Ultrastructural investigations on the host-parasite interactions in the rice leaf parenchymatous tissue infiltrated with bacterial leaf blight and leaf streak pathogens.

Abstract

Xanthomonas campestris pv. oryzae and X. campestris pv. oryzicola, the pathogens incompatible and compatible to parenchymatous tissue of rice leaves, respectively, were infiltrated into intercellular spaces of the tissue to investigate host-parasite interactions. Both bacteria induced secondary water-soaking at the infiltrated sites by the 3rd day and yellowish or brownish lesions restricted in size developed by the 7th day after infiltration. X. campestris pv. oryzicola caused typical symptom of the translucent and yellowish streaks later on whereas X. campestris pv. oryzae did not. Ultrastructural changes of the host tissues and parasites were investigated on the 3rd, 7th and 14th days after infiltration. In the specimens infiltrated with X. campestris pv. oryzae, swelled, loosen, and partially peeled host cell walls were frequently observed at the site close to the bacterial cells on the 3rd day after infiltration. The host plasmalemma adjacent to the pathogen was receded from cell wall showing vesiculation and became indistinct. Up to the 7th day after infiltration, the bacteria multiplied in some degree in the intercellular spaces and inside cells of host tissue. Most of them, however, were morphologically abnormal and surrounded by fibrillar material (FM) which appeared to be originated from host cell wall and cytoplasm. On the 14th day after infiltration, the majority of the bacterial cells were surrounded by much amount of granular materials (GM) originated from denatured host cell wall and cytoplasm, showing morphological distortion. On the contrary, X. campestris pv. oryzicola multiplied vigorously with normal shapes in the intercellular spaces and inside cells of the host parenchymatous tissue up to the 14th day after infiltration. Neither FM nor GM appeared in this combination. These facts suggest that FM and GM observed in the rice leaf parenchymatous tissue infiltrated with X. campestris pv. oryzae seemed to be closely related to the defense mechanism of host tissue against the incompatible pathogen.