Studies on the Photosythetic Tissues in the Leaves of Cereal Crops : IV. Effect of shading on the mesophyll structure of the rice leaves.

Rice plants were grown under the shade of natural daylitght during the 13th and 14th leaves were expanded. The mesophyll structure of those leaves were observed and following results were obtained. 1) The mesophyll thickness of the shaded leaf is thinner than that of the unshaded leaf, as a result of diminution of the individual cell volume and the cell number per unit leaf area. 2) Adaxial surface of the shaded leaf is flatter than that of the unshaded leaf, as a result of reduction of the differences in mesophyll thickness between the ribs and furrows and elongation of the distance between the vascular bundles. Therefore, the ratio of the adaxial mesophyll surface area to the leaf area (MS/LA) is reduced in the shaded leaf. 3) The total cell surface area per unit leaf area is reduced in the shaded leaf, as a result of diminution of the cell number and the individual cell surface. 4) The effect of shading on the mesophyll structure of the 13th leaf is not always the same as that of the 14th leaf. In the 13th leaf, the number of cells per unit leaf area and the distance between the vascular bundles are not affected by shading, but the protuberance number per cell and the protuberance length at the adaxial surface are reduced in the shaded leaf. From the observations of this study, it will be suggested that the mesophyll thickness, the ratio of the adaxial mesophyll surface area to the leaf area and the total cell surface area per unit leaf area may be anatomical characteristics, lowering the photosythetic activity of rice leaves developing in the shade.