CHANGES IN MICROTUBULE ARRAYS IN SYMBIOTIC ORCHID PROTOCORMS DURING FUNGAL COLONIZATION AND SENESCENCE

Microtubule arrays were studied in Spiranthes sinensis (Pers.) Ames pr otocorms cultured in vitro either asymbiotically or symbiotically with the fungus Ceratobasidium cornigerum (Bourdot) Rogers by localizing b eta-tubulin in hand sections observed with laser scanning confocal mic roscopy. Cortical microtubules present in uncolonized cells disappeare d when cells became colonized by the fungus. However, microtubules wer e observed between the hyphae forming hyphal coils (pelotons) in colon ized cells. In these cells a close relationship between pelotons, micr otubules and nuclei was often observed, and microtubules associated wi th hyphae formed a net-like structure through the pelotons. During sen escence and condensation of the pelotons, microtubules were observed s urrounding the pelotons, between collapsing hyphae and as circular pro files within the collapsed hyphal masses. In cells which contained com pletely collapsed hyphal masses and which were not recolonized, cortic al microtubules reappeared and continued from the cell periphery throu gh the hyphal remains to the collapsed hyphal masses. Microtubules ass ociated with hyphae seemed to be involved in the condensation of hypha l masses in the host cells. Microtubules were also observed within hyp hae, except in those which were collapsing or had collapsed.