Optical properties of developing pip and stone fruit reveal underlying structural changes

Analyzing the optical properties of fruits represents a powerful approach for non‐destructive observations of fruit development. With classical spectroscopy in the visible and near‐infrared wavelength ranges, the apparent attenuation of light results from its absorption or scattering. In horticultural applications, frequently, the normalized difference vegetation index (NDVI) is employed to reduce the effects of varying scattering properties on the apparent signal. However, this simple approach appears to be limited. In the laboratory, with time‐resolved reflectance spectroscopy, the absorption coefficient, μ_a, and the reduced scattering coefficient, μ_s′, can be analyzed separately. In this study, these differentiated optical properties were recorded (540–940 nm), probing fruit tissue from the skin up to 2 cm depth in apple (Malus × domestica ‘Elstar’) and plum (Prunus domestica ‘Tophit plus’) harvested four times (65–145 days after full bloom). The μ_a spectra showed typical peak at 670 nm of the chlorophyll absorption. The μ_s′ at 670 nm in apple changed by 14.7% (18.2–15.5 cm^?1), while in plum differences of 41.5% (8.5–5.0 cm^?1) were found. The scattering power, the relative change of μ_s′, was zero in apple, but enhanced in plum over the fruit development period. This mirrors more isotropic and constant structures in apple compared with plum. For horticultural applications, the larger variability in scattering properties of plum explains the discrepancy between commercially assessed NDVI values or similar indices and the absolute μ_a values in plum (R < 0.05), while the NDVI approach appeared reasonable in apple (R ≥ 0.80).     

Dynamics of long-term continuous culture of Limnospira indica in an air-lift photobioreactor

MELiSSA (Microecological Life Support System Alternative) is a developing technology for regenerative life support to enable long-term human missions in Space and has developed a demonstration Pilot Plant. One of the components of the MELiSSA Pilot Plant system is an 83L external loop air-lift photobioreactor (PBR) where Limnospira indica (previously named Arthrospira sp. PC8005) is axenically cultivated in a continuous operation mode for long-periods. Its mission is to provide O₂ and consume CO₂ while producing edible material. Biological and process characterization of this PBR is performed by analysing the effect of two main variables, dilution rate (D) and PFD (Photon Flux Density) illumination. A maximum oxygen productivity () of 1.35 mmol l⁻¹ h⁻¹ is obtained at a D of 0.025 h⁻¹ and PFD of 930 µmol m⁻² s⁻¹. Photoinhibition can occur when a 1 g l⁻¹ cell density culture is exposed to PFD higher than 1700 µmol m⁻² s⁻¹. This process is reversible if the illumination is returned to dim light (150 µmol m⁻² s⁻¹), proving the cell adaptability and capacity to respond at different illumination conditions. Influence of light intensity in cell composition is also described. Specific photon flux density (qPFD) has a direct effect on phycobiliproteins and chlorophyll content causing a decrease of 62.5% and 47.8%, respectively, when qPFD increases from 6.1 to 19.2 µmol g⁻¹ s⁻¹. The same trend is observed for proteins and the opposite for carbohydrate content. Morphological and spiral structural features of L. indica are studied by confocal microscopy, and size distribution parameters are quantified. A direct effect between trichome width and CDW/OD ratio is observed. Changes in size distribution are not correlated with environmental factors, further confirms the adaptation capacity of the cells. The systematic analysis performed provides valuable insights to understand the key performance criteria of continuous culture in air-lift PBRs.     

Physicochemical studies on xylinan (acetan). III. Hydrodynamic characterization by analytical ultracentrifugation and dynamic light scattering

