Protection of Photosynthesis against Ultraviolet-B Radiation by Carotenoids in Transformants of the CyanobacteriumSynechococcus PCC79421

Abstract

The cyanobacterium Synechococcus PCC7942 was transformed with various carotenogenic genes, and the resulting transformants either accumulated higher amounts of ␤-carotene and zeaxanthin or showed a shift in the carotenoid pattern toward the formation of zeaxanthin. These transformants were exposed to ultraviolet-B (UV-B) radiation, and the degradation of phycobilins, the inactivation of photosynthetic oxygen evolution, and the activity of photosystem II were determined. In the genetically modified cells, the influence on destruction of phycobilins was negligible. However, protection of photosynthetic reactions against UV-B damage was observed and was dependent on the carotenoid concentrations in the different transformants. Furthermore, it was shown that endogenous zeaxanthin is more effective than ␤-carotene. Our results suggest that carotenoids exert their protective function as antioxidants to inactivate UV-B-induced radicals in the photosynthetic membrane.

Developmental stage is an important factor that determines the antioxidant responses of young and old grapevine leaves under UV irradiation in a green-house

“…Although most carotenoids are known to be capable of singlet oxygen scavenging [57] and specific carotenoids were shown to protect cyanobacteria against UV-B photodamage [58] we found no correlation between total carotenoid contents and singlet oxygen scavenging capacities of grapevine leaves. Our earlier studies showed that singlet oxygen was not produced in response to strong oxidative stress achieved by high UV-B doses [59] and in a spectral comparison of the ROS generating efficacies of UV we showed that longer wavelengths (UV-A) irradiation was more efficient in triggering detectable amounts of singlet oxygen [21].…”

Biological weighting function for xanthophyll de‐epoxidation induced by ultraviolet radiation

“…It has been suggested that the presence of Z limits damage of the PSII reaction centre and also decreases D1 protein degradation avoiding the inactivation of PSII (Gö tz et al 1999, Jahns et al 2000. We do not know if this occurs in Nannochloropsis under our experimental conditions, but it is possible that in a similar way, Z accumulation could be a response to a decrease in PSII activity because of direct UVR damage (Renger et al 1986, Trebst and Depka 1990, Turcsanyi and Vass 2000.…”

The effects of enhanced ultraviolet-B and nitrogen supply on growth, photosynthesis and nutrient status of Abies faxoniana seedlings

“…Carotenoid protects chlorophyll from photooxidative destruction (Singh 1996). Carotenoid is the quenching agent of short wave radiation with high energy and could exert their protective function as antioxidants to inactivate UV-B-induced radicals in the photosynthetic membrane (Götz et al 1999). The decrease in Car content suggested that enhanced UV-B caused considerable oxidative stress by accumulation of reactive oxygen species (data not shown).…”