Visualizing rhizosphere chemistry of legumes with mid-infrared synchrotron radiation

A bright synchrotron light source operated by the Lawrence Berkeley National Laboratory served as an external source for infrared (IR) microscopy of plant root microcosms. Mid-IR light from synchrotrons is 2-3 orders of magnitude brighter than conventional sources, providing contrast based on the chemical information in the reflected signal at a spatial resolution near the diffraction-limit of 3-10 microm. In an experiment using plant root microcosms fitted with zinc selenide IR-transmissive windows (50 mm x 20 mm x 1 mm), we describe chemical differences and similarities within the root zone of mung bean (Vigna radiata L.), grown with or without phosphorus, and revealed by reflectance spectromicroscopy. Comparative root and root-exudate profiles are described in sand/silt culture over the wavelength range of 2.5 to 16 pm (4.000 to 650 cm(-1) ) in the mid-IR. the spectral region most useful for the analytical identification of small organic molecules. Root epidermal tissue of plants grown with low phosphorus showed a greater lipid contribution and less lignin than nutrient-sufficient plants. In the zone 200 microm from the root axis, control plants were enriched with simple sugars and monomeric lignin precursors. In low-phosphorus plants, the rhizosphere possessed IR signatures from protein and sugars. Individual soil minerals could be easily discriminated from biological material. Synchrotron IR spectromicroscopy, therefore, complements existing root imaging techniques.     

IR spectroscopic characteristics of cell cycle and cell death probed by synchrotron radiation based Fourier transform IR spectromicroscopy

Synchrotron radiation based Fourier transform IR (SR-FTIR) spectromicroscopy allows the study of individual living cells with a high signal to noise ratio. Here we report the use of the SR-FTIR technique to investigate changes in IR spectral features from individual human lung fibroblast (IMR-90) cells in vitro at different points in their cell cycle. Clear changes are observed in the spectral regions corresponding to proteins, DNA, and RNA as a cell changes from the G(1)-phase to the S-phase and finally into mitosis. These spectral changes include markers for the changing secondary structure of proteins in the cell, as well as variations in DNA/RNA content and packing as the cell cycle progresses. We also observe spectral features that indicate that occasional cells are undergoing various steps in the process of cell death. The dying or dead cell has a shift in the protein amide I and II bands corresponding to changing protein morphologies, and a significant increase in the intensity of an ester carbonyl C===O peak at 1743 cm(-1) is observed. Copyright John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 329-335, 2000     

Monitoring and manipulation of the pH of single cells using infrared spectromicroscopy and a molecular switch

Background

The pH of a biological system is a crucial determinant of the structures and reactivity of its components and cellular homeostasis of H⁺ is critical for cell viability. Control and monitoring of cellular acidity are highly desirable for the purpose of studying biochemical processes in vivo.

Methods

The effect of photolysis of a caged strong acid, the ester 1-(2-nitrophenyl)-ethylhexadecyl sulfonate (HDNS) is used to cause a controlled drop in pH in single cells. An isolated cell is selected under the IR microscope, irradiated with near-UV light and monitored by FTIR.

Results

We demonstrate the use of FTIR spectromicroscopy to monitor light-induced acidification of the cellular medium by measuring the increased concentration of CO₂ and corresponding decrease of HCO₃⁻ in the cell and in the surrounding medium.

Conclusions

We have demonstrated a method to control and accurately monitor the changes in pH of a cellular system by coupling a caged proton-releasing agent with FTIR spectromicroscopy detection. The overall implementation of photolysis and spectroscopic detection in a microscope optical configuration ensures single cell selectivity in both acidification and monitoring. We show the viability of monitoring of pH changes by FTIR spectromicroscopy with sensitivity comparable to that of glass electrodes, better than the existing methods for determining cell pH.

General significance

Reporting the effect of small variations of cellular acidity provides a major improvement in the understanding of the interplay between molecular properties as assessed in vitro and cell physiology.     

Imaging interactions of cationic antimicrobial peptides with model lipid monolayers using X-ray spectromicroscopy

The interaction of antimicrobial peptide anoplin with 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] lipid monolayers was imaged with atomic force microscopy, scanning transmission X-ray microscopy, and X-ray photoemission electron microscopy. X-ray absorption spectromicroscopy of the surface revealed the domains of the phase-segregated surface to be composed of 98(±5)% lipid while the matrix consisted of a ~50:50 lipid-peptide mixture. We show X-ray spectromicroscopy to be a valuable quantitative tool for label-free imaging of lipid monolayers with antimicrobial peptides at a lateral spatial resolution below 80 nm.     

