Application of electrospun silk fibroin nanofibers as an immobilization support of enzyme

Silk fibroin (SF) nanofibers were prepared by electrospinning and their application as an enzyme immobilization support was attempted. By varying the concentration of SF dope solution the diameter of SF nanofiber was controlled. The SF nanofiber web had high capacity of enzyme loading, which reached to 5.6 wt%. The activity of immobilizedα-chymotrypsin (CT) on SF nanofiber was 8 times higher than that on silk fiber and it increased as the fiber diameter decreased. Sample SF8 (ca. 205 nm fiber diameter) has excellent stability at 25°C by retaining more than 90 % of initial activity after 24 hours, while sample SF11 (ca. 320 nm fiber diameter) shows higher stability in ethanol, retaining more than 45% of initial activity. The formation of multipoint attachment between enzyme and support might increase the stability of enzyme. From these results, it is expected that the electrospun SF nanofibers can be used as an excellent support for enzyme immobilization.     

Preparation and properties of polarizing films for liquid crystal display prepared using iodine vapor

The properties of polarizing films prepared using iodine vapor and using I₂/KI solution are compared to investigate the possibility of using vapor phase iodine adsorption in preparing polarizing film. The structure of PVA films drawn to different draw ratios and the amount of iodine adsorbed in drawn PVA films using iodine vapor were investigated. Increases in the degree of crystallinity, crystalline orientation index and birefringence with increase in draw ratio of PVA film, were observed by WAXD and polarizing microscope analysis. The amounts of iodine adsorbed by PVA film were 2–4 wt% for 20 min. UV-visible analysis suggests that I₃ ^? and I₅ ^? structures of iodine exist in the polarizing film after drawing in boric acid solution. Single transmittance and degree of polarization of polarizing films prepared using iodine vapor were about 30–50 % and over 99 %, respectively, at total draw ratios of over 3. The possibility of employing vapor phase adsorption of iodine instead of solution adsorption to prepare commercial polarizing film is suggested.     

Structure and properties of silk fibroin modified cotton

In this research, a novel cotton fiber with a silk fibroin (SF) coating was prepared by the oxidation of a cotton thread with sodium periodate and subsequent treatment in a solution of silk fibroin. The structures of both the oxidized cotton samples and the SF modified cotton samples were investigated by Fourier transform infrared (FT-IR) in combination with X-ray photoelectron spectroscopy (XPS) analysis. Other performances such as surface morphology and breaking strength were also studied. The results indicated that the weight of the oxidized cotton samples increased during SF treatment, while that of the un-oxidized cotton (pure cotton) samples reduced after SF treatment. Compared with the pure cotton samples, the oxidized cotton clearly showed a characteristic absorption band at 1730 cm⁻¹ due to the stretching vibration of the C=O double bond of the aldehyde group. After being treated with the SF solution, the oxidized cotton fiber showed a weakened characteristic absorption band at 1730 cm⁻¹ and a new absorption band at round 1540 cm⁻¹, suggesting the formation of C-N bond between aldehyde groups in the oxidized cotton and primary amines in the silk fibroin. The results were also confirmed by XPS analysis. Compared with the oxidized cotton samples, the SF treated cottons had relatively smooth surfaces, similar breaking strength, and the improved wrinkle recovery angles. The results in this research suggest that cotton based materials with protein coating can be achieved without using any other crosslinking agents by the method introduced.     

Growth of primary hippocampal neurons on multichannel silk fibroin scaffold

Particular attention has been given to axonal outgrowth of neurons to understand how topographical surface cues influence attachment and subsequent directional migration and growth. In present study, the silk fibroin (SF) scaffold with uniaxial channels was prepared by directional freeze-drying processes. The average pore diameter, the porosity, and pore density of the scaffold are 120 µm, 88 %, and 203 mm^?2, respectively. Further, hippocampal neurons were seeded onto the scaffold and the hippocampal neurons morphology was investigated. Cell-cell networks and cell-matrix interactions had been established by newly formed axons and the diversity of neurons was much higher after culturing 7 days. The neurons expressed β-III-tubulin and nerve filament, while glial fibrillary acidic protein immunofluorescence was barely above background. These results indicated that the SF scaffolds with uniaxial multichannels could be guided axons of neurons spread along the channels. SF scaffolds with oriented pores have a potential for nerve tissue regeneration.     

