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.