A laboratory-made sample of the polysaccharide xylinan (acetan) has been further characterized with respect to (i) purity, (ii) molar mass and polydispersity, and (iii) gross conformation by a combination of hydrodynamic measurements (sedimentation velocity and equilibrium analytical ultracentrifugation, viscometry, and dynamic light scattering) in aqueous NaCl (I = 0.10 mol·L⁻¹). Sedimentation velocity diagrams recorded using Schlieren optics revealed highly pure material sedimenting as a single boundary [s^o_20.w = 9.5 ± 0.7) S; k_s = (273 ± 112) mL/g]. The hypersharp nature of these boundaries is symptomatic of a polydisperse and highly nonideal (in the thermodynamic sense) system. Low speed sedimentation equilibrium in the analytical ultracentrifuge using Rayleigh interference optics and two different types of extrapolation procedure (involving point and whole-cell molar masses) gave a weight average molar mass M_w of (2.5 ± 0.5) × 10⁻⁶ g·mol⁻¹ and also a second virial coefficient, B = (2.8 ± 0.7) × 10⁻⁴ mL·mol·g⁻², both values in good agreement with those from light scattering-based procedures (Part II of this series). A dynamic Zimm plot from dynamic light scattering measurements gave a z-average translational diffusion coefficient D^o_20.w = (3.02 ± 0.05) × 10⁻⁸ cm²·s⁻¹ and the concentration-dependence parameter k_D = (370 ± 15) mL/g. Combination of s^o_20.w with D^o_20.w via the Svedberg equation gave another estimate for M_w of ≅ 2.4 × 10⁶ g/mol, again in good agreement. Both the Wales-van Holde ratio (k_s/[η]) ≅ 0.4 (with [η] = (760 ± 77) mL/g) and the ρ-parameter (ratio of the radius of gyration from static light scattering to the hydrodynamic radius from dynamic light scattering) as ρ > 2.0 all indicate an extended conformation for the macromolecules in solution. These findings, plus Rinde-type simulations of the sedimentation equilibrium data are all consistent with the interpretation in terms of a unimodal wormlike coil model performed earlier. © 1996 John Wiley & Sons, Inc.     

Andreaea Hartmanii Thed.—A histological study

Abstract

Photosynthetic responses to light intensity were studied under laboratory conditions in seven bryophyte species from evergreen laurel forest, a threatened habitat, on Terceira island in the Azores. Four mosses (Andoa berthelotiana, Echinodium prolixum, Fissidens serrulatus, Myurium hochstetteri) and three liverworts (Bazzania azorica, Frullania tamarisci, Lepidozia cupressina) were selected to encompass a range of potential responses to variations in the forest light environment. Carbon dioxide exchange measurements were made, using an infra-red gas-analyser, at photosynthetic photon flux densities (PPFD) of 0-900 µmol m^-2 s^-1 and a mean temperature of 21°C in fully hydrated shoots. Most species achieved light saturation of photosynthesis below 30 µmol m^-2 s^-1, the lowest value being for A. berthelotiana (20 µmol m^-2 s^-1) and the highest for M. hochstetteri (68 µmol m^-2 s^-1). The liverwort F. tamarisci had the highest maximum photosynthetic rate (P_max, 23 µmol CO₂ g^-1 h^-1) whereas P_max was lowest in the mosses E. prolixum and M. hochstetteri (10 µmol CO₂ g^-1 h^-1). Dark respiration rate, a critical factor in toleration of shade by forest floor plants, was highest in the species with the highest values for P_max. Compensation point was extremely low (7 µmol photons m^-2 s^-1) in Fissidens serrulatus, a species found in the deep shade of forest ravines and caves, and highest in M. hochstetteri a moss restricted to better illuminated habitats within and outside the forest. No photoinhibition was detected during the relatively short exposures to high irradiances. Comparison of these responses with data on the forest light environment indicates that, despite the possession of considerable shade adaptations, during winter in the evergreen laurel forest, low light levels may often limit photosynthetic rates of the bryophytes.     

Flow injection chemiluminescence study of acridinium ester stability and kinetics of decomposition

Decomposition of phenyl acridinium-9-carboxylate is monitored using electrogenerated chemiluminescence in a flow system. The formation of the pseudobase from the acridinium ester [AE] is described by rate = k′₁[AE] + k″₁[AE][OH^?]^0.5, where k′₁ = 0.020 ± 0.006 s^?1 and k″₁ = 2.1 ± 0.8 (L/mol)^?0.5 s^?1. Irreversible decomposition of the pseudobase is described by rate = k′₂[AE][OH^?], where k′₂ = 20.1 ± 3.8 (L/mol s). These kinetic equations, plus measurement of variation in emission intensity for constant acridinium ester concentration, are used to predict the resulting emission intensity v. pH behaviour given various contact times (in the 0.25 to 25 s range) for the acridinium ester to be in an alkaline solution prior to initiation of the chemiluminescence reaction.     

