title: Influence of heat stress on leaf ultrastructure, photosynthetic performance, and ascorbate peroxidase gene expression of two pear cultivars (Pyrus pyrifolia).
abstract: Plants encounter a variety of stresses in natural environments. One-year-old pot-grown trees of pear (Pyrus pyrifolia Nakai cv. Cuiguan and Wonhwang) were exposed to two heat stress regimes. Under constant short-term heat stress, chloroplasts and mitochondria were visibly damaged. Relative chlorophyll content and maximum photochemical efficiency of photosystem II were significantly decreased, which indicated that the leaf photosynthetic capability declined. Under chronic heat stress, mesophyll cell ultrastructure was not obviously damaged, but leaf photosynthetic capability was still restrained. As chronic heat stress was a simulation of the natural environment in summer, further study of the responses under this stress regime was undertaken. Ascorbate peroxidase (APX) activity was increased in 'Cuiguan', but not in 'Wonhwang'. Inducible expression of PpAPX genes in the cytoplasm, chloroplasts and peroxisomes was consistent with increased APX activity in 'Cuiguan', whereas only weak induction of PpAPX genes was observed in 'Wonhwang'. The isoenzymes cytosolic APX1 (cAPX1) and stromal APX (sAPX) were confirmed to be localized in the cytoplasm and chloroplasts, respectively.
authors.affiliation: State Agricultural Ministry Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Department of Horticulture, Zhejiang University, Hangzhou 310058, China; College of Horticulture, Northwest A&F University, Yangling 712100, China.
authors.forename: Dong-feng
authors.initials: DF
authors.lastname: Liu
authors.forename: Dong
authors.initials: D
authors.lastname: Zhang
authors.forename: Guo-qin
authors.initials: GQ
authors.lastname: Liu
authors.forename: Sayed
authors.initials: S
authors.lastname: Hussain
authors.forename: Yuan-wen
authors.initials: YW
authors.lastname: Teng
mesh_terms: D060387:Ascorbate Peroxidases / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D018869:Heat-Shock Response / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology* / Q000648:ultrastructure*; D031989:Pyrus / Q000145:classification / Q000502:physiology*; D013045:Species Specificity
chemical_list: D060387:Ascorbate Peroxidases