Ultrastructure and Chemistry of Cuticular Waxes of Developing Citrus Leaves and Fruits1

Abstract

Abstract The ultrastructure of leaf and fruit surface waxes of citrus developed similarly. The wax layers of immature leaves and fruits were initially amorphous. Small protrusions and isolated regions of upright platelets then developed. All surfaces eventually cracked and uplifted to form large flat irregular plates. Epicuticular wax concentrations (μg/cm2) of new spring flush leaves were initially high, declined rapidly in March-April, and increased to June maxima after which levels declined slightly. Fruit epicuticular wax concentration generally declined in May-June and then increased into November. Secondary alcohols dominated citrus leaf waxes in March-April but quickly decreased or were diluted to trace levels. Overall, the major citrus leaf wax fractions were primary alcohols, with paraffins 2nd in importance. Aldehydes and fatty acids were dominant in citrus fruit waxes. For each cultivar, the relative proportions of individual wax fractions changed during the year. The intracuticular waxes were mainly fatty acids. The relationships between wax ultrastructure and chemistry in developing leaves and fruits are discussed.