title: A high throughput gas exchange screen for determining rates of photorespiration or regulation of C4 activity.
abstract: Large-scale research programmes seeking to characterize the C4 pathway have a requirement for a simple, high throughput screen that quantifies photorespiratory activity in C3 and C4 model systems. At present, approaches rely on model-fitting to assimilatory responses (A/C i curves, PSII quantum yield) or real-time carbon isotope discrimination, which are complicated and time-consuming. Here we present a method, and the associated theory, to determine the effectiveness of the C4 carboxylation, carbon concentration mechanism (CCM) by assessing the responsiveness of V O/V C, the ratio of RuBisCO oxygenase to carboxylase activity, upon transfer to low O2. This determination compares concurrent gas exchange and pulse-modulated chlorophyll fluorescence under ambient and low O2, using widely available equipment. Run time for the procedure can take as little as 6 minutes if plants are pre-adapted. The responsiveness of V O/V C is derived for typical C3 (tobacco, rice, wheat) and C4 (maize, Miscanthus, cleome) plants, and compared with full C3 and C4 model systems. We also undertake sensitivity analyses to determine the impact of R LIGHT (respiration in the light) and the effectiveness of the light saturating pulse used by fluorescence systems. The results show that the method can readily resolve variations in photorespiratory activity between C3 and C4 plants and could be used to rapidly screen large numbers of mutants or transformants in high throughput studies.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: Chandra
authors.initials: C
authors.lastname: Bellasio
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Burgess
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: Howard
authors.initials: H
authors.lastname: Griffiths
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: Julian M
authors.initials: JM
authors.lastname: Hibberd
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D019069:Cell Respiration; D031485:Cleome / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D012275:Oryza / Q000378:metabolism / Q000528:radiation effects; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism* / Q000528:radiation effects; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D014026:Nicotiana / Q000378:metabolism / Q000528:radiation effects; D014908:Triticum / Q000378:metabolism / Q000528:radiation effects; D003313:Zea mays / Q000378:metabolism / Q000528:radiation effects
chemical_list: D002247:Carbon Isotopes; D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase
keywords: C3; C4; Cleome gynandra; Miscanthus.; RuBisCO; carbon concentration mechanism (CCM); carboxylation; maize; oxygenation; photosynthesis; rice; wheat