褪黑素处理对高节竹笋低温贮藏过程中木质化的影响

Effect of Melatonin Treatment on Lignification of Phyllostachys prominens Shoots during Low Temperature Storage

【目的】 探讨褪黑素处理条件下,高节竹笋采后低温(4 ℃)贮藏过程中木质素形成、抗氧化酶活性、转录因子基因表达的变化模式,为阐明褪黑素处理对竹笋采后木质化过程的影响及其调控机制提供参考。【方法】 以高节竹笋为试验材料,分析低温(4 ℃)贮藏过程中(0、3、6、9、12天)褪黑素(1.0 mmol·L^-1)处理组和对照组竹笋硬度、黄度、亮度,木质素、纤维素含量,木质素合成相关的苯丙氨酸裂解酶(PAL)、过氧化物酶(POD)活性,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸还原酶(APX)活性以及NAC、MYB转录因子基因表达等指标。【结果】 与对照相比,外源褪黑素处理减缓笋体变硬和黄化的速度以及木质素和纤维素的积累速度,显著抑制PAL和POD活性,提高了SOD、CAT和APX活性,有效延缓高节竹笋木质化的发生进程;转录因子MYB20、MYB63、MYB85、SND2和VND7的表达随竹笋采后贮藏时间的延长均受到不同程度的诱导,而MYB42、MYB43、NST1和KNAST7的表达量则有所下降。褪黑素处理一定程度上抑制了MYB20、MYB42和KNAT7的表达,促进了MYB43、MYB63、MYB85和SND2的表达。【结论】 外源褪黑素处理有效延缓了高节竹笋采后低温贮藏过程中木质化的发生进程,其机制可能是褪黑素处理降低了木质素生物合成相关酶的活性,提高了抗氧化能力。此外,褪黑素也可能参与竹笋木质化的转录调控过程。

【Objective】 This study was designed to investigate the effect of melatonin on lignin formation, scavenging-enzyme activity, and transcription-factor expression in Phyllostachys prominens shoots stored at 4 ℃. 【Method】 We investigated the changes in the firmness, yellowness and brightness, lignin and cellulose contents, phenylalanine ammonia-lyase (PAL) and peroxidase (POD) activities, superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities, as well as the gene expression of NAC and MYB transcription factors in bamboo shoots of P. prominens during the different storage time (0, 3, 6, 9 and 12 d) under low temperature (4 ℃) with or without melatonin (1.0 mmol·L^-1) treatment conditions.【Result】Compared with the control, the exogenous melatonin slowed down the rate of hardening and yellowing of the shoots, and reduced lignin and cellulose contents, which proved that it effectively retarded shoot lignification. Furthermore, melatonin treatment inhibited PAL and POD activities significantly, while it enhanced SOD, CAT, and APX activities at different storage stages. Additionally, transcription factors of MYB20, MYB63, MYB85, SND2 and VND7 from the NAC and MYB families were up-regulated, MYB42, MYB43, NST1 and KNAST7 were down-regulated during postharvest storage of the bamboo shoots, and melatonin treatment inhibited the expression of MYB20, MYB42 and KNAT7, while induced the expression ofMYB43, MYB63, MYB85 and SND2 to some extent. 【Conclusion】 These results indicate that melatonin treatment can effectively delay the occurrence of lignification in the process of postharvest low-temperature storage of P. prominens shoots. The delaying effect of postharvest bamboo shoot lignification was mainly attributed to reduction of activities of lignin biosynthesis-related enzymes and improvement of antioxidant capacity of bamboo shoots. Moreover, exogenous melatonin may be involved in the transcriptional regulation of the lignification process of bamboo shoots.