Fourier transform infrared evaluation of microscopic scarring in the cardiomyopathic heart: effect of chronic AT1 suppression

Our primary aim was to investigate the use of Fourier transform infrared (FTIR) spectromicroscopy as an accurate assay of cardiac extracellular matrix remodeling. Abnormal rearrangement or remodeling of the cardiac extracellular matrix is known to contribute to cardiac dysfunction. The microscopic multifocal necrosis and scarring are modulated by chronic AT(1) receptor blockade in experimental cardiomyopathy; thus, we also wished to rationalize the spectromicroscopic differences among control, untreated cardiomyopathic (CMP), and losartan-treated cardiomyopathic (LOS) hearts according to the pathogenesis of experimental cardiomyopathy. Male UM-X7.1 cardiomyopathic Syrian hamsters at early and late (65 and 200 days) stages of cardiomyopathy were subjected to 4-week losartan (15 mg/kg/day continuous infusion) treatment. Focal collagen microdomain distribution was confirmed spectroscopically by observation of the collagen IR fingerprint in the 1000-1800 cm(-1) region. Synchrotron FTIR spectromicroscopic map data were obtained from control (F1-beta strain) hamsters, nontreated cardiomyopathic, and losartan-treated CMP animals and imaged with mapping software, according to intensity of collagen fingerprint. Compared to controls, untreated late-stage CMP myocardium was characterized by elevated levels of fibrillar collagens and this was partially normalized with a 4-week losartan treatment. FTIR spectromicroscopy revealed that elevated collagen expression in focal microdomains is present in late-stage cardiomyopathy, and 4-week AT(1) blockade is associated with attenuation of collagen absorption in these lesions.     

Soft x-ray microscopy

Soft x-ray microscopes are beginning to provide information to complement that obtained from optical and electron microscopy. Soft x-ray microscopy can deliver 30-nm resolution images of hydrated cells up to approximately 10 microns thick, and efforts towards obtaining higher resolution are under way. Although living specimens cannot be studied readily except in single exposures, fixed samples can be imaged at high resolution, and flash-frozen specimens can be studied without chemical modification and without significant radiation damage. Tomography is being developed for 3-D imaging, and spectromicroscopy offers unique capabilities for biochemical mapping of unlabelled structures beyond those of gold and fluorescent labels. Currently, most soft x-ray microscopes operate at synchrotron radiation facilities, but laboratory-scale microscopes are being developed too.     

Quantifying nanoscale biochemical heterogeneity in human epithelial cancer cells using combined AFM and PTIR absorption nanoimaging

Subcellular chemical heterogeneity plays a key role in cell organization and function. However the biomechanics underlying the structure‐function relationship is governed by cell substructures which are poorly resolved using conventional chemical imaging methods. To date, advances in sub‐diffraction limited infrared (IR) nanoscopy have permitted intracellular chemical mapping. In this work we report how image analysis applied to a combination of IR absorption nanoimaging and topographic data permits quantification of chemical complexity at the nanoscale, enabling the analysis of biochemical heterogeneity in mammalian cancer cells on the scale of subcellular features. (© 2013 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effect of Sugars on Rabbit Serum Albumin Stability and Induction of Secondary Structure

The effect of sugars (sucrose, maltose, and glucose) on the thermal and chemical denaturation of rabbit serum albumin (RSA) has been examined by viscosity and far UV circular dichroism measurements. The viscosity measurements indicate a change in the reduced viscosity from 4.18 to 16.23 ml/g in the temperature range from 20 to 90°C. The T _m value for RSA obtained by viscosity measurements in the absence of sugar was found to be 63.2°C, but this value increased to 68.4, 70.3, and 73.2°C in the presence of 0.5 M sucrose, 0.5 M glucose, and 0.5 M maltose, respectively. Further, the stability of RSA in the presence of 0.5 M sugars was also investigated by measuring the mean residue ellipticity at 222 nm (MRE₂₂₂) using chemical (0-6 M guanidine hydrochloride) and thermal (20-90°C) transition processes. At the midpoint of the chemical denaturation, the increase in the MRE values at 222 nm in the presence of 0.5 M sugars were of the same order as the increase in the T _m values, i.e., maltose > glucose > sucrose. Interestingly, a mixture of 0.25 M glucose and 0.25 M fructose showed a cumulative effect on the thermal as well as chemical stability as compared to 0.5 M sucrose alone. In the case of both thermal and chemical denaturation, there was an increase in the MRE₂₂₂ values upon addition of various sugars, this indicating induction of secondary structure in the protein.     

