Pigment protein complexes and the concept of the photosynthetic unit: Chlorophyll complexes and phycobilisomes

The photosynthetic unit includes the reaction centers (RC 1 and RC 2) and the light-harvesting complexes which contribute to evolution of one O₂ molecule. The light-harvesting complexes, that greatly expand the absorptance capacity of the reactions, have evolved along three principal lines. First, in green plants distinct chlorophyll (Chl) a/b-binding intrinsic membrane complexes are associated with RC 1 and RC 2. The Chl a/b-binding complexes may add about 200 additional chromophores to RC 2. Second, cyanobacteria and red algae have a significant type of antenna (with RC 2) in the form of phycobilisomes. A phycobilisome, depending on the size and phycobiliprotein composition adds from 700 to 2300 light-absorbing chromophores. Red algae also have a sizable Chl a-binding complex associated with RC 1, contributing an additional 70 chromophores. Third, in chromophytes a variety of carotenoid-Chl-complexes are found. Some are found associated with RC 1 where they may greatly enhance the absorptance capacity. Association of complexes with RC 2 has been more difficult to ascertain, but is also expected in chromophytes. The apoprotein framework of the complexes provides specific chromophore attachment sites, which assures a directional energy transfer whithin complexes and between complexes and reaction centers. The major Chl-binding antenna proteins generally have a size of 16–28 kDa, whether of chlorophytes, chromophytes, or rhodophytes. High sequence homology observed in two of three transmembrane regions, and in putative chlorophyll-binding residues, suggests that the complexes are related and probably did not evolve from widely divergent polyphyletic lines.Abbreviations APC allophycocyanin - B phycoerythrin-large bangiophycean phycoerythrin - Chl chlorophyll - L_CM linker polypeptide in phycobilisome to thylakoid - FCP fucoxanthin Chl a/c complex - LHC(s) Chl-binding light harvesting complex(s) - LHC I Chl-binding complex of Photosystem I - LHC II Chl-binding complex of Photosystem II - PC phycocyanin - PCP peridinin Chl-binding complex - P700 photochemically active Chl a of Photosystem I - PS I Photosystem I - PS II Photosystem II - RC 1 reaction center core of PS I - RC 2 reaction center core of PS II - R phycoerythrin-large rhodophycean phycoerythrin - sPCP soluble peridinin Chl-binding complex     

Variation in growth rate,carbon assimilation,and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay

Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH₄⁺), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (F_v/F_m) was a sensitive indicator of NH₄⁺ toxicity, manifested by a suppression of F_v/F_m in a dose‐dependent manner. Two chlorophytes were the least sensitive to NH₄⁺ inhibition, at concentrations of >3,000 μmoles NH₄⁺ · L^?1, followed by two estuarine diatoms that were sensitive at concentrations >1,000 μmoles NH₄⁺ · L^?1, followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 μmoles NH₄⁺ · L^?1. At non‐inhibiting concentrations of NH₄⁺, the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO₃^?), whereas the other grew significantly faster on NH₄⁺. All four diatoms tested grew faster on NH₄⁺ compared with NO₃^?. We showed that in cases where growth rates were faster on NH₄⁺ than they were on NO₃^?, the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH₄⁺ dominates the total N pool and they will also not have a growth advantage when NO₃^? is dominant, as long as N concentrations are sufficient.     

TEMPORAL AMMONIUM PATCHINESS AND GROWTH RATE IN CODIUM AND ULVA (ULVOPHYCEAE)1

The growth rates of two chlorophyte macroalgae, Codium fragile and Ulva curvata, are compared in response to varied, but non-random, NH₄⁺ enrichments (pulses). The species were chosen to contrast radically different morphologies. Pulse frequency and pulse duration were varied independently; however, an equivalent mass of NH₄⁺ was added in each treatment. The growth rate of Codium varied neither as a function of pulse frequency nor duration; the growth rate of Ulva varied with pulse frequency, but not pulse duration. These data are combined with life form and physiological characters, and are discussed in the context of the “function form” hypothesis. From the evidence we argue that by virtue of its life form, Ulva is capable of utilizing transiently high NH₄⁺ concentrations and is capable of high growth rates, attributes contributing to its role as a ruderal species. In contrast, Codium's life form does not allow utilization of transiently high NH₄⁺ concentrations or high growth rates, thereby contributing to its role as a persistent species.     

Trophic transfer of biodiversity effects: functional equivalence of prey diversity and enrichment?

