Cytology Of Ustilago Esulenta-Zizania Latifolia Interactions

Ustilago esculenta is a biotrophic smut fungus that parasitizes Zizania latifolia, an edible aquatic vegetable of the southern China region. Infection results in swelling of the upper parts of the Z.latifolia culm which are called jiaobai and have a unique flavor and delicacy and are popular among Chinese. The infection process of Z.latifolia by U.esculenta was investigated with light and electron microscopy. The results as follows:1Cytology and ultrastructure of interactions between Ustilago esculenta and Zizania latifoliaDistribution of hyphae was uneven in plants; hyphae were mainly present in the swollen upper parts (jiaobai), the nodal regions of mature culms and old rhizomes and buds or shoots. Hyphae were rare in the internodes of mature culms and were fewer in the internodes of old rhizomes. All new buds produced on the nodes of culms and rhizomes were infected by hyphae in November before and in March after overwintering. The hyphae grew into the buds from the parent nodes via intervascular tissues only or via parenchyma tissues and vascular bundles. Hyphae extended within and between the host cells and frequently formed hyphal aggregations or clusters, not only in the mature tissues but also in developing tissues. The typical interface between the fungal hyphal wall and invaginated host plasma membrane comprised a sheath. The sheath surrounding a hyphae comprised an outer electron-opaque matrix and an inner electron-dense layer. The electron-opaque matrix layers were thicker in jiaobai tissues, ranging from0.28to0.85uμm. The electron-dense hyphal coatings were more conspicuous in the young buds or shoots and mature culms than in the jiaobai. The intercellular hyphae caused large cavity formation between the cells or rupture of host cell walls for gaining entry into host cells. The broken host cell wall fused with the electron-opaque matrix of the hyphal sheath as an interactive interface. The teliospore wall and wall ornamentation development was the same in postmature jiaobai tissues with sporadic sori and in the huijiao (jiaobai tissues containing the massive sori), but a sheath enveloping the teliospore was more transparent in the process of teliospore development in the jiaobai than in the huijiao.2Cytological and ultrastructural characters of sorus development in Ustilago esculentaIn some cases, however, massive dark sori develop throughout the jiaobai tissues. These are called huijiao and are produced on shorter plants; they cannot be eaten and are discarded. The process of sorus development in huijiao prior to and after upper culm swelling was investigated with light and electron microscopy.Large numbers of hyphal aggregations were distributed in the tissues of internodes and nodes prior to culm swelling. At the ultrastructural level the interactive interface between the fungal hyphal wall and host plasma membrane comprised an outer electron-opaque layer and an inner electron-dense layer. Disintegration of the inner electron-dense layer was sometimes adjacent to discontinuous sites of host plasma membrane at the interactive interface. Hyphal aggregation within a cell caused the host plasma membrane to rupture. The inner electron-dense layers covering the fungal cell walls became distinctively thin and the appearance of massive lipid globules in hyphae was common. Sorus development occurred with the commencement of upper culm swelling, as revealed in the tissues by cytological and ultrastructural examination. Sorus development differed in the same tissues and teliospore development was also uneven in a sorus. The development of the inner layer of a sorus, was earlier than that of its outer layer.