the physiological function and molecular properties of APX isoenzymes in photosynthesizing organisms. In addition, the pathway of AsA biosynthesis is highlighted, given the recent elucidation of the entire D-mannose (D-Man)/L-galactose (L-Gal) pathway in plants.…”

Singlet oxygen-mediated and EXECUTER-dependent signalling and acclimation of Arabidopsis thaliana exposed to light stress

“…Stress acclimation is often triggered by minor environmental changes and results in an enhanced protection against a subsequent more severe stress [2][3][4]. Such an enhanced stress resistance may be confined to the stress that triggers acclimation or it may provide cross-protection also against other forms of stress [5][6][7]. In order to acclimate, plants need to monitor and sense continuously their environment.…”