Effect of temperature on germination and early growth of subterranean clover, capeweed and Wimmera ryegrass

Germination of annual pasture species was studied under controlled‐environment conditions in south‐western Australia at temperatures in the range from 4°C to 35°C. Subterranean clover (Trifolium subterraneum) and Wimmera ryegrass (Lolium rigidum) had a germination of 90% between 12°C and 29°C, whereas capeweed (Arctotheca calendula) had a high germination percentage in a much narrower temperature range with an optimum of 25°C. Growth of subterranean clover, capeweed and Wimmera ryegrass between 28 and 49 days after sowing (DAS) was also studied at two photon flux densities, 13 and 30 mol m^?2 d^?1, and at diel temperatures in the range from 15/10°C to 33/28°C. Pasture species grown at a density of 1000 plants m^?2 accumulated at least twice the amount of shoot dry matter when subjected to temperatures of 21/16°C and 27/22°C, compared with a lower temperature of 15/10°C and a higher temperature of 33/28°C. Except at the highest temperature and at high photon flux density, capeweed had lower green area indices (GAI) than the other two species at 28 DAS. Crop growth rates between 28 and 49 DAS were higher in Wimmera ryegrass than in the other two species, whereas subterranean clover had a lower relative growth rate than the other two species at all temperatures and both photon flux densities. Subterranean clover and capeweed intercepted a greater proportion of the incident radiation compared with Wimmera ryegrass. The values of radiation interception and GAI were used to estimate the number of DAS to reach 75% radiation interception [f_(0·75)]. The number of days to reach f_(0·75) decreased with increasing temperature from 15/10°C to reach a minimum at 27/22°C. The time taken to achieve f_(0·75) was always shorter by about 10 d when the photon flux density was 30 mol m^?2 d^?1 in the autumn compared with 13 mol m^?2 d^?1 in the winter. These results are discussed in relation to the early growth of annual pasture in the field.     

Modelling net photosynthetic rate of field-grown cocksfoot leaves under different nitrogen, water and temperature regimes

A simple multiplicative model using temperature, foliage nitrogen (N) concentration and water status was developed to predict the maximum photosynthetic rate (Pmax) of field‐grown cocksfoot (Dactylis glomerata L.) leaves when none, one, two or all the factors were limiting. The highest Pmax was 27·4 μmol CO₂ m^–2 s^?1 in non‐limited conditions, which was defined as the standardized Pmax value dimensionless (Pmax_s=1). Pmax_s increased 0·058 units per °C from 10°C to the optimum range (19–23°C) (Pmax_s=1) and then declined 0·077 units of Pmax_s per °C from 23 to 31°C. Pmax_s=1 was also measured from 59 to 52 g N kg^?1 dry matter (DM) foliage N. Pmax_s then decreased at the rate of 0·115 units per 10 g N kg^?1 DM from 52 to 26 g N kg^?1 DM, and 0·409 units of Pmax_s per 10 g N kg^?1 DM from 26 to 15 g N kg^?1 DM. For predawn leaf water potential (ψ_lp), Pmax_s=1 was measured from ?0·1 to ?1·2 bar but declined linearly at a rate of 0·078 units per bar of ψ_lp from ?1·2 to ?14·0 bar because of a linear decrease in stomatal conductance. An interaction between low N content (≤20 g N kg^?1 DM) and high temperature (>23°C) was also detected. Together, this multiplicative model accounted for 0·82 of the variation in Pmax_s.     

Prediction of potato yield using temperature and insolation data

A linear polynomial model is presented $$Y = \beta _0 + \beta _1 X_1 + \beta _2 X_2 + \beta _3 X_3 + \xi $$ where Y = plant yield of tubers > 1 cm diameter, X₁ = revised growing degree days $$\begin{gathered} RGDD = \frac{{max temp \left( { \leqslant 30^ \circ C} \right) + \min temp \left( { \geqslant 4.4^ \circ C} \right)}}{2} - 4.4^ \circ C \hfill \\ - \frac{{min temp \left( { > 4.4^ \circ C} \right) - 4.4^ \circ C}}{2} \hfill \\ \end{gathered} $$ X₂ = total insolation in cal cm^-2 at 350 to 1150 nm and X₃ = mean daily air temperature range in °C. The β₀ and ξ, (Y intercept and error term) and β₁, β₂ and β₃ coefficients are derived from fitting the experimental data. The model was developed by growing ‘Kennebec’ in large containers at sites ranging from 1533 m to 3198 m elevation under shaded (48% insolation reduction) and unshaded conditions at 39° to 41° N latitude. Mean maximum and minimum temperatures and insolation ranged from 29°C to 19°C, 14°C to 6°C, and 200 cal cm^?2 day^?1 to 530 cal cm² day^?1 respectively. Soil matric potential and soil fertility were not included as variables in the model since they were physically controlled. The model does not include the period from planting to emergence since environment was not permitted to vary differentially. A highly significant multiple linear model with a coefficient of determination of 0.93 was obtained. It is suggested that including the revision $$ - \frac{{min temp \left( { > 4.4^ \circ C} \right) - 4.4^ \circ C}}{2}$$ in the heat input estimation (GDD) as well as air temperature range, emphasizes the influence of respiration on productivity. The model should be tested further and adapted as a practical method for predicting potato yield under “grower” conditions.     

