742. STAUNTONIA CHAPAENSIS

The occurrence of more than a single species of Lardizabalaceae in Thailand is confirmed and the second species, the Vietnamese‐Chinese Stauntonia chapaensis (Gagnep.) Christenh., is described and illustrated here based on the Thai specimens at Crûg Farm Plants.     

743. STAUNTONIA BRACHYANDRA

Stauntonia brachyandra (H.N.Qin) Christenh., was collected in Vietnam in 2003, a new record for the country. This Stauntonia has the largest flowers known in the genus and was previously only known from just across the Vietnamese‐Chinese border in Yunnan. It is described and illustrated here based on material from Crûg Farm Plants.     

820. STAUNTONIA LIBERA

Stauntonia libera, collected as ‘KWJ 12218’ from Vietnam and cultivated by Crûg Farm Plants, is an evergreen vine with scented flowers and edible fruit. It is described and illustrated here and details of the distribution and habitat are also provided. It is a plant with horticultural potential, but remains a rarity in cultivation.     

741. STAUNTONIA LATIFOLIA

Stauntonia latifolia (Wall.) Christenh. is described and illustrated here and its history of introduction is discussed. As Holboellia it was one of the first species of Stauntonia to appear in cultivation, and is currently one of the most widely grown.     

744. STAUNTONIA ANGUSTIFOLIA

Stauntonia angustifolia (Wall.) Wall. ex Christenh., formerly Holboellia angustifolia Wall. is described and illustrated. Its recent history in cultivation in Cambridge is discussed.     

Proteolysis at Arg740 facilitates subsequent bond cleavages during thrombin-catalyzed activation of factor VIII

Thrombin activates factor VIII by proteolysis at three P1 residues: Arg372, Arg740, and Arg1689. Cleavage at Arg372 and Arg1689 are essential for procofactor activation; however cleavage at Arg740 has not been rigorously studied. To evaluate the role for cleavage at Arg740, we prepared and stably expressed two recombinant B-domainless factor VIII mutants, R740H and R740Q to slow and eliminate, respectively, cleavage at this site. Specific activity values for the variants were approximately 50 and 20%, respectively, that of wild-type factor VIII. Activation of factor VIII R740H by thrombin showed an approximately 40-fold reduction in the rate of A2 subunit generation, which reflected an approximately 20-fold reduction in cleavage rate at Arg372. Similarly, a approximately 40-fold rate reduction in cleavage at Arg1689 and consequent generation of the A3-C1-C2 subunit were observed. Rate values for A2 and A3-C1-C2 subunit generation were reduced by >700-fold and approximately 140-fold, respectively, in the R740Q variant. These results suggest that initial cleavage at Arg740 affects cleavage at both Arg372 and Arg1689 sites. Results obtained evaluating proteolysis of the factor VIII mutants by factor Xa revealed more modest rate reductions (<10-fold) in generating A2 and A3-C1-C2 subunits from either variant, suggesting that factor Xa-catalyzed activation of factor VIII was significantly less dependent upon prior cleavage at residue 740 than thrombin. Overall, these results support a model whereby cleavage of factor VIII by thrombin is an ordered pathway with cleavage at Arg740 facilitating cleavages at Arg372 and Arg1689, which result in procofactor activation.     

Antenna organization in green photosynthetic bacteria. 1. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes

Bacteriochlorophyll (BChl) c was extracted from Chloroflexus aurantiacus and purified by reverse-phase high-pressure liquid chromatography. This pigment consists of a complex mixture of homologues, the major component of which is 4-ethyl-5-methylbacteriochlorophyll c stearyl ester. Unlike previously characterized BChls c, the pigment from C. aurantiacus is a racemic mixture of diastereoisomers with different configurations at the 2a chiral center. Diluting a concentrated methylene chloride solution of BChl c with hexane produces an oligomer with absorption maxima at 740-742 and at 460-462 nm. Both the absorption spectrum and the fluorescence emission spectrum (maximum at 750 nm) of this oligomer closely match those of BChl c in chlorosomes. Further support for this model comes from the ability of alcohols, which disrupt BChl c oligomers by ligating the central Mg atom, to convert BChl c in chlorosomes to a monomeric form when added in low concentrations. The lifetime of fluorescence from the 740 nm absorbing BChl c oligomer is about 80 ps. Although exciton quenching might be unusually fast in the in vitro BChl c oligomer because of its large size and/or the presence of minor impurities, this result suggests that energy transfer from the BChl c antenna in chlorosomes must be very fast if it is to be efficient.     

