为了探明一氧化氮(NO)抑制采后芒果软化的作用机理,将"台农"芒果果实在0.25 mmol/L硝普钠(SNP,NO供体)溶液浸泡处理20 min,常温(20±2) ℃贮藏20 d,定期测定果实硬度、细胞壁组分含量、细胞壁水解酶活性。结果表明,与未处理果实相比,SNP处理显著降低贮藏20 d内果实中多聚半乳糖醛酸酶(PG)活性(p<0.05),显著抑制贮藏10 d内果实纤维素酶(CX)(p<0.05)活性,极显著抑制β-半乳糖苷酶(β-Gal)和α-L-阿拉伯呋喃糖苷酶(α-L-Af)活性(p<0.01),但使贮藏15~20 d期间果实CX和β-Gal活性及贮藏第20 d的α-L-Af活性均显著增加(p<0.05)。SNP处理显著抑制贮藏5 d内果胶甲酯酶(PME)活性(p<0.05),但在贮藏10~20 d期间保持较高的PME活性(p<0.05)。此外,SNP处理极显著延缓原果胶和纤维素的降解(p<0.01),减少可溶性果胶含量的增加(p<0.05),从而降低贮藏期间果实硬度的损失。硬度与原果胶、纤维素含量均呈极显著正相关(p<0.01),而与CX活性呈显著负相关(p<0.05),与可溶性果胶含量、PG、β-Gal和α-L-Af活性均呈极显著负相关(p<0.01)。可溶性果胶含量与纤维素含量呈极显著负相关(p<0.01),而与α-L-Af活性均呈显著正相关(p<0.05),与PG和β-Gal活性均呈极显著正相关(p<0.01)。因此,采后SNP处理可以通过调节果实细胞壁降解酶活性,减少细胞壁组分的降解,从而延缓芒果采后软化,延长贮藏期。
To elucidate the inhibitory mechanism of nitric oxide (NO) on softening of postharvest mango (Mangifera indica L.) fruit, mango fruits at green mature stage were dipped into 0.25 mmol/L sodium nitroprusside (SNP, a nitric oxide donor) solution for 20 min and storage at (20±2)℃ for 20 d. During storage, fruit firmness, cell wall component, and activities of cell wall degrading enzymes were investigated at regular intervals. The results showed that SNP treatment significantly suppressed the activities of polygalacturonases (PG) (p<0.05) during storage period of 20 d, and significantly inhibited the activities of cellulose (CX) (p<0.05), β-galactosidase (β-Gal) (p<0.01) and α-L-arabinofuranosidase (α-L-Af) (p<0.01) during storage period of 10 d. However, it significantly increased the activities of CX and β-Gal (p<0.05) from 10 d to 20 d, and α-L-Af activity (p<0.05) on the 20 th day, as compared with control fruit. SNP treatment significantly inhibited the increase of pectin methylesterase (PME) activity during storage period of 5 d (p<0.05), but maintained higher PME activity from 10 d to 20 d (p<0.05). In addition, SNP treatment delayed the degradation of propectin and cellulose extremely significantly (p<0.01), and inhibited the increase of soluble pectin content (p<0.05), therefore delayed the loss of fruit firmness, as compared with control fruit. There were extremely significant positive correlations between fruit firmness and the contents of propectin and cellulose (p<0.01), however, there were significant negative correlations between fruit firmness and the activity of CX (p<0.05), soluble pectin content (p<0.01) and the activities of PG, β-Gal and α-L-Af (p<0.01). There were extremely significant negative correlations between soluble pectin content and cellulose content (p<0.01), however, there were significant positive correlations between the soluble pectin content and the activitiy of α-L-Af (p<0.05), the activities of PG and β-Gal (p<0.01). Thus, it could be concluded that SNP treatment could delay fruit softening of postharvest mangoes by regulating cell wall degrading enzyme activities and decreasing the degradation of cell wall component, which would help to maintain the integrity of cell wall structure.