Degradation of Carotenoids in Apricot (Prunus armeniaca L.) During Drying Process

Carotenoids are natural compounds whose nutritional importance comes from the provitamin A activity of some of them and their protection against several serious human disorders. The degradation of carotenoids was investigated during apricot drying by microwave and convective hot-air at 60 and 70 °C. Seven carotenoids were identified: antheraxanthin, lutein, zeaxanthin, β-cryptoxanthin, 13-cis-β-carotene, all-trans-β-carotene and 9-cis-β-carotene; among these, all-trans-β-carotene was found to be about 50 % of total carotenoids. First-order kinetic models were found to better describe all-trans-β-carotene reduction during drying, with a degradation rate constant (k₁) that increased two folds when temperatures increased by 10 °C, in both methods. No differences were found in k₁ between apricots dried by hot air at 70 °C (k₁?=?0.0340 h^?1) and by microwave at 60 °C. The evolution of total carotenoids (117.1 mg/kg on dry basis) during drying highlighted a wider decrease (about 50 %) when microwave heating was employed, for both set temperatures. Antheraxantin was found to be the carotenoid most susceptible to heat, disappearing at 6 h during both trials with microwave as well as during convective hot-air at 70 °C. For this reason, antheraxanthin could be a useful marker for the evaluation of thermal damage due to the drying process. Also the degree of isomerization of all-trans-β-carotene could be a useful marker for the evaluation of the drying process.     

Relationships between antithrombogenicity and surface free energy of regenerated silk fibroin films

Silk fibroin (SF) was dissolved in calcium chloride/ethanol/water mixture (1/2/8 in mole ratio) at 70°C for 4 h. The dissolved silk fibroin was regenerated by casting the dialyzed solution into the films. The films were treated with 50% aqueous solution of methanol for different times, and their antithrombogenicity was evaluated byin vitro andin vivo tests.In vivo blood tests were made by a method of peripheral vein indwelling suture. It was found that the silk fibroin had a good anti-thrombogenicity and an absorbability even though the polymer showed foreign body reaction. Finally, the blood compatibilty of silk fibroin films which were subjected to structural change by the methanol treatment, was examined in connection with their interfacial surface energy, and a correlation between these properties was found to be present.     

Waste cotton fibers based activated carbon: Optimization of process and product characterization

Waste cotton fibers were used to produce activated carbon fiber (ACF) via chemical activation method with phosphoric acid. The effect of different operational parameters on the adsorption capacity and yield of activated carbon fibers was studied by Taguchi experimental design. Optimized conditions were: Activation temperature of 450 °C, activation time of 0.5 h, impregnation ratio of 2, and the rate of temperature rising of 10 °C min^?1. The activated carbon fiber produced under optimized conditions was characterized by pore structure analysis, scanning electron microscopy (SEM), X-ray energy-dispersion spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). The obtained results showed that the produced activated carbon has developed porous structure, fibrous shape, predominantly amorphous structure, large number of oxygen functional groups, and acidic nature.     

Graft copolymerization of acrylamide onto rayon by chemical and radiation methods

The inherent properties of rayon fibre have been changed with additional properties through graft copolymerization of acrylamide, AAm, by chemical method using ceric ammonium nitrate/nitric acid, (CAN/HNO₃), as a redox initiator and γ-radiation induced mutual method. Reaction conditions such as monomer and initiator concentration, liquor ratio, temperature and time of reaction, amount of radiation dose have been optimized with respect to percentage of grafting. Maximum percentage of grafting (Pg), (40 %) using CAN/HNO₃ was obtained at [CAN]=31.92×10^?3 moles/l, [HNO₃]=79.36×10^?2 moles/l, [AAm]=14.07×10² moles/l in 20 ml of H₂O at 45 °C within 120 min while in case of radiation induced method, maximum Pg (30 %) was obtained at higher monomer concentration (28.14×10^?2 moles/l) and time (180 min) in 10 ml of H₂O at room temperature with total dose exposure of 11.178 kGy. The graft copolymers were characterized by FTIR, thermogravimetric and scanning electron micrographic analysis. Swelling behaviour in water, methanol, ethanol, acetone and DMF and dyeing and flame retarding properties of rayon fibre and grafted rayon fibre were investigated. Percent dye uptake (71.8 %) was found to be higher than that observed for the pristine fibre (57.4 %) and the grafted fibre after post phosphorylation reaction showed excellent flame retarding properties.     

