Morphological and physiological responses of canola (Brassica napus) siliquas and seeds to UVB and CO2 under controlled environment conditions

Combined effects of UVB radiation and CO₂ concentration on plant reproductive parts have received little attention. We studied morphological and physiological responses of siliquas and seeds of canola (Brassica napus L. cv. 46A65) to UVB and CO₂ under four controlled experimental conditions: UVB radiation (4.2 kJ m⁻² d⁻¹) with ambient level of CO₂ (370 μmol mol⁻¹) (control); UVB radiation (4.2 kJ m⁻² d⁻¹) with elevated level of CO₂ (740 μmol mol⁻¹); no UVB radiation (0 kJ m⁻² d⁻¹) with ambient level of CO₂ (370 μmol mol⁻¹); and no UVB radiation (0 kJ m⁻² d⁻¹) with elevated level of CO₂ (740 μmol mol⁻¹). UVB radiation affected the outer appearance of siliquas, such as colour, as well as their anatomical structures. At both CO₂ levels, the UVB radiation of 4.2 kJ m⁻² d⁻¹ reduced the size of seeds, which had different surface patterns than those from no UVB radiation. At both CO₂ levels, 4.2 kJ m⁻² d⁻¹ of UVB decreased net CO₂ assimilation (A_N) and water use efficiency (WUE), but had no effect on transpiration (E). Elevated CO₂ increased A_N and WUE, but decreased E, under both UVB conditions. At both CO₂ levels, the UVB radiation of 4.2 kJ m⁻² d⁻¹ decreased chlorophyll fluorescence, total chlorophyll (Chl), Chl a and Chl b, but had no effect on the ratio of Chl a/b and the concentration of UV-screening pigments. Elevated CO₂ increased total Chl and the concentration of UV-screening pigments under 4.2 kJ m⁻² d⁻¹ of UVB radiation. Neither UVB nor CO₂ affected wax content of siliqua surface. Many significant relationships were found between the above-mentioned parameters. This study revealed that UVB radiation exerts an adverse effect on canola siliquas and seeds, and some of the detrimental effects of UVB on these reproductive parts can partially be mitigated by CO₂.     

Determination of kinetic constants of hybrid textile wastewater treatment system

The present study is related to treatment of textile wastewater in microaerophilic–aerobic hybrid reactor. The study showed the effectiveness of biological treatment of wastewater involving appropriate microorganism and suitable reactors. COD and color were reduced to 82–94%, and 99% respectively for textile wastewater. The reactor was operated at highest loading of 16.4 g COD g l⁻¹ d⁻¹ and obtained 80% COD and 72% color removal. Biokinetic models were applied to data obtained from experimental studies in continuously operated hybrid reactor. Treatment efficiencies of the reactor were investigated at different hydraulic retention times (2.3–9.1 d) and organic loading rates (2.6–16.4 g COD l⁻¹ d⁻¹). Second-order and a Stover–Kincannon models were best fitted to the hybrid column reactor. The second-order substrate removal rate constant (k_2(S)) was found as 41.44 d⁻¹ for hybrid reactor. Applying the modified Stover–Kincannon model to the hybrid reactor, the maximum removal rate constant (U_max) and saturation value constant (K_B) were found to be 212 g l⁻¹ d⁻¹ and 22.89 g l⁻¹ d⁻¹, respectively.     

