Detection of internal water flow in germinating corn seeds based on low field nuclear magnetic resonance

Abstract: In order to study the rule of internal water flow in corn seed germination process, the internal physiological metabolism state was analyzed, which changed the traditional research on the germination rate based on quantitative statistics, or considering the change of water from a point of view of time, or to explain the malpractice of the distribution of its internal water by the physiological anatomy of the seed. In this experiment, 3 varieties of corn seeds i.e. Nongda 108, Liaodan 565 and Yuqing 1 were used, which were from the Agricultural College, Shenyang Agricultural University and were the seeds in 2016. The dynamic monitoring of maize seeds at 3 stages of imbibition, germination and sprouting was performed by low field nuclear magnetic resonance (NMR) technique for 60 h, and 160 seeds were selected for each species, every 4 seeds are divided into a group, and 40 parallel test samples were prepared for each species (the sample quality was 1.685 g). The transverse relaxation time (T2) signal of NMR was collected for maize seeds in 2 constant-temperature germination environments at 25 and 31 ℃, their germination time was 0, 12, 36 and 60 h, each collection was repeated 4 times, the inversion spectrum of the T2 was obtained by the inversion. At the same time, the number of germinated seeds in the test sample was counted (taking embryo expansion and skin broken as a criterion), and then the seed germination rate was calculated. Water was replenished for the experimental samples, which were then continually cultivated in the artificial climate box, and the monitoring of the germination process of maize seeds was realized. The experimental results show that: Through the T2, the internal moisture of maize seed can be divided into 3 water phase states: bound water (0.1< T2 <10 ms), semi bound water (10 < T2 < 100 ms) and free water (100 < T2 < 1000 ms); the combination of water molecules and biological macromolecules is closer, which has low kinetic activity, and the amplitude of the signal is expressed as A21; the fluidity of semi bound water is restricted by certain constraints, and the amplitude of the signal is expressed as A22; free water molecules have strong mobility, and the amplitude of the signal is expressed as A23. With the prolongation of germination time, the water content of 3 varieties of maize seeds increases rapidly and then decreases gradually in 2 germinating environments, and the increase speed is also weakened. The content of free water shows a tendency to decrease firstly and then increase, and its increase speed is also increasing, while semi bound water and total water content are increasing. The corn seeds have the following absorption: rapid water absorption in the stage of suction, steady water absorption at the stage of initiation, water concussive absorption during the germination stage. The result from the low field NMR detection is consistent with that from the traditional drying weighing method. The influence of external temperature on the water content of 3 phase states is not the same, and there is no consistency between the change of water at each phase and the temperature of germination, however, when the external temperature increases, the semi bound water and the total water in the seed are shown to be gradually enhanced at every typical time of germination process. It is suggested that the increase of germination temperature can promote the combination of seed cell and water, improve the overall speed on water absorption and increase the germination rate of corn seeds. The result provides an important theoretical basis for the study of the mechanism of maize seed germination, and has important guiding significance for the determination of the maize growth and development of the later period, the formation of quality and the practice of production.