Photo-oxidation of P740, the primary electron donor in photosystem I from Acaryochloris marina

Fourier transform infrared spectroscopy (FTIR) difference spectroscopy in combination with deuterium exchange experiments has been used to study the photo-oxidation of P740, the primary electron donor in photosystem I from Acaryochloris marina. Comparison of (P740(+)-P740) and (P700(+)-P700) FTIR difference spectra show that P700 and P740 share many structural similarities. However, there are several distinct differences also: 1), The (P740(+)-P740) FTIR difference spectrum is significantly altered upon proton exchange, considerably more so than the (P700(+)-P700) FTIR difference spectrum. The P740 binding pocket is therefore more accessible than the P700 binding pocket. 2), Broad, "dimer" absorption bands are observed for both P700(+) and P740(+). These bands differ significantly in substructure, however, suggesting differences in the electronic organization of P700(+) and P740(+). 3), Bands are observed at 2727(-) and 2715(-) cm(-1) in the (P740(+)-P740) FTIR difference spectrum, but are absent in the (P700(+)-P700) FTIR difference spectrum. These bands are due to formyl CH modes of chlorophyll d. Therefore, P740 consists of two chlorophyll d molecules. Deuterium-induced modification of the (P740(+)-P740) FTIR difference spectrum indicates that only the highest frequency 13(3) ester carbonyl mode of P740 downshifts, indicating that this ester mode is weakly H-bonded. In contrast, the highest frequency ester carbonyl mode of P700 is free from H-bonding. Deuterium-induced changes in (P740(+)-P740) FTIR difference spectrum could also indicate that one of the chlorophyll d 3(1) carbonyls of P740 is hydrogen bonded.     

Tyrosine 740 phosphorylation of discoidin domain receptor 2 by Src stimulates intramolecular autophosphorylation and Shc signaling complex formation

DDR2 is a receptor tyrosine kinase whose activating ligands are various collagens. DDR2-mediated cellular signaling has been shown to require Src activity. However, the precise mechanism underlying the Src dependence of DDR2 signaling is unknown. Here, using baculoviral co-expression of the DDR2 cytosolic domain and Src, we show that Src targets three tyrosine residues (Tyr-736, Tyr-740, and Tyr-741) in the activation loop of DDR2 for phosphorylation. This phosphorylation by Src stimulates DDR2 cis-autophosphorylation of additional tyrosine residues. In vitro Shc binding assays demonstrate that phosphotyrosines resulting from DDR2 autophosphorylation are involved in Shc binding to the DDR2 cytosolic domain. Mutating tyrosine 740 of DDR2 to phenylalanine stimulates autophosphorylation of DDR2 to an extent similar to that resulting from Src phosphorylation of DDR2. In addition, the DDR2 Y740F mutant protein displays collagen-independent, constitutively activated signaling. These findings suggest that tyrosine 740 inhibits DDR2 autophosphorylation. Collectively, our findings are consistent with the following mechanism for Src-dependent DDR2 activation and signaling: 1) ligand binding promotes phosphorylation of Tyr-740 in the DDR2 activation loop by Src; 2) Tyr-740 phosphorylation stimulates intramolecular autophosphorylation of DDR2; 3) DDR2 autophosphorylation generates cytosolic domain phosphotyrosines that promote the formation of DDR2 cytosolic domain-Shc signaling complexes.     

Efficient Solar‐Driven Water Oxidation over Perovskite‐Type BaNbO2N Photoanodes Absorbing Visible Light up to 740 nm

Photoelectrochemical water splitting using semiconductors absorbing a wide range of visible light is a potentially attractive means of harvesting large portions of the solar spectrum. However, this is also very challenging because narrowing the semiconductor band gap lowers the driving force for photoreactions. Herein, a highly active perovskite BaNbO₂N exhibiting photoexcitation up to 740 nm for water oxidation is reported. The synthesis route, consisting of moderate nitridation and subsequent annealing in inert Ar flow, enhances the crystallinity of the BaNbO₂N surface without inducing the reduction of the Nb species. As a result, a particulate BaNbO₂N photoanode exhibits a photocurrent of 5.2 mA cm^?2 at 1.23 V_RHE under simulated solar irradiation, which is the highest yet reported for an oxynitride responsive at wavelengths above 600 nm. Suppressing the reduction of B‐site cations during the synthesis of perovskite AB(O,N)₃, which otherwise results in surface defects or impurities, is critical for achieving high water oxidation activity.     

