Supplementary file 1_Effects of bunch heating on Pinot noir grape ripening: changes in berry anthocyanin and malic acid concentrations and their regulation.docx

Cool-climate wine regions will face significant impacts from climate change over the coming decades. To predict the likely effects of climate change-associated high temperatures on berry ripening, a series of field-based grape bunch heating experiments were conducted on Pinot noir (Vitis vinifera L.) berries in Marlborough, New Zealand. Pinot noir bunches were heated for 7 days at the beginning of ripening (véraison) to a diurnal temperature range of 20 °C–39 °C, while unheated control bunches experienced an ambient diurnal temperature range of 11 °C–31 °C. This heating resulted in changes to several key quality criteria. The organic acid composition was altered by heat in favour of hastened reduction in malic acid concentration for a given total sugar concentration post-véraison. The sensitivity of anthocyanin accumulation in berry skins to heating varied depending on season: major inhibition in season 1 and minor inhibition in season 2. Abscisic acid (ABA) plays a pivotal role in the initiation of berry ripening, including the onset of anthocyanin accumulation in berry skins. Seasonal variation in peak berry ABA concentration was associated with seasonal drought, suggesting that the higher ABA concentrations in the drier second season of experimentation may have masked the heating effect on anthocyanin accumulation. While perception of heat (expression of heat shock factor HsfA2) by the berries was found to occur as quickly as 4 hours after heating, changes in berry composition and the expression of genes and transcription factors regulating malic acid and anthocyanins took two or more days to respond in a manner that was mostly in proportion to the concentrations observed. The study illustrates that hot periods, with daily maximum temperatures up to 40 °C over periods of time (7 days), may have direct impacts on the ripening of Pinot noir grapes, reducing organic acid and anthocyanins.