MR microscopy has been used for studying seeds complementary to traditional methods and recent studies have largely focused on the monitoring of water uptake and oil distribution during imbibition, which is a crucial process in seed germination [48, 49]. Although many NMR and MRI studies have been conducted on various seeds, very "small (< 1 mm) dry seeds" have not been studied extensively except one study . In this study, the fundamental measurements (NMR spectra, T1 and T2) and magnetic resonance imaging of small dry seeds of four different plant species were conducted using NMR microscopy system which is capable of investigating miniature objects (up to 750 μm in diameter and 2mm in length). In addition, the spectroscopic and anatomical changes of a single Nicotiana tabacum seed embedded in wet sand were monitored during an extended imbibition period (7 days) to evaluate the role of NMR and MRI to study germination and as a complementary method to the conventional conductivity test. All NMR/MRI experiments were conducted on a 9T magnet controlled by NTNMR console (TecMag, Inc., Houston, TX) with custom-built RF and gradient coils.
The spectral line widths of oil rich seeds were defined with two main peaks. The follow-up study revealed the existence of multiple T1 and T2 components in all seeds. T2 of Silene compacta seeds showed much broader line-width and shorter T 2 than those of other seeds in this study. Images of dry seeds did not show clear internal structures, presumably, due to the broad line-width.
In the study of imbibition of a single Nicotiana tabacum seed embedded in wet sand, apparent change in NMR line shape occurred around the water chemical shift (~ 4.6 ppm), whereas no significant changes in seed anatomy were observed. Noticeable changes in SNR of exterior region adjacent to seed coat were observed during imbibition.
Proton NMR and MRI method are still useful in the study of water uptake in the physiological processes in the seeds, because once water content increases then mobile water increases MRI visible signal and results in better resolution. Although biochemical origin was not revealed, apparent splitting of chemical shift of water peak was observed. Noticeable change in SNR of exterior just next to the seed coat implied that certain leakage of seed material occurred during the imbibition. This finding (with further study) could be used potentially as a complementary method to conductivity test for assessment of seed quality. Furthermore, the current NMR microscopy system potentially could be used for MR biopsy or autopsy of small amount of tissues.
A preliminary study on an implementation of DESIRE experiment was attempted by a suggested 2D hole-burning pulse sequence. In this study, the suggested pulse sequence worked well. However, the size of the hole was bigger to expect good DESIRE effect. To apply this method in real experiment, improvement of hardware is essential.
|Commitee:||Hammel, Peter, Zhong, Dongping|
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Keywords:||Desire, Microscopy, Mri, Nmr, Seed|
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