外源褪黑素调控活性氧代谢诱导采后杏果实对黑斑病的抗性

以新疆‘赛买提’杏为试验材料，探究外源褪黑素对采后杏果实黑斑病抑制效果及活性氧代谢的影响。将杏果实分别置于50、100、200 μmol/L褪黑素溶液进行减压（0.05 MPa）处理2 min后，常压状态下浸泡8 min，以蒸馏水同样处理作为对照，自然晾干后的杏果实转入温度（0±1）℃，相对湿度90%~95%条件下放置48 h后，损伤接种互隔交链孢（Alternaria alternata）于相同条件下贮藏，定期测定杏果实接种发病率和病斑直径及超氧化物歧化酶（Superoxide dismutase，SOD）、过氧化氢酶（Catalase，CAT）、过氧化物酶（Peroxidase，POD）酶活力，及超氧阴离子（Superoxide anion，O₂?·）产生速率、细胞膜渗透率、过氧化氢（Hydrogen peroxide，H₂O₂）和丙二醛（Malondialdehyde，MDA）含量。结果表明:与对照组相比，不同浓度外源褪黑素处理显著延缓了杏果实发病率的上升（P<0.05），抑制了杏果实病斑直径的增大，贮藏结束时50、100、200 μmol/L褪黑素处理组杏果实的病斑直径比对照组显著低11.92%、28.49%、19.67%（P<0.05），其中100 μmol/L褪黑素处理效果最好；贮藏前期100 μmol/L外源褪黑素处理提高了杏果实超氧化物歧化酶活力，降低了超氧阴离子产生速率，抑制了过氧化氢酶活力，诱导了杏果实贮藏前期快速积累H₂O₂；贮藏结束时100 μmol/L褪黑素处理组的过氧化氢酶和过氧化物酶活力分别比对照组高39.13%、78.91%（P<0.05），100 μmol/L褪黑素处理组杏果实的H₂O₂含量比对照组显著低19.74%（P<0.05），减少了杏果实内H₂O₂的积累，延缓了细胞膜渗透率和丙二醛含量的上升。由此说明，外源褪黑素可调控活性氧代谢诱导采后杏果实对黑斑病的抗性。

Melatonin Regulates Reactive Oxygen Species Metabolism to Induce Resistance to Black Spot of Postharvest Apricot Fruit

Xinjiang 'Saimaiti' apricot fruit were used as the material to study the inhibitory effects of postharvest treatment with melatonin on black spot and its influence on reactive oxygen species metabolism. Fruit were vacuum impregnated into different concentrations of melatonin (50, 100, 200 μmol/L) under pressure of 0.05 MPa for 2 min, then atmospheric pressure was restored, and the fruit was maintained in the same solution for 8 min. The distilled water treatment was used as blank control. After naturally drying, the fruit were refrigerated (0±1℃, RH 90%~95%) for 48 h. After that, apricot fruits were inoculated with Alternaria alternata and stored at the same conditions.The lesion diameter and disease incidence of apricot fruit inoculated with A.alternata, the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and superoxide anion radical (O₂?·) production rate, cell membrane permeability, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents were measured regularly. Results showed that compared with the control group, different concentrations of exogenous melatonin treatment significantly delayed the increase of apricot fruit morbidity and inhibited the increase of apricot fruit the lesion diameter. At the end of storage, the spot diameters of apricot fruit were significantly lower in the 50, 100, and 200 μmol/L melatonin-treated groups by 11.92%, 28.49%, and 19.67% (P<0.05) than in the control group. And 100 μmol/L melatonin had the best effect on black spot diseases of apricot fruits. In the early stage of storage, 100 μmol/L exogenous melatonin treatment increased the apricot fruit superoxide dismutase activity, decreased the rate of superoxide anion, inhibited catalase activity, and induced rapid accumulation of H₂O₂ in apricot fruit. At the end of storage, catalase and peroxidase activities in the 100 μmol/L melatonin-treated group were 39.13% and 78.91% higher than those in control, respectively (P<0.05). The H₂O₂ content of apricot fruit in the 100 μmol/L melatonin-treated group was significantly lower than that in the control group by 19.74% (P<0.05), which reduced the accumulation of H₂O₂ in apricot fruit, and delayed the rise of cell membrane permeability and malondialdehyde content. These findings suggested that melatonin could regulate reactive oxygen species metabolism to induce resistance to black spot in postharvest apricot fruit.