Mechanisms Of Potato Onion Root Exudates Alters The Root Distribution Of Tomato

Intercropping is a widely practiced to increase production in modern agriculture in China,which plays an important role in agricultural economy of the country.In recent years,it has been proved that one of the mechanisms of intercropping increasing the crop yield is to improve the utilization rate of belowground resources by changing the distribution of plant roots.However,there are still relatively few studies on the interaction mechanism of subterranean species that alter root distribution.Our previous study has found that potato onion(S)with strong promoting potential could increase tomato yield and change in tomato root distribution pattern,but the mechanism is poorly known.Therefore,we used potato onion with different promoting effects to understand the mechanism underlying potato onion affecting tomato root distribution in potato onion/tomato companion cropping system.GC-MS and UPLC-MS/MS techniques were used to isolate and identify the active substances in potato onion root exudates.Through tissue culture test and transcriptome sequencing technology,it is clear that the effect of this substance on the gravitation and growth direction of tomato roots and the expression of gravity-related genes.This study was conducted with the aim to understand the mechanism of potato onion root exudates affecting root distribution of tomato,which will provide theoretical basis for the root interaction mechanism of crops in the intercropping(companion cropping)system and theoretical reference for the establishment of the root model of efficient nutrient utilization in agricultural production.Main results of this study were as follow:1.The results of pot experiment showed that potato onion(S)with strong allelopathy made the root distribution of tomato grew away from potato onion,while potato onion(N)with weak allelopathy had no significant effect on the root distribution of tomato,and the root distribution tended to be evenly distributed on both sides.2.Exogenous application of different potato onion root exudates in one side of tomato revealed that addition the root exudates of strong promoting potato onion(S)could decrease the root length density and distribution range,while addition of root exudates of weak promoting potato onion(N)could increase the root length density and distribution range of tomato.Namely,the root exudates of strong allelopathy potato onion made the tomato root grow away from addition side,while the root exudates of weak allelopathy potato onion made tomato roots grow towards the addition side.The three different components preliminarily analyzed from the two variety root exudates using GC-MS were Disulfide,di-tert-dodecyl and Phenol,2,2’-methylenebis[6-(1,1-dimethylethyl)-4-methyl-,while L-phenylalanine was identified by UPLC-MS /MS.3.Exogenous application of l-phenylalanine reduced the distribution density of tomato roots in the soil and made the roots grow far away from the addition side.With the increase of l-phenylalanine concentration,the percentage of deviation angle from the vertical direction of tomato root increased.The results were consistent with the effect of strong promoting potato onion root exudates on root distribution of tomato.4.Transcriptome results showed that l-phenylalanine down-regulated the expression of genes related to amyloplast synthesis in tomato roots,and up-regulated the expression of auxin transporter-related genes.In the amyloplast synthesis pathway,the key genes in amylose,such as solyc01g109790.2 and solyc09g091030.2 were significantly down-regulated from G1 P to adp-glucose and then to solyc01g109799.2.Auxin transporter S1 PIN and LAX protein families were significantly up-regulated.At the same time,the results of tissue culture test showed that l-phenylalanine could cause the decrease of amyloplast deposition and the uneven distribution of auxin.In conclusion,this study proved that companion cropping with potato onion changing the tomato root distribution is closely related to root exudates of potato onion.From the two-variety potato onion root exudates,the identified active substance was l-phenylalanine.L-phenylalanine through down-regulated the root amyloplast synthesis related genes expression and increased the auxin transport gene expression.The decrease in amyloplast deposition and uneven root auxin distribution reduce the gravity of the tomato root,thereby change the direction of tomato root growth and distribution.