Growth and photosynthesis of Hydrocotyle ranunculoides L. fil. in Central Europe

Floating Pennywort (Hydrocotyle ranunculoides L. fil.) is a worldwide distributed aquatic plant. The species is native to North America and quite common also in Central and South America. In Europe, Japan and Australia it is known as an alien plant, sometimes causing serious problems for affected ecosystems and human use of water bodies. Starting from Western Europe with an eastwards directed spread, Floating Pennywort was recorded in Germany in 2004 for the first time. Since then, the species spread out and got established in western parts of Central Europe. For a definite prediction of the potential of a further spread, data about biology, in particular growth and photosynthesis are needed. Here, regeneration capacity, growth at different nutrient availabilities and photosynthesis of H. ranunculoides were investigated. In addition biomass samples were taken in the field. Results show an enormous regeneration capacity (e.g., by forming new shoots from small shoot fragments), increasing growth rates under increasing nutrient availability and a maximum increase of biomass reaching 0.132±0.008 g g⁻¹ dw d⁻¹. Dense populations of H. ranunculoides growing in ponds and oxbows were found at high nutrient content of the substrate, the biomass reaching there up to 532.4±14.2 g dw m⁻². Gas exchange analysis showed a physiological optimum of H. ranunculoides CO₂ uptake at temperatures between 25 and 35 °C and high photon flux densities (PPFD) above 800 μmol photons m⁻² s⁻¹. In comparison, native Hydrocotyle vulgaris showed an optimum of net photosynthesis at 20–30 °C and a light saturation of CO₂ gas exchange at 350 μmol photons m⁻² s⁻¹.     

The response of an emergent sedge Bolboschoenus medianus to salinity and nutrients

The potential for nutrient load (30, 100 and 350 g N m⁻² per year) to alter plant performance under saline conditions (control, 4.5, 9 and 13 dS m⁻¹) was examined in the sedge Bolboschoenus medianus. Relative growth rates (RGR) across nutrient loadings ranged from 30.2 to 41.8 mg g⁻¹ per day in controls and were reduced to 20.9–28.5 mg g⁻¹ per day by salinities of 13 dS m⁻¹. Whilst higher nutrient loads generally increased RGR, the response was smaller at higher salinities. Responses to salinity and nutrient load were specific. Nutrient load increased the RGR via increases in the leaf area ratio (LAR). The LAR ranged from 1.9 to 2.1 m² kg⁻¹ across salinity treatments at 30 g N m⁻² per year, and increased to 2.5–2.8 m² kg⁻¹ at 350 g N m⁻² per year. Salinity reduced the RGR via a reduction in the net assimilation rate (NAR). The NAR in control plants ranged from 14.7 to 16 g m⁻² per day across nutrient loadings and decreased to 11–12 g m⁻² per day at 13 dS m⁻¹. Carbon isotope discrimination of leaves decreased by 2–3‰ in response to 13 dS m⁻¹ at the lower nutrient loadings. A prominent response of B. medianus to salinity was a change in biomass allocation from culms to tubers. In contrast, the response to nutrient load was characterised by a shift in biomass allocation from roots to leaves.     

Anaerobic digestion of solid slaughterhouse waste (SHW) at laboratory scale: Influence of co-digestion with the organic fraction of municipal solid waste (OFMSW)

Mesophilic anaerobic digestion of slaughterhouse waste (SHW) and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been evaluated. These processes were carried out in a laboratory plant semi-continuously operated and two set-ups were run. The first set-up, with a hydraulic retention time (HRT) of 25 days and organic loading rate (OLR) of 1.70 kg VS m⁻³ day⁻¹ for digestion, and 3.70 kg VS m⁻³ day⁻¹ for co-digestion, was not successful. The second set-up was initiated with an HRT of 50 days and an OLR of 0.9 kg VS m⁻³ day⁻¹ for digestion and 1.85 kg VS m⁻³ day⁻¹ for co-digestion. Under these conditions, once the sludge had been acclimated to a medium with a high fat and ammonia content, it was possible to decrease the HRT while progressively increasing the OLR to the values used in the first set-up until an HRT of 25 days and OLRs of 1.70 and 3.70 kg VS m⁻³ day⁻¹, for digestion and co-digestion, respectively (the same conditions of the digesters failures previously). These digesters showed a highly stable performance, volatile fatty acids (VFAs) were not detected and long chain fatty acids (LCFAs) were undetected or only trace levels were measured in the analyzed effluent. Fat removal reached values of up to 83%. Anaerobic digestion was thus found to be a suitable technology for efficiently treating lipid and protein waste.     

