The mechanism of starch metabolism in the endosperm of germinating rice (Oryza sativa L.) seed (caryopsis) has been well studied; however, little is known about the occurrence and function of transitory starch in germinating rice embryos. During rice seed germination and seedling establishment, starch in the endosperm is hydrolysed to glucose, which is taken up by scutellar epithelial cells, converted to sucrose, and transported through vascular bundles to other embryonic tissues, such as growing shoots and roots. In this study, we found that soluble sugar was converted to starch in the scutellum 6 d after imbibition (DAI). Starch appeared primarily in cells surrounding the vascular bundles of the embryonic axis 12 DAI. The removal of growing shoots caused hyper-accumulation of starch in embryonic tissues, including the scutellum. In contrast, placing seedlings in the dark, which reduced photosynthetic efficiency, lowered starch levels in the embryonic axis cells. The disappearance of transitory starch from embryonic tissues of dark-grown seedlings was accompanied by a reduction of soluble sugar content and the down-regulation of the expression and activity of starch biosynthesis enzymes. These results suggest that the amount of transitory starch in embryonic tissues was dependent on the demand of growing sink tissues.