Ultrastructural Changes in the Early Stages of Interaction between Rice Leaf Parenchymatous Tissue and Infiltrated Bacteria

Abstract

Ultrastructural changes in the early stages of interaction between rice leaf parenchymatous tissue and infiltrated bacteria such as Xanthomonas campestris pv. oryzicola, X. c. pv. oryzae, X. c. pv. citri. X. c. pv. campestris and Pseudomonas fluorescens were investigated. Most of the cells of all bacteria tested attached tightly on the surface of rice cells by 5 hr after infiltration. The bacteria pathogenic to rice leaves, X. c. pv. oryzicola and X. c. pv. oryzae, induced fluid sphere (FS) formation around their bodies in the intercellular spaces associating with distortion of rice plasmalemma adjacent to the bacterial cells by 10 hr after infiltration. FS was enlarged to fill up rice intercellular spaces with bacterial multiplication by 2 days after infiltration. It was conceivable that FS was composed of the liquid leaked from rice cells due to bacterial attack against rice cell wall and membrane systems. FS was also induced by the bacteria non-pathogenic to rice leaves, X. c. pv. citri and X. c. pv. campestris, but its frequency and extension were less than those in the case of the former. Rice cells adjacent to these bacteria accumulated electron dense materials (EDM-p) at periplasmic spaces and formed vesicles from membrane systems near bacterial cells. The bacteria increased their population slightly, but some of them were abnormal in shape. The cells of P. fluorescens did not induce FS. Some bacterial cells were surrounded by loose network fibrils on the rice cells in which EDM-p was accumulated at periplasmic space by 1-2 days after infiltration. It was suggested that FS formation was a phenomenon of compatible interaction and EDM-p accumulation was that of incompatible interaction. The rapidity and degree of FS formation and EDM-p accumulation were different depending upon compatibility between rice leaf parenchymatous cells and infiltrated bacteria.