Vine Nitrogen Status Does Not Have a Direct Impact on 2-Methoxy-3-isobutylpyrazine in Grape Berries and Wines

Methoxypyrazines (MP) constitute a large family of compounds that contribute to the vegetative varietal aroma of many grapevine varieties and wines. The berry content in 2-methoxy-3-isobutylpyrazine (IBM]?), a major MP reminiscent of green-pepper aroma, can be influenced by environmental factors or cultural practices such as water status or mineral nutrition. To date, no study has investigated a possible direct effect of nitrogen (N) on TEMP synthesis without possible interference from water status and vigor variations. In this study, only vine nitrogen status was significantly different among treatments. Water status was controlled during the season, and vine vigor was similar among treatments. IBM? level was maximal at bunch closure and decreased during the season. There was no significant effect of nitrogen nutrition on this metabolite. Moreover, the expression profiles of VvOMT3 and VvOMT4, key genes in the IBM? biosynthetic pathway, were similar between treatments. This result indicates that when an effect of N on IBMP was found in previous studies, it was likely mediated through the modification of bunch-zone microclimate, induced by the higher vigor of high N-status vines.