Photosynthetic and biochemical characterization of in vitro-derived African violet (Saintpaulia ionantha H. Wendl) plants to ex vitro conditions

African violet (Saintpaulia ionantha H. Wendl) is one of the most easily and commonly tissue-cultured ornamental plants. Despite this, there are limited reports on photosynthetic capacity and its impact on the plant quality during acclimatization. Various growth, photosynthetic and biochemical parameters and activities of antioxidant enzymes and dehydrins of micropropagated plants were assessed under three light intensities (35, 70, and 100 µmol m^?2 s^?1 photosynthetic photon flux density – PPFD). Fresh and dry plant biomass, plant height, and leaf area were optimal with high irradiance (70–100 µmol m^?2 s^?1 PPFD). Chlorophyll and carotenoid contents and net photosynthesis were optimal in plants grown under 70 µmol m^?2 s^?1 PPFD. Stomatal resistance, malondialdehyde content, and F_v/F_m values were highest at low light irradiance (35 µmol m^?2 s^?1 PPFD). The activities of three antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase, increased as light irradiance increased, signaling that high light irradiance was an abiotic stress. The accumulation of 55, 33, and 25 kDa dehydrins was observed with all light treatments although the expression levels were highest at 35 µmol m^?2 s^?1 PPFD. Irradiance at 70 µmol m^?2 s^?1 PPFD was suitable for the acclimatization of African violet plants. Both low and high irradiance levels (35 and 100 µmol m^?2 s^?1 PPFD) induced the accumulation of antioxidants and dehydrins in plants which reveals enhanced stress levels and measures to counter it.     

Photon irradiance required to support optimal growth and interrelations between irradiance and pigment composition in the green alga Haematococcus pluvialis

The aim of the work was to find the optimal photon irradiance for the growth of green cells of Haematococcus pluvialis and to study the interrelations between changes in photochemical parameters and pigment composition in cells exposed to photon irradiances between 50 and 600?µmol?m^?2?s^?1 and a light:dark cycle of 12:12?h. Productivity of cultures increased with irradiance. However, the rate of increase was higher in the range 50–200?µmol?^?2?s^?1. The carotenoid content increased with increasing irradiance, while the chlorophyll content decreased. The maximum quantum yield of PSII (F_v/F_m) gradually declined from 0.76 at the lowest irradiance of 50?µmol?^?2?s^?1 to 0.66 at 600?µmol?^?2?s^?1. Photosynthetic activity showed a drop at the end of the light period, but recovered fully during the following dark phase. A steep increase in non-photochemical quenching was observed when cultures were grown at irradiances above 200?µmol?^?2?s^?1. A sharp increase in the content of secondary carotenoids also occurred above 200?µmol?m^?2?s^?1. According to our results, with H. pluvialis green cells grown in a 5-cm light path device, 200?µmol?^?2?s^?1 was optimal for growth, and represented a threshold above which important changes in both photochemical parameters and pigment composition occurred.     

Control of transpiration in an irrigated Eucalyptus globulus Labill. plantation

Stomatal conductance and transpiration were measured concurrently in an irrigated Eucalyptus globulus Labill. plantation. Canopy stomatal conductance, canopy boundary layer conductance and the dimensionless decoupling coefficient (Ω) were calculated (a) summing the conductance of three canopy layers (g_c) and (b) weighting the contribution of foliage according to the amount of radiation received (g_c′). Canopy transpiration was then calculated from g_c and g_c′ for Ω = 1 (E_eq), Ω = 0 (E_imp) and by weighting E_eq and E_imp using Ω (E_Ω). E_eq, E_imp and E_Ω were compared to transpiration estimated from measurements of heat pulse velocity. The mean value of Ω was 0·63. Transpiration calculated using g_c and assuming perfect coupling (12·5 ± 0·9 mmol m^?2 s^?1) significantly overestimated measured values (8·7 ± 0·8 mmol m^?2 s^?1). Good estimates of canopy transpiration were obtained either (a) calculating E_Ω separately for the individual canopy layers or (b) treating the canopy as a single layer and using g_c′ in a calculation of E_imp (Ω = 0). The latter approach only required measurement of stomatal conductance at a single canopy position but would be unsuitable for use in combined models of canopy transpiration and assimilation. It should however, be suitable for estimating transpiration in forests regardless of the degree of coupling.     

