Markus Riederer

Biology of the Plant Cuticle.

1. Introduction: Biology of the plant cuticle. Markus Riederer, Julius--von--Sachs--Institut fur Biowissenschaften, Universitat Wurzburg, Wurzburg, Germany. 2. The fine structure of the plant cuticle. Christopher E. Jeffree, Science Faculty Electron Microscope Facility, Edinburgh, UK. 3. The cutin biopolymer matrix. Ruth E. Shark and Shiying Tian, Department of Chemistry and Institute for Macromolecular Assemblies, City University of New York, College of Staten Island, 2800 Victory Boulevard, Staten Island, NY 10314--6600, USA. 4. Composition of plant cuticular waxes. Reinhard Jetter, Departments of Botany and Chemistry, University of British Columbia, Vancouver, Canada Ljerka Kunst and A. Lacey Samuels, Department of Botany, University of British Columbia, Vancouver, Canada. 5. Biosynthesis and transport of plant cuticular waxes. Ljerka Kunst, Department of Botany, University of British Columbia, Vancouver, Canada Dr Reinhard Jetter, Departments of Botany and Chemistry, University of British Columbia, Vancouver, Canada and A. Lacey Samuels, Department of Botany, University of British Columbia, Vancouver, Canada. 6. Optical properties of plant surfaces. Erhard E. Pfundel, Julius--von--Sachs--Institut fur Biowissenschaften, Universitat Wurzburg, Wurzburg, Germany Giovanni Agati, Istituto di Fisica Applicata, Firenze, Italy and Zoran G. Cerovic, LURE--CNRS, Orsay, France. 7. Transport of lipophilic non--electrolytes across the cuticle. Markus Riederer, Julius--von--Sachs--Institut fur Biowissenschaften, Universitat Wurzburg, Wurzburg, Germany and Adrian A. Friedmann, Syngenta Inc, Bracknell, Berkshire, UK. 8. Characterisation of polar paths of transport in plant cuticles. Lukas Schreiber, A-kophysiologie der Pflanzen, Botanisches Institut, Bonn, Germany. 9. Cuticular transpiration. Markus Burghardt and Markus Riederer, Julius--von--Sachs--Institut fur Biowissenschaften, Universitat Wurzburg, 082 Wurzburg, Germany. . 10. The cuticle and cellular interactions. Hirokazu Tanaka and Yasunori Machida, Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan. 11. Microbial communities in the phyllosphere. Johan H. J. Leveau, Centre for Terrestrial Ecology, Heteren, The Netherlands. 12. Filamentous fungi on plant surfaces. Tim L. W. Carver, Plant Genetics and Breeding, IGER, Aberystwyth, UK and. Sarah J. Gurr, Plant Sciences, University of Oxford, Oxford, UK. 13. Plant--Insect interactions on cuticular surfaces. Caroline Muller, Julius--von--Sachs--Institut fur Biowissenschaften, Universitat Wurzburg, Wurzburg, Germany

Foliar Penetration and Accumulation of Organic Chemicals in Plant Cuticles

Industrialization and growth of the human population have led to a progressive deterioration in the quality of the earth’s environment. Huge amounts of chemicals are constantly being released into rivers, lakes, oceans, soils, and atmosphere, and their toxic effects to man, animals, and plants are beginning to cause great concern.

Plant Surface Properties in Chemical Ecology

The surface of the primary aerial parts of terrestrial plants is covered by a cuticle, which has crucial autecological functions, but also serves as an important interface in trophic interactions. The chemical and physical properties of this layer contribute to these functions. The cuticle is composed of the cuticular layer and the cuticle proper, which is covered by epicuticular waxes. Whereas the cutin fraction is a polyester-type biopolymer composed of hydroxyl and hydroxyepoxy fatty acids, the cuticular waxes are a complex mixture of long-chain aliphatic and cyclic compounds. These highly lipophilic compounds determine the hydrophobic quality of the plant surface and, together with the microstructure of the waxes, vary in a species-specific manner. The physicochemical characteristics contribute to certain optical features, limit transpiration, and influence adhesion of particles and organisms. In chemical ecology, where interactions between organisms and the underlying (allelo-) chemical principles are studied, it is important to determine what is present at this interface between the plant and the environment. Several useful equations can allow estimation of the dissolution of a given organic molecule in the cuticle and its transport properties. The implementation of these equations is exemplified by examining glucosinolates, which play an important role in interactions of plants with other organisms. An accurate characterization of physicochemical properties of the plant surface is needed to understand its ecological significance. Here, we summarize current knowledge about the physical and chemical properties of plant cuticles and their role in interactions with microorganisms, phytophagous insects, and their antagonists.

