Biochemical basis of thermoregulation of ethylene production and ripening of 'Hayward' kiwi fruit

It has been shown in a previous work that there is thermoregulation of ethylene biosynthesis and ripening in kiwifruit. The aim of this research was to study the effect of temperatures from 10 degrees to 40 degrees C on the enzymes of ethylene biosynthetic pathway in connection with ripening induced by propylene. 'Hayward' kiwifruit were treated with or without 130p propylene at temperatures 10 degrees, 20 degrees, 30 degrees, 34 degrees, 38 degrees and 40 degrees C. Ethylene production, 1-aminocyclepropane-1-carboxylic acid content (ACC) and ACC synthase and ACC oxidase also named ethylene-forming enzyme (EFE) activities, as well as changes in respiration rate, soluble solids content (SSC) and flesh firmness were measured during a storage period of 120 to 350 hours. Propylene induced the fruit to ripen in temperatures from 10 degrees to 38 degrees C while control showed no ripening response. Propylene also induced ethylene and ACC production in the temperature range from 20 degrees to 34 degrees C with concomitant induction of ACC synthase and EFE activities. There was a strong inhibition of ethylene production at 10 degrees, 38 degrees and 40 degrees C. Ripening as evaluated by flesh firmness and SSC was inhibited at high temperatures (38 degrees-40 degrees C). As temperature was increased the respiration rate was also increased. Propylene treatment enhanced the respiration rate in all temperatures except 40 degrees C.