Grape Marc Extract-Induced Defense Reactions and Protection against Phytophthora parasitica Are Impaired in NahG Tobacco Plants.

Grape marc extract (GME) acts as an elicitor of plant defense responses. This study analyzed GME-induced plant defense reactions in NahG transgenic tobacco. Leaf infiltration of NahG leaves revealed HR-like reactions with reduced lesions and weak deployment of autofluorescent compounds in the surrounding infiltrated tissues. The β-1,3-glucanase PR2-, endochitinase PR3-, and osmotin PR5-target transcript levels were strongly lowered in NahG leaves, and the mutant failed to accumulate the antimicrobial PR1 transcripts. GME-induced protection against Phytophthora parasitica var. nicotianae (Ppn) was evaluated on tobacco leaves. The antimicrobial properties of GME against Ppn were evidenced using a range of in vitro tests. GME-sprayed wild-type leaves showed reduced infection areas, whereas GME failed to induce a protective effect against Ppn in NahG leaves. The results suggest that GME-induced plant defense reactions in tobacco plants was mediated by salicylic acid (SA) and that GME-induced protection against Ppn could be the combined result of antimicrobial and defense actions.