Metabolic Engineering for Carotenoids Enrichment of Plants

Metabolic Engineering for Carotenoids Enrichment of Plants

Several recent hypotheses consider oxidative stress (OSs) to be a primary constraint that ensures the sincerity of signaling based on condition-dependent carotenoids (CARs). The key testable difference between these hypotheses is the assumed importance of CARs for redox homeostasis, the CARs being either antioxidants, prooxidants, or unimportant. Because the current controversy over the importance of CARs as antioxidants could result from the hydrophilic basis of commonly used antioxidant tests, we used the new measure of lipophilic antioxidant capacity (AC) in vivo . The oxidative challenge reduced the pigmentation of the sieve, but led to an increase in AC suggesting the reallocation of resources from signaling to redox homeostasis. CARs have counteracted the effect of oxidative challenge on lipophilic (but not hydrophilic) AC, thus supporting CAR antioxidant function in vivo . This is inconsistent with the assumptions that signaling ability is maintained either by ROS-induced CAR degradation or by the pro-oxidant effect of high levels of CAR cleavage products that act as a physiological impairment. In order to fully understand the role of redox processes in ecology and evolution, it is necessary to evaluate the lipophilic AC of CARs.