Ethylene-independent and ethylene-dependent biochemical changes in ripening tomatoes

Abstract

Fruits of Lycopersicon esculentum Mill cv Sonatine stored in 6% CO(2), 6% O(2), and 88% N(2) for 14 weeks at 12 degrees C, exhibited a temporal separation of certain biochemical events associated with ripening.The specific activity of two citric acid cycle enzymes, citrate synthase and malate dehydrogenase, fell substantially during the first 2 weeks of storage when changes in organic acid concentration also occurred. During this period, lycopene, polygalacturonase, and ethylene were undetectable.When fruit were removed from store, ethylene was evolved and polygalacturonase and invertase activity were rapidly initiated as was synthesis of lycopene.To determine whether the changes in organic acid metabolism were affected by ethylene, fruit was kept at 22 degrees C in either a normal atmosphere or a normal atmosphere supplemented with 27 microliters per liter of ethylene, and it was shown that in both atmospheres similar quantitative changes to those described above occurred in the citric acid cycle enzymes specific activities before any detectable increase in the specific activities of invertase and polygalacturonase. These latter changes, together with pigment changes, occurred between 2 and 3 days earlier in fruit exposed to ethylene, compared with those kept in a normal atmosphere.