title: High resolution imaging of photosynthetic activities of tissues, cells and chloroplasts in leaves.
abstract: Through imaging of chlorophyll fluorescence, it is possible to produce parameterized fluorescence images that estimate the operating quantum efficiency of photosystem II (PSII) photochemistry and which can be used to reveal heterogeneous patterns of photosynthetic performance within leaves. The operating quantum efficiency of PSII photochemistry is dependent upon the effective absorption cross-section of the light-harvesting system of PSII and the photochemical capacity of PSII. The effective absorption cross-section is decreased by the process of down-regulation, which is widely thought to operate within the pigment matrices of PSII and which results in non-photochemical quenching of chlorophyll fluorescence. The photochemical capacity is non-linearly related to the proportion of PSII centres in the 'open' state and results in photochemical quenching of chlorophyll fluorescence. Examples of heterogeneity of the operating quantum efficiency of PSII photochemistry during the induction of photosynthesis in maize leaves and in the chloroplast populations of stomatal guard cells of a leaf of Tradescantia albifora are presented, together with analyses of the factors determining this heterogeneity. A comparison of the operating quantum efficiency of PSII photochemistry within guard cells and adjacent mesophyll cells of Commelina communis is also made, before and after stomatal closure through a change in ambient humidity.
authors.affiliation: Department of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK. baken@essex.ac.uk
authors.forename: N R
authors.initials: NR
authors.lastname: Baker
authors.forename: K
authors.initials: K
authors.lastname: Oxborough
authors.forename: T
authors.initials: T
authors.lastname: Lawson
authors.forename: J I
authors.initials: JI
authors.lastname: Morison
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000502:physiology; D003952:Diagnostic Imaging / Q000295:instrumentation / Q000379:methods*; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008156:Luciferases / Q000494:pharmacology; D008962:Models, Theoretical; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D059828:Plant Cells; D018515:Plant Leaves / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010944:Plants / Q000187:drug effects / Q000378:metabolism; D013057:Spectrum Analysis
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D008156:Luciferases