Frank Kühnemann

Herbivore-induced ethylene suppresses a direct defense but not a putative indirect defense against an adapted herbivore.

Abstract. Herbivory induces both direct and indirect defenses in plants; however, some combinations of these defenses may not be compatible. The jasmonate signal cascade activated both direct (nicotine accumulations) and indirect (mono- and sesquiterpene emissions) whole-plant defense responses in the native tobacco Nicotiana attenuata Torr. Ex Wats. Nicotine accumulations were proportional to the amount of leaf wounding and the resulting increases in jasmonic acid (JA) concentrations. However, when larvae of the nicotine-tolerant herbivore, Manduca sexta, fed on plants or their oral secretions were applied to leaf punctures, the normal wound response was dramatically altered, as evidenced by large (4- to 10-fold) increases in the release of (i) volatile terpenoids and (ii) ethylene, (iii) increased (4- to 30-fold) accumulations of endogenous JA pools, but (iv) decreased or unchanged nicotine accumulations. The ethylene release, which was insensitive to inhibitors of induced JA accumulation, was sufficient to account for the attenuated nicotine response. Applications of ethylene and ethephon suppressed the induced nicotine response and pre-treatment of plants with a competitive inhibitor of ethylene receptors, 1-methylcyclopropene, restored the full nicotine response. This ethylene burst, however, did not inhibit the release of volatile terpenoids. Because parasitoids of Manduca larvae are sensitive to the dietary intake of nicotine by their hosts, this ethylene-mediated switching from direct to a putative indirect defense may represent an adaptive tailoring of a plants defense response.

Rapid regulation of the methylerythritol 4-phosphate pathway during isoprene synthesis.

More volatile organic carbon is lost from plants as isoprene than any other molecule. This flux of carbon to the atmosphere affects atmospheric chemistry and can serve as a substrate for ozone production in polluted air. Isoprene synthesis may help leaves cope with heatflecks and active oxygen species. Isoprene synthase, an enzyme related to monoterpene synthases, converts dimethylallyl diphosphate derived from the methylerythritol 4-phosphate pathway to isoprene. We used dideuterated deoxyxylulose (DOX-d2) to study the regulation of the isoprene biosynthetic pathway. Exogenous DOX-d2 displaced endogenous sources of carbon for isoprene synthesis without increasing the overall rate of isoprene synthesis. However, at higher concentrations, DOX-d2 completely suppressed isoprene synthesis from endogenous sources and increased the overall rate of isoprene synthesis. We interpret these results to indicate strong feedback control of deoxyxylulose-5-phosphate synthase. We related the emission of labeled isoprene to the concentration of labeled dimethylallyl diphosphate in order to estimate the in situ Km of isoprene synthase. The results confirm that isoprene synthase has a Km 10- to 100-fold higher for its allylic diphosphate substrate than related monoterpene synthases for geranyl diphosphate.

Cellulysin from the plant parasitic fungus Trichoderma viride elicits volatile biosynthesis in higher plants via the octadecanoid signalling cascade.

Cellulysin, a crude cellulase from the plant parasitic fungus Trichoderma viride, induces the biosynthesis of volatiles in higher plants (Nicotiana plumbaginifolia, Phaseolus lunatus, and Zea mays) when applied to cut petioles by the transpiration stream. The pattern of the emitted volatiles largely resembles that from a herbivore damage or treatment of the plants with jasmonic acid (JA) indicating that cellulysin acts via activation of the octadecanoid signalling pathway. The treatment with cellulysin raises the level of endogenous JA after 30 min and is followed by a transient emission of ethylene after 2–3 h. Volatile production becomes significant after 12–24 h. Inhibitors of the JA pathway effectively block the cellulysin‐dependent volatile biosynthesis.

Parts per trillion sensitivity for ethane in air with an optical parametric oscillator cavity leak-out spectrometer

Spectroscopic detection of ethane in the 3-microm wavelength region was performed by means of a cw optical parametric oscillator and cavity leak-out. We achieved a minimum detectable absorption coefficient of 1.6 x 10(-10) cm 1/square root of Hz, corresponding to an ethane detection limit of 6 parts per trillion/square root of Hz. For 3-min integration time the detection limit was 0.5 parts per trillion. The levels are to our knowledge the best demonstrated so far. These frequency-tuning capabilities facilitated multigas analysis with simultaneous monitoring of ethane, methane, and water vapor in human breath.

