title: Acclimation to low light by C4 maize: implications for bundle sheath leakiness.
abstract: C4 plants have a biochemical carbon concentrating mechanism (CCM) that increases CO2 concentration around ribulose bisphosphate carboxylase oxygenase (Rubisco) in the bundle sheath (BS). Under limiting light, the activity of the CCM generally decreases, causing an increase in leakiness, (Φ), the ratio of CO2 retrodiffusing from the BS relative to C4 carboxylation processes. Maize plants were grown under high and low light regimes (respectively HL, 600 versus LL, 100 μE m(-2)  s(-1) ). Short-term acclimation of Φ was compared from isotopic discrimination (Δ), gas exchange and photochemistry. Direct measurement of respiration in the light, and ATP production rate (JATP ), allowed us use a novel approach to derive Φ, compared with the conventional fitting of measured and predicted Δ. HL grown plants responded to decreasing light intensities with the well-documented increase in Φ. Conversely, LL plants showed a constant Φ, which has not been observed previously. We explain the pattern by two contrasting acclimation strategies: HL plants maintained a high CCM activity at LL, resulting in high CO2 overcycling and increased Φ; LL plants acclimated by down-regulating the CCM, effectively optimizing scarce ATP supply. This surprising plasticity may limit the impact of Φ-dependent carbon losses in leaves becoming shaded within developing canopies.
authors.affiliation: Physiological Ecology Group, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK.
authors.forename: Chandra
authors.initials: C
authors.lastname: Bellasio
authors.forename: Howard
authors.initials: H
authors.lastname: Griffiths
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects*; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D008027:Light; D008954:Models, Biological; D010100:Oxygen / Q000494:pharmacology; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D058526:Plant Vascular Bundle / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D003313:Zea mays / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*
chemical_list: D002247:Carbon Isotopes; D045332:Photosystem II Protein Complex; D002244:Carbon; D010100:Oxygen
keywords: C4 photosynthesis; Zea mays L; bundle sheath conductance; carbon isotope discrimination; efficiency; gBS; Δ13C