BABA-induced resistance: milestones along a 55-year journey

β-aminobutyric acid (BABA) has been known as an inducer of disease-resistance since 1963, however, only in the recent two decades an increasing number of reports have been published shedding light on its spectrum of activity, physiological impacts, and mode of action. BABA has been shown to protect about 40 plant species against about 80 pathogens and pests, including a virus, protista, bacteria, oomycetes, fungi, nematodes and arthropods. Interestingly, it is also active against abiotic stress and enhances salt, heat and drought tolerance in several plant species. Although generally regarded as a xenobiotic, there are a few reports that mention its occurrence in plants. BABA-treated plants react faster and in a more robust manner to a stress situation, a phenomenon that has been termed priming. ¹⁴C BABA is highly systemic, readily taken up by roots and leaves, and translocate both acropetally and basipetally. No metabolites of BABA are known. BABA is effective as a foliar spray, soil drench and seed treatment. Seeds derived from treated plants may produce primed progeny, making BABA the first agent with transgenerational efficacy. BABA induces numerous biochemical changes in treated plants. Among them are the induction of reactive oxygen species (ROS) and glycolate oxidase (GO) that are tightly linked to defense. ROS scavengers may alleviate the activity of BABA. Interestingly, only the R but not the S enantiomer of BABA primes for resistance. Unfortunately, BABA can also impose growth stress (and phytotoxicity) in some treated plants therefore BABA analogs with reduced stress effects are highly desirable for agricultural use.