Leaf cuticle

By way of contrast, a study of the leaf cuticle alkanes of Sedum lanceolatum Torrey (Crassulaceae) from 44 populations showed no correlation with elevation. 

Bowman, R. N. 1983. Intraspecffic variabihty of leaf cuticle alkanes in Sedum lanceolatum along an elevahonal gradient. Biochem. Syst. Ecol. 11 195-198. 

Fig. 7 Overview of the partitioning among the liquid, solid and/or gas phases of individual compartments [8], Note In the current version of CalTOX (CalTOX4), the plant compartment comprises two sub-compartments [plant surfaces (cuticle) and plant leaf biomass (leaves)]...

The major function of cutin is to serve as the structural component of the outer barrier of plants. As the major component of the cuticle it plays a major role in the interaction of the plant with its environment. Development of the cuticle is thought to be responsible for the ability of plants to move onto land where the cuticle limits diffusion of moisture and thus prevents desiccation [141]. The plant cuticle controls the exchange of matter between leaf and atmosphere. The transport properties of the cuticle strongly influences the loss of water and solutes from the leaf interior as well as uptake of nonvolatile chemicals from the atmosphere to the leaf surface. In the absence of stomata the cuticle controls gas exchange. The cuticle as a transport-limiting barrier is important in its physiological and ecological functions. The diffusion across plant cuticle follows basic laws of passive diffusion across lipophylic membranes [142]. Isolated cuticular membranes have been used to study this permeability and the results obtained appear to be valid... 

Tegelaar E, deLeeuw J, Largeau C, Derenne S, Schulten H, Muller R, Boon J, Nip M, Sprenkels J (1989) Scope and limitations of several pyrolysis methods in the structural elucidation of a macromolecular plant constituent in the leaf cuticle of Agave americana L. J Anal Appl Pyrolysis 15 29-54... 

Canet D, Rohr R, Chanel A, Guilliam F. Atomic force microscopy study of isolated ivy leaf cuticles observed directly and other embedding in Epon. New Phytologist 1996 134 571-577. 

Niche The section of the environment with which a particular property of the chemical product interacts is referred to as niche. For example, a pesticide can have as the environment the plant, the atmosphere, and the human beings. The pesticide interacts with the environment through its properties. There are different kinds of interaction depending on the niche. For example, some properties such as the contact area depend on the surfactant characteristics and the surface of the leaf. The niche is the surface of the leaf. The absorption of the pesticide depends on the characteristics of the layers, like the cuticle [25], In this case, the niche consists of the layers of the plant s leaves. Also, the diffiisivity of the active product in the layers of the plant leaves corresponds to a property that depends on the environment-product interaction. Some other pesticide properties, such as solubility of the active agent in the solvent, do not depend on the environment. 

It must be able to enter the sap by diffusion through the leaf or root cuticle. Hence some degree of lipoid solubility is desirable. Larger molecular size will be disadvantageous. 

Terrestrial BMOs have also been widely used for monitoring environmental contaminants. In particular, the lipid-like waxy cuticle layer of various types of plant leaves has been used to monitor residues of HOCs in the atmosphere. However, some of the problems associated with aquatic BMOs apply to terrestrial BMOs as well. For example, Bohme et al. (1999) found that the concentrations of HOCs with log KoaS < 9 (i.e., those compounds that should have attained equilibrium) varied by as much as 37-fold in plant species, after normalization of residue concentrations to levels in ryegrass (Lolium spp.). These authors suggested that differences in cuticular wax composition (quality) were responsible for this deviation from equilibrium partition theory. Other characteristics of plant leaves may affect the amount of kinetically-limited and particle-bound HOCs sampled by plant leaves but to a lesser extent (i.e., <4-fold), these include age, surface area, topography of the surface, and leaf orientation. 

Note These (maceral) constituents can be identified and quantitatively measured by examining thin sections or polished surfaces under a microscope, and reflect the nature of the primordial source material as well as the conditions under which it was deposited. Vitrinites derive from humic gels, wood, bark and cortical tissues eoi lnites are the remains of fungal spores, leaf cuticles, algae, resins and waxes and inertinites comprise unspecified detrital matter, "carbonized" woody tissues and fungal sclerotia and mycelia. 

The hydrophobic waxy cuticle of plants can inhibit the movement and accessibility of nutrients to bacterial cells. However, biosurfactants produced by the majority of epiphytic Pseudomonas spp. decreases the water tension, enabling relatively free movement across the leaf surface to nutrient sources and natural openings such as stomata. Pseudomonas are also known to release a toxin called syringomycin that can produce holes in the plant cell membrane allowing access to intracellular nutrients without necessarily resulting in disease symptoms (Cao et al.r 2005). 

Figure 2.21 schematically depicts the dry deposition of a pollutant to a typical surface in the form of resistances (Lovett, 1994 Wesely and Hicks, 1999). In this case, the surface resistance rsurf has been broken down even further into a combination of parallel and series resistances (rs, rm, rct, rsoil, rwa(cl, etc.). Since leaves may absorb pollutants either through stomata or through the cuticles, the absorption into the leaf is represented by two parallel resistances, rcl for the cuticular resistance and rs for the stomatal resistance, which is in series with a mesophyllic resistance rm. Also shown are resistances for uptake into the lower part of the plant canopy and into water, soil, or other surfaces. 

Method. Whether to use stomatal density or stomatal index from leaf fossils for paleoelevation reconstruction depends on the availability of modern reference material and the quality of the fossil cuticle. Ideally both should be used on the same material to increase the confidence in the provided estimates. In cases, however, when the quality of the fossil cuticle does not allow epidermal cells to be recognized with the necessary accuracy, and stomatal index can not be determined, stomatal density measurements are the only available option. To use stomatal index, a training set of modem and herbarium material grown under different C02 pressure provides the necessary calibration. Because stomatal density is influenced by more factors than just the C02 partial pressure, the actual response of stomatal density of the chosen fossil taxon has to be confirmed by analyzing leaves from actual elevation transects. Stomatal density is physiologically more informative than stomatal index as SD is strongly related to maximum stomatal conductance. 

Riederer (1990) published a more complex method based on two lipid-like compartments, an acylglycerol lipid compartment and a cuticle compartment. The acylglycerol-air partition coefficient was assumed to equal Kow/Kaw, while measured values of the cuticle-water partition coefficient were employed for the cuticle compartment. Riederer (1995) later modified this model to include a predictive equation for the cuticle-water partition coefficient, based on Kerler and Schonherr s measurements (1988) of eight chemicals with log KqW values ranging from 1.92 to 7.86. They used isolated citrus and rubber plant leaf cuticles as well as tomato and green pepper fruit cuticles. The resulting equation is... 

Deshmukh, A. P., Simpson, A., Hadad, C. M., and Hatcher, P. G. (2005). Insights into the structure of cutin and cutan from Agave americanas leaf cuticle using HRMAS NMR spectroscopy. Org. Geochem. 36,1072-1085. 

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