^1H-NMR Imaging Analysis of Changes of Free Water Distribution in Barley and Soybean Seeds during Maturation

Abstract

Free water content of barley seeds, as detected by a NMR, paralleled respiratory activity. Therefore, the amount and the mobility of free water were considered to be usable as indices of biological activity condition in seeds. The changes of the distribution map and the relaxation time of free water in barley and soybean seeds during maturation were traced by ¹H-NMR imaging (MRI). The disappearance of free water signal which is considered to indicate the decline of biological activities and the accumulation of stored materials such as polysaccharides and proteins, proceeded ununiformly in the endosperm of barley seed. Vascular bundles, each containing a water filled cavity, became thick at 14th day after heading, early stage of accumulation of stored materials, and it became thin following ripening, and no free water was detected in the vascular bundle at 39th day after heading. On the other hand, free water was detected uniformly in the developing seeds but not in those after the stage of maximum seed size and the dry seeds of soybean. The spin-lattice relaxation time (T) of free water in seed shortened while that in pod lengthened with the progress of ripening of soybean. Free water in rachises and awns was observed in barley after the late maturation stage and that in pod was also observed in soybean at the stage of maximum seed size. The proton signal due to triglyrceride fatty acids stored in spherosomes was detectable in the dry soybean seed.