Stefan Persijn

Nitric oxide in plants: an assessment of the current state of knowledge.

BACKGROUND AND AIMS After a series of seminal works during the last decade of the 20th century, nitric oxide (NO) is now firmly placed in the pantheon of plant signals. Nitric oxide acts in plant-microbe interactions, responses to abiotic stress, stomatal regulation and a range of developmental processes. By considering the recent advances in plant NO biology, this review will highlight certain key aspects that require further attention. SCOPE AND CONCLUSIONS The following questions will be considered. While cytosolic nitrate reductase is an important source of NO, the contributions of other mechanisms, including a poorly defined arginine oxidizing activity, need to be characterized at the molecular level. Other oxidative pathways utilizing polyamine and hydroxylamine also need further attention. Nitric oxide action is dependent on its concentration and spatial generation patterns. However, no single technology currently available is able to provide accurate in planta measurements of spatio-temporal patterns of NO production. It is also the case that pharmaceutical NO donors are used in studies, sometimes with little consideration of the kinetics of NO production. We here include in planta assessments of NO production from diethylamine nitric oxide, S-nitrosoglutathione and sodium nitroprusside following infiltration of tobacco leaves, which could aid workers in their experiments. Further, based on current data it is difficult to define a bespoke plant NO signalling pathway, but rather NO appears to act as a modifier of other signalling pathways. Thus, early reports that NO signalling involves cGMP-as in animal systems-require revisiting. Finally, as plants are exposed to NO from a number of external sources, investigations into the control of NO scavenging by such as non-symbiotic haemoglobins and other sinks for NO should feature more highly. By crystallizing these questions the authors encourage their resolution through the concerted efforts of the plant NO community.

Singly resonant cw OPO with simple wavelength tuning

A singly resonant continuous-wave optical parametric oscillator (cw OPO) is described. The OPO contains no intracavity etalon, which makes its wavelength tuning simple and straightforward, including only temperature tuning of the nonlinear crystal and wavelength tuning of the pump laser. The OPO provides watt-level output in the mid-infrared region and operates reliably without mode hops for several hours.

The form of nitrogen nutrition affects resistance against Pseudomonas syringae pv. phaseolicola in tobacco

Different forms of nitrogen (N) fertilizer affect disease development; however, this study investigated the effects of N forms on the hypersensitivity response (HR)—a pathogen-elicited cell death linked to resistance. HR-eliciting Pseudomonas syringae pv. phaseolicola was infiltrated into leaves of tobacco fed with either or . The speed of cell death was faster in -fed compared with -fed plants, which correlated, respectively, with increased and decreased resistance. Nitric oxide (NO) can be generated by nitrate reductase (NR) to influence the formation of the HR. NO generation was reduced in -fed plants where N assimilation bypassed the NR step. This was similar to that elicited by the disease-forming P. syringae pv. tabaci strain, further suggesting that resistance was compromised with feeding. PR1a is a biomarker for the defence signal salicylic acid (SA), and expression was reduced in -fed compared with fed plants at 24h after inoculation. This pattern correlated with actual SA measurements. Conversely, total amino acid, cytosolic and apoplastic glucose/fructose and sucrose were elevated in - treated plants. Gas chromatography/mass spectroscopy was used to characterize metabolic events following different N treatments. Following nutrition, polyamine biosynthesis was predominant, whilst after nutrition, flux appeared to be shifted towards the production of 4-aminobutyric acid. The mechanisms whereby feeding enhances SA, NO, and polyamine-mediated HR-linked defence whilst these are compromised with , which also increases the availability of nutrients to pathogens, are discussed.

LASER PHOTOACOUSTIC TRACE GAS DETECTION, AN EXTREMELY SENSITIVE TECHNIQUE APPLIED IN BIOLOGICAL RESEARCH

The use of infrared laser based photo-acoustic trace gas detection equipment in biological research is discussed on the basis bf two examples. A CO2 laser based photo-acoustic trace gas detection system is employed to follow the time-dependent pattern of the nitrogen fixation process by the cyanobacteria Nodularia Spumigena on a one-minute time scale. Due to the high sensitivity of the detection system for ethylene (detection limit 6 part per trillion; 6.10(12)), the fixation process can be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a certain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation. [KEYWORDS: CO-LASER; PLANTS; ACETALDEHYDE; SPECTROSCOPY; ADAPTATIONS; CO2-LASER; RESPONSES; ETHYLENE; ECOLOGY; ANOXIA]

Selective trace gas detection of complex molecules with a continuous wave optical parametric oscillator using a planar jet expansion

The authors present a trace gas detection method for complex molecules using continuous cavity ring-down spectroscopy in combination with a continuous wave optical parametric oscillator (tunability wavelength: 2.8–4.8μm; power: 1W) sampling a supersonic planar jet expansion (nozzle dimension: 3cm×80μm). The improved molecular selectivity allows simultaneous detection of larger numbers of complex molecules. With a total optical path length of 180m in the planar jet, a detection limit for methanol in an air expansion was determined at 70ppbv, corresponding to a minimal detectable absorption of 2.2×10−8cm−1 (over 90s).

