Changes in water status and water distribution in maturing lupin seeds studied by MR imaging and NMR spectroscopy

The changes in water distribution in maturing lupin (Lupinus luteus L.) seeds were visualized with magnetic resonance imaging (MRI). MRI data showed local inhomogeneities of water distribution inside the seed. At the late seed-filling stage the most intense signal was detected in the seed coat and the outer parts of cotyledons in the hilum area, but during maturation drying the decline in MR image intensity was faster in the outer part of the seed than in the central part. The changes in water status were characterized by NMR spectroscopy. Analyses of T(2) relaxation times revealed a three-component water proton system in maturing lupin seeds. Three populations of protons found during seed maturation, each with a different magnetic environment causing a different relaxation rate, were correlated with three fractions of water (structural, intracellular, and extracellular) that were observed during seed germination. This study provides evidence that lupin seeds have similar states of the different water components with regard to seed moisture content at two distinct physiological stages, seed maturation and germination. The unique feature of maturing lupin seeds is the presence of the high (1)H-NMR signal in areas corresponding to the vascular bundles. Tissue localization of dehydrins showed the presence of dehydrin protein in the area of vascular tissue. An anti-dehydrin antibody detected three polypeptides in lupin embryos with molecular masses of 73, 43 and 28 kDa, respectively. The temporal pattern of dehydrin protein accumulation correlates well with seed desiccation.