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C. Larrigaudiere, E. Pinto, and M. Vendrell

The differential effects of two color improving products, ethephon an ethylene-releasing compound, and seniphos, a nonethylene-releasing product, were studied on `Starking Delicious' apples (Malus domestica Borkh L.). Ethephon and seniphos were applied 2 or 3 weeks before commercial harvest. Ethephon- and seniphos-treated fruit showed a significant improvement of peel color associated with a sharp increase in anthocyanin content and chromaticity values. Color improvement in ethephon-treated apples occurred during the preharvest period and cold storage. The seniphos-treated fruit stopped color development in cold conditions. In comparison to the ethephon-treated fruit, the seniphos-treated apples showed lower internal ethylene concentrations and a ripening delay. Both treatments sharply increased the activity of phenylalanine-ammonia-lyase enzyme, which seemed to be the determining factor of color enhancement. The seniphos-treated apples compared to ethephon had higher fruit firmness and lower soluble solids concentrations. Anthocyanin biosynthesis may be enhanced by seniphos treatment without inducing ethylene production or other ripening associated changes. As a consequence, fruit treated with seniphos can be held longer in storage.

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C. Larrigaudière, A. Latché, J.C. Pech, and C. Triantaphylidès

Changes in ACC metabolism induced by gamma irradiation have been studied during ripening of cherry tomatoes (Lycopersicon esculentum L. cv. Sweet 100) treated at the mature-green stage. Irradiation caused a sharp and transient dose-dependent increase in ethylene production during the first 24 hours that was associated with an increase in ACC synthase activity. The activity of ethylene-forming enzyme (EFE) was also stimulated but was never limiting. Nine days following irradiation, ACC metabolism was more active in irradiated fruits, with ACC being mainly directed to ethylene [80% at 3 kilogray (kGy; 1 Gray = 100 Rad = 1 J·kg-1)] rather than to malonyl ACC (MACC). As a consequence, fruit ripening was accelerated. For doses <1 kGy, the time required for 50% of the fruits to reach breaker stage (the onset of climacteric ethylene production) was inversely correlated with radiation dose and the amount of stress ethylene produced during the first 24 hours. At doses >1 kGy, in spite of a continuous stimulation of stress ethylene production, no additional acceleration of ripening occurred. At 3- to 5-kGv doses. fruit ripening was impaired transiently with a fast subsequent recovery. As a result a significant synchronizȧtioṅ 'ȯḟ fruit ripening (presumed to be caused by enhanced ethylene production) was observed. Chemical, names use: l-aminocyclopropane-l-carboxylic acid (ACC).