Results from growth parameters revealed that 0.5 mM and2.0 mM of MeJA were the most effective treatments in increas-ing the fruit size (both volume and weight) for BS and RR plums,respectively, and thus could be the most suitable concentrationfor practical purposes in order to increase crop yield. Thus, theseconcentrations were chosen for further studies on the effect of MeJAon bioactive compounds. The most significant changes in pheno-lics, carotenoids and total antioxidant activity took place at the last3 sampling dates and thus data at 14 days before harvest (DBH),7 DBH and harvest (H) are given. In relation to total phenolics,the concentration increased continuously with on-tree ripening forboth plum cultivars, and generally values were significantly higherin MeJA-treated fruit than in controls (Fig. 5). Between cultivars,BS had significantly higher phenolic contents than RR plums whencomparing control fruit, which is in agreement with the concen-tration of individual phenolic profiles (Fig. 4). The same effect wasobserved when total antioxidant activity in the hydrophilic frac-tion (HTAA) was measured, that is, a progressive increase from14 DBH to H, and again the levels were significantly higher inthose fruit treated with 0.5 mM or 2.0 mM MeJA for BS and RR,respectively.