Systemic translocation of ¹⁴C-dl-3-aminobutyric acid in tomato plants in relation to induced resistance against Phytophthora infestans

This paper provides evidence that the systemic resistance induced by dl-3-amino-n-butanoic acid, β-aminobutyric acid (BABA), against late blight in tomato is associated with the systemic acropetal translocation of BABA in the plant. Thus, when ¹⁴C-BABA was applied to the bottom leaves, the upper, but not the adjacent leaves, accumulated the compound and the upper leaves only were protected against disease. Similarly, when BABA was applied to the root system it was preferentially translocated to the uppermost leaves and these leaves showed the greatest protection. These data support the hypothesis that resistance induced by BABA is dependent on the actual presence of the compound in the leaf. Almost all ¹⁴C-BABA supplied to the tomato plants was recovered unchanged with only a small proportion of the ¹⁴C-label being retained by cell wall fractions, probably in the form of covalently-bound proteins. We suggest that apart from enhancing pathogenesis-related protein accumulation in tomato, BABA alters cell wall structure or metabolism so making the tissues more resistant to fungal enzyme attack.