SUMMARYMicrotubule arrays were studied in Spiranthes sinensis (Pers.) Ames protocorms cultured in vitro either asymbiotically or symbiotically with the fungus Ceratobasidium cornigerum (Bourdot) Rogers by localizing /?-tubulin in hand sections observed with laser scanning confocal microscopy. Cortical microtubules present in uncolonized cells disappeared when cells became colonized by the fungus. However, microtubules were observed between the hyphae forming hyphal coils (pelotons) in colonized cells. In these cells a close relationship between pelotons, microtubules and nuclei was often observed, and microtubules associated with hyphae formed a net-like structure through the pelotons. During senescence and condensation of the pelotons, microtubules were observed surrounding the pelotons, between collapsing hyphae and as circular profiles within the collapsed hyphal masses. In cells which contained completely collapsed hyphal masses and which were not recolonized, cortical microtubules reappeared and continued from the cell periphery through the hyphal remains to the collapsed hyphal masses. Microtubules associated with hyphae seemed to be involved in the condensation of hyphal masses in the host cells. Microtubules were also observed within hyphae, except in those which were collapsing or had collapsed.Key words: Microtubules, orchid protocorms, hyphal senescence, immunolabelling, confocal microscopy.
INTRODUCTION''^•' ^^^^^^ Similarly, Dearnaley & McGee (1996) reported the loss of plant MTs upon colonization of Microtubules (MTs), along with microfilaments, are protocorms of the orchid species Microtis parvifiora components of the cytoskeleton of plant cells and can R. Br. by a mycorrhizal fungus. Prelitninary results be altered by a variety of external influences (Lloyd, in our laboratory, however, with a different orchid 1982, 1991). Interactions between fungi and plant species and using different methods of tissue prepcells also result in changes in the arrays of MTs in aration did not support this finding, plant cells. For example, various biotrophic fungal Mycorrhizal fungal associations with orchids are pathogens cause varying degrees of cortical MT of particular interest because of their essential role in depolymerization in plant cells during infection peg seed germination and protocorm development and or haustorium formation ; their similarity in many respects to biotrophic fungal Gross et al., 1993; Kobayashi, Kobayashi & infections. In most orchid species, fungal hyphae Hardham, 1994). Microtubules are absent from host invade the very reduced embryo and form hyphal cell cytoplasm contiguous to the haustorium coils called pelotons, which are separated from the branches, which are surrounded by host cell mem-host cytoplasm by an interfacial matrix and host brane. Mycorrhizal fungal species also alter the plasma membrane (Hadley, 1982; Peterson & cytoskeleton of higher plant cells (Timonin et al., Currah, 1990;Uetake, Kobayashi & Ogoshi, 1992;Dearnaley & McGee, 1996). In ectomycor-Rasmussen, 1995). P...
