Deep chlorophyll-<Emphasis Type="Italic">a</Emphasis> maxima (DCMs) in Antarctic waters

The US Antarctic Marine Living Resources (AMLR) program has, since 1990, conducted annual surveys from early January through mid-March in a large sampling grid around Elephant Island, Antarctica. Approximately 100 hydrographic stations were occupied twice during each field season, with physical, chemical, optical, and biological data acquired from the surface to 750 m depth or to within 10 m of the bottom at shallower stations. During these 14 years, most of the stations in pelagic waters to the northwest of Elephant Island had very low chlorophyll-a (Chl-a) concentrations (<0.2 mg m^–3) in the upper mixed layer (UML) of ~45 m, but a deep chlorophyll-a maximum (DCM) existed between 50 and 100 m, with a peak at approximately 75 m. This was in contrast to adjacent stations which had higher Chl-a concentrations (approximately 1.0 mg m^–3) in the UML and no DCM. We provide evidence that the higher Chl-a concentrations that occur at depths of 50–100 m result from increased photosynthetic activity and not from a passive sinking of cells from the UML or by the intrusion of Chl-a rich coastal waters. Data to support this conclusion include (1) elevated dissolved oxygen concentrations between 50 and 100 m, (2) evidence of active photosynthesis at the depth of the DCM as indicated by increased natural upwelling radiation at 683 nm, and (3) water samples obtained from the DCM at 75 m and incubated under simulated conditions of temperature and light had assimilation numbers of approximately 1.0–1.5 mg carbon fixed per milligram Chl-a per hour. DCMs occur in the same depth range as the temperature minimum layer (TML) (the winter remnant of Antarctic surface water, AASW), which is known to have elevated concentrations of inorganic nutrients essential for growth of phytoplankton. Our data indicate that a DCM develops as a result of (1) depletion of iron (Fe) in the UML with the onset of the summer season, and (2) growth of phytoplankton in the TML where both Fe concentrations and solar irradiance levels are high enough to permit an increase of phytoplankton biomass.     

Light-harvesting properties of zinc complex of chlorophyll-<Emphasis Type="Italic">a</Emphasis> from <Emphasis Type="Italic">spirulina</Emphasis> in surfactant micellar media

Zn chlorophyll-a was prepareted from Mg chlorophyll-a from spirulina and the optical properties of the ground state and the photoexited state of Zn chlorophyll-a in aqueous surfactant micellar media were studied using UV-vis absorption, fluorescence emission spectra, electrochemical and fluorescence lifetime measurements. In comparison of the UV-vis absorption and fluorescence emission spectra of Zn chlorophyll-a and Mg chlorophyll-a, the blue-shift in the absorption bands and emission peak of Zn chlorophyll-a was observed. The energies of the first excited singlet state of Zn chlorophyll-a was 1.87eV. The first oxidation and reduction potentials of the photoexcited singlet state of Zn chlorophyll-a were −0.67 and 0.60V, respectively. Fluorescence lifetime of Zn chlorophyll-a was 9.0 ns in CTAB micellar solution. The fluorescence lifetime of Zn chlorophyll-a is shorter than that of Mg chlorophyll-a (9.8 ns). The photositability of Zn chlorophyll-a was superior to that of Mg chlorophyll-a in various pH conditions. Published online December 2004     

Polyamines stimulate non-photochemical quenching of chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence in <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis>

Polyamines (PAs) are small metabolites that are produced and oxidized in chloroplasts with an obscure mode of action. Recently, we showed that qE is stimulated by PAs in higher plants (Nicotiana tabacum) and in genetically modified plants with elevated thylakoid-associated PAs (Ioannidis and Kotzabasis Biochim Biophys Acta 1767:1371–1382, 2007; Ioannidis et al. Biochim Biophys Acta 1787:1215–1222, 2009). Here, we investigated further their quenching properties both in vivo in green algae and in vitro is isolated LHCII. In vivo spermine up-regulates NPQ in Scenedesums obliquus about 30%. In vitro putrescine—the obligatory metabolic precursor of PAs—has a marginal quenching effect, while spermidine and spermine exhibit strong quenching abilities in isolated LHCII up to 40%. Based on available 3D models of LHCII we report a special cavity of about 600 Å³ and a near-by larger pocket in the trimeric LHCII that could be of importance for the stimulation of qE by amines.     

