Inhibition of ethylene evolution in papaya pulp tissue by benzyl isothiocyanate

Papaya (Carica papaya L.) pulp tissue disks in an incubation medium composed of 0.4 m sucrose evolve ethylene at an optimum pH of 5.25 at 30 C. Disks of young preclimacteric fruit evolve the gas linearly with fruit age until fruit age reaches 4 months. Disks from 5-month-old postclimacteric fruit produce approximately 5-fold more ethylene than disks from 4-month-old fruit. Ethylene evolution by unaged papaya disks is inhibited potently by benzyl isothiocyanate. The compound inhibits production of ethylene by approximately 60% at a concentration of 0.046 mm. However, in aged papaya disks benzyl isothiocyanate causes no inhibition of ethylene production indicating that the compound inhibits the induction of the ethylene-producing system rather than the evolution of the gas per se. Even at a 2-fold higher concentration benzyl isothiocyanate has no effect on respiration of unaged papaya disks. It is proposed that benzyl isothiocyanate may act as an endogenous regulator of ethylene evolution in papaya fruit.