THE SIGNIFICANCE OF INTRACELLULAR SELF-SHADING ON THE BIOOPTICAL PROPERTIES OF BROWN,RED, AND GREEN MACROALGAE1

The spectral light absorption and fluorescence excitation spectra from thalli (in vivo) and thylakoid micelles (no intracellular self-shading) from the macroalgae Laminaria digitata (L.) Edmonson, Palmaria palmata (L.) Kuntze, and Ulva sp. were examined. In all the examined species, the intracellular self-shading (i.e. the package effect) was highly significant to the extent that absorption peaks related to individual pigments were significantly suppressed. Thus, for studies related to taxonomy and physiology, “unpacked”spectra may be more informative. Thylakoid micelle preparations offer opportunities to examine more closely species-specific differences in the packaging effect, light harvesting and utilization, and pigmentation. As well, the thylakoid micelles, when analyzed with biochemical assays or fluoromtry, may provide insight into components of the photosynthetic machinery that are specific to different classes of mncroalgne. We present the Chl a-specific absorption coefficients and the corresponding fluorescence excitation spectra of macroalgal thylakoid micelles for the three species.     

18O Labeling of Chlorophyll d in Acaryochloris marina Reveals That Chlorophyll a and Molecular Oxygen Are Precursors

The cyanobacterium Acaryochloris marina was cultured in the presence of either H₂¹⁸O or ¹⁸O₂, and the newly synthesized chlorophylls (Chl a and Chl d) were isolated using high performance liquid chromatography and analyzed by mass spectroscopy. In the presence of H₂¹⁸O, newly synthesized Chl a and d, both incorporated up to four isotopic ¹⁸O atoms. Time course H₂¹⁸O labeling experiments showed incorporation of isotopic ¹⁸O atoms originating from H₂¹⁸O into Chl a, with over 90% of Chl a ¹⁸O-labeled at 48 h. The incorporation of isotopic ¹⁸O atoms into Chl d upon incubation in H₂¹⁸O was slower compared with Chl a with ∼50% ¹⁸O-labeled Chl d at 115 h. The rapid turnover of newly synthesized Chl a suggested that Chl a is the direct biosynthetic precursor of Chl d. In the presence of ¹⁸O₂ gas, one isotopic ¹⁸O atom was incorporated into Chl a with approximately the same kinetic incorporation rate observed in the H₂¹⁸O labeling experiment, reaching over 90% labeling intensity at 48 h. The incorporation of two isotopic ¹⁸O atoms derived from molecular oxygen (¹⁸O₂) was observed in the extracted Chl d, and the percentage of double isotopic ¹⁸O-labeled Chl d increased in parallel with the decrease of non-isotopic-labeled Chl d. This clearly indicated that the oxygen atom in the C3¹-formyl group of Chl d is derived from dioxygen via an oxygenase-type reaction mechanism.     

Crystal Structure of the Nitrogenase-like Dark Operative Protochlorophyllide Oxidoreductase Catalytic Complex (ChlN/ChlB)2

During (bacterio)chlorophyll biosynthesis of many photosynthetically active organisms, dark operative protochlorophyllide oxidoreductase (DPOR) catalyzes the two-electron reduction of ring D of protochlorophyllide to form chlorophyllide. DPOR is composed of the subunits ChlL, ChlN, and ChlB. Homodimeric ChlL₂ bearing an intersubunit [4Fe-4S] cluster is an ATP-dependent reductase transferring single electrons to the heterotetrameric (ChlN/ChlB)₂ complex. The latter contains two intersubunit [4Fe-4S] clusters and two protochlorophyllide binding sites, respectively. Here we present the crystal structure of the catalytic (ChlN/ChlB)₂ complex of DPOR from the cyanobacterium Thermosynechococcus elongatus at a resolution of 2.4 Å. Subunits ChlN and ChlB exhibit a related architecture of three subdomains each built around a central, parallel β-sheet surrounded by α-helices. The (ChlN/ChlB)₂ crystal structure reveals a [4Fe-4S] cluster coordinated by an aspartate oxygen alongside three cysteine ligands. Two equivalent substrate binding sites enriched in aromatic residues for protochlorophyllide substrate binding are located at the interface of each ChlN/ChlB half-tetramer. The complete octameric (ChlN/ChlB)₂(ChlL₂)₂ complex of DPOR was modeled based on the crystal structure and earlier functional studies. The electron transfer pathway via the various redox centers of DPOR to the substrate is proposed.     

