The lg1-D mutation affected grain size by increased cell proliferation. A, Spikelets of the wild type (WT) and lg1-D mutant prior to flowering. Dotted white lines indicate sites of cross sections in B and C. B and C, Cross sections of wild-type (B) and lg1-D mutant (C) spikelet hulls. Bars = 500 μm. D and E, Magnified images of the boxed areas in B and C, respectively. Bars = 50 μm. F to H, Comparison of total length (F) and cell number (G) of the spikelet hull and average length of each cell (H) in the outer parenchyma layer. All data are means ± sd (n = 10). **, P < 0.01 and *, P < 0.05, determined by Student’s t test. I, Transcript levels of cell cycle-related genes in 0.5-cm young panicles of lg1-D relative to the wild type. The rice Ubiquitin gene was used as an internal control. Data are means ± sd (n = 3). **, P < 0.01, determined by Student’s t test.