Transportable, highly sensitive photoacoustic spectrometer based on a continuous-wave dualcavity optical parametric oscillator

We present an all solid state, transportable photoacoustic spectrometer for highly sensitive mid-infrared trace gas detection. A complete spectral coverage between 3.1 and 3.9 microm is obtained using a PPLN-based continuous-wave optical parametric oscillator pumped by a Nd:YAG laser at 1064 nm. A low threshold is achieved by resonating the pump, and spectral agility by employing a dual-cavity setup. An etalon suppresses mode-hops. Active signal cavity stabilization yields a frequency stability better than +/- 30 MHz over 45 minutes. Output idler power is 2 x 100 mW. The frequency tuning qualities of the OPO allow reliable scan over gas absorption structures. A detection limit of 110 ppt for ethane is achieved.

SIMULTANEOUS ETHANE AND ETHYLENE DETECTION USING A CO-OVERTONE LASER PHOTOACOUSTIC SPECTROMETER: A NEW TOOL FOR STRESS/DAMAGE STUDIES IN PLANT PHYSIOLOGY

Abstract The simultaneous measurement of the C2H6 and C2H4 emission by plant material is known to be a good stress/damage indicator. A photoacoustic spectrometer, utilizing the CO-Overtone laser, has been used for such measurements for the first time. For the simultaneous online detection of C2H6 and C2H4 in plant physiological studies, a sensitivity was achieved of 370 ppt and 2 ppb, respectively. The performance of the system has been demonstrated measuring the stress/damage behaviour of rhododendron leaves after the application of freezing stress.

CO-laser side-band spectrometer: Sub-Doppler heterodyne frequency measurements around 5 µm

We report the realization of a tunable sub-Doppler heterodyne spectrometer with high absolute accuracy, employing side-band generation with a CO laser. The fixed-frequency CO-gas laser, working from 4.7 to 8.4µm, is made partially tunable by the use of microwave side-band generation in a CdTe Electro-Optical Modulator (EOM). This leads to tunable radiation of high spectral purity. We describe the design of the microwave EOM, adapted to the CO laser, its performance and its first application to highly accurate frequency measurements. The side-band radiation is used for sub-Doppler stabilization of the CO laser, while the carrier frequency is mixed with the frequencies of two CO2 reference lasers. As a first result, we present measurements of OCS transitions in the 4.9µm (61 THz) region, reaching an absolute accuracy of 30 kHz (Δν/ν = 5×1O−10). Further application of our spectrometer to calibration gases will establish a variety of InfraRed (IR) calibration standards with a new quality of accuracy.

Light-dependent production of ethylene in Tillandsia usneoides L.

Abstract.Tillandsia usneoides L. is a favorite model plant for investigating ethylene biosynthesis because no soil is needed for cultivation (important for long-term measurements) and small plants and different clones are available. We investigated the endogenous production of ethylene in relation to temperature, light, daylength and CO2 concentration. Using a novel and most sensitive technique to measure ethylene, laser-driven photoacoustic spectroscopy, real-time online measurements were performed. Since T. usneoides is a crassulacean acid metabolism (CAM) plant and does not take up CO2 during the day we could show that ethylene production is strictly light dependent and does not follow any endogenous rhythm. In contrast to reports on other plants, CO2 concentration did not influence the production of ethylene by T. usneoides. However, high ethylene production was obtained after application of 1-aminoacyclopropane-1-carboxylic acid (ACC).

Lithium niobate: wavelength and temperature dependence of the thermo-optic coefficient in the visible and near infrared

The thermo-optic coefficient of lithium niobate (LiNbO3) has been measured in the temperature range from 10 to 160 °C using an interferometric setup. Undoped and magnesium-doped congruently melting LiNbO3 and undoped stoichiometric LiNbO3 were studied over a wide wavelength range in the visible and near infrared (450 – 600 nm and 900 – 1130 nm) using a frequency-doubled cw optical parametric oscillator. Experimental results for congruently grown lithium niobate were aggregated using a Schott equation to describe the wavelength and temperature dependence of the thermo-optic coefficient.

A continuous-wave optical parametric oscillator for mid infrared photoacoustic trace gas detection

We present a continuous-wave, pump-resonant, singly-resonant optical parametric oscillator based on periodically poled lithium niobate in a linear dual-cavity design which is applied for photoacoustic trace gas detection between 2.35 and 3.75 μm. Pumped by a Nd:YAG laser at 1064 nm a single-frequency output power of 2 x 100 mW is achieved. The frequency tuning qualities of the OPO allow to scan gas absorption structures. An ethane detection limit of 110 ppt is achieved. Sensitivity, tuning qualities and compact design make this OPO an ideal laser source in a transportable photoacoustic spectrometer.