Folded structure of cell surface in dry seeds: Real or artifact?

In order to find out how plants maintain cell surfaces in a state that allows the rapid increase in surface area and volume of cells during imbibition, we examined the embryo cell shape in dry seeds of Glycine max cv. Hakuchou, Lotus miyakojimae and Arabidopsis thaliana. SEM observations showed that cell walls in dry seeds were often folded (see outline of the yellow-colored cell in Fig. 1A) although they were flat in imbibed seeds (Fig. 1B). To investigate whether the folded cell walls in the dry seeds really exist or not, we further examined seeds in vivo using X-ray micro-CT equipment in BL47XU at SPring-8 and also observed chemically fixed, plastic embedded seeds by high-voltage electron tomography. Our observations suggest that folded cell walls in dry seed embryos are a common structure.