褪黑素对采后荔枝果实冷害及生理变化的影响

Effect of Melatonin on Chilling Injury and Physiological Changes in Litchi Fruit during Cold Storage

以采后“紫娘喜”荔枝果实为试材,使用0.5 mmol/L褪黑素(MT)溶液对其浸泡处理10 min,晾干后置于(4±1)℃、(85±5)%条件下冷藏30 d,研究MT处理对荔枝果实冷害及抗冷相关生理代谢的影响。结果表明,MT处理显著降低了荔枝果实冷害指数,推迟了果皮色度a*值下降;冷害指数在冷藏第30天较对照果实降低49.4%,果皮色度a^(*)值在第10~30天期间平均提高37.2%。MT处理减缓了果实膜相对电导率升高,抑制了丙二醛(MDA)、超氧阴离子(O_(2)·-)和过氧化氢(H_(2)O_(2))积累,如第30天时相对电导率、丙二醛含量、O_(2)·-生成率和H_(2)O_(2)含量较对照组分别降低29.6%,16.9%,6.9%和6.3%,从而减轻了果实氧化胁迫并使膜完整性得到维持。MT处理降低了果实多酚氧化酶(PPO)和过氧化物酶(POD)活性,同时提高了总酚、类黄酮和花色素苷含量,导致果实酶促褐变减轻。MT处理提高了果实超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)等抗氧化酶的活性,维持了较高的抗坏血酸(AsA)和还原性谷胱甘肽(GSH)含量及AsA/脱氢抗坏血酸(DHA)和GSH/氧化型谷胱甘肽(GSSG)比值,从而增强了冷藏荔枝果实的抗氧化活性。此外,MT处理促进了冷藏期间荔枝果实LcMsrA1、LcMsrA2、LcMsrB1和LcMsrB2上调表达,进而改善了果实蛋白质氧化损伤修复能力。结论:外源MT处理可通过调节冷藏荔枝果实抗冷相关生理代谢使果实冷害得到缓解。

Postharvest'Ziniangxi'litchi fruit were used as experimental materials and dipped in 0.5 mmol/L melatonin(MT)solution for 10 min.After drying,the fruit was refrigerated at(4±1)℃ and(85±5)%relative humidity for 30 d.During refrigeration,the effects of MT treatment on the chilling injury(CI)and its related physiological metabolism in litchi were investigated.The results showed that MT treatment reduced the chilling injury index and delayed the decrease in the chromaticity a*value in cold-stored litchi fruit.The CI index in MT-treated fruit was 49.4%lower than that in control fruit at 30 d,while chromaticity a*value in MT-treated fruit was 37.2%on average higher than that in control fruit from 10 to 30 d of refrigeration.MT treatment significantly inhibited the increases in membrane relative conductivity while suppressing the accumulations of malondialdehyde(MDA),superoxide anion(O_(2)·-)and hydrogen peroxide(H_(2)O_(2)),as shown by the decreases of 29.6%,16.9%,6.9%and 6.3%in relative conductivity,MDA content,O_(2)·-production rate and H_(2)O_(2) content in MT-treated fruit at 30 d,respectively,thus contributing to mitigation of oxidative stress and maintenance of membrane integrity.MT reduced the activities of polyphenol oxidase(PPO)and peroxidase(POD)as well as inhibited the decreases in total phenolics,flavonoids and anthocyanins contents in cold-stored litchi fruit,thereby ameliorating enzymatic browning.MT treatment significantly enhanced the activities of superoxide dismutase(SOD),catalase(CAT),ascorbate peroxidase(APX),monodehydroascorbate reductase(MDHAR),dehydroascorbate reductase(DHAR)and glutathione reductase(GR),and maintained higher levels of ascorbic acid(AsA)and reduced glutathione(GSH)contents and the higher ratios of AsA/dehydroascorbic acid(DHA)and GSH/oxidizided glutathione(GSSG)when compared to control fruit,which could lead to increases in antioxidant activity in litchi fruit during cold storage.In addition,MT treatment up-regulated the expression abundance of LcMsrA1,LcMsrA2,LcMsrB1 and LcMsrB2 during cold storage,thereby promoting the improvement in repair capacity of oxidized protein.The results indicate that exogenous MT treatment could alleviate the CI occurrence in cold-stored litchi fruit by modulating the chilling tolerance-related physiological metabolisms.