Antimicrobial electrospun silk fibroin mats with silver nanoparticles for wound dressing application

In this report, silk fibroin (SF) mats coated with silver nanoparticles (AgNPs) were manufactured as a prototypic wound dressing and evaluated for antimicrobial properties. SF was extracted from cocoons of Thai silkworms Bombyx mori (variant Nangnoi Si Sa Ket) and fabricated into nonwoven mats by electrospinning. In a one-step synthesis method, colloidal AgNPs were prepared from silver nitrate by gamma irradiation and inspected by transmission electron microscopy. Using the in vitro disc diffusion and growth-inhibition assays, AgNP-coated SF mats effectively inhibited the growth of Staphyllococus aureus and Pseudomonas aeruginosa when the coating solution containing colloidal AgNPs was 4 mM, or equivalent to 50.4 ng/cm² of adsorbed AgNPs. Based on these results, the AgNP-coated SF mats can potentially be used as antimicrobial wound dressings.     

Development and growth characteristics of Caucasian and white clover seedlings, compared with perennial ryegrass

Seedling competition for resources during establishment affects the potential success of individual species within a pasture. Germination, emergence and leaf expansion are key characteristics that contribute to the competitive ability of species. In this study, development and growth characteristics of Caucasian clover, white clover and perennial ryegrass (PRG) seedlings were quantified. A base temperature of <4°C and an optimum temperature of ～27°C were found for development in each species. Thermal time (Tt) requirements for 75% of final germination were lower for Caucasian clover (46°C d) and white clover (40°C d) than for PRG (76°C d), but Tt requirements for 50% of final emergence were similar (～110°C d). The phyllochron (°C d leaf^?1) for primary stem leaves was slower for Caucasian clover (109°C d) than for white clover (94°C d) and PRG (101°C d). Appearance of the first PRG tiller, which indicates the initiation of secondary leaf development, occurred after 373°C d, compared with 532°C d for the first white clover stolon. Caucasian clover crown shoots did not develop until >1180°C d. Consequently, white clover and PRG had more leaves (～15 plant^?1) and faster shoot relative growth rates (～0·062 mg mg^?1 d^?1) than Caucasian clover (5 leaves plant^?1, 0·049 mg mg^?1 d^?1).     

Zeolite for Enhancing Yield and Quality of Potatoes Cultivated Under Water-Deficit Conditions

This study examined the effect of application of different doses of the natural zeolite clinoptilolite and different irrigation levels on yield and quality of potatoes (Solanum tuberosum L.), cv. Agria, and the nutrient contents of the soil under water-deficit stress in Konya-Karap?nar, Turkey. The study was established in a split-plot design with three replications. The main factor was the zeolite dose (Z₀:0, Z₃:30, Z₆:60, Z₉:90 and Z₁₂:120 t ha^?1) and the sub factor the irrigation level (I₅₀: 0.50, I₇₅: 0.75 and I₁₀₀:1.00). In I₁₀₀ treatment, irrigation was applied to fill 0–60-cm soil-depth until field capacity. In other treatments (I₇₅-I₅₀), it was given up to 75 and 50% of water applied to I₁₀₀ treatment at 6-day intervals. The amounts of irrigation water were determined by class-A pan evaporation using canopy area. For potato tuber yield, several quality characteristics and some nutrient element content in the soil, significant interaction occurred between zeolite doses and irrigation level (P?<?0.01). The highest crop yields, 33.9–39.1 and 33.5–34.3 kg ha^?1, respectively, were obtained from Z₆I₁₀₀ and Z₆I₇₅ applications in both years. There were no significant differences between these two treatments and also several other treatments (Z₃I₁₀₀, Z₉I₁₀₀ and Z₁₂I₁₀₀). In the experimental years, water consumption of Z₆I₇₅ treatment was determined as 509 and 420 mm, respectively. Some physical and chemical contents (the cation exchange capacity—CEC, exchangeable sodium percentage—ESP and total P, K, Ca, Mg, Zn and Mn contents) of the experiment soil were affected by zeolite treatments. These results showed that certain zeolite doses with optimum irrigation can be helpful for potato grown in water-deficit stress conditions because of positive effects on some soil physical and chemical properties and crop quality.     

