ABSTRACT
Citrus plants are exposed to various abiotic [such as high light, flooding, high temperature (heat), freezing, salinity, ultraviolet radiation, and drought] and biotic stresses under field conditions, which limit the fruit yields and cause detrimental effects on plant growth and fruit quality. In this chapter, we will focus on the high light stress effect on the photosynthetic system of citrus plants and will highlight the different metabolic and antioxidant defense systems of citrus plants to cope with the damaging effects of high light stress. We also mentioned some promising antioxidant metabolites such as phenolic compounds and flavonoids and elaborated their role in meditating the negative effects of high light stress. Moreover, we discussed the genes that are involved in high light stress tolerance in citrus. We speculated that the citrus species which possess high antioxidant metabolites with high total contents of chlorophyll ‘a’ and ‘b’ such as citrus relative and wild citrus species (Murraya paniculata and Poncirus trifoliata) can tolerate the high light stress effectively compared to the varieties that have lower antioxidant metabolites and chlorophyll ‘a’ and ‘b’ such as sweet orange (Citrus sinensis) and mandarins. Enhancing tolerance of citrus species by boosting endogenous synthesis of antioxidant metabolites will be an alternative strategy to induce tolerance against single (high light stress) or combined abiotic stresses in citrus plants.
