Salicylic acid treatment inhibits ethylene synthesis and starch-sugar conversion to maintain apple fruit quality during shelf life

Starch and sugars are widely acknowledged as taste determinants, energy substances, and signal molecules in fruits. Salicylic acid (SA) regulates many physiological and biochemical processes during fruit ripening. In this work, we investigated the effects of SA treatment on physiological parameters and SA synthesis, ethylene production, and starch-sugar metabolism of apples during shelf life. Results showed that SA maintained fruit firmness, reduced weight loss, and inhibited starch to sugar conversion during shelf life. The endogenous SA level was increased in SA-treated fruits, mediated by MdPAL, MdICS2, and MdNPR1, thus decreasing MdACS1 and MdACO1 expressions and inhibiting ethylene biosynthesis. Furthermore, the expression of starch and sugar-related genes, MdAMY, MdBam5, MdBam8, MdSPS, MdSUSY, MdNINV, and MdAINV, were inhibited by SA treatment during shelf life. It was inferred that exogenous SA could inhibit ethylene synthesis and starch-sugar conversion, maintain the quality, and prolong the shelf life of apples