Spatial patterns of histone mRNA expression during grain development and germination in rice.

The pattern of distribution of histone H3 mRNA during the development of the rice grain and its germination was monitored by in situ hybridization and confirmed by Northern blot analysis. In ovaries sampled before and after fertilization, a 3H-labeled histone RNA probe was localized in the cells of the pericarp, outer integument and nucellus but binding of the probe decreased as these tissues senesced. In the developing embryo, the histone message was first detected in the scutellum; later, all parts of the embryo except the shoot apex, newly formed leaf primordia and the quiescent center of the root, revealed the presence of transcripts. Considerable binding of the probe also occurred in the endosperm as its cells began to accumulate starch. Cells of the embryo and endosperm of mature grains displayed very little or no histone mRNA, although during germination, these transcripts reappeared in the cells of both embryo and endosperm. There was a good correlation between the presence or absence of binding to the 32P-labeled histone gene DNA by RNA extracted from grains of different stages of development and germination, as revealed by Northern blot analysis and by spatial localization following in situ hybridization.