The effect of the environment on the permeability and composition of Citrus leaf cuticles : II. Composition of soluble cuticular lipids and correlation with transport properties.

The constituents of the soluble cuticular lipids (SCL) of the leaf blades of Citrus aurantium L. were identified by gas chromatography-mass spectrometry and quantified. Major components were 1-alkanols (C24 to C40), n-alkyl esters (C36 to C56), n-alkanoic acids (C28 to C34), n-alkanes (C22 to C40) and triterpenones, while n-alkanals (C29 to C38), sterols, and alkyl benzenes (molecular weights 260, 274 and 288) made minor contributions. Leaf age and side significantly affected the quantitative composition of SCL. Increased day temperature during the development of leaves led to decreased amounts per unit area of n-alkanes, 1-alkanols, n-alkanoic acids and n-alkyl esters while increased night temperatures resulted in increased amounts of n-alkanes n-alkanoic acids and 1-alkanols. Relative humidity had no effect on the amounts or composition of SCL. The permeability of cuticular membranes to water (described in part I of this paper) and the composition of SCL were not related. A model for the molecular structure of the transport-limiting barrier of plant cuticles and for the transport of water across it is proposed.