Chitosan treatment elicited defence mechanisms, pentacyclic triterpenoids and stilbene accumulation in grape (Vitis vinifera L.) bunches

The stimulation of the plant response to pathogen attack by the application of resistance inducers, called elicitors, could represent an environmentally and commercially viable alternative or complement to existing pathogen control methods. In this work, the elicitor chitosan was sprayed on grape (Vitus vinifera L.) berries growing on the vine to shed light into the elicitation mechanisms underlying its application, with untreated bunches as controls. To gain a more comprehensive picture of the complex molecular processes elicited by chitosan, a proteomic approach was complemented by target and untargeted mass spectrometric analyses. The treatment altered the regulation of reactive oxygen species, with Cu/Zn superoxide dismutase and glyoxal oxidase showing up-accumulation. This might lead to an increased lignification via hypersensitive response mechanisms. Furthermore, enzymes involved in anthocyanin rather than stilbene phytoalexins accumulated in treated bunches. Stilbenes increased from 1.6 times (resveratrol) up to 3.8 times (piceid) over untreated bunches. The up accumulation of hydroperoxide lyase might lead to accumulation of oxylipins. Furthermore, the pentacyclic triterpenoids ursolate, oleanoate and betulinate increased by 1.25, 1.47 and 3.68 times in treated grape bunches (p < 0.01). Hence, the main processes underlying the response of grape fruits to chitosan treatment involved the accumulation of phenylpropanoid and triterpenoids phytoalexins, as well as the modulation of oxidative stress-related enzymes.