ABSTRACT
Sunlight provides the necessary energy for plant growth and development. Photosynthetic organisms totally depend on sunlight for their source of energy. Ultraviolet (UV) irradiations cause stress to plants. UV radiation above the threshold causes reduction in plant biomass, decreases the integrity of membranes with degradation of enzymes, damages the photosystem proteins, and augments the ROS production. UV radiation directly degrades the photosynthetic pigments and causes damage to the light-harvesting systems in plants. The partial breakdown of thylakoid membrane causes the reduction of photosystem II (PSII) activity during UV stress conditions. The activity of PSII was more reduced under UV stress and it was correlated with the extensive accumulation of reactive oxygen species (ROS) in thylakoid membranes, which hinders the oxygen evolution at the oxygen-evolving complex of PSII. Moreover, UV stress also reduces the leaf photosynthetic rate (Pn), stomatal conductance (gs), ribulose-1,5-bisphosphate carbox-ylase/oxygenase content, protein content, nitrogen concentration, and alter photosynthesis-related gene expressions. A high level of UV radiation leads to a stress effect in plants, while low levels of UV radiation bring priming effect. UV priming significantly influences the photosynthetic activity, which increases the photosynthetic pigments, photosystem activities, Pn, gs, etc. This chapter provides an overview of different ways and means by which UV radiation influences the photosynthetic capacity of plants.