Susceptibility to photoinhibition of three deciduous broadleaf tree species with different successional traits raised under various light regimes

The susceptibility to photoinhibition of tree species from three different successional stages were examined using chlorophyll fluorescence and gas exchange techniques. The three deciduous broadleaf tree species were Betula platyphylla var. japonica, pioneer and early successional, Quercus mongolica, intermediate shade‐tolerant and mid‐successional, and Acer mono, shade‐tolerant and late successional. Tree seedlings were raised under three light regimes: full sunlight (open), 10% full sun, and 5% full sun. Susceptibility to photoinhibition was assessed on the basis of the recovery kinetics of the ratio of vaviable to maximum fluorescence (F_v/F_m) of detached leaf discs exposed to about 2000 μmol m^?1 s^?1 photon flux density (PFD) for 2 h under controlled conditions (25 to 28 °C, fully hydrated). Differences in susceptibility to photodamage among species were not significant in the open and 10% full sun treatments. But in 5% full sun, B. platyphylla sustained a significantly greater photodamage than other species, probably associated with having the lowest photosynthetic capacity indicated by light‐saturated photosynthetic rate (B. platyphylla, 9·87, 5·85 and 2·82; Q. mongolica, 8·05, 6·28 and 4·41; A. mono, 7·93, 6·11 and 5·08 μmol CO₂ m^?1 s^?1for open, 10% and 5% full sun, respectively). To simulate a gap formation and assess its complex effects including high temperature and water stress in addition to strong light on the susceptibility to photoinhibition, we examined photoinhibition in the field by means of monitoring ΔF/F′_m on the first day of transfer to natural daylight. Compared with ΔF/F′_m in AM, the lower ΔF/F′_m in PM responding to lower PFD following high PFD around noon indicated that photoinhibition occurred in plants grown in 10 and 5% full sun. The diurnal changes of ΔF/F′_m showed that Q. mongolica grown in 5% full sun was less susceptible to photoinhibition than A. mono although they showed little differences both in photosynthetic capacity in intact leaves and susceptibility to photoinhibition based on leaf disc measurements. These results suggest that shade‐grown Q. mongolica had a higher tolerance for additional stresses such as high temperature and water stress in the field, possibly due to their lower plasticity in leaf anatomy to low light environment.     

Comparative characterization of the two primary pumps, H+-ATPase and Na+-ATPase, in the plasma membrane of the marine alga Tetraselmis viridis

The transport characteristics of the plasma membrane H⁺‐ATPase (PMHA) and Na⁺‐ATPase (PMNA) from marine unicellular green alga Tetraselmis viridis Rouch. were studied using sealed plasma membrane vesicles isolated from this species. The activities of the ATPases were investigated by monitoring the ATP‐dependent pH changes in the vesicle lumen. PMHA operation led to acidification of the vesicle lumen, whereas Na⁺ translocation into plasma membrane vesicles catalysed by PMNA was accompanied by H⁺ efflux, namely the alkalization of the vesicle lumen (Balnokin et al., FEBS Lett 462: 402–406, 1999). The intravesicular acidification and alkalization were detected with the ΔpH probe acridine orange and the pH probe pyranine, respectively. PMHA and PMNA were found to operate in distinct pH regions, maximal activity of PMHA being observed at pH 6.5 and that of PMNA at pH 7.8. Kinetic studies revealed that the ATPases have similar affinities to their primary substrate, MgATP complex (an apparent K_m = 34 ± 6.2 µM for PMHA and 73 ± 8.7 µM for PMNA). At the same time, the ATPases were differently affected by free Mg²⁺ and ATP. Free Mg²⁺ appeared to be a mixed‐type inhibitor for PMNA (K_i′ = 210 µM) but it did not suppress PMHA. Conversely, free ATP markedly suppressed PMHA being a mixed‐type inhibitor (K_i′ = 330 µM), but PMNA was affected by free ATP only slightly. Furthermore, the ATPases substantially differed in their sensitivities to the inhibitors of membrane ATPases, such as orthovanadate, N‐ethylmaleimide and N,N′‐dicyclohexylcarbodiimide. The differences found in the properties of the PMHA and PMNA are discussed in terms of regulation of their activities and their capacity to be involved in cytosolic ion homeostasis in T. viridis cells.     

