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Plant Physiology 132:1529-1539 (2003) © 2003 American Society of Plant Biologists Photoacoustic Analysis Indicates That Chloroplast Movement Does Not Alter Liquid-Phase CO2 Diffusion in Leaves of Alocasia brisbanensis1,2Department of Biology, St. Mary's College of Maryland, St. Mary's City, Maryland 20686–3001 (H.L.G.); and Department of Botany, University of Wyoming, Laramie, Wyoming 82071–3165 (S.K.H, T.C.V.)
Light-mediated chloroplast movements are common in plants. When leaves of Alocasia brisbanensis (F.M. Bailey) Domin are exposed to dim light, mesophyll chloroplasts spread along the periclinal walls normal to the light, maximizing absorbance. Under high light, the chloroplasts move to anticlinal walls. It has been proposed that movement to the high-light position shortens the diffusion path for CO2 from the intercellular air spaces to the chloroplasts, thus reducing CO2 limitation of photosynthesis. To test this hypothesis, we used pulsed photoacoustics to measure oxygen diffusion times as a proxy for CO2 diffusion in leaf cells. We found no evidence that chloroplast movement to the high-light position enhanced gas diffusion. Times for oxygen diffusion were not shorter in leaves pretreated with white light, which induced chloroplast movement to the high-light position, compared with leaves pretreated with 500 to 700 nm light, which did not induce movement. From the oxygen diffusion time and the diffusion distance from chloroplasts to the intercellular gas space, we calculated an oxygen permeability of 2.25 x 10–6 cm2 s–1 for leaf cells at 20°C. When leaf temperature was varied from 5°C to 40°C, the permeability for oxygen increased between 5°C and 20°C but changed little between 20°C and 40°C, indicating changes in viscosity or other physical parameters of leaf cells above 20°C. Resistance for CO2 estimated from oxygen permeability was in good agreement with published values, validating photoacoustics as another way of assessing internal resistances to CO2 diffusion.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.102.019612. 1 This work was funded by the National Science Foundation (grant nos. IBN–0075847 and DBI–9724499). 2 Alocasia brisbanensis (F.M. Bailey) Domin is the currently accepted name of the only Alocasia species endemic to the Australian mainland (Hay and Wise, 1991). The species has previously been known as Alocasia macrorrhiza (L.) G. Don. 3 Present address: Botany and Agricultural Biochemistry, Marsh Life Science Building, 109 Carrigan Drive, University of Vermont, Burlington, Vermont 05405–0086. * Corresponding author; e-mail hlgorton{at}smcm.edu; fax 240–895–4996. Received December 21, 2002; returned for revision January 21, 2003; accepted March 28, 2003. This article has been cited by other articles:
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