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In Vivo³¹P NMR Studies of Corn Root Tissue and Its Uptake of Toxic Metals

Eastern Regional Research Center, United States Department of Agriculture, Agriculture Research Service, Philadelphia, Pennsylvania 19118

Excised corn root tissue has been evaluated for its viability, integrity of compartmentation, intracellular pH gradients, total mobile phosphorus content and nucleotide concentrations under different levels of acidity, and mineral stresses using in vivo³¹P nuclear magnetic resonance spectroscopy at 21 to 23°C. Perfusion with Al³⁺ ion at low pH (4.0) for 20 hours caused the overall concentration of nucleotides in the cytoplasm to decrease significantly relative to the control. Respiratory activity as measured by O₂ uptake decreased by a comparable amount over this time period. The addition of glucose to the Al-containing perfusate negated the inhibitory effects on the respiratory system. Treatment of the tissue with paramagnetic manganese ion while perfusing in the presence of O₂ allowed for the observation of the sequence of events leading to the irreversible trapping of Mn²⁺ in the vacuole. Pretreatment of the roots with Mg²⁺ prevented Mn²⁺ migration to the vacuole over the time period of this experiment. Hypoxia prevented all but a limited uptake of Mn²⁺ into the cytoplasm of the root tips. No evidence of Mn²⁺ complexation of either cytoplasmic or vacuole Pi suggests that the energy derived from O₂ consuming processes is necessary for the facilitated movement of this divalent cation.

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