Plants in the Brassicaceae family – cabbage, broccoli, cauliflower and mustard – contain glucosinolates, sulfur-containing compounds that give those vegetables their unique flavor and smell. Some studies have shown that glucosinolates may also be beneficial in preventing cancer and cardiovascular diseases.
New research from Kyushu University in Japan explains how these chemicals in the cabbage family are broken down to promote plant growth in conditions lacking sufficient sulfur – and how this information could help in the future development of broccoli and cabbage that are even healthier for consumers.
The scientists working on this study reported that disrupting the production of two enzymes in thale cress plants (a relative of cabbage) reduced the conversion of glucosinolates to simpler compounds and even further slowed growth when the plants didn’t receive proper amounts of sulfur from their environment. The plants will break down glucosinolates as a way to keep growing under these deprived conditions – but knowledge of how the process occurs and contributes to adaptation to sulfur deficiency is still limited.
That’s where a team led by Akiko Maruyama-Nakashita stepped in. Their research provides a deeper understanding of this process through the study of genetically modified model plants.
“While we had previous evidence suggesting two particular enzymes may be key based on their increased presence when sulfur is deficient, our new results show that removing these enzymes through genetic modification dramatically disrupts this breakdown,” Maruyama-Nakashita said.
Maruyama-Nakashita and her team studied thale cress that had been modified by the insertion of DNA from bacteria to prevent one of the two enzymes from being produced. Through cross-fertilizing, they created plants that lacked both enzymes (BGLU28 and BGLU30). All the plants had similar levels of glucosinolates in conditions where enough sulfur was available. Levels of the sulfur-containing compounds were much higher in plants missing both enzymes compared to unmodified plants and those missing only one enzyme when grown in sulfur-deficient conditions.
In the plants missing both enzymes, plant growth was dramatically stunted when compared to the other plants when sulfur was scarce. This illustrated that the breakdown of glucosinolates contributes greatly to sustaining plant growth in environments lacking in sulfur. This in turn demonstrates that one of the roles of glucosinolates may be to store sulfur that can be released when needed.
Why is sulfur important for humans? It is considered an essential dietary mineral, and conditions like a nitrogen imbalance and protein-energy malnutrition may result from not ingesting enough of it. When cruciferous vegetables have more sulfur available, the humans who eat them can be healthier.
“The knowledge obtained here deepens our understanding of plant adaptation strategies to sulfur-deficient environments, and thus provides implications for promoting effective sulfur utilization in modern agriculture,” researcher Liu Zhang said. “We hope that characterization of key enzymes that regulate glucosinolate breakdown will shed light on designing strategies to improve the content of these functional compounds in Brassica crops.”