Underestimated chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence measurements on <Emphasis Type="Italic">Buxus microphylla</Emphasis> red winter leaves

Leaves under stressful conditions usually show downregulated maximum quantum efficiency of photosystem II [inferred from variable to maximum chlorophyll (Chl) a fluorescence (F_v/F_m), usually lower than 0.8], indicating photoinhibition. The usual method to evaluate the degree of photoinhibition in winter red leaves is generally by measuring the F_v/F_m on the red adaxial surface. Two phenotypes of overwintering Buxus microphylla ‘Wintergreen’ red leaves, with different measuring site and leaf thickness, were investigated in order to elucidate how red pigments in the outer leaf layer affected the Chl a fluorescence (F_v/F_m) and photochemical reflectance index. Our results showed that the F_v/F_m measured on leaves with the same red surface, but different leaf thickness, exhibited a slightly lower value in half leaf (separated upper and lower layers of leaves by removing the leaf edge similarly as affected by winter freezing and thawing) than that in the intact leaf (without removing the leaf edge), and the F_v/F_m measured on the red surface was significantly lower than that on the inner or backlighted green surface of the same thickness. Our results suggest that the usual measurement of F_v/F_m on red adaxial surface overestimates the actual degree of photoinhibition compared with that of the whole leaf in the winter.     

Leaf gas exchange and chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence of <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> in response to <Emphasis Type="Italic">Puccinia psidii</Emphasis> infection

One of the most important diseases of eucalyptus plantations is caused by the rust fungus Puccinia psidii. While the genetic basis of rust resistance has been addressed recently, little is known about the physiological aspects of Eucalyptus–P. psidii interaction. In order to fill this gap, we undertook a study investigating the effects of P. psidii infection on photosynthetic processes of two E. urophylla clones with contrasting resistance to the pathogen. Our results show that gas exchange and chlorophyll a fluorescence parameters were virtually unaffected in the resistant clone. In the susceptible clone, photosynthetic rates were chiefly constrained by biochemical limitations to carbon fixation. Photosynthesis was impaired only in symptomatic tissues since the reductions in photosynthetic rates were proportional to the diseased leaf area. Rust infection provoked chronic photoinhibition to photosynthesis in the susceptible clone. Overall, differences in the ability for light capture, use and dissipation may play a significant role in explaining the clonal differences in Eucalyptus in response to P. psidii infection. To our knowledge, this is the first report of the effect of rust infection on gas exchange and chlorophyll a fluorescence parameters in Eucalyptus.     

Expression of a<Emphasis Type="Italic"> SoxB</Emphasis> and a<Emphasis Type="Italic"> Wnt2/13</Emphasis> gene during the development of the mollusc<Emphasis Type="Italic"> Patella vulgata</Emphasis>

We cloned and analysed the expression of a SoxB gene (PvuSoxB) in the marine mollusc, Patella vulgata. Like its orthologues in deuterostomes, after an early broad ectodermal distribution, PvuSoxB expression only persists in cells competent to form neural structures. In the post-gastrulation larva, PvuSoxB is expressed in the prospective neuroectoderm in the head and in the trunk. No expression can be seen dorsally, around the mouth and the anus, or along the ventral midline. We also report the expression of a Wnt2/13 orthologue (PvuWnt2) in Patella. After gastrulation, PvuWnt2 is expressed in the posterior part of the mouth, along the ventral midline and around the anus. This expression seems to be complementary to that of PvuSoxB in the trunk. We suggest the existence of a fundamental subdivision of the Patella trunk ectoderm into midline (mouth, midline, anus) and more lateral structures.Edited by D. Tautz     

