Limits to photosynthesis: seasonal shifts in supply and demand for CO2 in Scots pine.

Boreal forests undergo a strong seasonal photosynthetic cycle; however, the underlying processes remain incompletely characterized. Here, we present a novel analysis of the seasonal diffusional and biochemical limits to photosynthesis (Anet ) relative to temperature and light limitations in high-latitude mature Pinus sylvestris, including a high-resolution analysis of the seasonality of mesophyll conductance (gm ) and its effect on the estimation of carboxylation capacity ( VCmax ). We used a custom-built gas-exchange system coupled to a carbon isotope analyser to obtain continuous measurements for the estimation of the relevant shoot gas-exchange parameters and quantified the biochemical and diffusional controls alongside the environmental controls over Anet . The seasonality of Anet was strongly dependent on VCmax and the diffusional limitations. Stomatal limitation was low in spring and autumn but increased to 31% in June. By contrast, mesophyll limitation was nearly constant (19%). We found that VCmax limited Anet in the spring, whereas daily temperatures and the gradual reduction of light availability limited Anet in the autumn, despite relatively high VCmax . We describe for the first time the role of mesophyll conductance in connection with seasonal trends in net photosynthesis of P. sylvestris, revealing a strong coordination between gm and Anet , but not between gm and stomatal conductance.

Going Beyond the Carothers, Flory and Stockmayer Equation by Including Cyclization Reactions and Mobility Constraints.

A challenge in the field of polymer network synthesis by a step-growth mechanism is the quantification of the relative importance of inter- vs. intramolecular reactions. Here we use a matrix-based kinetic Monte Carlo (kMC) framework to demonstrate that the variation of the chain length distribution and its averages (e.g., number average chain length xn), are largely affected by intramolecular reactions, as mostly ignored in theoretical studies. We showcase that a conventional approach based on equations derived by Carothers, Flory and Stockmayer, assuming constant reactivities and ignoring intramolecular reactions, is very approximate, and the use of asymptotic limits is biased. Intramolecular reactions stretch the functional group (FG) conversion range and reduce the average chain lengths. In the likely case of restricted mobilities due to diffusional limitations because of a viscosity increase during polymerization, a complex xn profile with possible plateau formation may arise. The joint consideration of stoichiometric and non-stoichiometric conditions allows the validation of hypotheses for both the intrinsic and apparent reactivities of inter- and intramolecular reactions. The kMC framework is also utilized for reverse engineering purposes, aiming at the identification of advanced (pseudo-)analytical equations, dimensionless numbers and mechanistic insights. We highlight that assuming average molecules by equally distributing A and B FGs is unsuited, and the number of AB intramolecular combinations is affected by the number of monomer units in the molecules, specifically at high FG conversions. In the absence of mobility constraints, dimensionless numbers can be considered to map the time variation of the fraction of intramolecular reactions, but still, a complex solution results, making a kMC approach overall most elegant.

Using multirate rapid A/Ci curves as a tool to explore new questions in the photosynthetic physiology of plants.

Steady-state photosynthetic CO2 responses (A/Ci curves) are used to assess environmental responses of photosynthetic traits and to predict future vegetative carbon uptake through modeling. The recent development of rapid A/Ci curves (RACiRs) permits faster assessment of these traits by continuously changing [CO2 ] around the leaf, and may reveal additional photosynthetic properties beyond what is practical or possible with steady-state methods. Gas exchange necessarily incorporates photosynthesis and (photo)respiration. Each process was expected to respond on different timescales due to differences in metabolite compartmentation, biochemistry and diffusive pathways. We hypothesized that metabolic lags in photorespiration relative to photosynthesis/respiration and CO2 diffusional limitations can be detected by varying the rate of change in [CO2 ] during RACiR assays. We tested these hypotheses through modeling and experiments at ambient and 2% oxygen. Our data show that photorespiratory delays cause offsets in predicted CO2 compensation points that are dependent on the rate of change in [CO2 ]. Diffusional limitations may reduce the rate of change in chloroplastic [CO2 ], causing a reduction in apparent RACiR slopes under high CO2 ramp rates. Multirate RACiRs may prove useful in assessing diffusional limitations to gas exchange and photorespiratory rates.

Prominent Study on Surface Properties and Diffusion Coefficient of Urease-Conjugated Magnetite Nanoparticles.

Herein, the magnetite nanoparticles (MNs) were prepared by facile solvothermal method and its porous nature was modified using 3-(2-aminoethyl)-3-aminopropyl trimethoxysilane (AEAPS). Magnetite formation, successful amino tagging, and urease conjugation on the surface were confirmed from the presence of certain functional groups in Fourier transform infrared (FT-IR) spectra. Also, nanosize (13.2 nm) and spherical morphology of MNs were evaluated from diffraction patterns and electron micrographs respectively. Lower retentivity and coercivities in magnetization curve revealed the superparamagnetic behavior, and nitrogen adsorption/desorption curves exhibited decrease in its surface porosity. Conductivity measurements showed lower diffusion coefficient (De = 1.9 × 10-17 cm2/min) and higher diffusion with limited hydrolytic reaction in native urease and improved activity of conjugated urease with higher De (12.62 × 10-16 cm2/min). Hence, this study revealed that the surface porous nature of MNs can be altered effectively by amino tagging in order to overcome diffusional limitations thereby enhancing enzyme activity.

The ability of an antimicrobial agent to penetrate a biofilm is not correlated with its killing or removal efficiency.

The penetration ability of 12 antimicrobial agents, including antibiotics and biocides, was determined against biofilms of B. cereus and P. fluorescens using a colony biofilm assay. The surfactants benzalkonium chloride (BAC) and cetyltrimethyl ammonium bromide (CTAB), and the antibiotics ciprofloxacin and streptomycin were of interest due to their distinct activities. Erythromycin and CTAB were retarded by the presence of biofilms, whereas ciprofloxacin and BAC were not. The removal and killing efficacies of these four agents was additionally evaluated against biofilms formed in microtiter plates. The most efficient biocide was CTAB for both bacterial biofilms. Ciprofloxacin was the best antibiotic although none of the selected antimicrobial agents led to total biofilm removal and/or killing. Comparative analysis of the results obtained with colony biofilms and microtiter plate biofilms show that although extracellular polymeric substances and the biofilm structure are considered a determining factor in biofilm resistance, the ability of an antimicrobial agent to penetrate a biofilm is not correlated with its killing or removal efficiency. Also, the results reinforce the role of an appropriate antimicrobial selection as a key step in the design of disinfection processes for biofilm control.