Effects of aluminum stress on cassava growth and root exudates

【Objective】 This study aimed to investigate effects of aluminum stress on cassava growth and root exudates，thereby providing theoretical references for elucidating toxic effects of aluminum stress on cassava， investigating response mechanism of cassava to aluminum stress， and breeding cassava germplasms tolerant to aluminum toxicity. 【Method】 Taking seedlings of cassava SC205 at 47 d after cutting as experimental materials， their plant height，leaf malon-dialdehyde （MDA） content， and root proline （Pro） content were determined after treated with 200 mmol/L aluminum chloride solution for 19 d， seedlings without stress treatment were taken as the control group. Ultra-high performance li-quid chromatography mass spectrometry （UPLC-MS/MS） was used to determine the types and compositions of root exudates of the treatment groups and control， and effects of aluminum treatment on root exudates were analyzed using untargeted metabolomics. Differential metabolites were screened to perform functional annotation and enrichment analysis of metabolic pathways based on databases such as HMDB， Lipidmaps， and KEGG. 【Result】 After aluminum treatment，the cassava leaves gradually wilted， with their plant height significantly lower than that of the control （P<0.05， the same below）， and leaf MDA content and root Pro content significantly increased. A total of 2948 metabolites were detected from cassava root exudates，and 1882 differential metabolites were screened，among which 768 differential metabolites up-regulated and 1114 differential metabolites down-regulated.The KEGG enrichment results showed that metabolites with high differential significance were mainly distributed in seven pathways： pantothenate and CoA biosynthesis； β-alanine metabolism； glycine， serine， and threonine metabolism； pyrimidine metabolism； phenylalanine， tyrosine， and tryptophan biosynthesis； purine metabolism； and tyrosine metabolism. Metabolites like N,N-dimethylglycine，acetoacetate，4-aminobutanoate，oxalic acid， xanthosine， phenol， adenine， L-tyrosine，L-phenylalanine，L-tryptophan，L-aspartic acid，L-histidine， and L-glutamine significantly up-regulated，among which four matabolites （N,N-dimethylglycine， acetoace-tate， 4-aminobutanoate， and oxalic acid） exhibited up-regulated fold changes of more than 35.40； while choline， 3-phosphonooxypyruvate phosphate， L-dopachrome， glyceric acid， and panthenol significantly down-regulated， among which choline exhibited a down-regulated fold change of 33.75. 【Conclusion】 Aluminum stress has obviously toxic effects on cassava，leading to damage of cell membrane lipids，inhibition of normal growth，causing significant changes in composition of cassava root metabolites，as obvious changes are found in important metabolites such as pantothenate，amino acids， and oxalic acid.