Ups and downs in alfalfa: Proteomic and metabolic changes occurring in the growing stem

•Each region of the stem is characterized by a unique metabolic fingerprint.•Mitochondrial and chloroplast-related proteins are abundant where fibres develop.•The enzyme systems for secondary cell-wall deposition are set up in the apical region.•Forisomes and stress-related proteins accumulate in the most mature, basal region.