Excitation kinetics during induction of chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence

We present a chlorophyll fluorometer module system which adapts the intensity to the individual leaf sample by adjusting the quantum flux density of the excitation light so that the fluorescence signal is kept constant. This is achieved by means of a feedback power adjustment of the fluorescence exciting laser diode. Thus, the intensity of the excitation light is adapted to the actual need of a particular sample for quantum conversion without applying exaggeratedly high quantum flux density. We demonstrate the influence of the initial laser power chosen at the onset of irradiation and kept constant during fluorescence rise transient within the first second. Examples are shown for measuring upper and lower leaf sides, a single leaf with different pre-darkening periods, as well as yellow, light green and dark green leaves. The novel excitation kinetics during the induction of chlorophyll fluorescence can be used to study the yield and regulation of photosynthesis and its related non-photochemical processes for an individual leaf. It allows not only to sense the present state of pre-darkening or pre-irradiation but also the light environment the leaf has experienced during its growth and development. Thus, the individual physiological capacity and plasticity of each leaf sample can be sensed being of high importance for basic and applied ecophysiological research which makes this new methodology both innovative and informative.     

In vivo analysis of chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence induction

Quantitative characteristics of photosynthetic electron transport were evaluated in vivo on the basis of the multi-exponential analysis of OJIP fluorescence transients induced by saturating actinic light. The OJIP fluorescence curve F(t), measured in Chlamydomonas reinhardtii cells, was transformed into the (1 − F _O/F(t)) × (F _V /F _M)⁻¹ transient, which is shown to relate to PS 2 closure. We assumed that kinetics of PS 2 closure during OJIP rise reflects time-separated processes related to the establishment of redox equilibrium at the PS 2 acceptor side (OJ), PQ pool (JI), and beyond Cyt b/f (IP). Three-exponential fitting was applied to (1 − F _O/F(t)) × (F _V /F _M)⁻¹ transient to obtain lifetimes and amplitudes of the OJ, JI, and IP components of PS 2 closure, which were used to calculate overall rates of reduction and re-oxidation of the PS 2 acceptor side, PQ pool, and intermediates beyond Cyt b/f complex. The results, obtained in the presence of inhibitors, oxidative reagents, and under different stress conditions prove the suggested model and characterize the introduced parameters as useful indicators of photosynthetic function.     

Growth,fluorescence, photosynthetic O<Subscript>2</Subscript> production and pigment content of salt adapted cultures of <Emphasis Type="Italic">Arthrospira</Emphasis> (<Emphasis Type="Italic">Spirulina</Emphasis>) <Emphasis Type="Italic">platensis</Emphasis>

The effect of salt concentration (NaCl) on growth, fluorescence, photosynthetic activities and pigment content of the cyanobacterium Arthrospira platensis has been investigated over 15 days. It has been observed that high NaCl concentration induces an increase of the growth, photosynthetic efficiency (α), phycobilin/chlorophyll ratio and a slight decrease of dark respiration and compensation points. Moreover, high NaCl concentration enhances photosystem II (PSII) activity compared to photosystem I (PSI). Results show that the phycobilin-PSII energy transfer compared to the chlorophyll-PSII (F_695,600/F_695,440) increases. However, data obtained about the maximal efficiency of PSII photochemistry are controversial. Indeed, the Fv/Fm ratio decreases in salt adapted cultures, while at the same time the trapping flux per PSII reaction center (TR₀/RC) and the probability of electron transport beyond Q_A (₀) remain unchanged at the level of the donor and the acceptor sites of PSII. This effect can be attributed to the interference of phycobilin fluorescence with Chl a when performing polyphasic transient measurements.     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.     

