Exogenous l-glutamate treatment could induce resistance against Penicillium expansum in pear fruit by activating defense-related proteins and amino acids metabolism

Abstract Glutamate is a versatile amino acid and occupies a pivotal position in both mammals and higher plants. Here, we investigated the effects of exogenous l -glutamate (L-Glu) treatment on the inhibition of Penicillium expansum in postharvest pear fruit and possible mechanisms involved. The results showed that application of l -Glu at 1.00 mM induced strong resistance against blue mold rot caused by P. expansum in pear fruit under either 25 °C or 4 °C condition. Meanwhile, l -Glu reduced spore germination of P. expansum both in fruit wounds and in vitro after 24 h of treatment. With the treatment of l -Glu, the activities of five representative defense-related enzymes (β-1,3-glucanase, chitinase, phenylalnine ammonialyase, peroxidase and polyphenol oxidase) and the expression of four pathogenesis-related protein genes ( PR1 , GLU , CHI3 and CHI4 ) as well as PAL were all significantly enhanced. More interestingly, our results also revealed the possible involvement of amino acid metabolism, especially the accumulation of Glu, γ-aminobutyric acid (GABA) and arginine, may account for decay inhibition in the postharvest pear fruit to an extent.