外源氰化物对毛桃幼苗根系生理及代谢的影响

Effects of exogenous cyanide on root physiology and metabolism of peach seedlings

【目的】探究外源氰化物(CN-)处理对桃根系生长、生理特性及代谢的影响。【方法】对桃园内死树和活树根系环境进行田间调查,测定土壤和根系中CN-含量。以萌发的桃种子为试验材料,观察不同浓度CN-处理下根系生长情况,测定根系中过氧化氢和丙二醛含量、抗氧化酶活性以及初生代谢物变化情况。【结果】CN-主要分布在0~40 cm土层,且死树土壤中CN-含量显著高于活树;随着时间推移,死树和活树根围土中CN-含量都呈现上升趋势;0.5 mmol·L^(-1)CN-处理显著降低了桃根系长度和侧根数量,并增加了根系中过氧化氢和丙二醛含量,诱导超氧化物歧化酶、过氧化物酶、过氧化氢酶活性及相关基因表达量的明显升高;0.5 mmol·L^(-1)CN-处理改变了根系中大部分氨基酸(甘氨酸、丝氨酸、丙氨酸、脯氨酸等)、糖及有机酸的含量。【结论】高浓度CN-处理显著抑制桃根系生长,导致根系中活性氧爆发和膜脂过氧化,并显著干扰根系中氨基酸和碳水化合物代谢。

【Objective】Peach(Prunus persica)is an economically important fruit crop worldwide.With the increasing demand and the reduced cultivated land acreage of peach,replant problem(also known as replant disease)has become increasingly prominent,and has been causing severe economic losses Autotoxicity is a special kind of allelopathy,and is considered to be a major factor resulting in the prevalence of peach replant problem.Cyanide(CN;)is a major autotoxin that causes peach replant problem but the information on physiological and metabolic responses of peach plants under CN;treatment is quite limited.Thus,the specific responsive mechanisms of peach plants to CN;are worthy of in-depth exploration.The study aimed to investigate the effects of CN;treatment on the morphological,physiological,and metabolic parameters in roots of peach seedlings,so as to provide new insights into the response mechanisms of peach plants to CN;treatment.【Methods】The natural root environment of dead and living trees was investigated in the peach orchard of Huazhong Agricultural University.The effects of exogenous CN;treatment on root growth and seed germination were assessed on peach germinatedseeds(treated with 0,0.25,0.5,and 1.0 mmol·L^(-1)CN;)and lettuce seeds(treated with 0 and 0.5 mmol·L^(-1)CN;).The peach root tips treated with 0 and 0.5 mmol·L^(-1)CN;were subjected to anatomical assessments using paraffin sectioning and staining(including transverse and longitudinal sections).The contents of H;O;and MDA,as well as the activities of CAT,POD,and SOD from 0 and 0.5 mmol·L^(-1)CN;stressed peach roots were detected.The expression levels of CAT,POD,and SOD-encoding genes were tested using q RT-PCR.To further understand the CN;-induced metabolic changes,peach roots treated with 0 and 0.5 mmol·L^(-1)CN;for 5 d were subjected to gas chromatography-mass spectrometry(GC-MS)analysis.【Results】The CN;was mainly distributed in 0-40 cm soil layer,and the content was significantly higher in the soil with dead trees than with living trees.The CN;content in soil was predominantly detected adjacent to peach roots,and gradually decreased with the distance from peach roots The CN;contents showed an upward trend year by year in the bulk soils with the dead and living trees where the dead trees contained more CN;than the living trees.The CN;contents varied in different size of peach roots,the fine roots(Φ<5 mm)contained more CN;than the middle size(5 mm≤Φ≤10mm)and the large size roots(Φ>10 mm).We evaluated the effect of different CN;concentrations(00.25,0.5,and 1.0 mmol·L^(-1))on the growth performance of peach germinated-seeds.The result showed that 0.25 mmol·L^(-1)CN;treatment boosted root growth,while 0.5 and 1.0 mmol·L^(-1)inhibited roo growth with decreased root length and lateral root numbers.The allelopathy sensitivity index indicated that the effects of CN;treatment on peach growth in a concentration-dependent manner,showing low concentration promoted growth but high concentration inhibited it.Additionally,with 0.5 mmol·L^(-1)CN;treatment,the transverse and longitudinal sections of the root tip showed a severely wrinkled root epidermis,ruptured root cortex cells,and larger intercellular spaces.0.5 mmol·L^(-1)CN;treatment also significantly inhibited lettuce seed germination and biomass.The contents of H;O;and MDA in peach roots significantly increased,and the activities of SOD,POD,and CAT,as well as their respective encoding genes expression,significantly increased with 0.5 mmol·L^(-1)CN;treatment.The GC-MS analysis showed that 0.5 mmol·L^(-1)CN;treatment dramatically increased contents of numerous amino acids,including proline,glycine,serine,asparagine,alanine,glutamate,GABA etc.Moreover,CN;treatment significantly affected carbohydrate levels in peach roots.【Conclusion】The CN;contents were associated with the distribution and size of plant roots,and the decomposition of plant residuals.Exogenous CN;supply markedly retarded peach root growth.CN;feeding also gave rise to oxidative stress,reflecting by the increased ROS and MDA levels,and antioxidant enzyme activities.CN;supplementation also induced metabolic reprogramming,displaying a disorder of amino acid and carbohydrates metabolism.