Spatiotemporal calcium signaling in a<Emphasis Type="Italic"> Drosophila melanogaster</Emphasis> cell line stably expressing a<Emphasis Type="Italic"> Drosophila</Emphasis> muscarinic acetylcholine receptor

A muscarinic acetylcholine receptor (mAChR), DM1, expressed in the nervous system of Drosophila melanogaster, has been stably expressed in a Drosophila S2 cell line (S2-DM1) and used to investigate spatiotemporal calcium changes following agonist activation. Carbamylcholine (CCh) and oxotremorine are potent agonists, whereas application of the vertebrate M1 mAChR agonist, McN-A-343, results in a weak response. Activation of S2-DM1 receptors using CCh resulted in an increase in intracellular calcium ([Ca²⁺]_i) that was biphasic. Two distinct calcium sources were found to contribute to calcium signaling: (1) internal stores that are sensitive to both thapsigargin and 2-aminoethoxydiphenyl borate and (2) capacitative calcium entry. Spatiotemporal imaging of individual S2-DM1 cells showed that the CCh-induced [Ca²⁺]_i transient resulted from a homogeneous calcium increase throughout the cell, indicative of calcium release from internal stores. In contrast, ionomycin induced the formation of a "calcium ring" at the cell periphery, consistent with external calcium influx.     

Multiple defaults: feminine -<Emphasis Type="Italic">et</Emphasis> and -<Emphasis Type="Italic">a</Emphasis> in Hebrew present tense

In this paper, we study the distribution of the feminine singular suffixes -et and -a in the present tense of Hebrew verb paradigms. The question we ask is which of these two suffixes is the default allomorph. The answer is not trivial. In terms of distribution, -a appears with limited environments and -et is clearly the elsewhere case, and thus the default. In terms of order, however, -et is the feminine singular suffix associated with the present tense, while -a emerges only when -et is blocked. We thus argue for multiple defaults, distinguishing between local and global default; -et is the local default, uniquely associated with feminine singular verbs in the present tense, while -a is the global default, associated with feminine singular but not specified for the present tense. We provide a formal analysis for the distribution of these suffixes within the framework of Optimality Theory, which allows the interaction of phonological constraints with constraints on morpho-syntactic feature mapping. We further study the partially unpredictable distribution of -et and -a in vowel final verbs, and present the results of an experiment where speakers employed unique strategies in order to assign the local default -et.     

A new <Emphasis Type="Italic">Em</Emphasis>-like protein from <Emphasis Type="Italic">Lactuca sativa</Emphasis>, <Emphasis Type="Italic">LsEm1</Emphasis>, enhances drought and salt stress tolerance in <Emphasis Type="Italic">Escherichia coli</Emphasis> and rice

Late embryogenesis abundant (LEA) proteins are closely related to abiotic stress tolerance of plants. In the present study, we identified a novel Em-like gene from lettuce, termed LsEm1, which could be classified into group 1 LEA proteins, and shared high homology with Cynara cardunculus Em protein. The LsEm1 protein contained three different 20-mer conserved elements (C-element, N-element, and M-element) in the C-termini, N-termini, and middle-region, respectively. The LsEm1 mRNAs were accumulated in all examined tissues during the flowering and mature stages, with a little accumulation in the roots and leaves during the seedling stage. Furthermore, the LsEm1 gene was also expressed in response to salt, dehydration, abscisic acid (ABA), and cold stresses in young seedlings. The LsEm1 protein could effectively reduce damage to the lactate dehydrogenase (LDH) and protect LDH activity under desiccation and salt treatments. The Escherichia coli cells overexpressing the LsEm1 gene showed a growth advantage over the control under drought and salt stresses. Moreover, LsEm1-overexpressing rice seeds were relatively sensitive to exogenously applied ABA, suggesting that the LsEm1 gene might depend on an ABA signaling pathway in response to environmental stresses. The transgenic rice plants overexpressing the LsEm1 gene showed higher tolerance to drought and salt stresses than did wild-type (WT) plants on the basis of the germination performances, higher survival rates, higher chlorophyll content, more accumulation of soluble sugar, lower relative electrolyte leakage, and higher superoxide dismutase activity under stress conditions. The LsEm1-overexpressing rice lines also showed less yield loss compared with WT rice under stress conditions. Furthermore, the LsEm1 gene had a positive effect on the expression of the OsCDPK9, OsCDPK13, OsCDPK15, OsCDPK25, and rab21 (rab16a) genes in transgenic rice under drought and salt stress conditions, implying that overexpression of these genes may be involved in the enhanced drought and salt tolerance of transgenic rice. Thus, this work paves the way for improvement in tolerance of crops by genetic engineering breeding.     

