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NMR microscopic imaging of the single cell : Acetabularia mediterranea Munasinghe, Jeeva Prasanna


NMR imaging studies performed in the microscopic realm using the cell organelles of the single celled marine green alga, Acetabularia mediterranea, are presented. The study had two main objectives. First, to attain microscopic spatial resolution. Second, to monitor development stages in the reproductive structure, the cap. The images of caps which are flat, oriented in the xy plane, have been obtained as 2-dimensional images. Using a 270 MHz spectrometer and an imaging probe made in this department, a lower resolution of 40-50 µm is reported. The probable causes for the limitation of resolution are discussed in terms of the molecular diffusion of the vacuolar water and the magnetic field inhomogeneity caused by the susceptibility differences at the interfaces of the sample and the sample holder on which the sample was mounted. Proton density images of immature, mature and partly mature caps are presented in order to portray the attainable resolution. Images obtained at higher gradients (~50 Gauss cm⁻¹) are presented and compared with those obtained at moderate gradients (~15 Gauss cm⁻¹). The necessity to perform the imaging sequence at a shorter time, in order to minimize molecular diffusion, is highlighted. T₁ contrast imaging experiments were performed to investigate the different maturation stages. The main attention is given to the partly mature caps, which have a mixture of mature and partly mature rays. Images obtained by T₁ contrasting, and the T₁values determined in a preliminary study, are discussed in relation to the probable changes in mobile and bound water during maturation. The variation of the T₁ values from long (immature) to short (partly mature) is explained in accordance with the ultrastructural development of the cap. Results of contrasting using T₂ values and paramagnetic ions (Mn²⁺) are presented briefly. Imaging of the rhizoid has been done, demonstrating the possibility of monitoring the large nucleus during maturation.

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