PLANT PHYSIOLOGY , Vol 114, Issue 1 145-152, Copyright © 1997 by American Society of Plant Biologists
Modification of Photosystem I Light Harvesting of Bundle-Sheath Chloroplasts Occurred during the Evolution of NADP-Malic Enzyme C4 Photosynthesis
E. Pfundel and M. Pfeffer
Institut fur Pflanzengenetik und Kulturpflanzenforschung, Corrensstrasse 3, D-06466 Gatersleben, Germany (E.P., M.P.)
Low-temperature emission spectra and excitation spectra for chlorophyll
fluorescence were recorded from leaves of species of the genus Flaveria
(Asteraceae) with C3, C3-C4-intermediate, C4-like, and C4 photosynthesis.
Among the latter two groups, high chlorophyll b absorption was observed in
excitation spectra for photosystem I (PSI) fluorescence. By comparing leaf
data with those from isolated chloroplast fractions, the high chlorophyll b
absorption was attributed to the specific properties of the bundle-sheath
chloroplasts in leaves from C4 plants. The deconvolution of the PSI
excitation spectra and the use of a model revealed that the contribution of
photosystem II absorption to the functional antenna of PSI was markedly
increased in leaves from three of the five C4-like and C4 species
investigated in detail. The two other species exhibited normal, C3-like
light-harvesting properties of PSI. The former species are known for
efficient carbon assimilation, the latter for decreased efficiencies of
carbon assimilation. It is concluded that photosystem II becomes a
substantial part of the functional PSI antenna late in the evolution of C4
photosynthesis, and that the composite antenna optimizes the
light-harvesting of PSI in bundle-sheath chloroplasts to meet the energy
requirements of C4 photosynthesis.
