1-MCP处理对采后‘澳洲青苹’苹果叶绿素降解的影响

Effect of 1-MCP treatment on chlorophyll degradation in postharvest ‘Granny Smith’ apple fruit

【目的】以‘澳洲青苹’苹果为试材,研究1-甲基环丙烯(1-MCP)对果实采后叶绿素降解代谢的影响,为果实采后贮藏、保鲜及保绿技术提供新的理论基础。【方法】采用1μL·L^-11-MCP处理‘澳洲青苹’苹果果实,定期测定果实色泽、乙烯释放量和呼吸强度,通过高效液相色谱法(HPLC)对果皮中的叶绿素及其降解代谢产物进行定性定量分析,并采用实时荧光定量PCR技术检测叶绿素降解途径中关键基因的表达水平。【结果】1-MCP处理显著延缓‘澳洲青苹’果皮颜色转变,降低乙烯释放量和呼吸强度。1-MCP处理能保持果皮叶绿素a、b含量处于较高水平,并抑制脱镁叶绿素a和脱镁叶绿酸a的生成。叶绿素降解相关基因MdSGR、MdHCAR、MdPPH和MdNYC1的表达量受到1-MCP的调控,1-MCP抑制基因MdPAO和MdRCCR的表达,推迟叶绿素降解代谢的下游反应;MdPAO表达量与果皮色泽和叶绿素含量显著相关。【结论】1-MCP可调节叶绿素降解途径相关基因表达水平来控制代谢产物的降解和生成,从而延缓果皮叶绿素降解,其中,MdPAO是调控叶绿素降解的关键基因。

【Objective】The effect of 1-methylcyclopropene(1-MCP) on the post-harvest chlorophyll degradation and metabolism was studied in’Granny Smith’apple fruit in order to provide new understanding for improved post-harvest storage and green preservation techniques.【Methods】The’Granny Smith’apple used in the experiment were picked from the Haisheng Apple Co., Ltd.,(Qianyang, Baoji,China) during commercial harvesting period. 400 health fruit with even size and maturity and no mechanical damage were selected. Half of the fruit were fumigated with 1 μL · L-11-MCP at room temperature for 24 hours, and the remaining half were air-sealed as the control group(CK). After treatment, the fruit were packed in PE bags with 40 fruit per bag and stored at room temperature(20±2 ℃), with a relative humidity of 80%-90%. Physiological parameters such as fruit color, ethylene production, and respiratory intensity were regularly measured, and qualitative and quantitative analyses of chlorophylls and their degradation metabolites in the peel were performed using high-performance liquid chromatography(HPLC). Real-time fluorescence quantitative PCR was used to detect expression of key genes involved in chlorophyll degradation.【Results】The results showed that with the prolonged storage time,the color of’Granny Smith’apple peel became yellow, and the color values L*and h? changed significantly. The magnitude of change in the color value was significantly reduced. 1-MCP treatment delayed the occurrence of ethylene peak in’Granny Smith’fruit and inhibited ethylene production and respiration intensity. The CK group showed an ethylene peak at 60 days and the ethylene production rate was25.9 μL · kg-1· h-1, while the 1-MCP treatment group showed an ethylene peak at 70 days, and the ethylene production rate was 22.1 μL · kg-1· h-1. Fruit respiration intensity gradually increased in the late storage period. The peak of respiration occurred at 70 days in both groups. The maximum respiration intensity in the control and the treatment was 15.1 mg · kg-1· h-1 and 10.6 mg · kg-1· h-1, respectively. The respiratory intensity of the CK group was significantly higher than that of the 1-MCP group. HPLC results showed that after 1-MCP treatment, chlorophyll a and chlorophyll b decreased slowly, and their contents were significantly higher than in the CK group. The accumulation levels of pheophytin a and pheophorbide a after 1-MCP treatment were lower than those in the CK group, indicating that 1-MCP was effective to delay the chlorophyll degradation by inhibiting the further generation of pheophytin a and pheophorbide a. qRT-PCR analysis showed that 1-MCP treatment inhibited the expression of related genes in chlorophyll degradation pathway, especially MdPAO and MdRCCR, which regulate the degradation of pheophytin a and pheophorbide a, respectively, in’Granny Smith’. It shows that 1-MCP regulates chlorophyll degradation and metabolism during peel yellowing by delaying gene expression and accumulation of metabolites downstream of chlorophyll degradation pathway. In the fruit of CK group, MdNYC1 was significantly positively correlated;the L*value was significantly negatively correlated;and the h? value was extremely significantly positively correlated with the content of chlorophyll a and pheophorbide a. Expression of MdSGR was significantly positively correlated with L*value and significantly negatively correlated with chlorophyll b content. In the fruit of 1-MCP treatment group,the expression of MdPAO was significantly negatively correlated with the L*value, and chlorophyll a,chlorophyll b, and pheophorbide a were extremely significantly positively correlated. The expression levels of MdNYC1, MdPAO, and MdRCCR were negatively correlated with L*values and positively correlated with h value. MdPPH, MdSGR, and MdHCAR expression levels were positively correlated with L*value and negatively correlated with h? value.【Conclusion】Under normal temperature storage, 1-MCP treatment can delay the occurrence of ethylene and respiration peaks in’Granny Smith’apple fruit, reduce ethylene release and respiration intensity, and plays a role in delaying fruit senescence.When the L*value is higher than 75 or h value lower than 112°, the peel will enter a significant yellowing period, and 1-MCP treatment significantly inhibits the coloration process in the peel. 1-MCP treatment inhibited the expression of genes MdPAO and MdRCCR, which regulate the degradation of pheophorbide a and chlorophyll a, delay the expression of genes downstream of the chlorophyll degradation pathway and the accumulation of its metabolites, and reduced the production of pheophytin a and pheophorbide a. Therefore, 1-MCP is effective in regulating chlorophyll degradation and metabolism during the yellowing of the peel. The genes MdNYC1, MdPPH, MdPAO, and MdSGR are significantly correlated with the peel color of’Granny Smith’apple. MdPAO in the 1-MCP treatment group showed a strong positive correlation with chlorophyll content and is likely a key gene regulating chlorophyll degradation.