Abstract
Aims: The alkaloid hordenine is one of the major allelochemicals involved in the allelopathic ability of barley (Hordeum vulgare L.), whose biosynthesis and accumulation is preferentially located in roots. Hordenine appears to have been unintentionally favored during domestication in modern and cultivated barley cultivars at the expense of another alkaloid, gramine. In this study, we assessed the content of hordenine and its two precursors, N-methyltyramine (NMT) and tyramine, in roots and root exudates of the modern spring barley cv. Solist, and particularly how they are affected due to nutrient deficiencies. Methods: We monitored the three metabolites during the early phases of barley growth i.e., up to 8 days, applying HPLC time-course and both target and untargeted metabolomic approaches. Barley plants were grown either in full nutrient solutions
or in specific nutrient shortage conditions (N, S, P and Fe). Results: Results confirmed a strong decrease of
the allelochemical accumulation (hordenine and the two precursors) in roots and in root exudates during both 24 h and 8 days time-course experiments. Yet, the overall tyramine content was approximately tenfold lower compared to the other two compounds. In addition, plants subjected to nitrogen (-N), sulfur (-S), phosphorus (-P) and iron (-Fe) deprivation showed nutrient-dependent accumulation of hordenine, N-methyltyramine
and tyramine, as well as of other secondary metabolites. Indeed, the synthesis of hordenine and N-methyltyramine was trigged under nutrient deficiencies. Conclusions: In conclusion, this study highlighted
the impact of nutrient availability on the growth dependent accumulation patterns of all the three compounds investigated in modern barley roots.