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Halomicronema hongdechloris is a chlorophyll (Chl) f-producing cyanobacterium. Chl f biosynthesis is induced under far-red light, extending its photosynthetically active radiation range to 760 nm. In this study, PSI complexes were isolated and purified from H. hongdechloris, grown under white light (WL) and far-red light (FR), by a combination of density gradient ultracentrifugation and chromatographic separation. WL-PSI showed similar pigment composition as that of Synechocystis 6803, using Chl a in the reaction center. Both Chl a and f were detected in the FR-PSI, although Chl f was a minor component (~8% of total Chl). The FR-PSI showed a maximal fluorescence emission peak of 750 nm at 77 K, which is red-shifted ~20 nm compared to the 730 nm recorded from the WL-PSI. The absorption peaks of P700 for WLPSI and FR-PSI were 699 nm and 702 nm, respectively. The function of Chl f in FR-PSI is discussed. [ABSTRACT FROM AUTHOR]

Abstract: A novel chlorophyll a containing pigment–protein complex expressed by cells of Chromera velia adapted to growth under red/far-red illumination [1]. Purification of the complex was achieved by means of anion-exchange chromatography and gel-filtration. The antenna is shown to be an aggregate of ~20kDa proteins of the light–harvesting complex (LHC) family, unstable in the isolated form. The complex possesses an absorption maximum at 705nm at room temperature in addition to the main chlorophyll a maximum at 677nm producing the major emission band at 714nm at room temperature. The far-red absorption is shown to be the property of the isolated aggregate in the intact form and lost upon dissociation. The purified complex was further characterized by circular dichroism spectroscopy and fluorescence spectroscopy. This work thus identified the third different class of antenna complex in C. velia after the recently described FCP-like and LHCr-like antennas. Possible candidates for red antennas are identified in other taxonomic groups, such as eustigmatophytes and the relevance of the present results to other known examples of red-shifted antenna from other organisms is discussed. This work appears to be the first successful isolation of a chlorophyll a-based far-red antenna complex absorbing above 700nm unrelated to LHCI. [Copyright &y& Elsevier]

Abstract: Chromera velia is an alveolate alga associated with scleractinian corals. Here we present detailed work on chromatic adaptation in C. velia cultured under either blue or red light. Growth of C. velia under red light induced the accumulation of a light harvesting antenna complex exhibiting unusual spectroscopic properties with red-shifted absorption and atypical 710nm fluorescence emission at room temperature. Due to these characteristic features the complex was designated “Red-shifted Chromera light harvesting complex” (Red-CLH complex). Its detailed biochemical survey is described in the accompanying paper (Bina et al. 2013, this issue). Here, we show that the accumulation of Red-CLH complex under red light represents a slow acclimation process (days) that is reversible with much faster kinetics (hours) under blue light. This chromatic adaptation allows C. velia to maintain all important parameters of photosynthesis constant under both light colors. We further demonstrated that the C. velia Red-CLH complex is assembled from a 17kDa antenna protein and is functionally connected to photosystem II as it shows variability of chlorophyll fluorescence. Red-CLH also serves as an additional locus for non-photochemical quenching. Although overall rates of oxygen evolution and carbon fixation were similar for both blue and red light conditions, the presence of Red-CLH in C. velia cells increases the light harvesting potential of photosystem II, which manifested as a doubled oxygen evolution rate at illumination above 695nm. This data demonstrates a remarkable long-term remodeling of C. velia light-harvesting system according to light quality and suggests physiological significance of ‘red’ antenna complexes. [Copyright &y& Elsevier]

Abstract: Both chlorophyll f and chlorophyll d are red-shifted chlorophylls in oxygenic photosynthetic organisms, which extend photon absorbance into the near infrared region. This expands the range of light that can be used to drive photosynthesis. Quantitative determination of chlorophylls is a crucial step in the investigation of chlorophyll-photosynthetic reactions in the field of photobiology and photochemistry. No methods have yet been worked out for the quantitative determination of chlorophyll f. There is also no method available for the precise quantitative determination of chlorophyll d although it was discovered in 1943. In order to obtain the extinction coefficients (ε) of chlorophyll f and chlorophyll d, the concentrations of chlorophylls were determined by Inductive Coupled Plasma Mass Spectrometry according to the fact that each chlorophyll molecule contains one magnesium (Mg) atom. Molar extinction coefficient εchl f is 71.11×103 Lmol−1 A707nm cm−1 and εchl d is 63.68×103 Lmol−1 A697nm cm−1 in 100% methanol. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial. [Copyright &y& Elsevier]