New insights of translocation of smoke-related volatile phenols in vivo grapevines

Abstract

The increasing frequency of wildfires in grape-growing regions is seen as a significant risk for the grape and wine industry. Volatile phenols (VP) are taken up by grapevines during wildfires and contribute to the perception of smoke taint in wine. Seven VPs -guaiacol, 4-methylguaiacol, o-, p-, m-cresol, syringol and 4-methylsyringol- have been identified as the main predictors of smoke taint development in wine. A previous study using an isotope tracer technique with guaiacol and d₃-guaiacol demonstrated that it is possible for this compound to be absorbed by the leaves and transported to the bunches [1]. However, the mechanism of translocation of other VPs have not been extensively investigated. The aim of this study was to investigate VP absorption into bunches and leaves and their potential translocation to grape berries.

Leaves and berries of potted grapevines were placed in contact with an aqueous mixture of deuterated VPs (d₃-guaiacol, d₇–o-cresol, d₃-syringol and d₆-4-methylsyringol at 24 mg/L) at two different phenological stages (pre-veraison and post-veraison). Leaves, bunches, or leaves and bunches of one shoot were treated, while the second shoot was isolated with plastic bags and left untreated. Grape samples (exposed and non-exposed to the labelled volatile phenols) were taken after 1 and 7 days of treatment, as well as at ripeness (20º Brix) in triplicated. The free plus bound forms of VPs in grape were analyzed by GC-MS.

Data showed that not only guaiacyl type VPs can translocate from leaves to berries, but also p-coumaryl and syringyl type VPs. This process can occur from leaf to grape and even from bunch to bunch to a very limited extent. The concentration of deuterated VPs was higher in the grapes untreated at the post-veraison stage. However, the concentration of labeled VPs was higher in the grapes treated at the pre-veraison stage, which is in agreement with what other researchers have found [2].

Levels of labeled VPs decrease with sampling time in both pre-veraison and post-veraison samples. This may be due to multiple factors, from degradation-evaporation of the compounds remaining in the grape skin, translocation to other parts of the plant, dilution, and/or inclusion in metabolomic pathways to form more stable compounds. This study confirmed that several types of VPs can be translocated from leaves to berries as well as from bunch to bunch. Although translocation is fast (1 day), it was also limited with only very low quantities observed in non-exposed grape berries.

References

[1] Hayasaka, Y., Baldock, G. A., Pardon, K. H., Jeffery, D. W., & Herderich, M. J. (2010). Investigation into the Formation of Guaiacol Conjugates in Berries and Leaves of Grapevine Vitis vinifera L. Cv. Cabernet Sauvignon Using Stable Isotope Tracers Combined with HPLC-MS and MS/MS Analysis. Journal of Agricultural and Food Chemistry, 58(4), 2076–2081.

[2] Kennison, K. R.; Wilkinson, K. L.; Pollnitz, A. P.; Williams, H. G.; Gibberd, M. R. Effect of Timing and Duration of Grapevine Exposure to Smoke on the Composition and Sensory Properties of Wine. Aust J Grape Wine Res, 2009, 15 (3), 228–237.