Carbon exchange and water use efficiency of a growing, irrigated olive orchard

We measured eddy covariance fluxes of CO₂ and H₂O over a flat irrigated olive orchard during growth, in different periods from Leaf Area Index (LAI) of 0.3–1.9; measurements of soil respiration were also collected. The daily net ecosystem exchange flux (F_NEE) was practically zero at LAI around 0.4 or when the orchard intercepted 11% of the incoming daily radiation; at the end of the experiment, with LAI of 1.9 (and the fraction of intercepted daily radiation close to 0.5), F_NEE was around 10 g CO₂ m⁻² day⁻¹. The night-time ecosystem respiration (R_eco), calculated from eddy fluxes in well-mixed night conditions, show a clear but non-linear dependence with LAI; it ranged from 0.05 to 0.15 mg CO₂ m⁻² s⁻¹ (in average), being the lower limit ideally close to the heterotrophic soil respiration at the site. The gross primary production flux (F_GPP) was linearly related to LAI within the LAI range of this experiment (with 11 g CO₂ m⁻² day⁻¹ increments per unit of LAI) and to the fraction of intercepted radiation. The maximum rates of F_GPP (0.75 mg CO₂ m⁻² s⁻¹) were obtained in the summer mornings of 2002, at LAI close to 1.9. F_GPP was strongly modulated by vapour pressure deficit (VPD) through the canopy conductance, even in absence of water stress. Hence, especially in the summer, the maximum rates of carbon assimilation are reached always before noon. The daily course of F_GPP shows a two-phase pattern, first related to irradiance and then to canopy conductance. The water use efficiency (WUE) was, in average, 3.8, 6.3 and 7 g CO₂ L⁻¹ in 1999, 2001 and 2002, respectively, with maxima always in the early morning. Hourly WUE was strongly related to VPD (WUE = −10.25 + 22.52 × VPD^−0.34). Our results suggest that drip irrigated orchards in general, and olive in particular, deserve specific carbon exchange and carbon budget studies and cannot be easily included in other biomes.     

Photosynthetic response of Myriophyllum salsugineum A.E. orchard to photon irradiance, temperature and external free CO2

The photosynthetic capacity of Myriophyllum salsugineum A.E. Orchard was measured, using plants collected from Lake Wendouree, Ballarat, Victoria and grown subsequently in a glasshouse pond at Griffith, New South Wales. At pH 7.00, under conditions of constant total alkalinity of 1.0 meq dm⁻³ and saturating photon irradiance, the temperature optimum was found to be 30–35°C with rates of 140 μmol mg⁻¹ chlorophyll a h⁻¹ for oxygen production and 149 μmol mg⁻¹ chlorophyll a h⁻¹ for consumption of CO₂. These rates are generally higher than those measured by other workers for the noxious Eurasian water milfoil, Myriophyllum spicatum L., of which Myriophyllum salsugineum is a close relative. The light-compensation point and the photon irradiance required to saturate photosynthetic oxygen production were exponentially dependent on water temperature. Over the temperature range 15–35°C the light-compensation point increased from 2.4 to 16.9 μmol (PAR) m⁻² s⁻¹ for oxygen production while saturation photon irradiance increased from 41.5 to 138 μmol (PAR) m⁻² s⁻¹ for oxygen production and from 42.0 to 174 μmol (PAR) m⁻² s⁻¹ for CO₂ consumption. Respiration rates increased from 27.1 to 112.3 μmol (oxygen consumed) g⁻¹ dry weight h⁻¹ as temperature was increased from 15 to 35°C. The optimum temperature for productivity is 30°C.     

Growth and biochemical characterization of microalgal biomass produced in bubble column and airlift photobioreactors: studies in fed-batch culture

Relatively large (0.19 m column diameter, 2 m tall, 0.06 m³ working volume) outdoor bubble column and airlift bioreactors (a split-cylinder and a draft-tube airlift device) were compared for monoseptic fed-batch culture of the microalga Phaeodactylum tricornutum. The three photobioreactors produced similar biomass versus time profiles and final biomass concentration (4 kg m⁻³). The maximum specific growth rate observed within a daily illuminated period in the exponential growth phase, had a value of 0.08 h⁻¹ on the third day of culture. Because of night-time losses of biomass, the specific growth rate averaged over the 4-days of exponential phase was 0.021 h⁻¹ for the three reactors.

