Recently, bryophytes, which diverged from the ancestor of seed plants more than 400 million years ago, came into focus in photosynthesis research as they can provide valuable insights into the evolution of photosynthetic complexes during the adaptation to terrestrial life. This study isolated intact photosystem I (PSI) with its associated light-harvesting complex (LHCI) from the moss Physcomitr...

The electric field-induced absorption changes (Stark effect) of light-harvesting complex II (LHCII) in different oligomerisation states-monomeric, trimeric and aggregated-have been probed at 77 K. All the chlorophyll (Chl) a molecules exhibit electro-optic properties in the Q(y) absorption region characterized by a change in dipole moment /Deltamu-->/ =0.6+/-0.06D/f and polarizability, Tr(Delta...

We developed a novel method for the isolation of the PSI-LHCI-LHCII complex from spinach leaves. The supercomplex was resolved into a core complex (CPI), LHCII trimers, LHCI dimers and LHCII monomers using green gel electrophoresis. We then investigate changes in the fluorescence and absorption spectra of PSI-LHCI-LHCII under high light. In addition, we compared light-induced denaturation of th...

The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and em...

It is proposed that xanthophylls, and carotenoids in general, may assist in energy transfer from the chlorophyll Soret band to the Q band. Ground-state (1Ag ) and excited-state (1Bu ) optimizations of violaxanthin (Vx) and zeaxanthin (Zx) are performed in an environment mimicking the light-harvesting complex II (LHCII), including the closest chlorophyll b molecule (Chl). Time-dependent density ...

Laboratory and field studies have revealed that iron has multiple roles in phytoplankton physiology, with particular importance for light-harvesting cellular machinery. However, although iron-limitation is explicitly included in numerous biogeochemical/ecosystem models, its implementation varies, and its effect on the efficiency of light harvesting is often ignored. Given the complexity of the ...

Photosynthetic organisms have developed multiple mechanisms to protect the photosynthetic apparatus from high light stress. Plants and algae exhibit thermal dissipation of excitation energy in the membranebound light-harvesting complex of photosystem II (LHCII). In most species of cyanobacteria, which lack LHCII, light is captured by the phycobilisome, a membraneextrinsic complex attached to th...

The reaction of several plant chlorophyll-protein complexes with NaBH, has been studied by absorption spectroscopy. In all the complexes studied, chlorophyll b is more reactive than Chl a , due to preferential reaction of its formyl substituent at C-7. The complexes also show large variations in reactivity towards NaBH, and the order of reactivity is: LHCI > PSI1 complex > LHCII > PSI > P700 (i...

We created a Qo pocket mutant by site-directed mutagenesis of the chloroplast petD gene in Chlamydomonas reinhardtii. We mutated the conserved PEWY sequence in the EF loop of subunit IV into PWYE. The pwye mutant did not grow in phototrophic conditions although it assembled wild-type levels of cytochrome b6f complexes. We demonstrated a complete block in electron transfer through the cytochrome...

Nitrogen-limited Chlamydomonas reinhardtii is chlorotic and very deficient in chlorophyll a/b light-harvesting complexes (LHC). Rates of synthesis of photosynthetic proteins, but especially the LHC apoproteins, are reduced 10- to 40-fold. Moderately high levels of chloroplast transcripts accumulate in nitrogen-limited cells, and there is a correlation between chloroplast DNA levels and chloropl...