Biological applications of synchrotron radiation infrared spectromicroscopy

Extremely brilliant infrared (IR) beams provided by synchrotron radiation sources are now routinely used in many facilities with available commercial spectrometers coupled to IR microscopes. Using these intense non-thermal sources, a brilliance two or three order of magnitude higher than a conventional source is achievable through small pinholes (< 10 μm) with a high signal to-noise ratio. IR spectroscopy is a powerful technique to investigate biological systems and offers many new imaging opportunities. The field of infrared biological imaging covers a wide range of fundamental issues and applied researches such as cell imaging or tissue imaging. Molecular maps with a spatial resolution down to the diffraction limit may be now obtained with a synchrotron radiation IR source also on thick samples. Moreover, changes of the protein structure are detectable in an IR spectrum and cellular molecular markers can be identified and used to recognize a pathological status of a tissue. Molecular structure and functions are strongly correlated and this aspect is particularly relevant for imaging. We will show that the brilliance of synchrotron radiation IR sources may enhance the sensitivity of a molecular signal obtained from small biosamples, e.g., a single cell, containing extremely small amounts of organic matter. We will also show that SR IR sources allow to study chemical composition and to identify the distribution of organic molecules in cells at submicron resolution is possible with a high signal-to-noise ratio. Moreover, the recent availability of two-dimensional IR detectors promises to push forward imaging capabilities in the time domain. Indeed, with a high current synchrotron radiation facility and a Focal Plane Array the chemical imaging of individual cells can be obtained in a few minutes. Within this framework important results are expected in the next years using synchrotron radiation and Free Electron Laser (FEL) sources for spectro-microscopy and spectral-imaging, alone or in combination with Scanning Near-field Optical Microscopy methods to study the molecular composition and dynamic changes in samples of biomedical interest at micrometric and submicrometric scales, respectively.     

A newly-developed metal artifact reduction algorithm improves the visibility of oral cavity lesions on 320-MDCT volume scans

PurposeTo investigate whether a newly-developed single-energy metal artifact reduction (SEMAR) algorithm applied to images acquired on a 320-MDCT volume scanner reduces image artifacts from dental metal.MethodsWe inserted the lower right teeth covered with a dental metal alloy and crown in a skull phantom and performed single-volume scanning on a second-generation 320-MDCT scanner. A 12-mm diameter spherical lesion was placed either close to or far from the dental metal. The tube voltage and current were 120 kVp and 80 or 155 mA, respectively. Images were reconstructed with filtered back projection (FBP) or iterative reconstruction (IR), with or without SEMAR. We calculated the signal-to-artifact ratios (SAR) to quantify the visibility of the lesion. Two radiologists inspected 96 images (48 with lesion and 48 without) for the presence or absence of the lesion using a 5-point ordinal scale (1 = definitely absent to 5 = definitely present).ResultsOn images reconstructed with FPB and IR with SEMAR, streak artifacts from the dental metal were reduced substantially compared to images without SEMAR. At 155 mA with the lesion near the dental metal, the SARs were better on FBP and IR images (FBP: 1.7 and 0.5 with and without SEMAR, respectively; IR: 1.6 and 0.9 with and without SEMAR, respectively). The observer visual scores improved with SEMAR (FBP: 4.2 and 3.2 with and without SEMAR, respectively; IR: 4.2 and 3.0).ConclusionThe SEMAR algorithm reduces dental metal artifacts and improves lesion detectability and image quality in patients with oral cavity lesions.     

Synchrotron radiation FTIR detection of a metal-carbonyl tamoxifen analog. Correlation with luminescence microscopy to study its subcellular distribution

1,1-Di(4-hydroxyphenyl)-2-cyrhetrenylbut-1-ene 1 is an organometallic conjugate where a [(Cp)Re(CO)₃] unit is linked to a hydroxytamoxifen-like structure. Its subcellular nuclear distribution was previously observed in a single cell using the near-field technique AFMIR. We show here that synchrotron radiation FTIR spectromicroscopy (SR-FTIR-SM) enabled the mapping of 1 based on its IR-signature (characteristic bands in the 1850–2200 cm^− 1 range) and pointed out the colocalization of 1 with an area of high amide density. Fluorescence microscopy using DAPI staining performed on the same cells confirmed that this area corresponds to the cell nucleus.     

