Joseph A. Miehé

Fluorescence Imaging of Water and Temperature Stress in Plant Leaves

Summary Fluorescence images of leaves from tobacco plants (green wild type and aurea mutant) were determinedin the blue (F440), green (F520), red (F690) and far-red region (F740), and also expressed as fluorescence ratio images. Under long-term water stress tobacco plants initially showed constant ratios of the blue to red fluorescence (F440/F690) and the blue to far-red fluorescence (F440/F740). Below a distinct threshold in water content (84° in green and 88° in aurea tobacco), however, a linear increase of the fluorescence ratios blue/red and blue/far-red was observed. This was due to a distinct increase in the bluegreen fluorescence emission, whereas the red and far-red chlorophyll fluorescence increased to a lower proportion. These changes in fluorescence ratios could easily be monitored by high resolution fluorescence imaging of whole leaves. For each point of the leaf, the fluorescence ratio can be read from the fluorescence ratio images of the leaves. In contrast, a short-term heat plus water stress in green tobacco plants was very fast detected via fluorescence imaging as a significant increase of red and far-red chlorophyll fluorescence emission (F690 and F740) on the leaf rim, whereas the central part of the leaf still exhibited the regular fluorescence signatures of photosynthetically active leaves. A combined outdoor stress (light, heat and water stress) at a dry sunny summer period was detected in Rhododendron by fluorescence imaging due to a much reduced red and far-red chlorophyll fluorescence. The latter was caused by UV-absorbing substances (e.g. flavonols) which accumulated primarily in the epidermis of these stressed leaves. These compounds seemed to act as UV-radiation filter, thus reducing the amount of the UV-excitation radiation, which could penetrate the mesophyll and which resulted in a reduced chlorophyll fluorescence excitation and emission. These results demonstrate that fluorescence imaging of leaves in the blue, green, red and far-red emission bands is an excellent tool for an early stress detection in plants, which is much superior to the hitherto applied spectral point data measurements.

Detection of nutrient deficiencies of maize by laser induced fluorescence imaging

Summary Laser-induced fluorescence is an active method of sensing the state of health of the plants and the photosyntheticapparatus, as it is related not only to the pigment concentrations but also to the physiological activity. A high gain and high spatial resolution fluorescence imaging set up, consisting of a pulsed Nd:YAG laser for the excitation (355 nm) and of an intensified gated CCD numerical camera, has been used for monitoring various nutrient deficiencies of maize (Zea mays L.) by recording fluorescence images of the leaves at 440, 520, 690 and 740 nm. The plant status was characterised by the fluorescence ratios F440/F520, F440/F690, F440/F740 and F690/F740. The experiments performed on field maize supplied with various amounts of nitrogen and on greenhouse maize with defined mineral deficiencies showed that all the deficiencies could be monitored by the fluorescence ratios and in some cases directly on the fluorescence images by considering the spatial distribution of the emission on the leaf surface. From this work it appeared that the efficiency of detection depended on the period of measurements and on the age of the leaves. The fluorescence ratios F440/F690 and F440/F740 were found more sensitive to the growth conditions than the most frequently used chlorophyll fluorescence ratio F690/F740.

Towards molecular switching: Photophysical properties of N,N′-bis(4-cyanophenyl)piperazine, a bridging TICT molecule

Abstract The properties of N,N′-bis(4-cyanophenyl)piperazine are described. This molecule has been devised to exhibit bridging properties, together with the possibility of giving twisted internal charge transfer (TICT) states following irradiation. The crystal structure shows that the molecule is almost planar in the ground state. Photochemical excitation on the charge transfer band at 300 nm gives rise to a luminescence which is very sensitive to the solvent polarity. In butanol, the dual luminescence characteristic of TICT is observed, which is attributed to the twisting motion of the acceptor(s) part of the molecule with respect to the donor. Transient absorption measurements have been also performed, which characterize the triplet state. A comparison with dimethylaminobenzonitrile is made.

Remote Sensing of Plants by Streak Camera Lifetime Measurements of the Chlorophyll a Emissionα

Summary The possibility of time resolved chlorophyll a fluorescence measurements using an intensified and gatedstreak camera was demonstrated on different plants at a distance of 40-80 m. The investigations, carried out in various experimental conditions: different target geometries (one planar leaf, tilted leaves, sparce foliage, separated levels of leaves), variable slit widths (0.1 to 1 mm) of the camera and measurements at different weather conditions have shown a good reproducibility of the results. The decay profiles were analyzed in order to obtain the best fit between the experimental curves and those obtained by convoluting the experimental response function R exp ( t ) with the theoretical emission law F( t ) modelled by a sum of two or three exponentials. The mean value T m of the chlorophyll fluorescence lifetimes was determined for each experimental condition. For example for poplar leaves measured in October 1993, t m was equal to = 0.8 ns in the morning, decreased strongly to = 0.4 ns in midday and then slowly increased to 1.21 ns in the night.

