Department of Botany, Oxford
New Phytologist (Impact Factor: 6.74). 03/1959; 58(1):1 - 4. DOI: 10.1111/j.1469-8137.1959.tb05328.x

ABSTRACT Peas were sown in sand, which was treated with varying concentrations of trichloracetic acid. The behaviour of water droplets on the leaves of peas was observed, and it was found that the angle made by the droplet on the surface falls with increasing concentration of T.C.A. No changes in leaf structure, which could account for these changes in behaviour, were revealed by ordinary light microscopy. Investigation of the sub-microscopic anatomy of the surface by the carbon replica technique under the electron microscope did reveal significant differences in the leaf surfaces. A reduction in the number and a change in form of the minute wax structures occurs with an increased concentration of T.C.A. in the soil. These changes correlate well with an increase in the wettability of the leaf surface as determined by the contact angle of water droplets.

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    ABSTRACT: Haloacetic acids are atmospheric oxidation products of airborne C2-halocarbons which are important solvents and propellants. Levels of trichloroacetate (TCA) in conifer needles from mountain ranges in Germany (Black Forest, Erzgebirge) and from two sites in Finland are compared; TCA is present in conifer needles at concentrations up to 0.7 μmol/kg, MCA up to 0.2 μmol/kg. At the Finnish sites, TCA-concentrations and branch degeneration symptoms of Scots pine are correlated. Monochloroacetate (MCA) has been determined in needle samples from Southern Germany in concentrations exceeding its phytotoxicity threshold towards photoautotrophic organisms. Data on atmospheric chloroacetate levels in Germany are also given; ambient air levels of chloroacetic acids range from about 2 pmol/m(3) (TCA) to 390 pmol/m(3) (MCA). TCA and dichloroacetic acid (DCA) arise from atmospheric oxidation of airborne C2-chlorocarbons, while the source of MCA is not yet known; several tentative pathways are suggested.
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    ABSTRACT: The study has been performed in a supposedly clean-air region of a Northern Finnish forest with a homogeneous stand of Scots pine. Stomatal epicuticular wax layer erosion is described using a classification system of five erosion stages. The percentage of stomatal wax within each erosion stage is calculated and the results are treated statistically, which makes the morphological study of the needle surface semi-quantitative. Severe wax degradation has already been found in the current year, increasing with the age of the needles. In this area, the wax layer erosion is correlated with secondary air pollutants, as analyses have shown high trichloroacetate (TCA) levels in needles from the same trees. The wax layer analyses are in accordance with earlier findings which have demonstrated differences in tolerance to TCA.
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    ABSTRACT: The temperature dependence of the local diffusion of fluorescent molecular probes of various polarities (alkane, long-chain fatty acid, short-chain alcohol and fatty acid), all labelled with 7-nitrobenz-2-oxa-1,3-diazol-4-yl in the cuticle of Clivia miniata Regel was studied by the technique of fluorescence recovery after photobleaching. The technique yields the coefficient of diffusion, D, in the plane of the cuticle over distances of some 10 μm and the fraction, R, of mobile reporter molecules. The inner (more hydrophilic) and the outer (more hydrophobic) faces of the cuticle were studied separately by appropriate incubation. The value of D was found to depend sensitively on the polarity of the probe, the temperature and the position within the cuticle (outer hydrophobic or inner hydrophilic side). Depending on the type of probe, D increased (in the case of the alkane) or decreased (in the case of the alcohol) after removal of the (monomeric) waxes. The electron-spin-resonance (ESR) spectra of incorporated spin-labelled fatty-acid probes measured in the intact cuticle contained a major component similar to the spectrum recorded from the polymerized matrix from which waxes had been extracted, and a second component similar to the spectrum from the monomeric waxes. At low temperatures, the ESR spectra from labels at two different chain positions corresponded to chain motion which was slow on the ESR timescale. At high temperatures, the spectral component from the monomeric waxes indicated chain motions in the motional narrowing regime which were of an essentially isotropic nature.No evidence was found for a liquid-crystalline lipid phase such as found for the polar lipids in cell membranes, nor was there evidence for a sharp, thermotropic, lipid-phase transition either in the cuticle or in the waxes. Experiments with oriented samples did not demonstrate the presence of large domains with a uniform orientation of the lipid chains relative to the cuticular layers. The diffusion measurements and spin-label studies provide evidence for conformational changes of the cuticle extending over the whole temperature range studied (10° C to 70° C). These conformational changes are attributed to phase-separation processes within the cuticle. The phase separation in extracted waxes extended over a similar broad temperature range. This indicates that the transitions in the cuticle are largely determined by these components. At higher temperatures, however, the chain mobility in the regions of monomeric wax was considerably greater than that in the polymerized matrix. The experimental results strongly indicate that all three layers of the Clivia cuticle exhibit a multilamellar structure of alternatingly stacked, highly hydrophobic layers of welldefined thickness (5±0.5 nm) and more disordered layers of variable (4 to 15 nm) thickness. The lamellae are wellordered and extend over the whole leaf in the cuticle proper but are split-up into small domains in the inner and the external cuticular layer. Furthermore, changes of the molecular transport properties caused by the influence of ozone exerted during the growth of the plant were studied. We found that the diffusion coefficient increased both in the outer and the inner layer of the cuticle. A particularly large increase, by about a factor of three, was found for alkane diffusion in the hydrophobic outer face, pointing to defects in the polymerized matrix.
    Planta 07/1990; 181(4):475-86. · 3.38 Impact Factor