The Developmental Pattern of Tomato Fruit Wax Accumulation and Its Impact on Cuticular Transpiration Barrier Properties: Effects of a Deficiency in a β-Ketoacyl-Coenzyme A Synthase (LeCER6)

Cuticular waxes play a pivotal role in limiting transpirational water loss across the primary plant surface. The astomatous fruits of the tomato (Lycopersicon esculentum) ‘MicroTom’ and its lecer6 mutant, defective in a β-ketoacyl-coenzyme A synthase, which is involved in very-long-chain fatty acid elongation, were analyzed with respect to cuticular wax load and composition. The developmental course of fruit ripening was followed. Both the ‘MicroTom’ wild type and lecer6 mutant showed similar patterns of quantitative wax accumulation, although exhibiting considerably different water permeances. With the exception of immature green fruits, the lecer6 mutant exhibited about 3- to 8-fold increased water loss per unit time and fruit surface area when compared to the wild type. This was not the case with immature green fruits. The differences in final cuticular barrier properties of tomato fruits in both lines were fully developed already in the mature green to early breaker stage of fruit development. When the qualitative chemical composition of fruit cuticular waxes during fruit ripening was investigated, the deficiency in a β-ketoacyl-coenzyme A synthase in the lecer6 mutant became discernible in the stage of mature green fruits mainly by a distinct decrease in the proportion of n-alkanes of chain lengths > C28 and a concomitant increase in cyclic triterpenoids. This shift in cuticular wax biosynthesis of the lecer6 mutant appears to be responsible for the simultaneously occurring increase of water permeance. Changes in cutin composition were also investigated as a function of developmental stage. This integrative functional approach demonstrates a direct relationship between cuticular transpiration barrier properties and distinct chemical modifications in cuticular wax composition during the course of tomato fruit development.

Ecophysiology of cuticular transpiration : comparative investigation of cuticular water permeability of plant species from different habitats

Water permeabilities of astomatous, isolated cuticular membranes (CM) of 24 different plants species were measured. Permeances varied from 1.7×10−11 m·s−1 (Vanilla planifolia leaf) up to 2.1×10−9 m·s−1 (Malus cf. domestica fruit) among different plant species, thus covering a range of over 2 orders of magnitude. Ranking of species according to permeances resulted in four distinct groups. The first group, of species with the lowest cuticular transpiration rates, included evergreen species growing in warm dry tropical climates (e.g. Vanilla planifolia and Monstera deliciosa leaves). The second class, with slightly higher water permeabilities, included evergreen species with typical scleromorphic leaf properties, adapted to a typical mediterranean type of climate with a dry period during the year (e.g. Citrus limon and Olea europaea leaves). The third group of species, where the highest leaf cuticular transpiration rates were observed, included deciduous species normally growing in a tempeate climate (e.g. Juglans regia and Forsythia suspensa leaves). Fruit cuticular membranes (CM) made up the fourth group (e.g. Capsicum annuum and Malus cf. domestica fruits), with even higher permeances than leaves of species from group 3. Thus, it appears that the plant species investigated show ecophysiological adaptations to the climatic demands of their natural habitats in cuticular water permeability.

The effect of the environment on the permeability and composition of Citrus leaf cuticles : II. Composition of soluble cuticular lipids and correlation with transport properties.

The constituents of the soluble cuticular lipids (SCL) of the leaf blades of Citrus aurantium L. were identified by gas chromatography-mass spectrometry and quantified. Major components were 1-alkanols (C24 to C40), n-alkyl esters (C36 to C56), n-alkanoic acids (C28 to C34), n-alkanes (C22 to C40) and triterpenones, while n-alkanals (C29 to C38), sterols, and alkyl benzenes (molecular weights 260, 274 and 288) made minor contributions. Leaf age and side significantly affected the quantitative composition of SCL. Increased day temperature during the development of leaves led to decreased amounts per unit area of n-alkanes, 1-alkanols, n-alkanoic acids and n-alkyl esters while increased night temperatures resulted in increased amounts of n-alkanes n-alkanoic acids and 1-alkanols. Relative humidity had no effect on the amounts or composition of SCL. The permeability of cuticular membranes to water (described in part I of this paper) and the composition of SCL were not related. A model for the molecular structure of the transport-limiting barrier of plant cuticles and for the transport of water across it is proposed.

Occurrence, distribution and fate of the lipid plant biopolymers cutin and suberin in temperate forest soils

Abstract The occurrence, distribution and decomposition of the lipid plant biopolymers cutin and suberin have been investigated in forest soils and in an in vitro experiment. Samples were taken from the individual horizons of temperate forest soils receiving their litter input either from Fagus sylvatica L. or from Picea abies (L.) Karst. trees in NE Bavaria, FRG (two sites each). The soil samples were subjected to BF3/CH3OH-catalyzed transesterification. The depolymerisates (identified by capillary gas chromatography-mass spectrometry and quantified by capillary gas chromatography) consisted of the methyl esters of alkanoic and alkanedioic, ω- and 2-hydroxyalkanoic and di-, tri- and epoxyhydroxyalkanoic acids as well as of 1-alkanols and α,ω-alkanediols. The monomers released were characteristic of the cutins and suberins of the two dominant tree species. Concentrations of cutin and suberin monomers, on a dry soil-basis, were highest in the organic L and O horizons while, on an organic carbon-basis, high concentrations were also detected in the underlying mineral horizons. The results are discussed in terms of the contributions of cutin and suberin to the total lipid biopolymer contents of soils and the decomposition and turn-over of cutin in forest soils. Total inventories and depth profiles of soil cutin and suberin per ground area are estimated. Evidence is presented fore the preferential storage of cutin in the mineral horizons with total inventories exceeding yearly inputs by factors of 17 (P. abies) and 22 (F. sylvatica).