The biomass in the vertical column reactors did not experience photoinhibition under conditions (photosynthetically active daily averaged irradiance value of 1150±52 μE m⁻² s⁻¹) that are known to cause photoinhibition in conventional thin-tube horizontal loop reactors. Because of good gas-liquid mass transfer, the dissolved oxygen concentration in the reactors at peak photosynthesis remained <120% of air saturation; thus, oxygen inhibition of photosynthesis and photo-oxidation of the biomass did not occur. Carbohydrate accumulation (up to 13% w/w) by the biomass was favored during light-limited linear growth. A declining light intensity caused a more than five-fold increase in cellular carotenoids but the chlorophylls increased only by about 2.5-fold during the course of the culture. In the stationary phase, up to 2% of the biomass was chlorophylls and carotenoids constituted up to 0.5% of the biomass dry weight.     

Protein-based complex medium design for recombinant serine alkaline protease production

This work reports on the design of a complex medium based on simple and complex carbon sources, i.e. glucose, sucrose, molasses, and defatted-soybean, and simple and complex nitrogen sources, i.e. (NH₄)₂HPO₄, casein, and defatted-soybean, for serine alkaline protease (SAP) production by recombinant Bacillus subtilis carrying pHV1431::subC gene. SAP activity was obtained as 3050 U cm⁻³ with the initial defatted-soybean concentration C_soybean^o=20 kg m⁻³ and initial glucose concentration C_G^o=8 kg m⁻³; whereas, addition of the inorganic nitrogen source (NH₄)₂HPO₄ decreased SAP production considerably. Further increase in SAP production (3850 U cm⁻³) was obtained when sucrose was replaced with glucose at C_sucrose^o=15 kg m⁻³ and C_soybean^o=20 kg m⁻³. Nevertheless, when molasses was replaced with sucrose, the maximum activity was obtained with molasses having 10 kg m⁻³ initial sucrose concentration and C_soybean^o=15 kg m⁻³as 2130 U cm⁻³; moreover, when casein was replaced with defatted-soybean SAP production decreased considerably (ca. 250 U cm⁻³). Thereafter, the effects of inorganic ionic compounds were investigated; and except phosphate, inorganic compounds supplied from defatted-soybean were found to be sufficient for the bioprocess. The highest SAP activity was obtained as 5350 U cm⁻³ in the medium that contained (kg m⁻³): C_soybean^o=20, C_sucrose^o=15, C_Na2HPO4^o=0.021, and C_NaH2PO4^o=2.82, that was 6.5-fold higher than that of the SAP produced in the defined medium. By using the designed complex medium, oxygen transfer characteristics of the bioprocess were investigated; and, Damköhler number that is the oxygen transfer limitation increases with the cultivation time until t=14 h; and, at t>20 h both mass transfer and biochemical reaction resistances were effective. Overall oxygen transfer coefficient varied between 0.010 and 0.044 s⁻¹; volumetric oxygen uptake rate varied between 0.001 and 0.006 mol m⁻³ s⁻¹; and specific oxygen uptake rate varied between 0.0001 and 0.0022 mol kg⁻¹ DW s⁻¹ throughout the bioprocess.     

Diurnal light curves and landscape-scale variation in photosynthetic characteristics of Thalassia testudinum in Florida Bay

When using pulse-amplitude modulated (PAM) fluorometry to measure landscape-scale photosynthetic characteristics, diurnal variations in fluorescence during sampling may confound the assessment of the physiological condition. In this study, two photophysiological assessment techniques: Diurnal Yield and Diurnal Rapid Light Curve (RLC) were investigated in an attempt to incorporate the temporal and spatial scales of sampling into a physiological assessment of Thalassia testudinum in Florida Bay. Photosynthesis–irradiance (P–E) curves were calculated using both methods and the ability of each to predict the relationship between relative electron transport rates and irradiance was assessed. Both methods had limitations in providing consistent estimates of photosynthetic efficiency or capacity. The Diurnal Yield method produced unrealistically high predictions of photosynthetic capacity (relative electron transport rate (rETR_max), 417–1715) and saturation irradiance (I_k, 1045–4681 μmol photons m⁻² s⁻¹). In contrast, the Diurnal RLC method generally produced predictions of rETR_max (100–200) and I_k (300–500 μmol photons m⁻² s⁻¹) which were similar to average values calculated from each day's RLCs. The Diurnal RLC method was unable to predict photosynthetic efficiency () only when ambient irradiances were continuously >I_k during the sampling period. We believe that with sampling modifications in high-light or shallow environments, such as starting sampling earlier in the morning, extending sampling later in the day, or using the average from each day's RLCs, that the Diurnal RLC method can produce representative estimates of rETR_max, , and I_k, providing a method to characterize seagrass photosynthesis at the landscape-level. The Diurnal RLC method does not negate Diurnal variation but it produces a curve that incorporates the changing ambient light environment into the assessment of seagrass physiological status.     

