ULTRASTRUCTURAL-CHANGES DURING THE SYMBIOTIC DEVELOPMENT OF SPIRANTHES-SINENSIS (ORCHIDACEAE) PROTOCORMS ASSOCIATED WITH BINUCLEATE RHIZOCTONIA ANASTOMOSIS GROUP-C

The process of symbiotic development of Spiranthes sinensis seeds to p rotocorms with differentiated shoots associated with binucleate Rhizoc tonia anastomosis group C was divided into 7 stages (I-VII) based on i ncrease of embryo and protocorm width. Each stage was observed ultrast ructurally. The embryo contained large amount of lipid, small amount o f starch, and protein body-like structure in all its cells. The embryo began to swell (stage I) as soon as several hyphae invaded the basal cells. Hyphae penetrated into the inner cortical parenchyma (ICP) and subepidermal parenchyma (SEP) cells and formed pelotons. The meristema tic region (MR) was not colonized. Hyphal cell walls (FCW) were surrou nded by an encasement layer (EL) and by the host plasmalemma. Pelotons that formed in ICP had thin walls and were digested, whereas pelotons in SEP were not digested. In stage I, mitochondria, ribosomes, propla stids, microbodies, rough endoplasmic reticulum, dictyosomes and vacuo les were observed in the host cytoplasm Signs of hyphal digestion was already apparent in this stage. In stage II, dumps of digested peloton s consisted only of layers of FCW and EL and were surrounded by host c ytoplasm and vacuoles, and/or secondary infected hyphae. Hyphal digest ion and the reinfection of host cells occurred repeatedly throughout a ll growth stages. Protein body-like structures rapidly disappeared bef ore stage III. At stage V and subsequent stages, it was also seen that the dispersed contents of digested hyphae were surrounded by the host plasmalemma. When ICP cells contained pelotons, amyloplasts were not observed. However, proplastids usually existed in the cells, and amylo plasts were observed in all SEP cells and other uninfected cells. Lipi d bodies were slowly degraded throughout embryo