title: Acclimation of rice photosynthesis to irradiance under field conditions.
abstract: Acclimation to irradiance was measured in terms of light-saturated photosynthetic carbon assimilation rates (P(max)), Rubisco, and pigment content in mature field-grown rice (Oryza sativa) plants in tropical conditions. Measurements were made at different positions within the canopy alongside irradiance and daylight spectra. These data were compared with a second experiment in which acclimation to irradiance was assessed in uppermost leaves within whole-plant shading regimes (10% low light [LL], 40% medium light [ML], and 100% high light [HL] of full natural sunlight). Two varieties, japonica (tropical; new plant type [NPT]) and indica (IR72) were compared. Values for Rubisco amount, chlorophyll a/b, and P(max) all declined from the top to the base of the canopy. In the artificial shading experiment, acclimation of P(max) (measured at 350 microL L(-1) CO(2)) occurred between LL and ML for IR72 with no difference observed between ML and HL. The Rubisco amount increased between ML and HL in IR72. A different pattern was seen for NPT with higher P(max) (measured at 350 microL L(-1) CO(2)) at LL than IR72 and some acclimation of this parameter between ML and HL. Rubisco levels were higher in NPT than IR72 contrasting with P(max). Comparison of data from both experiments suggests a leaf aging effect between the uppermost two leaf positions, which was not a result of irradiance acclimation. Results are discussed in terms of: (a) acclimation of photosynthesis and radiation use efficiency at high irradiance in rice, and (b) factors controlling photosynthetic rates of leaves within the canopy.
authors.affiliation: Robert Hill Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom. e.h.murchie@sheffield.ac.uk
authors.forename: Erik H
authors.initials: EH
authors.lastname: Murchie
authors.forename: Stella
authors.initials: S
authors.lastname: Hubbart
authors.forename: Yizhu
authors.initials: Y
authors.lastname: Chen
authors.forename: Shaobing
authors.initials: S
authors.lastname: Peng
authors.forename: Peter
authors.initials: P
authors.lastname: Horton
mesh_terms: D000064:Acclimatization / Q000502:physiology* / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D018556:Crops, Agricultural / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D012275:Oryza / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
chemical_list: D010860:Pigments, Biological; D002734:Chlorophyll; C037184:chlorophyll b; D012273:Ribulose-Bisphosphate Carboxylase; D000077194:Chlorophyll A