Infrared laser‐mediated local gene induction in medaka,zebrafish and Arabidopsis thaliana

Heat shock promoters are powerful tools for the precise control of exogenous gene induction in living organisms. In addition to the temporal control of gene expression, the analysis of gene function can also require spatial restriction. Recently, we reported a new method for in vivo, single‐cell gene induction using an infrared laser‐evoked gene operator (IR‐LEGO) system in living nematodes (Caenorhabditis elegans). It was demonstrated that infrared (IR) irradiation could induce gene expression in single cells without incurring cellular damage. Here, we report the application of IR‐LEGO to the small fish, medaka (Japanese killifish; Oryzias latipes) and zebrafish (Danio rerio), and a higher plant (Arabidopsis thaliana). Using easily observable reporter genes, we successfully induced gene expression in various tissues in these living organisms. IR‐LEGO has the potential to be a useful tool in extensive research fields for cell/tissue marking or targeted gene expression in local tissues of small fish and plants.     

Malnutrition and Mortality Patterns among Internally Displaced and Non-Displaced Population Living in a Camp,a Village or a Town in Eastern Chad

Background

Certain population groups have been rendered vulnerable in Chad because of displacement of more than 200,000 people over the last three years as a result of mass violence against civilians in the east of the country. The objective of the study was to assess mortality and nutritional patterns among displaced and non-displaced population living in camps, villages and a town in the Ouddaï and Salamat regions of Chad.

Methodology

Between May and October 2007, two stage, 30-cluster household surveys were conducted among 43,900 internally displaced persons (IDPs) living in camps in Ouaddai region (n = 898 households), among 19,400 non-displaced persons (NDPs) living in 42 villages in Ouaddai region (n = 900 households) and among 17,000 NDPs living in a small town in Salamat region (n = 901 households). Data collection included anthropometric measurements, measles vaccination rates and retrospective mortality. Crude mortality rate (CMR), mortality rate among children younger than 5 years (U5MR), causes of death and the prevalence of wasting (weight-for-height z score <−2) among children aged 6 to 59 months were the main outcome measures.

Conclusions

The CMR among the 4902 IDPs in Gozbeida camps, 4477 NDPs living in a village and 4073 NDPs living in a town surveyed was 1.8 (95% CI, 1.2–2.8), 0.3 (95% CI, 0.2–0.4), 0.3 (95% CI, 0.2–0.5) per 10,000 per day, respectively. The U5MR in a camp (n = 904), a village (n = 956) and a town (n = 901) was 4.1 (95% CI, 2.1–7.7), 0.5 (95% CI, 0.3–0.9) and 0.7 (95% CI, 0.4–1.4) per 10,000 per day, respectively. Diarrhoea was reported to be the main cause of death. Acute malnutrition rates (according to the WHO definition) among 904 IDP children, 956 NDPs children living in a village, 901 NDP children living in a town aged 6 to 59 months were 20.6% (95% CI, 17.9%–23.3%), 16.4% (95% CI, 14.0%–18.8%) and 10.1% (95% CI, 8.1%–12.2%) respectively. The study found a high mortality rate among IDPs and an elevated prevalence of wasting not only in IDP camps but also in villages located in the same region. The town-dweller population remains at risk of malnutrition. Appropriate contingency plans need to be made to ensure acceptable living standards for these populations.     

Plants experiencing chronic internal exposure to ionizing radiation exhibit higher frequency of homologous recombination than acutely irradiated plants

