Snapshot Issue 41 December 2007

Stilbene synthase

Ballroom dresses, sparkling tinsel and fireworks of sumptuous dishes…the end of year festivities are an invitation to sharing and conviviality. And the party would not be what it is without the drop of mild madness in our glass that we turn with a twist of the wrist. If wine is to be tasted within reason, it is not a sin to be reminded of its blessings during a time of the year when excesses of all kinds are on our front doorstep. Today we know that wine can not only protect against cardiovascular disease but that it also has antioxidant and anticancer virtues, that are due – in part – to a molecule found abundantly in red wine: resveratrol.

Resveratrol or 3,5,4’-trihydroxystilbene belongs to a family of components found mainly in plants : polyphenols. Besides its presence in groundnuts, raspberries and blackberries for instance, it is also found in grapevine where it is expressed mainly in the leaves and the grapes’ skin. Resveratrol results from a chemical reaction which is catalysed by an enzyme, stilbene synthase, of which two copies associate to produce resveratrol from a derivative of the amino acid phenylalanine. Why is red wine far richer in resveratrol than white wine? Does it have something to do with stilbene synthase? Apparently not. The answer resides, it seems, in the way wine is made. Polyphenols are extracted faster in the process of making white wine than in that of making red wine.

Surprisingly, stilbene synthase is not a permanent part of the plant. It only appears following a form of stress, in particular UV radiation – i.e. during the summer months – or infection caused by certain kinds of fungus. Unfortunately, the production of resveratrol is altered towards the end of the summer, leaving the grapes unprotected – hence weakened – and prone to a fungus dreaded by many a wine grower: Botrytis cinerea responsible for what is known as 'grey rot'. On the other hand, the same Botrytis cinerea – known in this instance as noble rot – is more than welcomed by a handful of white wine growers, who produce liqueur-like wines. Indeed, Botrytis cinerea concentrates the sugars and the flavours in grapes, the result of which is found floating in bottles of Sauternes and Monbazillac.

Botrytis cinerea not only harms grape vine but also all fruit and vegetable in general. Could resveratrol prove to be a future remedy against grey rot? A number of experimental trials have been carried out. Grape vine plants have already been genetically modified by introducing an extra copy of the stilbene synthase gene. As a result, they were far more resistant to Botrytis cinerea. So, in the future, will we be opening bottles of wine with a discrete ‘genetically modified’ written on the label? Perhaps. In the meantime, let’s party. Santé!

Stilbene synthase 1, Vitis vinifera (Grape vine): P28343

L'édition française de cette chronique est disponible dans l'Instantanés du mois de Prolune.

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