Gas exchange and photosynthetic water use efficiency in response to light, CO2 concentration and temperature in Vicia faba

Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions.

Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 μmol m⁻² s⁻¹), CO₂ concentrations (ambient—350 μmol mol⁻¹ and short-term enriched—700 μmol mol⁻¹) and air temperature (from 7 up to 35 °C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO₂ enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina.

The positive effects of short-term CO₂ enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO₂ concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed.

The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26–27 °C and no relevant limitations were observed in the range between 21 and 32 °C.

Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria for the screening of genotypes.     

Annual biomass and production of epiphytes in three monospecific seagrass communities of Thalassia hemprichii (Ehrenb.) Aschers

The biomass of epiphytes and seagrasses has been measured in relation to leaf age in three monospecific seagrass stands of Thalassia hemprichii (Ehrenb.) Aschers. in Papua New Guinea. From June 1981 through August 1982, biomass values for epiphytes at the three sites ranged from 5 to 70 g ADW m⁻² sediment surface at site 1, from 5 to 14 g ADW m⁻² at site 2, and from 3.5 to 7.0 g ADW m⁻² at the site 3. Annual mean epiphyte biomass values for the different sites were 1.3 g ADW m⁻² leaf surface at site 1, 1.7 g ADW m⁻² leaf surface at site 2, and 1.5 g ADW m⁻² leaf surface at site 3.

The annual mean standing crop of T. hemprichii leaves was highest at site 1 (103 g ADW m⁻². Values for site 2 and site 3 were 60 g ADW m⁻² and 41 g ADW m⁻², respectively.

Production of epiphytes was calculated in three different ways: firstly, by using biomass values for each specific leaf-age group, with corrections for colonization; secondly, by fitting the biomass values with a specific growth curve; and thirdly, by estimated the rate of biomass accumulation. On an area basis, production of epiphytes on leaves of T. hemprichii ranged from 0.55 to 3.97 g ADW m⁻² day⁻¹ at site 1, from 0.17 to 0.73 g ADW m⁻² day⁻¹ at site 2, and from 0.24 to 0.68 g ADW m⁻² day⁻¹ at site 3.     

Sulfate reduction in lake sediments inhabited by the isoetid macrophytes Littorella uniflora and Isoetes lacustris

Sulfur cycling was examined in sediments inhabited with the isoetids Littorella uniflora and Isoetes lacustris in the oligotrophic soft-water Lake Kalgaard, Denmark. Based on short-term tracer incubations sulfate reduction was measured along a transect from the shore (0.6 m) to profundal sediments (4.6 m). The sulfate reduction rates were low (0.008–0.8 mmol m⁻² d⁻¹) in the sandy shallow sediments with low organic content (<1.3 mmol C g⁻¹ sed DW) and high redox potentials (>100 mV), whereas sulfate reduction was higher at the deeper sites (2.7–4.6 mmol m⁻² d⁻¹) with high organic content (max. 11.5 mmol C g⁻¹ sed DW) and lower redox potentials (<100 mV). High concentrations of dissolved organic carbon (DOC) were found in the low particulate organic sediments (up to 18.4 mM), and most of the DOC pool consisted of acetate (40–77%). Reoxidation of sulfides due to root oxygen release was probably important at all sites and a positive efflux of sulfate across the sediment–water interface was measured, attaining rates (up to 4.8 mmol m⁻² d⁻¹) similar to the sulfate reduction rates. Reoxidation of sulfides was also manifested by high fraction (>80%) of reduced sulfides being accumulated as elemental sulfur or pyrite (chromium reducible sulfur, CRS). The largest pools of CRS were found in high organic sediment with vertical distributions resembling those of the sulfate reduction rates. The overall effect of isoetid growth on sulfur cycling in the rhizosphere is a suppression of sulfate reduction in low organic sediments and the governing of sulfide reoxidation in sediments with higher organic content.     

