Expression patterns of volatile compounds during ‘FL 47′ tomato ripening and their response to exogenous methyl salicylate (MeSA) fumigation

Aroma, a complex mixture of volatiles, is essential for tomato flavor; however, the expression patterns of most volatile compounds and their response to exogenous methyl salicylate (MeSA) treatment are still unclarified. In this study, in association with the alteration in ethylene evolution and its biosynthetic genes (SlACO1 and SlACS2/4), 31 volatiles fluctuated or accumulated during ‘FL 47′ tomato ripening with a burst at pink or red stage, resulting in the alteration in aroma quality. Meanwhile, the alternation of 29 volatiles, lycopene and β-carotenoid content as well as SlPSY1 and SlCCD1A/B mRNAs demonstrated a strong correlation with ethylene evolution. Further study validated the role of ethylene in apocarotenoid volatile biosynthesis. The formation of 24 volatiles were greatly suppressed in MeSA-treated fruit at red stage along with lower ethylene. In addition, the reduction of apocarotenoid volatiles was associated with downregulated SlPSY1 and SlCCD1A/B mRNAs and carotenoid accumulation when compared with control. In combination with the alternation of ethylene evolution and apocarotenoid volatile formation in SlACS2-overexpressing fruit after MeSA treatment, our results implied that ethylene played a critical role in MeSA-induced reduction of apocarotenoid volatiles via its influence on carotenoid biosynthesis and SlCCD1A/B expression. Although the formation of over 60% of the tomato volatiles was altered by MeSA fumigation, no difference in total volatile abundance or aroma quality could be detected between samples. On the other hand, the taste quality was substantiality altered by MeSA treatment in association with the reduction of TSS and TSS/TA ratio as well as TA increment. Taken together, our results illustrated that MeSA application for fruit quality control was at the expense of flavor alternation.