An amino acid substitution at position 740 in sigma70 of Ralstonia solanacearum strain OE1-1 affects its in planta growth

Growth of Ralstonia solanacearum strain OE1-1 in roots after invasion is required for virulence. An Arg740Cys substitution in sigma(70) of OE1-1 resulted in loss of in planta growth and virulence. The negative dominance of mutant sigma(70) over the wild-type protein suggested that the amino acid substitution may affect the in planta growth of OE1-1, leading to a lack of virulence.     

Daylight spectra (400–740 nm) beneath sunny,blue skies in Tasmania,and the effect of a forest canopy

Abstract The photosynthetically active radiation (PAR) incident on a horizontal surface at an open mountain site is positively correlated with solar altitude for sunny, blue sky conditions. The proportion of red light in PAR decreases with increasing solar altitude, while that of blue increases. These results are consistent with the wavelength dependency of Rayleigh and Mie scattering. The ratio of near infrared radiation to PAR decreases with increasing solar altitude towards solar noon and with decreasing solar altitude towards sunset. Thus surface reflection seems to be an important part of the light climate. The relative transmission of daylight through a forest canopy to a horizontal surface is not correlated with solar altitude for sunny, blue sky conditions at a mountain site. The amount of diffuse daylight is negatively correlated with per cent canopy interception, and the amount of direct sunlight is negatively correlated with per cent solar track interception. Daylength is negatively correlated with both canopy and solar track interceptions. The proportion of red light in PAR increases with increasing solar altitude, while that of blue decreases. These results are opposite those for the open site and are due to the spatial patterns of canopy obstruction of the sky vault, and of the spectral quality of daylight across the sky. The ratio of near infrared radiation to PAR in shadelight increases with increasing canopy interception due to the selective scattering properties of the canopy. The ratio for shadelight is positively correlated with the ratio for sunflecks.     

Vibrational mode frequency calculations of chlorophyll-<Emphasis Type="Italic">d</Emphasis> for assessing (P740<Superscript>+</Superscript>-P740) FTIR difference spectra obtained using photosystem I particles from <Emphasis Type="Italic">Acaryochloris marina</Emphasis>

Acaryochloris marina is an oxygen-evolving organism that utilizes chlorophyll-d for light induced photochemistry. In photosystem I particles from Acaryochloris marina, the primary electron donor is called P740, and it is thought that P740 consist of two chlorophyll-d molecules. (P740⁺-P740) FTIR difference spectra have been produced, and vibrational features that are specific to chlorophyll-d (and not chlorophyll-a) were observed, supporting the idea that P740 consists chlorophyll-d molecules. Although bands in the (P740⁺-P740) FTIR difference spectra were assigned specifically to chlorophyll-d, how these bands shifted, and how their intensities changed, upon cation formation was never considered. Without this information it is difficult to draw unambiguous conclusions from the FTIR difference spectra. To gain a more detailed understanding of cation induced shifting of bands associated with vibrational modes of P740 we have used density functional theory to calculate the vibrational properties of a chlorophyll-d model in the neutral, cation and anion states. These calculations are shown to be of considerable use in interpreting bands in (P740⁺-P740) FTIR difference spectra. Our calculations predict that the 3¹ formyl C–H mode of chlorophyll-d upshifts/downshifts upon cation/anion formation, respectively. The mode intensity also decreases/increases upon cation/anion formation, respectively. The cation induced bandshift of the 3¹ formyl C–H mode of chlorophyll-d is also strongly dependant on the dielectric environment of the chlorophyll-d molecules. With this new knowledge we reassess the interpretation of bands that were assigned to 3¹ formyl C–H modes of chlorophyll-d in (P740⁺-P740) FTIR difference spectra. Considering our calculations in combination with (P740⁺-P740) FTIR DS we find that the most likely conclusions are that P740 is a dimeric Chl-d species, in an environment of low effective dielectric constant (∼2–8). In the P740⁺ state, charge is asymmetrically distributed over the two Chl-d pigments in a roughly 60:40 ratio. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.