Evaluating the Effect of Aging Process on the Physicochemical Characteristics of Rice Seeds by Low Field Nuclear Magnetic Resonance and Its Imaging Technique

In-depth investigation of the storability of rice seeds directly relies on the accuracy of the artificial accelerated aging method. In this study, Shennong 265 rice seed samples that underwent a 28 d artificial accelerated aging cycle were monitored by low field nuclear magnetic resonance (LF-NMR) and its imaging technique, the transverse relaxation times and proton density-weighted images of which were acquired at 0, 7, 14, 21 and 28 d during the aging process. Subsequently, the acquired information processed by NMR inversion and corresponding image processing software was combined with results from the standard germination test to describe the physicochemical characteristics of the rice seeds during the aging process. Results suggest that the rate of the T2 decay curve and the T2 relaxation time of the unaged rice seeds are higher than those of the aged rice seeds, and both values increase in positive correlation with the artificial aging duration. In addition, the contents of bound water, free water and total water of the aged seeds are all higher than those of the unaged seeds, although with prolonged aging, the contents of bound water and total water of the rice seeds fluctuates, whilst the content of free water consistently increases. Proton density images of the rice seed samples at different times of the aging process indicate that water distribution inside the seeds is inhomogeneous. Lastly, as aging duration increases, both the germination rate and germination potential of the seeds decrease. This study has determined the physiological and biochemical changes that the seeds undergo during aging, and revealed the relationship between these changes and the viability and vigor of the seeds, thereby providing references for studies on the internal mechanisms of seed deterioration.