Ionizing radiation (IR) is a known mutagen responsible for causing DNA strand breaks in all living organisms. Strand breaks thus created can be repaired by different mechanisms, including homologous recombination (HR), one of the key mechanisms maintaining genome stability [A. Britt, DNA damage and repair in plants, Annu. Rev. Plant. Phys. Plant Mol. Biol., 45 (1996) 75-100; H. Puchta, B. Hohn, From centiMorgans to basepairs: homologous recombination in plants, Trends Plant Sci., 1 (1996) 340-348.]. Acute or chronic exposure to IR may have different influences on the genome integrity. Although in a radioactively contaminated environment plants are mostly exposed to chronic pollution, evaluation of both kinds of influences is important. Estimation of the frequency of HR in the exposed plants may serve as an indication of genome stability.We used previously generated Arabidopsis thaliana and Nicotiana tabacum plants, transgenic for non-active versions of the beta-glucoronidase gene (uidA) [P. Swoboda, S. Gal, B. Hohn, H. Puchta, Intrachromosomal homologous recombination in whole plants, EMBO J., 13 (1994) 484-489; H. Puchta, P. Swoboda, B. Hohn, Induction of homologous DNA recombination in whole plants, Plant, 7 (1995) 203-210.] serving as a recombination substrate, to study the influence of acute and chronic exposure to IR on the level of HR as example of genome stability in plants. Exposure of seeds and seedlings to 0.1 to 10.0 Gy 60Co resulted in increased HR frequency, although the effect was more pronounced in seedlings. For the study of the influence of chronic exposure to IR, plants were grown on two chemically different types of soils, each artificially contaminated with equal amounts of 137Cs. We observed a strong and significant correlation between the frequency of HR in plants, the radioactivity of the soil samples and the doses of radiation absorbed by plants (in all cases r0.9, n=6, P<0.05). In addition, we noted that plants grown in soils with different chemical composition, but equal radioactivity, exhibited different levels of HR, dependent upon the absorbed dose of radiation. Remarkably, we observed a much higher frequency of HR in plants exposed to chronic irradiation when compared to acutely irradiated plants. Although acute application of 0.1-0.5 Gy did not lead to an increase of frequency of HR, the chronic exposure of the plants to several orders of magnitude lower dose of 200 muGy led to a 5-6-fold induction of the frequency of HR as compared to the control.     

Bioenergetics of early life: Coupling of reaction networks and compartments may have sparked the first life forms

Living cells are powered by intricate networks of chemical reactions of thousands of molecules. Understanding how living systems emerged through the assembly of chemical processes is one of the biggest challenges in science. Subject Categories: Biotechnology & Synthetic Biology, Evolution & Ecology, Metabolism

How can chemistry turn into biology? How can living cells be built from molecules? These are fundamental questions in biology and, despite much research efforts, remain unanswered. Yet, the past two decades have seen considerable advances in our knowledge of how and which (bio)physical and (bio)chemical processes could have driven the emergence of the first living cells. These achievements have led not only to a better understanding of the molecular origins of life, but also spurred significant developments in synthetic biology, biophysics and supramolecular chemistry. Although the exact events that sparked life on Earth will quite likely remain a mystery, at least partially, exploring the chemical origins of life offers clues about our primordial past and could contribute to shaping our future.

Although the exact events that sparked life on Earth will quite likely remain a mystery […] exploring the chemical origins of life offers clues about our primordial past and could contribute to shaping our future.

     

Expression and regulation of α‐transducin in the pig gastrointestinal tract

Taste signalling molecules are found in the gastrointestinal (GI) tract suggesting that they participate to chemosensing. We tested whether fasting and refeeding affect the expression of the taste signalling molecule, α‐transducin (G_αtran), throughout the pig GI tract and the peptide content of G_αtran cells. The highest density of G_αtran‐immunoreactive (IR) cells was in the pylorus, followed by the cardiac mucosa, duodenum, rectum, descending colon, jejunum, caecum, ascending colon and ileum. Most G_αtran‐IR cells contained chromogranin A. In the stomach, many G_αtran‐IR cells contained ghrelin, whereas in the upper small intestine many were gastrin/cholecystokinin‐IR and a few somatostatin‐IR. G_αtran‐IR and G_αgust‐IR colocalized in some cells. Fasting (24 h) resulted in a significant decrease in G_αtran‐IR cells in the cardiac mucosa (29.3 ± 0.8 versus 64.8 ± 1.3, P < 0.05), pylorus (98.8 ± 1.7 versus 190.8 ± 1.9, P < 0.0 l), caecum (8 ± 0.01 versus 15.5 ± 0.5, P < 0.01), descending colon (17.8 ± 0.3 versus 23 ± 0.6, P < 0.05) and rectum (15.3 ± 0.3 versus 27.5 ± 0.7, P < 0.05). Refeeding restored the control level of G_αtran‐IR cells in the cardiac mucosa. In contrast, in the duodenum and jejunum, G_αtran‐IR cells were significantly reduced after refeeding, whereas G_αtran‐IR cells density in the ileum was not changed by fasting/refeeding. These findings provide further support to the concept that taste receptors contribute to luminal chemosensing in the GI tract and suggest they are involved in modulation of food intake and GI function induced by feeding and fasting.     

