Morphology on Vascular Bundles of Leaves in Gramineous Crops : I. Observations on vascular bundles of leaf blades, sheaths and internodes in rice plants

Abstract

In the leaf blades, sheaths and internodes of rice plants, the large and small vascular bundles are arranged longitudinally. When the longitudinal vascular bundles of the leaf blades are traced backward into the culm, the large vascular bundles extend downward through the leaf sheath and two internodes. The small vascular bundles, which are located in the middle between large vascular bundles of leaf blade, extend downward through the leaf sheath and one internode, and the other small vascular bundles end blindly at the base of leaf blade. In the leaf blades and sheaths, the longitudinal vascular bundles are laterally interconnected by the transverse veins. The transverse veins have the most simple composition of the vascular element, that is, a sieve tube, a vessel, and only two files of vascular parenchyma cells. In the leaf blades at lower levels of shoot, the small vascular bundle is surrounded by a single layer of parenchymatous sheath cells with dense chloroplasts. However, in the leaf blades at higher levels of shoot, the small vascular bundle is surrounded by two layers of sheath cells. The outer layer is consisted of parenchymatous sheath cells with small numbers of chloroplasts, and the inner layer is consisted of mestome sheath cells with thickened walls. The mestome sheath of the large vascular bundle is more developed than that of the small vascular bundle. The vascular bundles of the leaf sheaths and internodes have more companion cells and larger sieve tubes and vessels than those of the leaf blades. On this histological observations, the functional significance of the vascular bundles in rice plants is discussed.