EFFECT OF A HIGH-TEMPERATURE STRESS ON ENDO-BETA-MANNANASE AND ALPHA-GALACTOSIDASE AND BETA-GALACTOSIDASE ACTIVITIES DURING TOMATO FRUIT RIPENING

Tomato fruit show physiological disorders when exposed to temperatures at or above 30 degrees C. It has been suggested that the alpha- and b eta-galactosidases (alpha- and beta-Gal), as well as the endo-beta-man nanase could play roles during fruit ripening. Their pattern of activi ties was followed in detached tomato fruit, and the degree of inhibiti on of the activity at high temperatures was evaluated. The potential r esumption of the enzyme activity when fruits were transferred to a roo m-temperature environment was also studied. Mature-green fruits were i ncubated at: (a) 36 degrees C for 2 days, (b) 40 degrees C for 2 days, or (c) 40 degrees C for 2 days +36 degrees C for another 2 days. Afte r heat treatments, fruits were transferred to a 21 degrees C dark envi ronment. Control fruit were stored at 21 degrees C. In the control fru it, activity was higher for alpha-Gal than for beta-Gal and revealed s lightly increasing patterns toward the red-ripe stage. Endo-beta-manna nase activity was not detected in mature-green tomatoes but appeared a t the breaker stage and rose rapidly, reaching constant values at the red-ripe stage. The firmness and enzymatic activities of fruits initia lly treated at 36 degrees C for 2 days were similar to those of the co ntrol group. Galactosidase activity decreased in tomatoes incubated at 40 degrees C for 2 days; and in those whose heat treatment was extend ed another 2 days at 36 degrees C the alpha- and beta-Gal reached a mi nimum of 1/5 and 1/25, respectively, of the initial activity on the fo urth day. The activity of the endo-beta-mannanase could be detected on ly 6 days after the fruit had been transferred to a 21 degrees C envir onment and increased slowly up to 24% of that attained by the control group. alpha-Gal showed a low rate of recovery but beta-Gal activity r ecovered after 16 days at 21 degrees C. Results could be associated wi th an active role of these enzymes on the fruit softening process.