Immunoreactivity of Glutamate in Mouse Retina Inner Segment of Photoreceptors With In Vivo Cryotechnique

The purpose of this study was to clarify a previously controversial issue concerning glutamate (Glu) immunoreactivity (IR) in the inner segment (IS) of photoreceptors by using in vivo cryotechnique (IVCT) followed by freeze substitution (FS), which enabled us to analyze the cells and tissues reflecting living states. Eyeballs from anesthetized mice were directly frozen using IVCT. The frozen tissues were processed for FS fixation in acetone containing chemical fixatives, and embedded in paraffin. Deparaffinized sections were immunostained with an anti-Glu antibody. The strongest Glu-IR was obtained in the specimens prepared by FS with paraformaldehyde or a low concentration of glutaraldehyde, whereas no Glu-IR was obtained without the chemical fixatives. The Glu was immunolocalized in the IS, outer and inner plexiform and ganglion cell layers. Thus, the immunolocalization of Glu in the IS was clearly demonstrated using IVCT. (J Histochem Cytochem 57:883–888, 2009)     

Dynamic recognition and repair of DNA complex damage

Irradiation (IR) can be used to treat cancer by inducing complex and irreparable DNA damage in the cancer cells, which may lead to their apoptotic death. However, little is known about the molecular mechanism of this DNA damage. Here, the non-small-cell lung cancer cell line A549 was treated with either X-ray or carbon ion combined with bleomycin (BLM). The cell survival rate, frequency of double-strand breaks (DSBs), dynamic changes in γH2AX, and p53 binding protein 1 (53BP1), and protein expression of Ku70, Rad51, and XRCC1 were determined by the clone formation assay, agarose gel electrophoresis, immunofluorescence, and western blot analysis. The results showed that the most obvious complex DSBs occurred in the carbon IR + BLM group. The number of γH2AX and 53BP1 foci in the 0.5 hr X-ray IR + BLM group was the highest (p < 0.001) among all the groups. γH2AX foci were detected in the nucleus at 0.5, 1, 2, and 4 hr, but were distributed throughout the cell at 6 hr after IR in the carbon ion IR + BLM group. The expression of Ku70 increased and XRCC1 decreased at 2 and 6 hr after IR. Our data indicate that a DNA damage frequency of 13.4/Mbp is caused by clustered DNA damage and further show a correlation between γH2AX, 53BP1, and XRCC1 levels and the extent of DNA damage. The results of this study provide insights into DNA damage recognition and a rationale for the clinical use of radiotherapy.     

Fluorimetric approaches to the study of calcium transients in living cells

This paper is a short review of the fluorimetric methods used to measure intracellular free Ca++ concetration in living cells. The availability of fluorescent probes has greatly contributed to the understanding of the mechanisms responsible for the cellular homeostasys of this second messenger. Data can be collected from populations of cells by spectrofluorimetry or from small groups or single cells by spectromicroscopy. Finally the fluorescent images can be captured by a high sensitivity camera, digitally processed and convert in Ca++ images of the cell. The technique allows recognition of differences in [Ca++]i transients among adjacent cells in a same field or in different regions of a cell and greatly contributes to the identification of the cellular mechanisms modulating [Ca++]i.     

The effect of plant surface characteristics on resistance of rice to the brown planthopper, Nilaparvata lugens

Increased activity of the brown planthopper, Nilaparvata lugens (Stål) on rice variety IR46 over that observed on varieties IR22 and IR62 was shown to be due to the chemical composition of the surface wax. Reduced settling and probing of the plant surface after exploration, and a tendency to move off the stem onto the leaves as a result of chemical cues from the wax make this a potentially important resistance mechanism in rice. Bioassays have shown that the effect is caused by the hydrocarbon- and carbonyl-containing fractions of the wax of IR46. An investigation of N. lugens behaviour on initial contact with the surface of several other varieties of rice has indicated a similar effect for IR36, and a much stronger effect with the wild rice WR221.

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Résumé La composition de la cire superficielle s'est révélée la cause de l'accroissement de l'activité de N. lugens sur la variété de rix IR46, par rapport aux variétés IR22 et IR62. Un mécanisme important de la résistance potentielle du riz est dû aux conséquences des caractéristiques chimiques de la cire: établissement et sondage de la plante réduits après exploration, et tendance à quitter la tige pour gagner les feuilles. Des expériences ont montré que ces effets étaient provoqués par les fractions de la cire de IR46 contenant des hydrocarbures et des carbonyls. L'étude du comportement de N. lugens, lors du premier contact avec la surface de plusieurs autres variétés, a montré un effet semblable pour IR36 et un effet beaucoup plus fort avec le riz sauvage WR221.