Investigation of the high-amylose maize starch gelatinization behaviours in glycerol-water systems

The effect of glycerol on gelatinization behaviours of high-amylose maize starch was evaluated by confocal laser scanning microscopy (CLSM), scanning electronic microscope (SEM), differential scanning calorimetry (DSC), texture analyzer (TPA) and rheometer. Gelatinization of the high-amylose maize starches with glycerol content of 10% (w/w) began at 95.4 °C (T_o), peaked at 110.3 °C (T_p), and completed at 118.9 °C (T_c). The birefringence began to disappear at around 100 °C and finished at 120 °C which corresponded well to the onset and conclusion temperatures obtained by DSC. The high-amylose maize starch granules maintained original morphological structure at 100 °C and swelled to a great degree at 110 °C. The high-amylose maize starch paste formed at 100 °C showed the lowest hardness (39.92 g), while at 120 and 130 °C, showed the highest hardness (610.89 g and 635.43 g, respectively). It should be noted that in going from 100 °C to 110 °C there is a significant increase in the viscosity of the slurry solution. The identical apparent viscosity was observed when the shear rate exceed 100 s⁻¹, resulting from the high-amylose maize starch granules were completely gelatinized at 120 °C, which was consistent with DSC analysis.     

Yield response,water productivity,and seasonal water production functions for maize under deficit irrigation water management in southern Taiwan

As the challenges toward increasing water for irrigation become more prevalent, knowledge of crop yield response to water can facilitate the development of irrigation strategies for improving agricultural productivity. Experiments were conducted to quantify maize yield response to soil moisture deficits, and assess the effects of deficit irrigation (DI) on water productivity (water and irrigation water use efficiency, WUE and IWUE). Five irrigation treatments were investigated: a full irrigation (I₁) with a water application of 60 mm and four deficit treatments with application depths of 50 (I₂), 40 (I₃), 30 (I₄), and 20 mm (I₅). On average, the highest grain yield observed was 1008.41 g m^?2 in I₁, and water deficits resulted in significant (p < .05) reduction within range of 6 and 33%. This reduction was significantly correlated with a decline in grain number per ear, 1000-grain weight, ear number per plant, and number of grain per row. The highest correlation was found between grain yield and grain number per ear. The WUE and IWUE were within range of 1.52–2.25 kg m^?3 and 1.64–4.53 kg m^?3, respectively. High water productivity without significant reduction in yield (<13%) for I₂ and I₃ compared to the yield in I₁ indicates that these water depths are viable practices to promote sustainable water development. Also, for assessing the benefits of irrigation practices in the region crop water production functions were established. Maize yield response to water stress was estimated as .92, suggesting the environmental conditions are conducive for implementing DI strategies.     

Surface modification of okra bast fiber and its physico-chemical characteristics

The effect of chemical treatment i.e. bleaching, alkalization and graft copolymerization on the morphology changes of okra bast fiber has been investigated by means of infrared spectroscopy (IR), scanning electron microscopy (SEM), water absorption and tensile properties measurements. The graft copolymerization reaction of bleached fiber with acrylonitrile monomer (AN) has been carried out under the catalytic influence of K₂S₂O₈ and FeSO₄ redox system. The maximum graft yield (11.43 %) has been found at 70°C temperature, 3×10⁻² mol/l acrylonitrile, 5×10⁻³ mol/l K₂S₂O₈, 5×10⁻³ mol/l FeSO₄ and for 90 min. On the contrary, the fiber has been treated with 10 % NaOH solution, which is much effective to remove the impurities. Based on findings of water absorption, tensile properties and SEM micrograph, the AN-grafted fiber has been showed better properties than bleached and alkali treated fibers. The degree of modification of okra bast fiber by chemical treatment has been evaluated by IR measurement.     