Effects of kinetin and nitrogen on growth rates,pigment and protein contents in wild and phycoerythrin-deficient strains of <Emphasis Type="Italic">Hypnea musciformis</Emphasis> (Rhodophyta)

Hypnea musciformis (Wulfen in Jacqu.) J.V. Lamour. is the main source for carrageenan production in Brazil and strains with selected characteristics could improve the production of raw material. The effects of kinetin on growth rates, morphology, protein content, and concentrations of pigments (chlorophyll a, phycoerythrin, phycocyanin, and allophycocyanin) were assessed in the wild strain (brown phenotype) and in the phycoerythrin-deficient strain (green phenotype) of H. musciformis. Concentrations of kinetin ranging from 0 to 50 μM were tested in ASP 12-NTA synthetic medium with 10 μM nitrate (N-limited) and 100 μM nitrate (N-saturated). In N-limited condition, kinetin stimulated growth rates of the phycoerythrin-deficient strain and formation of lateral branches in both colour strains. Kinetin stimulated protein biosynthesis in both strains. However, differences between both nitrogen conditions were significant only in the phycoerythrin-deficient strain. In the wild strain, effects of kinetin on concentrations of phycobiliproteins were not significant in both nitrogen conditions, except for chlorophyll content. However, the phycoerythrin-deficient strain showed an opposite response, and kinetin stimulated the phycobiliprotein biosynthesis, with the highest concentrations of phycoerythrin in N-saturated medium, while the highest concentrations of allophycocyanin and phycocyanin were observed in N-limited medium. These results indicate that the effects of kinetin on growth, morphology, protein and phycobiliprotein contents are influenced by nitrogen availability, and the main nitrogen storage pools in phycoerythrin-deficient strain of H. musciformis submitted to N-limited conditions were phycocyanin and allophycocianin, the biosynthesis of which was enhanced by kinetin.     

Growth and pigment composition in the red alga <Emphasis Type="Italic">Halymenia floresii</Emphasis> cultured under different light qualities

Halymenia floresii is an edible species consumed in some Asian markets. In the Yucatan peninsula coast of Mexico, H. floresii dominates rocky substrata between 3 and 40 m where it grows up to 50 cm high. After analyzing the seasonal pattern of pigment content on H. floresii, we evaluate if and how the spectral composition of light affects growth and pigment dynamics under laboratory cultivation. Unialgal cultures were exposed to white, blue, red and green light in a 3-week experiment. Green light resulted in the highest algal growth rates. Synthesis of chlorophyll a, α-carotene and lutein, but not of β-carotene, was induced by white or green light. Phycocyanin synthesis was stimulated by blue light and phycoerythrin synthesis by blue or red light. Light quality treatments may be used to manipulate pigment composition in Halymenia floresii cultures.     

Bacterial pigments and their applications

Natural pigments sourced from ores, insects, plants and animals were the colorants used since prehistoric period. Synthetic dyes which took the place of natural pigments in the middle of 19th century still rule the field to the maximum extent in spite of its hazardous effect to humans, animals and environment. As an alternative to synthetic pigments, bacterial pigments due to their better biodegradability and higher compatibility with the environment, offer promising avenues for various applications. The industry is now able to produce some bacterial pigments for applications in food, pharmaceuticals, cosmetics and textiles. Extraction of bacterial pigments in relatively pure and concentrated forms is the main technological challenge. Optimization of fermentation process and the medium components are reported as key strategies for economic recovery of pigments. Research work needs to be carried out to formulate the fermentation media for each bacterial pigment on large scale by using economical and easily available sources for commercial process. Recent advances in synthetic biology, metabolic engineering efforts of bacteria will greatly expand the pigments that could be produced economically in sufficient amounts for industrial application. This review summarizes the current technology status and challenges, economics, novel strategies for production of bacterial pigments and metabolic engineering of bacteria with a focus on applications of bacterial pigments in food industry, pharmaceutical industry, dyeing as well as on other applications.     