Effects of ultraviolet-B radiation on common bean (Phaseolus vulgaris L.) plants grown under nitrogen deficiency

This work reports on the significance of UV-B absorbing compounds and DNA photorepair in protecting bean plants from UV-B radiation under nitrogen restriction. Bean plants grown in sterile vermiculite and irrigated periodically with a nutrient solution containing 12 or 1 mM of nitrate were irradiated with 22 μW cm⁻² of UV-B, 4 h daily during 10 days after the first trifoliate leaf was developed. This intensity was equivalent to 3.2 kJ m⁻² per day, approximately. PAR fluence rate was 350 ± 50 μmol quanta m⁻² s⁻¹. Control plants did not receive UV-B irradiation. Leaf expansion was negatively affected by both nitrate restriction and UV-B irradiation. This decrease was paralleled by a significant increase in starch, which was exacerbated by the combined action of both factors. Combined action of low nitrogen and UV-B also negatively affected the CO₂ assimilation rate and the stomatal conductance. Formation of UV-B absorbing compounds was significantly increased by both UV-B irradiation and nitrogen restriction and this increase was exacerbated by the combination of both factors. No significant increase in dimer formation was detected in irradiated plants at the UV-B dose used. Significant dimer formation was only obtained by using very high UV-B intensities. This suggests that under an irradiation level of 22 μW cm⁻² of UV-B, which is close to natural conditions, protective mechanisms such as pigment screening and DNA photorepair were probably sufficient to prevent any dimer formation in leaves.     

Growth, nodulation and nitrate reductase activity in the aquatic legume Neptunia plena (L.) benth. At different external nitrate concentrations

The effects of different external nitrate concentrations (0 (control), 1, 50, 100, 500, 1000 and 20 000 mmol m⁻³) on growth, nodulation and nitrate-reductase activity (NRA) of inoculated Neptunia plena (L.) Benth. were examined.

Plants given 500 and 1000 mmol m⁻³ nitrate had greater (P < 0.05) shoot length, leaf, stem and root dry mass, and carbon and nitrogen contents than the controls and plants given 20 000 mmol m⁻³ nitrate. Nodule number was not significantly affected by nitrate concentration up to 50 mmol m⁻³, but 100 mmol m⁻³ nitrate reduced nodulation by 68% and concentrations above 100 mmol m⁻³ completely inhibited nodule development. Plants given 100–20000 mmol m⁻³ nitrate had a greater nitrate content per g leaf, stem and root dry mass (DM) than controls. Nitrate per g root DM did not increase with external nitrate concentration above 500 mmol m⁻³, but levels in leaf and stem were greater at 20 000 mmol m⁻³ nitrate than at all other concentrations. NRA per g leaf, stem and root fresh mass (FM) was greater for plants given 500–20000 mmol m⁻³ than for controls, but there was no significant increase with nitrate concentration above 500 mmol m⁻³. Substantial proportions of total plant nitrate and NRA were found in both root and shoot over the entire range of external nitrate concentrations given.

Findings for N. plena are compared with data obtained previously for terrestrial legumes.     

Effect of leaf age on CAM activity in Littorella uniflora

In this study the effect of ontogenetic drift on crassulacean acid metabolism (CAM) was investigated in the aquatic CAM-isoetid Littorella uniflora. The results of this study strengthen the general hypothesis of CAM being a carbon-conserving mechanism in aquatic plants, because high-CAM capacity (45–183 μequiv. g⁻¹ FW) was present in all leaves of L. uniflora irrespective of age. Since possession of CAM in aquatic plants allows CO₂ uptake throughout the light/dark cycle, presence of CAM in all leaves influences the carbon balance of L. uniflora positively. On average for all lakes, different leaf classes accounted for 11–36% of the total dark CO₂ uptake by the individual plant.

