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

Abstract: 【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-1CN-) and lettuce seeds (treated with 0 and 0.5 mmol·L-1CN-).The peach root tips treated with 0 and 0.5 mmol·L-1CN-were subjected to anatomical assessments using paraffin sectioning and staining (including transverse and longitudinal sections).The contents of H2O2and MDA,as well as the activities of CAT,POD,and SOD from 0 and 0.5 mmol·L-1CN-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-1CN-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-1CN-treatment boosted root growth,while 0.5 and 1.0 mmol·L-1inhibited 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-1CN-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-1CN-treatment also significantly inhibited lettuce seed germination and biomass.The contents of H2O2and 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-1CN-treatment.The GC-MS analysis showed that 0.5 mmol·L-1CN-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.