Elevated carbon dioxide and temperature effects on rice yield,leaf greenness,and phenological stages duration

The present field experiment was conducted during two consecutive cropping seasons in central Portugal to study the effects of simultaneous elevation of carbon dioxide concentration ([CO₂]) (550 μmol mol^?1) and air temperature (+2–3 °C) on japonica rice (Oryza sativa L. “Ariete”) yield, crop duration, and SPAD-values across the seasons compared with the open-field condition. Open-top chambers were used in the field to assess the effect of elevated air temperature alone or the combined effect of elevated air temperature and atmospheric [CO₂]. Open-field condition was assessed with randomized plots under ambient air temperature and actual atmospheric [CO₂] (average 382 μmol mol^?1). Results obtained showed that the rice “Ariete” had a moderate high yielding under open-field condition, but was susceptible to air temperature rise of +2–3 °C under controlled conditions resulting in reduction of grain yield. The combined increase of atmospheric [CO₂] with elevated air temperature compensated for the negative effect of temperature rise alone and crop yield was higher than in the open-field. SPAD-readings at reproductive stage explained by more than 60 % variation the straw dry matter, but this finding requires further studies for consolidation. It can be concluded that potential increase in air temperature may limit rice yield in the near future under Mediterranean areas where climate change scenario poses a serious threat, but long term field experiments are required.     

Radiation utilization efficiency,latent heat flux,and crop growth simulation in irrigated rice during post-flood period in east coast of India

To study the radiation utilization efficiency, latent heat flux, and simulate growth of rice during post-flood period in eastern coast of India, on-farm trial was conducted with three water regimes in main plots (W ₁ = continuous flooding of 5 cm, W ₂ = irrigation after 2 days of water disappearance, and W ₃ = irrigation after 5 days of water disappearance) and five nitrogen levels in subplots (N ₁ = 0 kg N ha^?1, N ₂ = 60 kg N ha^?1, N ₃ = 90 kg N ha^?1, N ₄ = 120 kg N ha^?1, and N ₅ = 150 kg N ha^?1) on a rice cultivar, ‘Lalat’. Average maximum radiation utilization efficiency (RUE) in terms of above ground dry biomass of 2.09 (±0.05), 2.10 (±0.02), and 1.9 (±0.08) g MJ^?1 were computed under W ₁, W ₂, and W ₃, respectively. Nitrogen increased the RUE significantly, mean RUE values were computed as 1.60 (±0.07), 1.78 (±0.02), 2.060 (±0.08), 2.30 (±0.07), and 2.34 (±0.08) g MJ^?1 when the crop was grown with 0, 60, 90, 120, and 150 kg ha^?1 nitrogen, respectively. Midday average latent heat flux (on clear days) varied from 7.4 to 14.9 and 8 to 13.6 MJ m^?2 day^?1 under W ₂ and W ₃ treatments, respectively, at different growth stages of the crop in different seasons. The DSSAT 4.5 model was used to simulate phenology, growth, and yield which predicted fairly well under higher dose of nitrogen (90 kg and above), but the model performance was found to be poor under low-nitrogen dose.     

Gas exchange characteristics of leaves of four species of grain amaranth

Four species of the C4 genus Amaranthus, A. cruentus, A. caudatus, A. hypochondriacus and A. hybridus, were grown at Salt Lake City, Utah for the determination of gas exchange characteristics of recently matured leaves.The response of CO₂ assimilation to leaf temperature, measured at high quantum flux, was very similar in all species, each exhibiting a temperature optimum of approximately 37°C. Above about 40°C, all species showed high temperature inhibition, manifested as an irrversible time-dependent decline in CO₂ assimilation.All four exhibited high rates of net CO₂ assimilation exceeding 40 μmol m⁻² s⁻¹ at quantum fluxes of 2.0 mmol m⁻² s⁻¹, but none was completely light-saturated at such intensities. Leaf conductance to water vapor declined with decreasing quantum flux in all species, but less rapidly than assimilation, resulting in increasing values of internal CO₂ concentration (c_i). Quantum yield values in three species (x=0.048±0.003 mol(CO₂/mol(photons))) were similar to those reported previously for NAD-malic enzyme type C4 dicots, but leaves of A. hybridus, which were deep purple in color, exhibited a lower quantum yield, presumably due to light absorption by betacyanin pigments not involved in photosynthesis.All four species had net photosynthesis versus c_i responses typical of C4 species, with a steep initial linear response to c_i followed by a fairly abrupt transition to saturation in the region of 100–150 μl l⁻¹. Under near-optimal measurement conditions and high quantum flux, all species maintained c_i values close to the region at which saturation was reached (x=148±17 μl l⁻¹).Data pooled acrossspecies relating net photosynthesis measured at 2.0 mmol m⁻² s⁻¹ quantum flux and 35°C to Kjeldahl nitrogen content revealed a linear relationship, the slope of which was not significantly different (P=0.05) from those reported in two otudies employing C4 species.