乙烯促进木质素合成减少镉吸收和积累提高番茄耐镉性

Ethylene Enhances Cd Tolerance through Promoting Lignin Synthesis and Reducing Cadmium Absorption and Accumulation in Tomato

镉(cadmium,Cd)胁迫强烈抑制植物生长发育,并且镉能够沿着食物链在人体中富集,对人体健康造成重大隐患。乙烯(ethylene,ETH)是一种重要的植物激素,在植物响应环境胁迫中发挥重要作用。但是,乙烯调节植物耐Cd的作用机制仍然未定论。本文发现3 mg/L Cd 2+处理能够提高乙烯合成关键蛋白质甲硫氨酸腺苷转移酶(methionine adenosyltransferase,MAT)活性,导致根中乙烯含量上升约44.6%。进一步研究发现,10和50μmol/L乙烯增强苯丙氨酸解氨酶(phenylalanine ammonia-lyase,PAL)、4-香豆酸辅酶A连接酶(4-coumarate coenzyme A ligase,4CL)、肉桂醇脱氢酶(cinnamyl alcohol dehydrogenase,CAD)和愈创木酚过氧化物酶(guaiacol peroxidase,PPOD)等木质素合成关键酶的活性,使番茄根系木质素含量提高约52.1%和83.8%,导致胞壁木质化程度提升。与对照相比,乙烯减少根表皮细胞Cd 2+内流40.2%~52.7%,显著降低体内Cd含量(P<0.05)。此外,乙烯处理减少毒性高的水提取态和乙醇提取态Cd的含量,增加了毒性低的盐酸、醋酸、氯化钠提取态和残渣态Cd的含量,同时增加Cd在细胞壁中的占比,降低在细胞器中的占比,从而降低植株的离子渗透率(electrolyte leakage,EL)和丙二醛(malondialdehyde,MDA)含量,增加叶绿素含量,提高了番茄植物对Cd 2+胁迫的耐受性。综上,本研究发现了Cd 2+胁迫之下MAT酶活性的变化,由此提出,MAT介导的乙烯合成与Cd 2+胁迫之间可能存在关联,为乙烯缓解植物Cd损伤提出新的可能机制,也为其在果蔬作物安全生产中的应用提供了初步的理论依据。

Cadmium(Cd)stress seriously inhibits the growth and development of plants,and Cd is enriched in the human body along the food chain,causing major risks to human health.Ethylene(ETH)is known for its role as a traditional plant hormone that plays a crucial part in various stress responses.However,the precise mechanisms by which ETH regulates plant tolerance to Cd remain unclear.In this study,we observed that treatment with 3 mg L-1 Cd 2+significantly increased the activity of Methionine adenosyltransferase(MAT)and the content of S-adenosylmethionine(SAM),resulting in about a 44.6%rise in ETH content in roots.Further investigations revealed that ETH concentrations of 10 and 50μmol/L enhanced the activity of enzymes involved in lignin synthesis,including phenylalanine ammonia-lyase(PAL),4-coumarate coenzyme A ligase(4CL),cinnamyl alcohol dehydrogenase(CAD),and Guaiacolperoxidase(PPOD),thereby leading to about 52.1%and 83.8%increase in lignin synthesis,respectively,resulting in increased lignification of cell walls.Compared to the control group,ETH effectively hindered the influx of Cd 2+in root epidermal cells by 40.2%-52.7%and reduced intracellular Cd accumulation in roots(P<0.05).Furthermore,ETH reduced the content of water-extractable and ethanol-extractable Cd,which are highly toxic.Conversely,it increased the content of hydrochloric acid-extractable,acetic acid-extractable,sodium chloride-extractable,and residual Cd,which have a lower toxicity.Moreover,ETH also increased proportion of Cd in the cell wall while reducing its presence in organelles.Consequently,ETH led to a reduction in electrolyte leakage(EL)and malondialdehyde(MDA)contents,increased the levels of chlorophyll,and improved the plants’tolerance to Cd 2+stress.In conclusion,our findings found the changes of MAT enzyme activity under Cd 2+stress.We propose that there may be a correlation between MAT-mediated ETH synthesis and Cd 2+stress,which provided a new possible mechanism for ETH to alleviate Cd damage in plants.Our work also provides a primary theoretical foundation into the potential application of ETH in the safe production of vegetable crops.