Nuclear Magnetic Resonance Relaxation Times and Plasmalemma Water Exchange in Ivy Bark

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Abstract
Measurement of NMR relaxation times (transverse [T2] and longitudinal [T1]) for Hedera helix L. cv. Thorndale (ivy) bark water indicates the presence of at least 2 populations of water with different relaxation characteristics. One population of water with short T2 and T1 was found to be composed of both hydration water and extracellular free water. The second population of water with long T2 and T1 was identified as intracellular bulk water. NMR relaxation of extracellular water protons is controlled by cell wall surface effects, possibly due to binding of paramagnetic cations by the cell walls. NMR relaxation of intracellular water protons is controlled by both water exchange to the extracellular environment and chemical exchange with a population of protons that is chemically shifted from that of the bulk water. The relaxation time of intracellular water is not measurably affected, either by intracellular paramagnetic ions or by increased viscosity of intracellular water. Mn flux into the cells occurs at 1.7 .times. 10-15 moles cm-2 s-1 and is independent of extracellular Mn2+ concentration in the range 5-20 mM. The intracellular-extracellular water exchange time of ivy bark was found to be predominantly limited by membrane water permeability. A diffusional water permeability coefficient (Pd) of approximately 3 .times. 10-2 cm s-1 was calculated for ivy cell membranes at 20.degree. C.