A metrological approach to improve accuracy and reliability of ammonia measurements in ambient air

The environmental impacts of ammonia (NH3) in ambient air have become more evident in the recent decades, leading to intensifying research in this field. A number of novel analytical techniques and monitoring instruments have been developed, and the quality and availability of reference gas mixtures used for the calibration of measuring instruments has also increased significantly. However, recent inter-comparison measurements show significant discrepancies, indicating that the majority of the newly developed devices and reference materials require further thorough validation. There is a clear need for more intensive metrological research focusing on quality assurance, intercomparability and validations. MetNH3 (Metrology for ammonia in ambient air) is a three-year project within the framework of the European Metrology Research Programme (EMRP), which aims to bring metrological traceability to ambient ammonia measurements in the 0.5–500 nmol mol−1 amount fraction range. This is addressed by working in three areas: (1) improving accuracy and stability of static and dynamic reference gas mixtures, (2) developing an optical transfer standard and (3) establishing the link between high-accuracy metrological standards and field measurements. In this article we describe the concept, aims and first results of the project.

Zero gas reference standards

High purity nitrogen or air, often referred to as zero gas, is essential for calibrating instrumentation used in a wide variety of measurements, such as air quality monitoring. Providing traceable and accurate quantification of impurities of the target component in zero gas is a major challenge, as the detection limits of appropriate analytical techniques are often close to the amount fraction of the measurand and accurate reference standards to underpin these measurements are yet to be developed. Purity analysis of zero gas is a significant contributor to the uncertainty budget and is compromised by a dependence on a zero reference for its realisation. This work describes state-of-the-art methods currently used to certify zero gas standards. We distinguish between absolute and relative techniques and provide guidance on calibration of the latter at trace amount fractions. Measurements to assess the performance of a selection of zero air generators and purifiers are also presented here.

Final report on EURAMET.QM-S8: Analysis of impurities in pure and balance gases used to prepare primary standard gas mixtures by the gravimetric method

This supplementary comparison (EURAMET.QM-S8) concerns the purity analysis of nitrogen as used in reference gas mixture preparation. This project was carried out without adding impurities to the gas used for this comparison, and is therefore more representative to evaluate the analysis of carbon monoxide, carbon dioxide, methane, oxygen, argon and water impurities in high-purity nitrogen. The analysis of the amount-of-substance fraction water was optional. Two 50 litre high purity nitrogen cylinders were purchased from a well-qualified supplier of specialty gases. The listed components were expected to be present in the pure nitrogen at the target levels as a result of the purification of the nitrogen. From the start of this comparison it was clear that the comparison may not lead to reference values for the constituents analysed. The results indicate that analyses of high purity gases are often limited by the limits of detection of analytical equipment used. The reports of the participating laboratories also indicate that there is no agreed method of determination of the uncertainty on a detection limit value. The results provide useful information on the performance of participants. For all analysed components there is reasonable agreement in results for LNE, VSL, METAS and NPL. For BAM only the argon result is in agreement. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Study of Gas Exchange in Insects by Sensitive Laser Photoacoustic Spectroscopy

Abstract Although quantifying gas exchange in small insect species is of great biological interest, the progress in this field of research is hampered by the inability of most gas detectors to monitor the low emission rates from these insects. Recently, laser based photoacoustic spectroscopy (LPAS) has emerged as a highly sensitive technique that allows gases to be detected at sub‐ppb level. In this work, LPAS was used to study gas exchange in two different insect species. Firstly, loss of water by the minute Western Flower thrips (Frankliniella occidentalis, average weight 50 µg) was recorded by means of CO‐laser PAS. Water loss by a single thrips could be on‐line recorded with a practical detection limit of 30 ppb. Insects released H2O in rather regular patterns, possibly due to discontinuous respiration. These data represent on‐line H2O loss recordings of the smallest insects measured hitherto. In a second experiment, the inert tracer gas SF6 was used to determine the tracheal volume of Attacus atlas pupae. Insects were loaded with SF6 and subsequent release of this gas was monitored using CO2‐laser PAS. Based on the amount of released SF6, one has determined the tracheal volume of Attacus atlas pupae. The value obtained (170±53 µL/g) is in good correspondence with data obtained by other techniques. In addition, with this technique, respiration patterns can be recorded; the results show a good correspondence with the simultaneous recordings of CO2 release using a commercial CO2 analyser.

Broadly tunable, continuous-wave OPO for high resolution spectroscopy

We present a high power, broadly tunable (2.75-3.83 mum) cw OPO based on PP-MgO-LN. Using a combination of tuning techniques, molecular absorption spectra can be continuously recorded over 450 cm-1 at Lt0.001 cm-1 resolution.