Water-stressed plants have higher levels of capsaisin, dihydrocapsaicin

Hot peppers represent both tradition and cultural identity in Mexico, where the pungent fruits have been a predominant part of the cuisine and culture for centuries. The Habanero pepper is in especially high demand for its unique flavor, aroma, and pungency. Grown predominately in the Yucatán, Habanero is an economically significant crop for the State's commercial growers.

The pungency of chili peppers is a result of compounds called "capsaicinoids" that are found only in the spicy fruit of plants in the Capsicum family. Two important capsaicinoids—capsaicin and dihydrocapsaicin—are responsible for 90% of Habanero peppers' pungency. Because capsaicinoids are in high demand for use in a variety of food products, cosmetics, and pharmaceuticals, producing peppers with high capsaicinoid content can naturally increase the economical viability of the plants.

Pungency levels in peppers are determined by two factors: genetics and plant environment. Environmental conditions such as water stress have been shown to have strong effects on capsaicinoid accumulation in some peppers. Research published in HortScience evaluated the susceptibility of the Habanero pepper (Capsicum chinense Jacq.) to water-deficit stress and the effect of this stress on capsaicin and dihydrocapsaicin production. "Although the Habanero pepper is a significant economic resource for the region, few studies have investigated the effects of abiotic stresses on capsaicinoid production," explained Manuel Martínez-Estévez, lead author of the report.

Habernero plants were subjected to water deficit stress treatments beginning 26 days after transplanting. One liter of water was applied either every 7th or 9th day, depending on the treatment, while the control plants were watered daily. The researchers measured the plants' shoot and root system development and extracted capsaicinoids from the pepper placentas for testing. Results showed that plants grown under water stress had less height, root dry weight, and root/shoot relation than plants which were irrigated daily, while fruit growth and production were unaffected by water stress. The data also confirmed that the water-stressed plants had increased capsaicin and dihydrocapsaicin concentrations compared to the control plants.

In another important finding, the scientists discovered that capsaicin synthase activity—a process in which the compound is biosynthesized through condensation of vanillylamine and 8-methyl nonenoic acid—is regulated in response to water deficit stress. "These results are novel because there are few reports on capsaicin synthase activity and none for the Habanero pepper," said Martínez-Estévez. "The role of these compounds and the importance of regulating their levels in fruits from plants under abiotic stress must be addressed in future works."

The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/cgi/content/abstract/46/3/487