The Nature of Oleocellosis in Citrus Fruits

Abstract

Oleocellosis phenomenon in citrus fruit is characterized by greenish-brown areas on an orange or yellow background of the flavedo. This color is the result of essential oil spillage into the subepidermal tissue between the oil glands, which prevents the usual differentiation of chloroplasts into chromoplasts. Ultrastructural observations show that during the early stage, oleocellosis is characterized by fused protoplasm, seen densely at the center of the cell lumen. The subepidermal cells later collapse and their cell lumen is occupied by a large plastid, which is termed a giant chloroplast. These giant chloroplasts include dense grana, thylakoidal apparatus, and starch grains but not osmiophyllic globules. As a result of oleocellosis the cell wall in the subepidermal cell layers collapses and thickens and no normal protoplasmic structure can be identified. The greenish spots that appear after degreening originate from large quantities of chlorophyll in the giant chloroplasts.