• Energy Research

During anaerobiosis in darkness the main route for ATP production in plants is through glycolysis in combination with fermentation. We compared the organ-specific anaerobic fermentation of flooding-tolerant rice (Oryza sativa) and sensitive wheat (Triticum aestivum) seedlings. A sensitive laser-based photoacoustic trace gas detection system was used to monitor emission of ethanol and acetaldehyde by roots and shoots of intact seedlings. Dark-incubated rice seedlings released 3 times more acetaldehyde and 14 times more ethanol than wheat seedlings during anaerobiosis. Ninety percent of acetaldehyde originated from shoots of both species. In comparison to wheat shoots, the high ethanol production of rice shoots correlated with larger amounts of soluble carbohydrates, and higher activities of fermentative enzymes. After 24 h of anaerobiosis in darkness rice shoots still contained 30% of aerated ATP level, which enabled seedlings to survive this period. In contrast, ATP content declined almost to zero in wheat shoots and roots, which were irreversibly damaged after a 24-h anaerobic period. When plants were anaerobically and dark incubated for 4 h and subsequently transferred back to aeration, shoots showed a transient peak of acetaldehyde release indicating prompt re-oxidation of ethanol. Post-anoxic acetaldehyde production was lower in rice seedlings than in wheat. This observation accounts for a more effective acetaldehyde detoxification system in rice. Compared to wheat the greater tolerance of rice seedlings to transient anaerobic periods is explained by a faster fermentation rate of their shoots allowing a sufficient ATP production and an efficient suppression of toxic acetaldehyde formation in the early re-aeration period.

Strong ro-vibrational transitions of molecules in the mid-infrared wavelength region, coupled with fast data acquisition of dual-comb spectroscopy (DCS), yields an effective tool for time-resolved simultaneous monitoring of the concentrations of different species involved in a gas-phase chemical reaction [1]. Here we used the broadband and high resolution properties of mid-infrared DCS, to monitor the static and dynamic concentrations of methane and the reaction products, in an electrical discharge. The mid-infrared dual comb source is based on an optical parametric oscillator (OPO) in a singly resonant cavity configuration, containing two temperature stabilized, 5 mm long, MgO: PPLN crystals. The crystals are pumped by two mode-locked Yb:fiber lasers, counter propagating and crossed polarized, emitting around 1040 nm. The two Yb:fiber lasers have a slightly different repetition rate (Δf rep ≈ 250 Hz) near 90 MHz [2]. The two coherent mid-infrared output combs, emitted from the OPO, are combined and sent through a discharge tube filled with methane. The discharge tube is 50 cm long, with an internal diameter of 3 mm, and is water cooled. The cathodes are at the two ends of the tube and the anode as at the center. A stabilized high-voltage (HV) power supply (25 kV, 50 mA) is used for making a DC discharge in the tube. To monitor the dynamic events in the discharge, the current of HV power supply is modulated (at 2 Hz) by an external signal generator. After the discharge tube, the two combs are focused on a single TE cooled HgCdTe photodetector (bandwidth 50 MHz). The time domain interferogram is recorded by a field-programmable gate array (FPGA) and post-processed to yield the spectrum after a Fourier transform. The voltage and current of the HV power supply, as well as the flow rate and the pressure of the sample gas are adjusted depending on the discharge operation.

Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150–1300 cm−1 in both broadband scan mode, as well as narrow scanning mode around 1216 cm−1, respectively, for detection of acetone in exhaled breath. This wavelength region is essential for accurate determination of breath acetone due to the relative low spectral influence of other endogenous molecules like water, carbon dioxide or methane. We demonstrated that ethanol has a strong spectroscopic influence on the acetone concentration in exhaled breath, an important detail that has been overlooked so far. An ethanol correction is proposed and validated with the reference measurements from a proton-transfer reaction mass spectrometer (PTR-MS) for the same breath samples from ten persons. With the ethanol correction, both broadband and narrowband molecular spectroscopy represent an attractive way to accurately assess the exhaled breath acetone. The importance of considering spectroscopic ethanol influence is essential, especially for the narrowband scans, (e.g., 1216 cm−1), for which the error in determining the acetone concentrations can rise up to 39% if it is not considered.

