The Dynamics of the Photosynthetic Apparatus in Algae

Higher plants and algae are subjected to changes in light quality and quantity, and in nutrient availability in their natural habitat. To adapt to these changing environmental conditions these organisms have developed efficient means to adjust their photosynthetic apparatus so as to preserve photosynthetic efficiency and appropriate photoprotection. Under limiting light this system optimizes light capture and photosynthetic yield through a reorganization of its light harvesting system. In contrast, under high light, when the absorption capacity of the system is exceeded, the excess absorbed light energy is dissipated as heat to prevent oxidative damage. One of the key photosynthetic complexes, photosystem II is prone to photodamage but is efficiently repaired. The photosynthetic machinery is also able to adjust when specific micronutrients such as copper, iron or sulfur become limiting by remodeling some of the photosynthetic complexes and metabolic pathways. While some of these responses occur in the short term, others occur in the long term and involve an intricate signaling system within chloroplasts and between the chloroplast and the nucleus accompanied with changes in gene expression. These signals involve the tetrapyrrole pathway, plastid protein synthesis, the redox state of the photosynthetic electron transport chain, reactive oxygen species and several metabolites.