Soil-surface carbon dioxide efflux and microbial biomass in relation to tree density 13 years after a stand replacing fire in a lodgepole pine ecosystem

The effects of fire on soil‐surface carbon dioxide (CO₂) efflux, F_S, and microbial biomass carbon, C_mic, were studied in a wildland setting by examining 13‐year‐old postfire stands of lodgepole pine differing in tree density (< 500 to > 500 000 trees ha^?1) in Yellowstone National Park (YNP). In addition, young stands were compared to mature lodgepole pine stands (～110‐year‐old) in order to estimate ecosystem recovery 13 years after a stand replacing fire. Growing season F_S increased with tree density in young stands (1.0 µmol CO₂ m^?2 s^?1 in low‐density stands, 1.8 µmol CO₂ m^?2 s^?1 in moderate‐density stands and 2.1 µmol CO₂ m^?2 s^?1 in high‐density stands) and with stand age (2.7 µmol CO₂ m^?2 s^?1 in mature stands). Microbial biomass carbon in young stands did not differ with tree density and ranged from 0.2 to 0.5 mg C g^?1 dry soil over the growing season; C_mic was significantly greater in mature stands (0.5–0.8 mg C g^?1 dry soil). Soil‐surface CO₂ efflux in young stands was correlated with biotic variables (above‐ground, below‐ground and microbial biomass), but not with abiotic variables (litter and mineral soil C and N content, bulk density and soil texture). Microbial biomass carbon was correlated with below‐ground plant biomass and not with soil carbon and nitrogen, indicating that plant activity controls not only root respiration, but C_mic pools and overall F_S rates as well. These findings support recent studies that have demonstrated the prevailing importance of plants in controlling rates of F_S and suggest that decomposition of older, recalcitrant soil C pools in this ecosystem is relatively unimportant 13 years after a stand replacing fire. Our results also indicate that realistic predictions and modeling of terrestrial C cycling must account for the variability in tree density and stand age that exists across the landscape as a result of natural disturbances.     

Weak Electron Phonon Coupling and Deep Level Impurity for High Thermoelectric Performance Pb1−xGaxTe

High ZT of 1.34 at 766 K and a record high average ZT above 1 in the temperature range of 300‐864 K are attained in n‐type PbTe by engineering the temperature‐dependent carrier concentration and weakening electron–phonon coupling upon Ga doping. The experimental studies and first principles band structure calculations show that doping with Ga introduces a shallow level impurity contributing extrinsic carriers and imparts a deeper impurity level that ionizes at higher temperatures. This adjusts the carrier concentration closer to the temperature‐dependent optimum and thus maximizes the power factor in a wide temperature range. The maximum power factor of 35 µW cm⁻¹ K⁻² is achieved for the Pb_0.98Ga_0.02Te compound, and is maintained over 20 µWcm⁻¹ K⁻² from 300 to 767 K. Band structure calculations and X‐ray photoelectron spectroscopy corroborate the amphoteric role of Ga in PbTe as the origin of shallow and deep levels. Additionally, Ga doping weakens the electron–phonon coupling, leading to high carrier mobilities in excess of 1200 cm² V⁻¹ s⁻¹. Enhanced point defect phonon scattering yields a reduced lattice thermal conductivity. This work provides a new avenue, beyond the conventional shallow level doping, for further improving the average ZT in thermoelectric materials.     

Light‐Dependent and Aeration‐Independent Gram‐Scale Hydroxylation of Cyclohexane to Cyclohexanol by CYP450 Harboring Synechocystis sp. PCC 6803

Oxygenase‐containing cyanobacteria constitute promising whole‐cell biocatalysts for oxyfunctionalization reactions. Photosynthetic water oxidation thereby delivers the required cosubstrates, that is activated reduction equivalents and O₂, sustainably. A recombinant Synechocystis sp. PCC 6803 strain showing unprecedentedly high photosynthesis‐driven oxyfunctionalization activities is developed, and its technical applicability is evaluated. The cells functionally synthesize a heterologous cytochrome P450 monooxygenase enabling cyclohexane hydroxylation. The biocatalyst‐specific reaction rate is found to be light‐dependent, reaching 26.3 ± 0.6 U g_CDW^?1 (U = μmol min^?1 and cell dry weight [CDW]) at a light intensity of 150 µmol_photons m^?2 s^?1. In situ substrate supply via a two‐liquid phase system increases the initial specific activity to 39.2 ± 0.7 U g_CDW^?1 and stabilizes the biotransformation by preventing cell toxification. This results in a tenfold increased specific product yield of 4.5 g_cyclohexanol g_CDW^?1 as compared to the single aqueous phase system. Subsequently, the biotransformation is scaled from a shake flask to a 3 L stirred‐tank photobioreactor setup. In situ O₂ generation via photosynthetic water oxidation allows a nonaerated process operation, thus circumventing substrate evaporation as the most critical factor limiting the process performance and stability. This study for the first time exemplifies the technical applicability of cyanobacteria for aeration‐independent light‐driven oxyfunctionalization reactions involving highly toxic and volatile substrates.     

