title: Light absorption by the chlorophyll a-b complexes of photosystem II in a leaf with special reference to LHCII.
abstract: To investigate the light-harvesting properties of the Photosystem II chlorophyll (chl) a-b complexes (major light-harvesting complex of Photosystem II [LHCII], CP24, CP26, CP29) in a mature leaf under natural "daylight" illumination, the absorption spectra of the isolated complexes were converted into the photon absorption spectrum (1-T) within a leaf, using the approach of Rivadossi et al. ([1999] Photosynth. Res. 60, 209-215). In the Qy region, significant enhancement of light harvesting by the chl b electronic transitions, with respect to the absorption spectra (optical density [OD]), as well as a large and generalized increase (between two- and four-fold) associated with the vibrational bands of both chl a and b, was observed, which acquires an important light-harvesting role (approximately 30-40% of total). In the Soret region, a small increase in light harvesting by chl b was indicated. To gain more detailed information on these aspects the light harvesting of LHCII in a leaf was investigated. This required describing the pigment absorption (chl a and b, carotenoids) in the LHCII OD spectrum in terms of spectral subbands, which were subsequently used to estimate the relative light harvesting of each pigment type in LHCII of a leaf. When the entire visible spectral interval between 400 and 730 nm is considered, the chl a light harvesting is essentially unchanged with respect to the absorption spectrum (OD) of isolated LHCII, whereas the chl b contribution is 20% higher and the carotenoids are 33% lower. The relative enhancement of the chl b absorption is principally associated with the Qy electronic transition region, the light-harvesting contribution of which becomes prominent in the leaf.
authors.affiliation: Istituto di Biofisica del Consiglio Nazionale delle Ricerche-Sezione di Milano, Dipartimento di Biologia, Università degli Studi di Milano, Milano, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Rivadossi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Zucchelli
authors.forename: Flavio M
authors.initials: FM
authors.lastname: Garlaschi
authors.forename: Robert C
authors.initials: RC
authors.lastname: Jennings
mesh_terms: D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects*; D011485:Protein Binding; D013057:Spectrum Analysis; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll