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The effect of a hormic dose of UV-C (254 nm) on changes in fruit firmness and cell wall-degrading enzyme (CWDE) activity was determined using tomato fruit. Throughout the storage period, a decrease in firmness was jointly observed with an increase of the CWDE (polygalacturonase, pectin methyl esterase, cellulase, xylanase, beta-D-galactosidase, and protease) activity for all treatments, suggesting the involvement of these enzymes in the ripening process. However, the enhancement in the activity of the CWDE was significantly less in fruit subjected to the hormic dose of UV-C. This reduction may explain why irradiated fruit were firmer than control and consequently may explain how UV-C could delay the ripening and senescence process. We suggest that the CWDE are one of the targets of the UV-C, and by this action, irradiation contributed to a delay of the cell wall degradation and consequently retarded softening of the tomato fruit tissues.
Barka et al. (Fri,) studied this question.