SUMMARY The slippery zone situated below the peristome inside pitchers of most carnivorous plants from the genus Nepenthes is covered with a thick layer of epicuticular wax. This slippery zone is reported to play a crucial role in animal trapping and prey retention. In N. alata, the wax coverage consists of two clearly distinguished layers. These layers differ in their structure, chemical composition and mechanical properties, and they reduce the insect attachment in different ways. The lower layer resembles foam, composed of interconnected membraneous platelets protruding from the surface at acute angles. The upper layer consists of densely placed separate irregular platelets, located perpendicular to the subjacent layer. Crystals of the upper layer bear small stalks, directed downwards and providing connections to the lower layer. These morphological distinctions correlate with differences in the chemical composition of waxes. The compound classes of alkanes, aldehydes, primary alcohols, free fatty acids, esters and triterpenoids occurred in extracts from both wax layers, but in different proportions. Chain length distributions in aliphatics were different in extracts from the lower and the upper wax layers. Waxes of the upper and lower layers exhibited different mechanical properties: wax of the lower layer is harder and stiffer than that of the upper layer. Moreover, crystals of the upper layer are brittle and may be easily exfoliated or broken to tiny pieces. Laboratory experiments using tethered insects showed that both wax layers reduce the attachment force of insects. It is assumed that a decrease in insect attachment on the two distinct wax layers is provided by the two different mechanisms: (1) crystals of the upper wax layer contaminate insects'adhesive pads; (2) the lower wax layer leads to a reduction of the real contact area of insects' feet with the plant surface.
Cuticular waxes of Viscum album subspecies and of V. cruciatum have been examined for their micromorphology and chemical composition. Wax crystalloids occur preferably as irregular platelets and rodlets, while deviant structures are found in small areas. Among the triterpenoids forming the wax layer, oleanolic acid is prevailing with some 80%. The quantitative composition of the long-chain aliphatics, which comprise several classes, is rather variable. Flavonoid aglycones, occurring as very minor components of the cuticular waxes, comprise the flavonols kaempferol and quercetin and a series of their methyl derivatives, in some taxa also the flavanone naringenin. Neither the crystalloid structures nor the chemical composition of the wax allow to discriminate the 2 species, or male and female plants, or plants grown on conifers or on dicotyledoneous hosts.
Water permeability and composition of soluble cuticular lipids of isolated cuticular membranes from leaves of Citrus aurantium L. were investigated for 3 successive years. The average water permeability coefficient determined using 169 cuticular membranes was 1.09·10(-7) cm s(-1) with a standard deviation of 0.78·10(-7) cm s(-1). There were no significant differences in water permeability between years. Cuticular membranes are characterized by a great variability in water permeability both within and between years. Both water permeability of individual membranes and variability between membranes are shown to be determined by soluble cuticular lipids contained within the cuticular membranes. The soluble cuticular lipids of Citrus leaves are composed of fatty acids, primary alcohols, esters, and hydrocarbons. They occur in amounts of 9.84 μg cm(-2), which represents approx. 3% of the total mass of isolated cuticular membranes. The specific weight of cuticular membranes (365.4 μg cm(-1)) and total amount of soluble cuticular lipids did not vary significantly between years. Significant differences were observed for the amounts and composition of the constituent classes of lipids. Six homologues comprise 86% of the fatty acids (C16; C18; C19; C21; C24; C26), 83% of the primary alcohols (C24; C26; C28; C30; C32; C34) and 88% of the esters (C36; C38; C40; C41; C42; C44). Eleven major homologues amount only to 62% of the total hydrocarbons (C16; C17; C18; C20; C26; C27; C29; C30; C31; C32; C33). Variability in the composition of soluble cuticular lipids between years was much smaller than variability of water permeability and, therefore, no relation between composition of soluble cuticular lipids and water permeability could be found. It is suggested that this may be due to the fact that the lipid composition observed represents the averages of 20 to 30 membranes analyzed so that differences between individual membranes may have been leveled out.
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