A red-shifted antenna protein associated with photosystem II in Physcomitrella patens

Antenna systems of plants and green algae are made up of pigment-protein complexes belonging to the light-harvesting complex (LHC) multigene family. LHCs increase the light-harvesting cross-section of photosystems I and II and catalyze photoprotective reactions that prevent light-induced damage in an oxygenic environment. The genome of the moss Physcomitrella patens contains two genes encoding LHCb9, a new antenna protein that bears an overall sequence similarity to photosystem II antenna proteins but carries a specific motif typical of photosystem I antenna proteins. This consists of the presence of an asparagine residue as a ligand for Chl 603 (A5) chromophore rather than a histidine, the common ligand in all other LHCbs. Asparagine as a Chl 603 (A5) ligand generates red-shifted spectral forms associated with photosystem I rather than with photosystem II, suggesting that in P. patens, the energy landscape of photosystem II might be different with respect to that of most green algae and plants. In this work, we show that the in vitro refolded LHCb9-pigment complexes carry a red-shifted fluorescence emission peak, different from all other known photosystem II antenna proteins. By using a specific antibody, we localized LHCb9 within PSII supercomplexes in the thylakoid membranes. This is the first report of red-shifted spectral forms in a PSII antenna system, suggesting that this biophysical feature might have a special role either in optimization of light use efficiency or in photoprotection in the specific environmental conditions experienced by this moss.     

Zinc stress induces physiological,ultra-structural and biochemical changes in mandarin orange (Citrus reticulata Blanco) seedlings

Zinc (Zn) is an essential micronutrient for higher plants; yet, at higher concentrations it is toxic. In order to explore the effect of Zn stress on growth, biochemical, physiological and ultra-structural changes, 1 year old mandarin plants were grown under various Zn concentrations (1, 2, 3, 4, 5, 10 15 and 20 mM) for 14 weeks. The biomass of the plants increased with increasing Zn concentrations and finally declined under excess Zn concentration but the prime increase was observed at 4 and 5 mM Zn. Zn stress reduced the photosynthetic rate, stomatal conductance, and transpiration along with reduction of chlorophyll a, chlorophyll b, and carotenoids content in leaf. Superoxide anion, malondialdehyde, hydrogen peroxide and electrolyte leakage were elevated in Zn stressed plants. The activities of ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) enzymes were increased in both Zn-deficient and Zn-excess plants. Therefore it is suggested that antioxidant defense system did not sufficiently protect the plants under rigorous Zn stress which was also corroborated by the alteration in cell ultrastructure as revealed by transmission electron microscopy.     

Effects of low night temperature on pigments,chl <Emphasis Type="Italic">a</Emphasis> fluorescence and energy allocation in two bitter gourd (<Emphasis Type="Italic">Momordica charantia</Emphasis> L.) genotypes

Using two different inbred lines of Momordica charantia (bitter gourd), Y-106-5 and Z-1-4, the cell membrane stability, leaf water potential, pigment contents and the chlorophyll a fluorescence were investigated with different low night temperature (LNT) treatments over a 7 day time period and the sequent a 7 day recovery. Under LNT treatments, electrolyte leakage increased in both inbred lines and it increased more significantly in Y-106-5 plants than that in Z-1-4. The content of Chl b and total Chl decreased, while the Chl a/b ratio increased in stressed plants of the two lines. Almost all LNT treatments induced little change in Chl a content in Z-1-4 whereas obvious decreases in 5 and 8°C treated Y-106-5 plants were observed. Chilling changed the water status of plants and induced decreases of leaf water potential (LWP) in 5 and 8°C treated plants. LNT treatments also resulted in changes in the chlorophyll fluorescence parameters in bitter gourd leaves. The potential PSII activity (F _v/F _o) was reduced obviously by LNT stress and showed more sensitive to LNT than the maximum quantum efficiency of PSII primary photochemistry (F _v/F _m). The efficiency of open PSII centers exhibited a slight decrease whereas the photochemical quenching efficient (q _P) was affected more seriously by LNT stress in both two inbred lines. The allocation of energy was rearranged by LNT stress. The light fraction used for PSII photochemistry (P) was reduced, while that used for heat dissipation (D) and the third fraction of absorbed light defines excess energy (E) increased due to the chilling stress. The impacts of LNT stress on bitter gourd generally increased with the number of LNT chilling and the severe night chilling. Plants were little affected by 12°C night chilling and the most acute damage was found in 5°C night chilling treatments. A 7 day recovery mitigated the adverse effects of LNT for both lines and almost all LNT treated plants restored to control levels except 5°C night chilling treated Y-106-5 plants. The two lines have a variance in tolerance to LNT stress and display obvious differences of phenotypes under extreme conditions.