The capacity for both CAM and photosynthesis declined with increasing leaf age, and was in the oldest leaves only 25–53% of the capacity in the youngest. The photosynthetic capacity was estimated to be sufficiently high to ensure refixation of the CO₂ released from malate during decarboxylation in the daytime. In line with this, a linear coupling between CAM capacity and photosynthetic capacity was found. Parallel to the change in photosynthetic capacity, an age-related change in total ribulose-bisphosphate carboxylase/oxygenase (rubisco) activity from 732 μmol C g⁻¹ DW h⁻¹ in the youngest leaves to 346 μmol C g⁻¹ DW h⁻¹ in the oldest was observed. In contrast, no significant change in phosphoenolpyruvate carboxylase (PEPcase) activity with leaf age was observed (means ranged between 46 and 156 μmol C g⁻¹ DW h⁻¹).     

Graft copolymerization of acrylic acid onto guar gum initiated by vanadium (V)–mercaptosuccinic acid redox pair

Guar gum has been modified by graft copolymerization with acrylic acid in aqueous medium using vanadium (V)–mercaptosuccinic acid redox system. The optimum reaction conditions affording maximum grafting ratio, efficiency, add on and conversion have been determined. The grafting parameters have been found to increase with increase in vanadium (V) concentration upto 1.0 × 10⁻² mol dm⁻³, but these parameters decrease on further increasing the vanadium (V) concentration. On increasing the mercaptosuccinic acid concentration from 1.0 × 10⁻² to 4.0 × 10⁻² mol dm⁻³ grafting ratio, efficiency and add on increase up to 2.0 × 10⁻² mol dm⁻³ but decrease with further increase in mercaptosuccinic acid concentration. On varying the acrylic acid concentration from 5.0 × 10⁻² to 30.0 × 10⁻² mol dm⁻³, maximum grafting ratio, efficiency and add on have been obtained at 20.0 × 10⁻² mol dm⁻³. The grafting ratio, add on and conversion increase, on increasing the H⁺ ion concentration from 1.5 × 10⁻¹ to 6.0 × 10⁻¹ mol dm⁻³. On increasing the guar gum concentration the grafting parameters increase. The grafting ratio, add on and conversion have been found to increase with time period while efficiency started decreasing after 120 min. It has been observed that %G increases on increasing the temperature up to 35 °C. The graft copolymer has been characterized by IR spectroscopy and thermogravimetric analysis.     

Sucrose conversion into palatinose with immobilized Serratia plymuthica cells in a hollow-fibre bioreactor

In recent decades, the production of palatinose has aroused great interest since this structural isomer of sucrose has a promising potential. Using immobilized in a hollow-fibre membrane reactor Serratia plymuthica cells, a complete conversion of concentrated sucrose solutions into palatinose was achieved. Under typical process conditions, the specific productivity of the membrane reactor was 16.8 g m⁻² h⁻¹ (flow rate 1.3 cm³ min⁻¹ and substrate concentration 40%) in continuous mode of action. The activity of the biocatalyst (productivity of the system) decreased slowly with the increase of operation time until the 15th day and remained almost constant to the end of the experiment. The loss of activity was 11% after 90 days of continuous operation. Conversion rate of over 90% was reached for 36–48 h for all concentrations (40–60%) of the substrate solution in cycle mode of action of the bioreactor. The best productivity (18.1 g palatinose m⁻² biocatalytic membrane) for the set period was observed during the recirculation of a 60% sucrose solution. The culture displayed a very good stability under the conditions of critical osmotic stress during the experiments. A microbiological analysis of the end product showed that the produced palatinose syrup measures up to the standards for products of this kind and can be used as an additive to different food products and functional foods.     

