Last updated March 8, 2018 at 10:36 am
Wine grapes can suffocate while still ripening on the vine, causing them to die and sending vineyard harvests into freefall.
The ability of grapes to absorb enough oxygen to survive varies between strains, new research has found, suggesting winemakers should adopt new strategies to match changing climates.
The research, led by Stephen Tyerman from the University of Adelaide, used tiny probes to discover that cell death inside grapes is caused by lack of oxygen.
In a paper published in the Journal of Experimental Botany, Tyerman and colleagues reveal how by using miniature probes and micro X-ray computed tomography (CT) they determined that oxygen enters grapes through tiny pores called lenticels situated on the small stalk, or pedicel, connecting each berry to the plant.
The process draws oxygen into the fruit, particularly into the flesh, or mesocarp.
Adapting to changing conditions
Using chardonnay and shiraz grapes – which both contain seeds – and another type called ruby seedless, which don’t, the scientists found that typically oxygen levels were highest in the skin of the grapes and then decreased towards the centre.
Oxygen levels dropped in the mesocarp during ripening, and if they dropped to near-zero cell death resulted.
Blocking the pores in chardonnay grapes caused hypoxia – a lack of oxygen – in the grapes resulting both in cell death and an increase in ethanol.
The efficiency of the grape oxygen-intake mechanism was affected by increasing temperatures, explaining why death is often accelerated as the fruits ripen.
Tyerman’s team found that shiraz vines contained a much smaller region of pores than chardonnay, explaining their greater sensitivity to heat.
The findings are likely to help wine-growers adapt to changing conditions.
“This breakthrough on how grapes breathe will provide the basis for further research into berry quality and cultivar selection for adapting viticulture to a warming climate,” says Vladimir Jiranek, director of the University of Adelaide’s ARC Training Centre for Innovative Wine Production.