A quasi-elastic laser light scattering study of tubulin and microtubule protein from bovine brain

Quasi-elastic light scattering has been used to characterize the oligomeric properties of solutions of glycerol-cycled bovine microtubule protein, and the properties of the 30 S oligomeric species and 6 S tubulin heterodimer prepared by gel filtration on Sepharose 6B. It is shown that in dimer preparations, as little as 0.04% by number of 30 S rings would account for the difference between an observed mean diffusion coefficient D_{20, W} = 3.1 × 10^?7 cm² s^?1 and the value of D_{20, W} = 5.1 × 10^?7 cm² s^?1 calculated for tubulin dimer of M_rel 100,000. The 30 S ring has an observed diffusion coefficient of D_{20, W} = 0.49 × 10^?7 cm² s^?1. These values are not changed significantly by the presence of 4 m-glycerol, indicating the persistence of 6 S and 30 S forms for dimer and ring, respectively.Mixtures of ring and dimer components of this preparation behave as a non-interacting two-component system, indicating the absence of substantial re-equilibration between the species at 5 °C and pH 6.5.The effect of salt on ring and microtubule protein samples indicates partial dissociation, consistent with the formation of additional intermediate oligomeric forms.In quasi-elastic light scattering measurements adapted to kinetic studies, changes in the oligomeric composition of microtubule protein are detected in the early stages of the reversible assembly process at pH 6.5. A 25% decrease in scattered light intensity, without significant change in mean diffusion coefficient, indicates the lability of the ring oligomeric structures, which undergo partial transformation to alternative oligomeric species under these assembly conditions.     

Effects of salinity,light intensity and sediment on growth,pigments, agar production and reproduction in Gracilaria tenuistipitata from Songkhla Lagoon in Thailand

The effects of salinity, light intensity and sediment on Gracilaria tenuistipitata C.F. Chang & B.M. Xia on growth, pigments, agar production, and net photosynthesis rate were examined in the laboratory under varying conditions of salinity (0, 25 and 33 psu), light intensity (150, 400, 700 and 1000 µmol photons m^?2 s^?1) and sediment (0, 0.67 and 2.28 mg L^?1). These conditions simulated field conditions, to gain some understanding of the best conditions for cultivation of G. tenuistipitata. The highest growth rate was at 25 psu, 700 µmol photons m^?2 s^?1 with no sediments, that provided a 6.7% increase in weight gain. The highest agar production (24.8 ± 3.0 %DW) was at 25 psu, 150–400 µmol photons m^?2 s^?1 and no sediment. The highest pigment contents were phycoerythrin (0.8 ± 0.5 mg g^?1FW) and phycocyanin (0.34 ± 0.05 mg g^?1 FW) produced in low light conditions, at 150 µmol photons m^?2 s^?1. The highest photosynthesis rate was 161.3 ± 32.7 mg O₂ g^?1 DW h^?1 in 25 psu, 400 µmol photons m^?2 s^?1 without sediment in the short period of cultivation, (3 days) and 60.3 ± 6.7 mg O₂ g^?1 DW h^?1 in 25 psu, 700 µmol photons m^?2 s^?1 without sediment in the long period of cultivation (20 days). The results indicated that salinity was the most crucial factor affecting G. tenuistipitata growth and production. This would help to promote the cultivation of Gracilaria cultivation back into the lagoon using these now determined baseline conditions. Extrapolation of the results from the laboratory study to field conditions indicated that it was possible to obtain two crops of Gracilaria a year in the lagoon, with good yields of agar, from mid‐January to the end of April (dry season), and from mid‐July to the end of September (first rainy season) when provided sediment was restricted.     

