Photosynthesis & Respiration in Developing Fruits. III. Variations in Photosynthetic Capacities during Color Change in Citrus

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Abstract
Low light intensity photosynthetic rates of intact fruits or peel disks from oranges and lemons in the transition from green to ripe color were found to be proportional to chlorophyll content. However, photosynthetic capacities appeared to be limited more by factors associated with respiratory metabolism. In the full green fruits, as well as in fruits with 40% loss of chlorophyll, the photosynthetic capacities coincided with respiratory compensation levels even when large changes were induced through temperature variations. Photosynthesis, but not respiration, was badly impaired in citrus peel disks when the diameter of the disks was less than 15 mm in diameter or when the albedo (white) tissue was removed from the flavedo (colored) layer. Use of disks of adequate diameter (15-20 mm) with retention of a thin layer of albedo allowed full retention of photosynthesis. Tracer studies showed that CO2 was rapidly assimilated into normal photosynthetic products in peel disks. A greater proportion of activity entered the organic acids in lemon peel than in orange peel.