Effects of Growth-Regulators on Cellulase, Polygalacturonase, Respiration, Color, and Texture of Ripening Tomatoes1

Abstract

Abstract Changes in firmness, protein, color, respiration, cellulase, and polygalacturonase were followed during maturation and ripening of tomatoes, Lycopersicon esculentum L., on the plant and in detached fruit allowed to ripen at 20°C. Cellulase activity in the young fruit increased steadily during the maturation period. Cellulase activity in detached fruit ripened at 20°C increased rapidly during the onset of ripening and reached a higher level than in fruit ripened on the plant. Polygalacturonase activity was not detectable in developing fruit until after the fruit had initiated ripening. Polygalacturonase activity in detached fruit ripened at 20°C did not appear until the onset of the climacteric and then increased rapidly. This corresponded to the polygalacturonase activity in fruit allowed to ripen on the plant. The changes during ripening appeared to follow a pre-determined pattern. Grow-regulating substances only moderately affected the onset of the climacteric rise, but markedly influenced the time interval to reach the climacteric peak. They also markedly affected the rate of the normal sequence of changes during ripening. Such changes as softening, color formation, and enzyme activities of cellulase and polygalacturonase were accelerated by ethephon and SADH and delayed by gibberellic acid and indoleacetic acid. Gibberellic acid suppressed polygalacturonase activity. After 14 days polygalacturonase activity in the control fruit was 25 times greater than in fruit treated with gibberellic acid. Cellulase activity in gibberellic acid treated fruit increased steadily during this period. The loss of firmness in treated fruit suggests that softening is initiated by action of cellulolytic enzymes and that pectinolytic enzymes are involved in subsequent changes in texture.