Lipids, leaf

Salt damage is due to the product of xylem concentration and transpiration rate over the life of the leaf. There are several pathways for salt entry into the root. In spite of many reports in the literature of correlative associations between the lipid analyses of relatively crude root membrane preparations and salt resistance (see Kuiper, 1985), we have not been able... 

The food technologist may be especially interested in the fate of the carotenoids in the seed oil. Like red palm oil, the resulting carotenoid-pigmented canola oil may be more stable due to the antioxidant properties of carotenoids and may be more attractive to consumers. Alternatively, for food security concerns, transgenic soybean or canola oils and seed meals that are genetically modified for more efficient bio-diesel production may be bio-safety marked with lipid-soluble carotenoids and water-soluble anthocyanins, respectively. Potatoes are excellent potential sources of dietary carotenoids, and over-expression of CrtB in tubers led to the accumulation of P-carotene. Potatoes normally have low levels of leaf-type carotenoids, like canola cotyledons. 

After the extraction of lipid and nonlipid components from the leaves of mandarin orange Citrus reticulata, the lipid fraction was further separated by PTLC to determine different lipid classes that affect the chemical deterrence of C. reticulata to the leaf cutting ecat Acromyrmex octopinosus. These lipids seem to be less attractive to the ants [81a]. The metabolism of palmitate in the peripheral nerves of normal and Trembler mice was studied, and the polar lipid fraction purified by PTLC was used to determine the fatty acid composition. It was found that the fatty acid composition of the polar fraction was abnormal, correlating with the decreased overall palmitate elongation and severely decreased synthesis of saturated long-chain fatty acids (in mutant nerves) [81b]. 

The reported (14) mechanisms of action of allelochemlcals Include effects on root ultrastructure and subsequent Inhibition of Ion absorption and water uptake, effects on hormone-induced growth, alteration of membrane permeability, changes In lipid and organic acid metabolism, inhibition of protein synthesis and alteration of enzyme activity, and effects on stomatal opening and on photosynthesis. Reduced leaf water potential Is one result of treatment with ferulic and p-coumaric acids (15). Colton and Einhellig (16) found that aqueous extracts of velvetleaf (Abutllon theophrastl Medic.) Increased diffusive resistance In soybean fGlycine max. (L.) Merr.] leaves, probably as a result of stomatal closure. In addition, there was evidence of water stress and reduced quantities of chlorophyll In Inhibited plants. 

Tea leaf, in common with all plant leaf matter, contains the full complement of genetic material, enzymes, biochemical intermediates, carbohydrates, protein, lipids, and structural elements normally associated with plant growth and photosynthesis. In addition, tea leaf is distinguished by its remarkable content of methylxathines and polyphenols. These two groups of compounds are predominantly responsible for those unique properties of tea that account for its popularity as a beverage. It must be noted that the chemical composition of tea leaf varies with climatic condi-... 

Leaf discs from rapidly expanding V.faba leaves incorporated 14C-labeled palmitic acid into cutin. After removal of the soluble lipids and other materials, the insoluble residue was subjected to LiAlH4 hydrogenolysis and the labeled reduction products of cutin monomers were identified by chromatography as hexadecane-... 

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. 

The major phytotoxic components of the photochemical oxidant system, discussed in Chapter 11, are ozone and peroxyacetylnitrate (PAN), but there is indirect evidence that other phytotoxicants are present. Con siderable effort has gone into controlled exposures to ozone and into field studies. Leaf stomata are the principal sites for ozone and PAN entry into plant tissue. Closed stomata will protect plants from these oxidants. Both ozone and PAN may interfere with various oxidative reactions within plant cells. Membrane sulfhydryl groups and unsaturated lipid components may be primary targets of oxidants. Young leaf tissue is more sensitive to PAN newly expanding and maturing tissue is most sensitive to ozone. Light is required before plant tissue will respond to PAN that is not the case with ozone. 

The toxic effects of ozone in plant systems have been studied for some time, yet the actual mechanisms of injury are not fully understood. In addition to visible necrosis which appears largely on upper leaf surfaces, many other physiological and biochemical effects have been recorded ( ). One of the first easily measurable effects is a stimulation of respiration. Frequently, however, respiration may not increase without concomitant visible injury. Furthermore, photosynthesis in green leaves as measured by CO2 assimilation, may decrease. It is well known that ozone exposure is accompanied by a dramatic increase in free pool amino acids ( ). Ordin and his co-workers ( ) have clearly shown the effect of ozone on cell wall biosynthesis. In addition, ozone is known to oxidize certain lipid components of the cell ( ), to affect ribosomal RNA (16) and to alter the fine structure of chloroplasts (7 ). 

The extraction procedure used to isolate lipids from biological tissue depends on the class of lipid desired and the nature of the biological source (animal tissue, plant leaf, plant seed, bacteria, cell membranes, etc.). Because lipids are generally less polar than other cell constituents, they may be selectively extracted with the use of organic solvents. Early studies of lipids used ether, acetone, hexane, and other organic solvents for extraction however, these solvents extract only lipids bound in a nonpolar or hydrophobic manner. In the 1950s, Folch s group reported the use of chloroform and methanol (2 1) in... 

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... 

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