Plant and Cell Physiology Advance Access originally published online on February 25, 2009
Plant and Cell Physiology 2009 50(4):684-697; doi:10.1093/pcp/pcp034
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This article appears in the following Plant and Cell Physiology issue: Special Issue Articles: Photosynthesis [View the issue table of contents]
Special Issue - Mini Review |
Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green
1Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
2Photobioenergetics Group, School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT 0200, Australia
*Corresponding author: E-mail, itera{at}biol.s.u-tokyo.ac.jp; Fax, +81-3-5841-4465.
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Abstract |
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The literature and our present examinations indicate that the intra-leaf light absorption profile is in most cases steeper than the photosynthetic capacity profile. In strong white light, therefore, the quantum yield of photosynthesis would be lower in the upper chloroplasts, located near the illuminated surface, than that in the lower chloroplasts. Because green light can penetrate further into the leaf than red or blue light, in strong white light, any additional green light absorbed by the lower chloroplasts would increase leaf photosynthesis to a greater extent than would additional red or blue light. Based on the assessment of effects of the additional monochromatic light on leaf photosynthesis, we developed the differential quantum yield method that quantifies efficiency of any monochromatic light in white light. Application of this method to sunflower leaves clearly showed that, in moderate to strong white light, green light drove photosynthesis more effectively than red light. The green leaf should have a considerable volume of chloroplasts to accommodate the inefficient carboxylation enzyme, Rubisco, and deliver appropriate light to all the chloroplasts. By using chlorophylls that absorb green light weakly, modifying mesophyll structure and adjusting the Rubisco/chlorophyll ratio, the leaf appears to satisfy two somewhat conflicting requirements: to increase the absorptance of photosynthetically active radiation, and to drive photosynthesis efficiently in all the chloroplasts. We also discuss some serious problems that are caused by neglecting these intra-leaf profiles when estimating whole leaf electron transport rates and assessing photoinhibition by fluorescence techniques.
Keywords: Chlorophyll - Fluorescence - Palisade tissue - Photoinhibition - Quantum yield - Spongy tissue
Abbreviations:
A, absorbance; An, net photosynthetic rate; E, excess energy; Fm (F
), maximum fluorescence in the fully relaxed state (in the light); F
, steady-state fluorescence in the light; Fv (Fv'), variable fluorescence in the fully relaxed state (in the light), Fv = Fm – F0 (Fv' = F–F0'); F0 (F0'), minimum fluorescence in the fully relaxed state (in the light); 
, mean quantum yield of monochromatic light in white light; 
, differential quantum yield of monochromatic light in white light; PAM, pulse amplitude modulated; PPFD, photo-synthetically active photon flux density; R, reflectance; RuBP, ribulose-1,5-bisphosphate; T, transmittance.
3Present address: Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, 980-8578 Japan
(Received January 4, 2009; Accepted February 24, 2009)
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