Ozone control as a novel method to improve health-promoting bioactive compounds in red leaf lettuce (Lactuca sativa L.)

Abstract

In this study, we determined the short-term effects of ozone exposure on the growth and accumulation of bioactive compounds in red lettuce leaves grown in a controlled environment plant factory with artificial light, also known as a vertical farm. During cultivation, twenty-day-old lettuce (Lactuca sativa L. var. Redfire) seedlings were exposed to 100 and 200 ppb of ozone concentrations for 72 h. To find out how plants react to ozone and light, complex treatments were done with light and ozone concentrations (100 ppb; 16 h and 200 ppb; 24 h). Ozone treatment with 100 ppb did not show any significant difference in shoot fresh weight compared to that of the control, but the plants exposed to the 200 ppb treatment showed a significant reduction in fresh weight by 1.3 fold compared to the control. The expression of most genes in lettuce plants exposed to 100 and 200 ppb of ozone increased rapidly after 0.5 h and showed a decreasing trend after reaching a peak. Even when exposed to a uniform ozone concentration, the pattern of accumulating bioactive compounds such as total phenolics, antioxidant capacity and total flavonoids varied based on leaf age. At a concentration of 200 ppb, a greater accumulation was found in the third (older) leaf than in the fourth leaf (younger). The anthocyanin of lettuce plants subjected to 100 and 200 ppb concentrations increased continuously for 48 h. Our results suggest that ozone control is a novel method that can effectively increase the accumulation of bioactive compounds in lettuce in a plant factory.

Effect of the Ozone Application in the Nutrient Solution and the Yield and Oxidative Stress of Hydroponic Baby Red Chard

“…The response to ozone in red lettuce varied as a function of gas concentration and the leaf age. The total phenol and flavonoid content and antioxidant capacity of the third leaves exposed to 100 ppb of ozone were like the control but in the fourth leaf, the antioxidant compounds significantly increased [61].…”

“…In wheat (Triticum aestivum L.) exposed to 0.384 mg•L −1 of O 3 , an increase in phenol content was also observed; however, this increase depended on the phenological stage of the crop, being higher at the grainfilling stage than during vegetative growth [60]. In another study of red lettuce grown under artificial light, the total phenolics, flavonoids, and anthocyanins showed a significant increase after 0.25 h of exposition on the fourth leaf [61]. The above could partly explain our results since the O 3 applications and the analyzes were performed at an early stage of the plant, after 5 days post-transplantation.…”

“…Although all the studies reviewed have shown that O 3 can induce an increase in one or more antioxidant enzymes such as SOD, CAT, and/or APX, no single effect has been determined in the same species. In fact, differential sensitivity to O 3 exhibited even by different varieties within the same plant species has been observed, which apparently depends on the efficiency of ROS scavenging [10,14,61].…”