Producer diversity is frequently assumed to be detrimental to herbivores, because less edible taxa are more likely to dominate diverse communities. Many producers are, however, complementary in their resource use, and primary production is often positively related to producer diversity. We performed an experiment with microalgae and a generalist herbivore to explore the hypothesis that such positive effects are transferred up the food chain and are functionally comparable to effects of enrichment with a limiting resource. In both absence and presence of grazers, primary production was positively affected by both light supply and producer diversity. Survival, reproduction, and biomass of herbivores were also positively affected by light supply and producer diversity, with both factors contributing equally to grazer performance. We conclude that producer diversity can indeed have similar positive effects on secondary production as enrichment with a limiting resource and discuss conditions under which such positive effects are likely to dominate over negative ones.     

Factors affecting the seasonality and distribution of cyanobacteria and chlorophytes: a case study from the large lakes south of the Alps,with special reference to Lake Garda

Chlorophytes and cyanobacteria are among the most typical algal groups, contributing to the aesthetic appearance and quality of the epilimnetic waters of the deep (251–410 m) and large (6.5–49×10⁹ m³) lakes located on the southern edge of the Alps (from oligo-mesotrophy to meso-eutrophy: Maggiore, Garda, Como, Iseo and Lugano). The results obtained from monthly surveys carried out in the largest of these lakes (Garda) have been reported in detail. The thermal stability of the water column and silica depletion were the main factors responsible for the decline of the great spring diatoms. The successive growth of Mougeotia sp. was favoured by its lower sinking velocity and resistance to the increasing grazing pressure. During summer, the maximum stability of the water column, with high vertical nutrient concentration gradients, determined a major algal differentiation with a typical increase, among others, of Chlorococcales at the surface and metalimnetic stratification of various Oscillatoriales. The development of oligotrophic blooms, caused by a rapid thickening at the surface of Anabaena in the eastern, sheltered basin, was also discussed in light of the trophic characterisation of Lake Garda. From autumn to spring, the decreasing light, the increasing mixing depth and nutrient availability favoured a progressive dominance of vertical homogeneous populations of Planktothrix (autumn) and colonial diatoms. The same functional groups of chlorophytes and cyanobacteria have been recognised in the studies published so far on the phytoplankton of deep southern subalpine lakes. In this respect, their morphometric and physical properties appear to constitute a sort of standardising factor, reducing the range of possible dominants. With increasing TP concentrations and biomass, filaments of Planktothrix and Planktolyngbya, along with the Chlorococcales, became important. The dominance of Mougeotia (one of the most characteristic features of these large lakes) appears restricted to a medium trophic range, whereas the distribution of the Chroococcales and other filaments ascribed to Pseudanabaena and/or Limnothrix is more irregular. The conspicuous presence of Aphanizomenon in Lake Lugano is typical and characteristic of a more productive lake. Among the Nostocales, a clear interpretation of the Anabaena blooms in lakes Garda and Iseo is complicated by the peculiar behaviour of filaments concentrating at the surface, which is apparently restricted, within the medium trophic range, to stable water columns.     

Chlorophytes of biological soil crusts in Gurbantunggut Desert, Xinjiang Autonomous Region, China

In this paper, chlorophytes collected from 253 biological soil crust samples in Gurbantunggut Desert in Xinjiang Autonomous Region, China were studied by field investigation and microscopical observation in lab. The flora composition, ecological distribution of chlorophytes in the desert and dynamic changes of species composition of chlorophytes in different developing stages of biological soil crusts are preliminarily analyzed. Results showed that there were 26 species belonging to 14 genera and 10 families, in which unicellular chlorophytes were dominant. There existed some differences in distribution of varied sand dune positions. The taxa of chlorophytes in leeward of sand dunes are most abundant, but the taxa in windward, interdune and the top of sand dunes reduced gradually. Chlorophytes were mainly distributed within the crust and the taxa of chlorophytes decrease obviously under the crust. In the developing stages of the biological soil crust, species diversity of chlorophytes changed a little, but species composition presented some differences. Chlorococcum humicola, Chlorella vulgaris, Chlamydomonas ovalis and Chlamydomonas sp. nearly existed in all developing stages of biological crusts. In several former stages of the biological soil crust there were spherical chlorophytes and filamentous ones. When moss crust formed, filamentous chlorophytes disappeared, such as Microspora and Ulothrix. __________ Translated from Arid Zone Research, 2006, 23(2): 189–193 [译自: 干旱区研究]     

Triosephosphate isomerase genes in two trophic modes of euglenoids (euglenophyceae) and their phylogenetic analysis