Twisted internal charge transfer (TICT) effect in bis(4-cyanophenyl)piperazine, a pseudo-dimer of dimethylaminobenzonitrile: a comparative study

Abstract Dimethylaminobenzonitrile (DMABN) and N,N′-bis(4-cyanophenyl)piperazine (BCPPZ) have been comparatively studied by X-ray diffraction, fluorescence and time-resolved emission and absorption. BCPPZ can be considered as a pseudo-dimer made up of two weakly interacting DMABN moieties. The crystal structure of DMABN is reported for the first time: it shows an almost perfect planarity. By contrast, BCPPZ is appreciably twisted around the C-N bonds connecting the piperazine part and the cyanophenyl group. The twist is assigned to intramolecular H·H repulsions and thus should also be present in solution. The photophysical properties of BCPPZ and DMABN are very similar and, in particular, the dual luminescence typical of the formation of a twisted internal charge transfer (TICT) state is also observed in BCPPZ. The only difference lies in the values of the kinetic and thermodynamic parameters describing the interconversion between the planar excited state and the TICT state: this latter state is thermodynamically more stable for BCPPZ than for DMABN. The general analogy in the photophysical behaviour implies that, while the ground state of BCPPZ is centrosymmetric, the excited states exhibit a broken symmetry which can be qualitatively attributed to the weak orbital interaction between the constituent parts.

Intramolecular charge-transfer fluorescence of a new class of sterically hindered bichromophoric molecules

Abstract We present an experimental study of the fluorescence properties of some diarylethylene derivatives whose excited states have charge-transfer character and whose emission spectra are strongly solvent dependent. Time-resolved experiments performed in propanol solutions at low temperature show that the total emission decays are strongly non-exponential, indicating the existence of an intramolecular reaction, with a time-dependent rate, from the initial perpendicular configuration to the nearly planar one. The time-resolved spectra show that an important spectral relaxation takes place with two characteristic times depending on the temperature.

State mixing in indoline derivatives: A steady-state and dynamical-fluorescence spectroscopic study

Abstract The polarity-dependent Herzberg—Teller mixing of 1 L a - and 1 L b -type excited states is investigated for N-ethyl indolines bearing as p-acceptor substituent a cyano (EIN) and a carboxylic acid ethyl ester (EICEE) function. EICEE shows strongly temperature-dependent fluorescence spectral shapes. Low-temperature time-resolved measurements indicate a temporal evolution of the excited-state nature on a time scale faster than that of the solvent relaxation and of the dynamical solvatochromism.

Laser wavelength dependence of YBa2Cu3Oy laser ablation plumes

Abstract The plume produced by laser ablation of an YBa 2 Cu 3 O y target under irradiation with different laser beam wavelengths has been studied by means of intensified CCD imaging. ArF excimer (193 nm) and Nd:YAG (532 and 1064 nm) laser beams were used. The fluence was about 1 J/cm 2 . The investigation was carried out under high vacuum. The plume images show the evolution of different velocity components which depend on the laser wavelength. The fastest one shows a front velocity near 10 4 m/s. It is the dominant feature during many μ s in the images obtained for 193 nm and can be also seen for the case of 532 nm. A slower emission, with an estimated velocity ≤ 3 × 10 2 m/s, can also be observed for the case of 193 nm laser irradiation. Two slower velocity components are present in the 532 and 1064 nm laser plumes. One of them has a front velocity around 3 × 10 2 and 7 × 10 2 m/s for 532 and 1064 nm laser wavelength, respectively. The velocity of the other one is estimated as ≤ 10 2 m/s.

Oscillator phase noise measurements by picosecond synchroscan streak camera

A new method/spl minus/with picosecond resolution/spl minus/allowing the recording of the instantaneous time phase fluctuations of a crystal controlled oscillator is presented. The oscillator under test drives the acoustooptic modelocker of a CW Nd:YAG laser associated with a synchronously pumped dye laser. By means of a streak camera illuminated by the ps dye laser pulses and synchronized by the oscillator signal the statistics of its zero crossings is analyzed.<<ETX>>

Test of the deterministic conjecture for the instantaneous time phase fluctuations of an oscillator

The fluctuations observed by recording the picosecond pulses of a mode-locked laser with a synchroscan streak camera are due to the laser jitter and to the variations of the zero crossing of the synchronization. By means of a simple model, it is shown that the dispersions measured when the synchronization is generated from the mode-locker oscillator reflect the instantaneous time phase fluctuations of this oscillator. From the study of the experimental recordings with methods of time series analysis it results that the phase noise of the electronic oscillator is consistent with an underlying low-dimensional strange attractor.RésuméLes fluctuations observées en enregistrant les impulsions picosecondes d’un laser à blocage de modes avec une caméra à balayage de fente fonctionnant en mode synchroscan sont dues à la gigue du laser et aux variations du passage par zéro de la synchronisation. Un modèle simple permet de montrer que les dispersions mesurées quand la synchronisation est générée par l’oscillateur du bloqueur de modes reflètent les fluctuations temporelles de la phase instantanée de cet oscillateur. L’étude des enregistrements, par des méthodes d’ana-lyse de séries temporelles, fait apparaître que les fluctuations de phase de l’oscillateur électronique sont compatibles avec la présence d’un attracteur étrange de faible dimension.