Isolation and Analysis of Plant Phenolics from Foliage in Relation to Species Characterization and to Resistance Against
Phenolic compounds have been shown to play key roles in the resistance of plants to disease-causing microorganisms (Farkas and Kiraly, 1962; Cruickshank, 1963; Tomiyama, 1963; Rohringer and Samborski, 1967; Kuc, 1972). In addition, phenolics may also serv
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Isolation and Analysis of Plant Phenolics from Foliage in Relation to Species Characterization and to Resistance Against Insects and Pathogens J.
LUNDERSTADT
Introduction Phenolic compounds have been shown to play key roles in the resistance of plants to disease-causing microorganisms (Farkas and Kiraly, 1962; Cruickshank, 1963; Tomiyarna, 1963; Rohringer and Samborski, 1967; Kuc, 1972). In addition, phenolics may also serve as protectants against leaf-eating insects as, for example, they may influence the availability or digestibility of proteins which insects obtain from leaves (Feeny, 1970). For these reasons, tree breeders and forest pathologists should be well acquainted with plant phenolics and the methods for their analysis. The phenolics that comprise resistance systems against disease organisms and insects are divided into three groups based upon the relation of their formation to pest attack (Rohringer and Samborski, 1967): 1. Phenols normally present in healthy plants (preformed resistance factors). 2. Phenols formed from plant metabolites as a result of pest attack (host-parasite interaction). 3. Phenols formed as host-specific defense products (phytoalexins). Trees are rich in phenolic compounds, especially those lignified portions resistant to decay (Scheffer and Cowling, 1966). Some of the information about phenolics in trees has been obtained in relation to: 1. seasonal changes in leaves (Feeny and Bostock, 1968; Thielges, l972a), 2. chemotaxonomy (Erdtman et al., 1966; Hillis, 1967), 3. speciation (Wellendorf et al., 1971), and clone identification (Sauer et al., 1973), 4. study of introgressive hybridization (Hanover and Wilkinson, 1970), and 5. study of interspecific (Thieland intraspecific (Thielges, 1972b) hybrids. ges, 1972a) Because of the importance of phenolics in the protection of plants from pests, and because of our scant knowledge of the phenolics important to trees in these situations, I have endeavored to detail the methods used in my laboratory to study phenolics.
Methods Phenolic compounds are a complex group of organic chemicals. Because of their heterogeneity, a host of different extraction and purification procedures have been developed. Phenolic compounds cannot be separated completely from other extractives on the basis of solubility alone (Browning, 1967), and, therefore, every extraction proce-
J. P. Miksche (ed.), Modern Methods in Forest Genetics © Springer-Verlag Berlin Heidelberg 1976
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dure yields phenolics somewhat contaminated with nonphenolic extractives, unless further purification is attempted, especially for simple ether-soluble phenols. Phenolics are classified into three main groups based upon their solubility: 1. simple phenols (ether-soluble), 2. polyphenols (etherinsoluble but n-butanol soluble), and 3. tannins (water soluble). In addition to the soluble phenolics above, bound phenols occur in some plants at high concentrations (Lunderstadt, 1972) which can be extracted only after alkali hydrolysis. These phenolic classes may be obtained regardless
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