title: The complex character of photosynthesis in cucumber fruit.
abstract: The surface area of a mature green cucumber (Cucumis sativa L.) fruit is comparable with that of a functional leaf, but the characteristics of fruit photosynthesis and its contribution to growth are poorly understood. Here, the photosynthetic properties of two genotypes of cucumber (dark green and light green fruits) were studied using a combination of electron microscopy, immunogold enzyme localization, chlorophyll fluorescence imaging, isotope tracer, and fruit darkening techniques. Chlorophyll content of the exocarp is similar to that of leaves, but there are no distinctive palisade and spongy tissues. The efficiency of PSII is similar to that in leaves, but with lower non-photochemical quenching (NPQ). Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is found mainly in the exocarp, while phosphoenolpyruvate carboxylase (PEPC) is primarily localized to vascular bundles and placenta tissue. Rubisco and PEPC expression at both transcriptional and translational levels increases concurrently during fruit growth. The contribution of fruit photosynthesis in exocarp to its own C accumulation is 9.4%, while ~88% of respiratory CO2 in fruit was captured and re-fixed. Photosynthesis by cucumber fruits, through direct fixation of atmospheric CO2 and recapture of respired CO2, as verified by 14CO2 uptake and gas exchange, makes an important contribution to fruit growth.
authors.affiliation: Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, College of Horticulture, China Agricultural University, Beijing 100193, China.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Sui
authors.affiliation: Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, College of Horticulture, China Agricultural University, Beijing 100193, China.
authors.forename: Nan
authors.initials: N
authors.lastname: Shan
authors.affiliation: Beijing Vegetable Research Center, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China.
authors.forename: Liping
authors.initials: L
authors.lastname: Hu
authors.affiliation: Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Cankui
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Ecological Laboratory, Ecotech Ecological Technology Ltd, Beijing 100190, China.
authors.forename: Changqing
authors.initials: C
authors.lastname: Yu
authors.affiliation: Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, College of Horticulture, China Agricultural University, Beijing 100193, China.
authors.forename: Huazhong
authors.initials: H
authors.lastname: Ren
authors.affiliation: Plant Biology Section, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Turgeon
authors.affiliation: Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, College of Horticulture, China Agricultural University, Beijing 100193, China.
authors.forename: Zhenxian
authors.initials: Z
authors.lastname: Zhang
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D018553:Cucumis sativus / Q000235:genetics / Q000378:metabolism*; D005638:Fruit / Q000235:genetics / Q000378:metabolism*; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D010788:Photosynthesis; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D010730:Phosphoenolpyruvate Carboxylase; D012273:Ribulose-Bisphosphate Carboxylase
keywords: Chloroplast; PEPC (phosphoenolpyruvate carboxylase); Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase).; cucumber; fruit photosynthesis; respiration