Overexpression of serine alkaline protease encoding gene in Bacillus species: performance analyses

Bacillus species carrying subC gene encoding serine alkaline protease (SAP) enzyme were developed in order to increase the yield and selectivity in the bioprocess for SAP production. For this aim, subC gene was cloned into pHV1431 Escherichia coli–Bacillus shuttle vector, and transferred into nine host Bacillus species, i.e. B. alvei, B. amyloliquefaciens, B. badius, B. cereus, B. coagulans, B. firmus, B. licheniformis, B. sphaericus and B. subtilis. The influence of the host Bacillus species on SAP production on a defined medium with glucose was investigated in bioreactor systems. For each of the recombinant (r-) Bacillus species, effects of initial glucose concentration on cell growth and SAP production were investigated; and, physiological differences and similarities between the wild-type and r-Bacillus species are discussed. The highest biomass concentration was obtained with r-B. coagulans as 3.8 kg m⁻³ at the initial glucose concentration of C_Go=20 kg m⁻³ and the highest volumetric SAP activity was obtained with r-B. amyloliquefaciens as 1650 U cm⁻³ at C_Go=20 kg m⁻³. Overall SAP activity per amount of substrate consumed was the highest for r-B. sphaericus (137 U g⁻¹ cm⁻³) and r-B. licheniformis (130 U g⁻¹ cm⁻³). Among the r-Bacillus species the highest activity increase compared to the wild types was obtained with r-B. sphaericus while the lowest increase was obtained with r-B. amyloliquefaciens and r-B. licheniformis due to high SAP production potential of the wild-type strains. During storage of the host microorganisms, r-B. alvei and r-B. amyloliquefaciens were not able to bear the recombinant plasmid, probably, due to the restriction enzymes synthesized. Due to the highest stable volumetric activities r-B. licheniformis (950 U cm⁻³) and r-B. sphaericus (820 U cm⁻³) appear to be the favorable hosts for the production of SAP. All the r-Bacillus species excreted organic acids oxaloacetic and succinic acids, but, none excreted the amino acid valine. The variations in by-product distributions with each recombinant organism were also discussed.     

Conceptual model of seagrass die-off in Florida Bay: Links to biogeochemical processes

Seagrasses are recognized as important plant communities in coastal estuaries and lagoons across both tropical and temperate climes; thus, large-scale seagrass die-off events worldwide are of general concern. In Florida Bay, at the southern terminus of the Florida peninsula, seagrass die-off events up to 4000 ha have been reported and smaller scale mortality events are noted annually. In the present study, we examined several hypothesized causative factors (high temperature, hypersalinity, sulfide toxicity) of seagrass (Thalassia testudinum) mortality in Florida Bay. To test sulfide effects, in situ sulfide production was stimulated by applying a labile carbon source (glucose) to sulfate reducers in the sediment at five sites across the bay (northeastern, northcentral, and southwestern basins). During the one year study, high temperature (32–36 °C) and salinity (> 50 psu) were recorded in the bay associated with a regional drought. We also experienced major seagrass die-off events at two of our southwestern bay sites. These field conditions provided an excellent opportunity to closely examine cause–effect relationships among stressors and die-off events in the field, and verify results of our previous mesocosm experiments. Even though glucose amendments stimulated porewater sulfides in bay sediments (4–8 mmol L^− 1), no significant differences in biomass, short shoot density or final growth rates were found between control and glucose plots. In addition, the highest growth rates and shoot densities were concomitant with maximum water column salinity (> 50 psu) and temperature (32–36 °C), when porewater sulfides were also in the millimolar range. Large-scale seagrass mortality events, encompassing  50% of the entire meadow at one site, occurred at southwestern bay sites when plants were down regulating (slower growth and shoot density), probably in response to shorter day length and lower temperature (30–34 to 23–26 °C) from October, 2004 to January, 2005. Sulfate reduction rates (SRR) were also 2-fold higher in the southwestern (214–488 nmol cm^− 3 d^− 1) versus northcentral and northeastern (97–240 nmol cm^− 3 d^− 1) bay sites, possibly limited by labile carbon, which we found to stimulate SRR 3-fold in northeastern and northcentral bay sites (461–708 nmol cm^− 3 d^− 1) and 4-fold at southwestern bay sites (1211–2036 nmol cm^− 3 d^− 1). Based on a synthesis of the field data reported herein, our mesocosm experiments to date, and contributions by others, we present a conceptual model of seagrass die-off in Florida Bay outlining a cascade of stressors, stimulated by P enrichment, which leads to high O₂ consumption in the system triggering a seagrass die-off event.