Two different length cDNAs encoding triosephosphate isomerase (TIM) were identified in the two trophic modes of euglenoids, the phototrophic Euglena gracilis and Euglena intermedia and the saprotrophic Astasia longa. Sequence analyses and presequence prediction indicated that the shorter cDNA encodes a cytosolic TIM and the longer cDNA encodes a plastid TIM (pTIM). The typical presequence of the putative A. longa pTIM and the high sequence similarity between A. longa pTIM and E. gracilis pTIM imply that A. longa pTIM is targeted to plastids. Therefore, although the plastids of A. longa have lost the ability of photosynthesis, they might retain other TIM-related function(s), such as glycolysis and the synthesis of isopentenyl diphosphate or fatty acids. Including the TIM sequences obtained by us from chlorophytes and rhodophytes, our phylogenetic analyses indicated that euglenoid TIMs group neither with TIMs of kinetoplastids, which share the nearest common ancestor with euglenoids, nor are closely related to TIMs of chlorophytes, which are considered to be the donors of euglenoid plastids through secondary endosymbiosis. Instead, they group with TIMs of rhodophytes. In addition, our amino acid sequence alignment and structure modeling showed that TIMs of euglenoids and rhodophytes share a unique 2-aa insertion within their loop-4 areas. Therefore, either tim convergent evolution or lateral gene transfer (more probably) might have occurred between euglenoids and rhodophytes after the divergence of euglenoids with kinetoplastids.     

Phytoplankton chlorophyte structure as related to ENSO events in a saline lowland river (Salado River,Buenos Aires,Argentina)

We analyzed the phytoplankton present in the lower sector of the Salado River (Buenos Aires, Argentina) for 10 years (1995–2005) and detected significant changes occurring in chlorophyte abundance and species richness during La Niña event (1998–1999), which period was analyzed throughout the entire basin (main stream and tributaries). We compared the physicochemical and biologic variables between two El Niño–La Niña–Southern Oscillation (ENSO) periods – El Niño (March 1997–January 1998) and La Niña (May 1998–May 1999) – to identify possible indicators of a relationship between climatic anomalies and chlorophyte performance. Chlorophyte density increased during the La Niña. Under normal or extreme hydrologic conditions, mobile (Chlamydomonas spp.) and nonmobile (Monoraphidium spp.) chlorophytes codominated. These species belonged to Reynolds's functional groups X1 and X2, those typical of nutrient‐enriched environments. Comparative analyses between El Niño and La Niña periods indicated significant differences in physicochemical (K⁺, dissolved polyphenols, particulate reactive phosphorus, alkalinity, pH) and biologic (species diversity and richness, phytoplankton and chlorophyte total densities) variables between the two periods at all basin sites. During the La Niña condition, species richness was greater owing to interconnected shallow lakes and drainage‐channel inputs, while the Shannon diversity index was lower because of the high abundance values of Monoraphidium minutum. A detailed analysis of the chlorophytes in the entire basin, indicated that changes in density and species dominance occurred on a regional scale although diverse chlorophyte assemblages were identified in the different sectors of the Salado River basin. After La Niña event, the entire basin had the potential to revert to the previous density values, showing the resilience to global environmental changes and the ability to reestablish the general conditions of stability.     

Novel green algal isolates from the Egyptian hyper‐arid desert oases: a polyphasic approach with a description of Pharao desertorum gen. et sp. nov. (Chlorophyceae,Chlorophyta)

The biodiversity of terrestrial algae is still grossly understudied, and African deserts in particular are barely touched in this respect. Here, four coccoid green algae from oases in the Western Desert of Egypt were characterized using a combination of morphotaxonomic, ecological and 18S rDNA data, with additional carotenoid and lipid analyses for two of the strains. Three strains were identified as affiliated with known taxa: Mychonastes sp., Asterarcys sp. (first report of this genus from a desert soil), and Stichococcus cf. deasonii. The fourth strain is proposed to represent a new cryptic genus Pharao gen. nov., with the type species P. desertorum sp. nov. The new taxon is sister to the clade of uncharacterized North American desert strains of Radiococcaceae (Chlorophyceae, Chlorophyta). The pigment profile of P. desertorum gen. et sp. nov. revealed carotenoids and chlorophylls typical of green algae. Bioorganic analysis showed a complex lipidome based on phospho‐ (PC), galacto‐ (MGDG and DGDG), betaine‐ (DGTS), and sulfoquinovosyl‐ (SQDG) membrane lipids, besides significant amounts of storage neutral lipids such as diacyl‐ (DAG) and triacylglycerols (TAG). The presence of saturated alkyl chains within all the membrane lipid classes in P. desertorum and Asterarcys sp. appears to reflect the need to maintain membrane fluidity and viscosity. In summary, African deserts likely still harbor new taxa to be described, and lipidomic analyses of such taxa may provide clues about their ability to survive in the extremely harsh desert habitats.