Studies on Morphogenesis in Rice Plant : X. Ultrastructure of the dorsal vascular bundle in the ovary and a transport mechanism.

Abstract

The dorsal vascular bundle of the rice ovary in milk-ripe stage has been observed with an electron microscope. The sieve elements are accompanied by few companion cells with small number of plasmodesmata (Fig. 1). Conducting networks composed of abundant cndoplasmic reticulum and plasmodesmata are ramified like a cobwebs through the bundle parenchyma cells and nucellar projection (Figs. 2, 3, 4 and 5). The parenchyma cells between phloem and xylem are controlled in low osmotic and low turgor pressure (Fig. 2), and some parenchyma cells adjacent to the vessels have many mitochondria (Fig. 4), but no transfer cell has been observed in the ovary. The cell walls of the nucellar projection commence to be thickened and lignified at about 7 days after flowering (Figs. 5 and 7). It may be possibly supposed that, the phloem current flows out directry to free space from the sieve elements, and the greater part of water is absorbed and drained out by the vessels, and the assimilates are absorbed by the bundle parenchyma cells and are transported to the endosperm through the networks composed of endoplasmic reticulum and plasmodesmata (Fig. 8).