Regulation of Light Harvesting in Barley Plants Under Drought and Salinity Conditions

Plants constantly face changes in environmental conditions, leading to the development of a range of acclimatory mechanisms in their photosynthetic apparatus. The regulation of light harvesting by plants under stress conditions represents one of the key acclimatory steps for the sustainability of photosynthetic organisms ensuring plant growth and development under new conditions. The light-harvesting regulation at the level of light quanta absorption is achieved by modulating the size of light-harvesting antenna of photosystem II (PS II) either due to post-translational protein modifications, such as state transitions, or changes in the gene expression level of the light-harvesting PS II antenna proteins. Another essential regulating mechanism is the enhancement of the energy dissipation as heat, protecting plants from photodamage. In this study, we investigated how barley (Hordeum vulgare) plants regulate light energy absorption under drought and soil salinity conditions. Changes in the energy dissipation capacity and in the PS II antenna size during short-term and long-term exposure to these factors were revealed. The dynamics of hydrogen peroxide accumulation closely paralleled changes in PS II organization, suggesting its involvement in signaling processes regulating light-harvesting. The novelty of this work is that drought and salinity in low light initiated the same mechanisms of light quantum absorption regulation as high light conditions, though with differing temporal responses. These responses are coordinated through redox signaling and serve to maintain the balance between energy input and utilization. The identified patterns provide insight into barley acclimatory strategies and their implication for crop sustainability.