original_query: What is the role of Mg2+ in plant physiology and how does it interact with the larger environment of the multicellular organism?
query: What is the role of Mg2+ in plant physiology and how does it interact with the larger environment of the multicellular organism?
answer: In plant physiology, Mg2+ is essential for growth, present in amounts around 80 μmol g⁻¹ dry weight.  Its uptake via roots interacts with other cations in the rhizosphere.  Within cells, Mg2+ stabilizes membranes, is vital for ATP utilization, is involved in nucleic acid biochemistry, and is a cofactor for many enzymes. It's also the coordinating ion in chlorophyll.  Intracellular compartmentalization adds complexity, with Mg2+ moving between cytoplasm, vacuoles, mitochondria, and chloroplasts.  Mg2+ transport within the plant involves xylem and phloem, cycling between roots and leaves.  Homeostasis is maintained by processes at plasma and vacuole membranes, utilizing H+-ATPases.  Mg2+ stress (deficiency or toxicity) affects photosynthesis and other cellular processes.  The interactions with the environment include uptake from soil, competition with other ions, and response to drought.