Photosystem II photochemistry and physiological parameters of three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis> under salt stress

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Salt stress caused a marked decrease in osmotic potential and a significant accumulation of Na⁺ and Cl⁻ in leaves of both species. Moderate salinity had a stimulating effect on growth rate, net CO₂ assimilation, transpiration and stomatal conductance for the xero-halophytic species. At higher salinities, these physiological parameters decreased significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea they decreased linearly with salinity. Nitraria retusa PSII photochemistry and carotenoid content were unaffected by salinity, but a reduction in chlorophyll content was observed at 800 mM NaCl. Similar results were found in A. halimus, but with a decrease in the efficiency of PSII (F′v/F′m) occurred at 800 mM. Conversely, in M. arborea plants we observed a significant reduction in pigment concentrations and chlorophyll fluorescence parameters. The marked toxic effect of Na⁺ and/or Cl⁻ observed in M. arborea indicates that salt damage effect could be attributed to ions’ toxicity, and that the reduction in photosynthesis is most probably due to damages in the photosynthetic apparatus rather than factors affecting stomatal closure. For the two halophyte species, it appears that there is occurrence of co-limitation of photosynthesis by stomatal and non-stomatal factors. Our results suggest that both N. retusa and A. halimus show high tolerance to both high salinity and photoinhibition while M. arborea was considered as a slightly salt tolerant species.     

<Emphasis Type="Italic">Agrobacterium</Emphasis><Emphasis Type="Italic">tumefaciens</Emphasis>-mediated transformation of callus cells of <Emphasis Type="Italic">Crataegus</Emphasis><Emphasis Type="Italic">aronia</Emphasis>

A genetic transformation system has been developed for callus cells of Crataegus aronia using Agrobacterium tumefaciens. Callus culture was established from internodal stem segments incubated on Murashige and Skoog (MS) medium supplemented with 5 mg l⁻¹ Indole-3-butyric acid (IBA) and 0.5 mg l⁻¹ 6-benzyladenine (BA). In order to optimize the callus culture system with respect to callus growth and coloration, different types and concentrations of plant growth regulators were tested. Results indicated that the best average fresh weight of red colored callus was obtained on MS medium supplemented with 2 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.5 mg l⁻¹ kinetin (Kin) (callus maintenance medium). Callus cells were co-cultivated with Agrobacterium harboring the binary plasmid pCAMBIA1302 carrying the mgfp5 and hygromycin phosphotransferase (hptII) genes conferring green fluorescent protein (GFP) activity and hygromycin resistance, respectively. Putative transgenic calli were obtained 4 weeks after incubation of the co-cultivated explants onto maintenance medium supplemented with 50 mg l⁻¹ hygromycin. Molecular analysis confirmed the integration of the transgenes in transformed callus. To our knowledge, this is the first time to report an Agrobacterium-mediated transformation system in Crataegus aronia.     

Revision of the <Emphasis Type="Italic">Serrulati</Emphasis> species of <Emphasis Type="Italic">Penstemon</Emphasis> section <Emphasis Type="Italic">Saccanthera</Emphasis> subsection <Emphasis Type="Italic">Serrulati</Emphasis>

A revision of Penstemon sect. Saccanthera subsect. Serrulati includes a new species (P. salmonensis), a new variety (P. triphyllus var. infernalis), and the elevation of a subspecies to species (P. curtiflorus), bringing the total number of species to eight, which are keyed and described, complete with nomenclature and type citations.