Slippery ant-plants and skilful climbers: selection and protection of specific ant partners by epicuticular wax blooms in Macaranga (Euphorbiaceae)

Abstract In many ant-plant species of the genus Macaranga in South-East Asia, conspicuous blooms of epicuticular wax crystals cover the stem surface. We found that many ant species were unable to walk on these surfaces. Only the specific ant partners of glaucous Macaranga host plants were capable of moving on the slippery stems without difficulty. Therefore, the epicuticular coatings of Macaranga myrmecophytes appear to have a selective function and protect the associated ants against competitors. The epicuticular aggregates function as a physical barrier; no evidence of chemical repellence was found. The extent to which ”foreign” ant species are excluded from a tree strongly depends on inclination, diameter and length of the glaucous stem sections. The particular growth form of some glaucous Macaranga ant-plants enhances the influence of the wax barriers. The ant associates of glaucous and glossy Macaranga ant-plants (genera Crematogaster and Camponotus) differ strongly in their capacity to adhere to the glaucous stems. For this reason, the wax blooms in Macaranga can act as an ecological isolation mechanism for the sympiotic ants. Within the genus Macaranga, we find a high correspondence between the occurrence of glaucousness and obligatory ant association (50% in ant-plants; 6.7% in non-myrmecophytes). The genus Macaranga thus represents one of the few cases known so far where epicuticular wax crystals are likely to have evolved in relation to insects.

A comparative study into the chemical constitution of cutins and suberins from Picea abies (L.) Karst., Quercus robur L., and Fagus sylvatica L.

The compositions of BF3/CH3OH depolymerisates of cutins and suberins from leaf and periderm samples from Picea abies [L.] Karst., Quercus robur L., and Fagus sylvatica L., respectively, were determined by quantitative capillary gas chromatography/mass spectroscopy. Long-chain monobasic, ω-hydroxymonobasic, dihydroxymonobasic, trihydroxymonobasic and epoxyhydroxymonobasic alkanoic acids constituted the major aliphatic monomers of leaf cutins. The total amounts of cutin monomers ranged from 629 mg · m−2 (Fagus) to 1350 mg · m−2 (Quercus). Cutin composition and amounts did not significantly differ between current year and three-year-old needles of Picea. Trans-esterification of periderm samples yielded a much greater variety of aliphatic monomers than obtained from cutins. In addition to the substance classes found with cutins, suberin depolymerisates also contained α, ω-dibasic acids while dihydroxymonobasic acids were lacking. Depolymerisates from periderms taken from different locations on a Picea tree did not differ significantly in their relative composition. The results are discussed in terms of the distinctive characteristics of the aliphatic portions of cutins and suberins, respectively. Discriminant analysis is applied for formulating a quantitative and inarbitrary classification rule for cutins and suberins. The precision, statistical significance and robustness of this classification rule are tested by employing it to a large set of compositional data (70 plant species) from the literature. The relevance of data obtained by depolymerization methods for elucidating the physical structure of cutins and suberins in situ is evaluated.

Epicuticular crystals of nonacosan-10-ol: in-vitro reconstitution and factors influencing crystal habits

The primary aerial surfaces of plant species from many families (e.g. Pinaceae, Liliaceae, Ranunculaceae, Papaveraceae) are covered by epicuticular tubules 5–20 μm long and 0.5 μn in diameter. The composition, mechanism of growth and molecular structure of this type of epicuticular aggregates have been studied. Pure nonacosan-10-ol extracted from Picea pungens needle surfaces formed, in vitro, tubular crystals like those occurring in vivo. This crystal habit was obtained irrespective of the type of solvent or substratum, if the solvent was evaporated within minutes. This shows that tubules of nonacosan-10-ol are formed in the kinetic regime of crystallization (limited by the diffusion of molecules from the solution to the crystal surface). Slow evaporation of the solvent or crystallization from the melt resulted in rhombic scales. These planar crystals represent the thermodynamic, stable modification of native nonacosan-10-ol. Homologous impurities in natural nonacosan-10-ol (3–14%) had no effect on the formation of the tubules. However, racemic nonacosan-10-ol invariably crystallized in scales. The phase behaviour of mixtures of natural nonacosan-10-ol and its synthetic racemate as well as synthetic (S)-nonacosan-10-ol provided evidence for the presence of the pure (S)-enantiomer on plant surfaces. The findings are discussed in terms of the mechanisms leading to epicuticular tubules consisting of nonacosan-10-ol and their molecular structure. Crystal structures for the pure enantiomer and the racemate of nonacosan-10-ol are proposed. It is concluded that the principles responsible for the formation of tubules are both the special molecular geometry of the naturally occurring (S)-nonacosan-10-ol and the mobility barrier of the plant cuticle. Further specific biological processes are not necessary for the formation of (S)-nonacosan-10-ol tubules. The alterations of epicuticular structures during ageing or the impact of pollutants are explained as spontaneous transitions between two crystal modifications of (S)-nonacosan-10-ol.