Carbon dioxide protects cold grapes

Table grapes are usually stored at 0 °C after harvesting to preserve the berries from water loss. In cold-sensitive plants, 'chilling injury' can occur due in part to reactive oxygen species (ROS) that damage cells and cause browning. In addition, plants may become more susceptible to fungal pathogens like grey mould that can grow at temperatures as low as – 5 °C.

To counteract this, table grapes respond to low temperatures by activating antifreeze proteins and enzymes that protect the fruit against ROS damage. Since exposing grapes to CO2 also reduces low-temperature damage, it is possible that the gas plays a role in this cold stress-response mechanism.

The EU-funded MOLCHARAVITIS (Study of the molecular mechanisms involved in the beneficial effect of high CO2 levels to preserve table grape quality during the storage at low temperature) project aimed to understand how CO2 protects table grapes from cold storage damage.

Researchers treated table grapes with CO2 for three days at 0 °C and looked at the genes that were activated during this time. They found high levels of proteins called transcription factors (TFs) that activate genes involved in protecting berries from cold stress and pathogens.

One of these protective proteins, dehydrin, is usually activated by a TF called C-repeat binding factor (CBF), which is itself activated by CO2. However, researchers found that in this case dehydrin was activated not by CBF but by another cold-inducible pathway.

Another TF called ethylene-responsive element-binding factor (ERS) did, however, activate a protein that defends plants from pathogens. Since higher levels of ERS were found in CO2-treated plants than in non-treated plants, CO2 may trigger this pathogen defence response.

Understanding the mechanisms underlying table grapes' responses to low temperatures is extremely useful to grape producers. Since sulphur dioxide is being restricted as a preservative in postharvest grapes due to health concerns, CO2 is a promising alternative treatment option.