A new on‐line method for measuring acetylene reduction is described. It consists of a gas‐flow cell connected to an electronic gas‐mixing system and an automatic sample loop in the gas chromatograph. Alternatively, ethylene can be determined by using laser‐based trace gas detection. The laser‐based trace gas detection technique achieves a detection limit that is three orders of magnitude better than gas chromatography. We have applied the on‐line method to the measurement of nitrogen fixation in a culture of the heterocystous cyanobacterium Nodularia spumigena and compared it with conventional batch‐type incubations. Incubation of N. spumigena in the gas‐flow cell resulted in very short response times with a steady‐state flux of ethylene obtained within 2 min. Nitrogenase was shown to respond immediately to changes in light and oxygen. Monitoring of nitrogenase activity could be continued for several hours without having a negative impact on nitrogen fixation rates in N. spumigena. This was not the case in batch incubations, in which changes in nitrogenase activities were recorded during incubations, probably as a result of varying oxygen concentrations. It was therefore concluded that the on‐line method is superior to batch incubations when rates of nitrogenase activity are to be measured. The method is suitable for natural samples (water or sediment).

(Uploaded by Plazi for the Bat Literature Project) Frugivorous bats from the Old and New World use odor cues to locate and assess fruit condition. We hypothesized that Egyptian fruit bats (Rousettus aegyptiacus) use as odor cues those volatile compounds that increase in emission rate as fruit ripens. We examined whether the smell of fermentation products may indicate the degree of ripeness to fruit bats. We analyzed volatile compounds in the headspace (the gas space above a fruit in a closed container) of dates (Phoenix dactylifera) and rusty figs (Ficus rubiginosa), both of which are consumed by fruit bats, to elucidate which compounds originate from fermentative pathways and to determine which change in emission rate during ripening. Ethanol, acetaldehyde, and acetic acid were the only volatile compounds detected as products of fermentation in both fruits. In dates, emission rates of these compounds increased during maturation, whereas in rusty figs, they decreased or remained constant. Methanol, although not a fermentation product, increased in emission rate during ripening in both fruits. We found that R. aegyptiacus was neither attracted nor deterred by the smell of methanol at any of the concentrations used. Although the odor of ethanol emanating from food containing concentrations similar to those found in ripe fruit did not attract the bats, at relatively high concentrations (Q1%), the smell of ethanol deterred them. Thus, ethanol at high concentrations may serve as a signal for bats to avoid overripe, unpalatable fruit.

Two important factors influencing rice plant survival during submergence are limitations to gas diffusion under water, and reduced irradiance that impair photosynthesis and efficient utilization of carbohydrates. Thus, survival during submergence may largely depend on accumulation of high carbohydrate concentrations prior to submergence and a capacity for maintaining energy production through rapid alcoholic fermentation under oxygen shortage. During flash flooding, a third factor thought to affect survival is the aerobic shock during the post-submergence period when floodwaters recede. Changes in the level of antioxidants and enzymes such as superoxide dismutase (SOD) suggest that tolerant rice cultivars develop protective systems to air after exposure to hypoxic or anoxic environments. These responses are similar to other wetland plants. The capacity to survive submergence depends not only on specific environmental factors, but also on the strategy that plants have evolved for adoption to particular flood-prone environments. In rice the two main strategies are to elongate and escape, or not to elongate and conserve resources. For rainfed lowland rice exposed to flash flooding, elongation growth during complete submergence has major adverse effects on survival, presumably since this competes with maintenance processes which require carbohydrates and energy. Selection for minimal elongation during submergence is currently being exploited as a trait for submergence tolerance by rainfed lowland rice breeders in south and southeast Asia. Gene mapping for submergence tolerance has been useful in identifying one prominent locus for submergence tolerance. Fine scale gene mapping and sequencing may facilitate further progress in the physiology and genetics of submergence tolerance. Recently published data demonstrate that improving submergence tolerance may be possible through up-regulation of genes for particular traits such as pyruvate decarboxylase (PDC) for alcoholic fermentation. Validation of appropriate mechanisms in other cultivars for target environments, and development and utilization of molecular markers to follow these traits in breeding programs, will therefore be high priorities for future work on submergence tolerance of rice.

We present a multi-species trace gas sensor based on a fast, compact home-built Fourier transform spectrometer (FTS) combined with a broadband mid-infrared supercontinuum (SC) source. The spectrometer covers the spectral bandwidth of the SC source (2 - 4 µm) and provides a best spectral resolution of 1 GHz in 6 seconds. It has a detection sensitivity of a few hundred of ppbv Hz-1/2 for different gas species. We study the performance of the developed spectrometer in terms of precision, linearity, long-term stability, and multi-species detection. We use the spectrometer for measuring fruit-produced volatiles under different atmospheric conditions and compare the performance with a previously developed scanning grating-based spectrometer.