Decoupling of expansive and structural growth induced by β-aminobutyric acid (BABA) is associated with metabolic reconfiguration in linseed (Linum usitatissimum L.)

β-aminobutyric acid (BABA) is a powerful priming agent of plant defences, but it may delay plant growth. To assess that BABA-induced growth delay is not detrimental to the incorporation of BABA-application in linseed (Linum usitatissimum L.) agronomic practices, such delay was characterised by the aid of physiological and metabolic analyses. Plant response to BABA was monitored in hydroponically-cultivated linseed plants over a period of 10 days, under continuous BABA-treatment. Fresh- and dry- mass relative growth rate (RGR) was assessed for the entire shoot, and then separately for young and mature leaves. Leaf water content, osmotic potential and metabolic profiling provided further insights into the spatial and temporal progress of plant response to BABA-treatment. Very early, at 8 hours post-treatment, plant water content decreased, affecting young leaves’ growth by expansion. Following this early interruption, growth was re-established thanks to a mechanism of osmotic adjustment based on the accumulation of metabolites. Only when BABA-treatment was prolonged over time, plant’s dry mass accumulation was affected. The multivariate analysis of the metabolic profiles of linseed young- and mature- leaves showed that metabolic reorganisation followed the various phases of plant growth-response to BABA. Overall, our results review the impact of BABA on plant growth and suggest a role for growth delay in BABA-induced tolerance to stress.