Plant leaf-surface lipids; age variation patterns in coffee Arabica l. and Thea sinensis l.

Abstract

As early as 1973, an antifungal compound was reported in a fraction from the cuticular wax of Coffea arabica L. leaf and berry, and an attempt to correlate the activfty of this fraction with the resistance of the plant species to Coffee Berry Disease in the field was made. The current study reports the results of examination of this "active fraction" by TLC. Its activity is attributed to caffeine and either long-chain primary alcohols or triterpenoids. The qualitative and quantitative composition of tissue surface of both Coffea arabica L. and Thea &tneneis L. is reported. Caffeine (and possibly its analogues) is present in the chloroform extracts of both species, Triterpenoids are absent in the tea leaf and very young coffee berry extracts. An age variation in the relative concentrations and chain length distribution patterns in the leaf wax alkaes, primary alcohols and free fatty acids of both coffee and tea has been established. The use of these 'W'ax constituents in delimiting plant taxa without due regard to the uniformity of the physiological age of the particular tissue examined would therefore appear misleading. In all three wax fractions of both coffee and tea, the results indicate that homo logs of increasing chain length are deposited as the leaf ages, The alkane distribution patterns of both species are such that the coffee leaf may be regarded as a n-nonacosane accumulator and the tea leaf a n-hentriacontane accumulator. From a biosynthetic point of view, very low coefficients of linear correlation exist between the n-alkanes and their "parent fatty acids in the case of coffee and fatty acids and primary alcohols in the case of tea, Except for the senescent leaf, the very young and expanded tea leaf alkanes and fatty acids are highly correlated. So are the fatty acids and primary alcohols of the coffee leaf at all stages of development.