Can light-saturated photosynthesis in lowland tropical forests be estimated by one light level?

Leaf-level net photosynthesis (A_n) estimates and associated photosynthetic parameters are crucial for accurately parameterizing photosynthesis models. For tropical forests, such data are poorly available and collected at variable light conditions. To avoid over- or underestimation of modeled photosynthesis, it is critical to know at which photosynthetic photon flux density (PPFD) photosynthesis becomes light-saturated. We studied the dependence of A_n on PPFD in two tropical forests in French Guiana. We estimated the light saturation range, including the lowest PPFD level at which A_sat (A_n at light saturation) is reached, as well as the PPFD range at which A_sat remained unaltered. The light saturation range was derived from photosynthetic light-response curves, and within-canopy and interspecific differences were studied. We observed wide light saturation ranges of A_n. Light saturation ranges differed among canopy heights, but a PPFD level of 1,000 µmol m⁻² s⁻¹ was common across all heights, except for pioneer trees species that did not reach light saturation below 2,000 µmol m⁻² s⁻¹. A light intensity of 1,000 µmol m⁻² s⁻¹ sufficed for measuring A_sat of climax species at our study sites, independent of the species or the canopy height. Because of the wide light saturation ranges, results from studies measuring A_sat at higher PPFD levels (for upper canopy leaves up to 1,600 µmol m⁻² s⁻¹) are comparable with studies measuring at 1,000 µmol m⁻² s⁻¹.     

Effects of age and size on critical swimming speed of juvenile Chinese sturgeon Acipenser sinensis at seasonal temperatures

Changes in the critical swimming speed (U_crit, cm s^?1) with ontogeny of 2·5–12·5 month‐old juvenile anadromous Chinese sturgeon Acipenser sinesis were measured in a modified Blazka‐type swimming tunnel. The absolute U_crit increased with length, mass and age; the relative U^′_crit (body lengths, s^?1), however, decreased. Juvenile A. sinesis did not display a parr–smolt transformation at the length or age threshold to tolerate full‐strength seawater.     

Physical measurements on the lipid-containing bacteriophage φ6

Bacteriophage φ6 has been studied by small-angle X-ray scattering, intensity-fluctuation spectroscopy, analytical ultracentrifugation, and spectroscopy. The sedimentation coefficient (s₂₀⁰, w) is 375 S, the diffusion coefficient (D₂₀⁰, w) is 2.66 · 10^?8 cm²/s. Using the Svedberg equation and an estimate of the partial specific volume, the M_r is 1.49 ± 0.32 · 10⁸.A simple model which describes φ6, is a central sphere consisting of RNA and protein of radius 330 Å and an outer shell of low electron density 40 Å thick. The RNA may form five concentric shells in the region $\text{r = 140?290}\text{A}\text{?}$     

Rapid, reversible alterations in spinach thylakoid appression upon changes in light intensity

Changes in light quantity and quality cause structural changes within the thylakoid membrane; long‐term responses have been described for so‐called ‘sun’ and ‘shade’ leaves. Many leaves, however, experience changes in irradiance on a time scale of minutes due to self‐shading and sun flecks. In this study, mature, attached spinach leaves were grown at 300 µmol photons m^?2 s^?1 then rapidly switched to a different light treatment. The treatment irradiances were 10, 800 or 1500 µmol m^?2 s^?1 for 10 min, or 10 or 20 min of self‐shading (about 10 µmol m^?2 s^?1). Image analysis of transmission electron micrographs revealed that a 10 min switch to a lower light intensity increased grana size and number per chloroplast profile by 10–20%. Returning the leaves to 300 µmol m^?2 s^?1 for 10 min reversed the phenomenon. Chlorophyll fluorescence measurements of detached, intact leaves at 77 K were suggestive of a transition from state 2 to state 1 upon shading. Diurnal ultrastructural measurements of granal size and number did not reveal a significant net change in ultrastructure over the time scale of hours. It is concluded that spinach chloroplasts can alter the degree of thylakoid appression in response to irradiance changes on a time scale of minutes. These ultrastructural responses are caused by biochemical and biophysical adjustments within the thylakoid membrane that serve to maximize photosynthesis and minimize photo‐inhibition under rapidly fluctuating light environments.