Macronutrient utilization by photosynthetic eukaryotes and the fabric of interactions

Organisms acclimate to a continually fluctuating nutrient environment. Accl imation involves responses specific for the limiting nutrient as well as re sponses that are more general and occur when an organism experiences differ ent stress conditions. Specific responses enable organisms to efficiently s cavenge the limiting nutrient and may involve the induction of high-affinit y transport systems and the synthesis of hydrolytic enzymes that facilitate the release of the nutrient from extracellular organic molecules or from i nternal reserves. General responses include changes in cell division rates and global alterations in metabolic activities. In photosynthetic organisms there must be precise regulation of photosynthetic activity since when sev ere nutrient limitation prevents continued cell growth, excitation of photo synthetic pigments could result in the formation of reactive oxygen species , which can severely damage structural and functional features of the cell. This review focuses on ways that photosynthetic eukaryotes assimilate the macronutrients nitrogen, sulfur, and phosphorus, and the mechanisms that go vern assimilatory activities. Also discussed are molecular responses to mac ronutrient limitation and the elicitation of those responses through integr ation of environmental and cellular cues.