Studies On The Effects Of Salicylic Acid On 1-Aminocyclopropane-1-Carboxylate Oxidase Activity And Its Mechanisms In Apple And Pear Fruits

Ethylene producing in great amount is one of the most important characteristics of senescing fruits. l-aminocyclopropane-I-carboxylate oxidase (ACO) is one of key enzymes during ethylene biosynthesis. It was known from post researches that Salicylic acid (SA) could inhibit ACO activity, but its mechanisms remain unknown. Many researches had showed that active oxygen species (AOS) and iron ions affected on ACO activity, and that SA could regulate AOS metabolism and could chelate iron ions. Whether SA could affect on ACO through its effects on AOS and iron ions metabolism or not have no researches to study, so our researches studied on which. The regulating effects of SA on the metabolism of AOS, iron ion contents and the relationships between SA inhibiting ACO activity and AOS metabolism, iron ion contents in senescing fruits of Ya-pear and Starkrimson Apple were studied with fruit discs. The main results were as follows: 1. Treating the fruits discs with different concentration (0.002 1 OmmolL?) of SA solutions showed that SA could inhibit ACO activity apparently, which had no relation to the existing of l-aminocyclopropane-1-carboxylic acid (ACC) acting as substrate of ACO. for there had had a great amount of ACC in senescing fruits. 2. The low concentrations of SA could clean AOS and decrease iron ions contents. High concentration of SA could increase AOS and iron ions contents. Further correlation analysis studies showed that there were correlated relations among O~ and H202 contents, iron ion (Fe2, Fe) contents and ACO activities to each other when SA concentration between 0.002 to 0.2 mmo[L. 3. SA could regulate protective enzymes supereoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (ASP) activities. As the concentration of SA solutions increasing from 0.002 mmol.L?to 5 mmol.L? superoxide anion radical( O ) contents, hydrogen peroxide (H202) contents, iron ion contents and POD activities decreased first and then increased; SOD, ASP activities increased first and then decreased; ACO and CAT ativities decreased apparently, and the higher the concentrations of SA solutions were, the more they decreased. 4. Experiments were conducted by treating with AOS generating systems and their scavengers to see the relation between AOS and ACO activities. The results showed that o contents positively correlation with ACO activities, and H2O2 could decrease ACO activities (especially in the concentration from 0.1 to 10mmolU?. Treatment of iron ions and their chelants (EDTA, DTPA) showed that iron ions (Fe2, Fe3) could increase ACO activities significantly in their concentration from 0.01 to 0.1 mmobL? when iron ions concentrations were over 0.5 mmoIU? the fruit discs might be damaged by iron toxicities. The results indicated that the mechanisms of SA inhibiting ACO activity related to that SA could clean O and OH as well as decrease iron ions contents.