[Relation between the decline of photosynthetic function and H2O2 accumulation in leaf life span of tobacco]

Correlations among H2O2 accumulation, chloroplast photosynthetic function decline and H2O2-scavenging enzymes of AsA-GSH cycle in leaf life span of tobacco (Nicotiana tabacum L. cv NC89) were studied. Photosynthetic rate displayed elevated phase,active photosynthesis duration and sharp fall phase while the chlorophyll content displayed elevated phase,relative steady phase and sharp fall phase during leaf life span. The decline of photosynthetic parameters was slow first and then sharp,and the decline of ribulose 1,5-bisphosphate carboxylase (RuBPCase) activity was obviously faster than that of photosynthetic electron transport activity during the decline of photosynthetic function. The decline of photosynthetic function was divided into reversible decline and irreversible decline. Ascorbate peroxidase (APX) and Glutathione reductase (GR) remained higher level in reversible decline stage,while declined fast in irreversible decline stage. H2O2 content was significantly negative correlated with chlorophyll content, photosynthetic rate, RuBPCase activity,APX and GR activity during the decline of photosynthetic function in tobacco leaves. Localized staining of H2O2 stated that the decline of photosynthetic function was closely correlative with H2O2 accumulation. The decline of photosynthetic function in tobacco leaves was faster than the decline of AsA-GSH cycle function.