Abstract: Mature Spathiphyllum sp. plants were grown in soil in pots under clinostatic or stationary condition. Photosynthetic rate fell to almost zero after 30 d in clinostat, but recovered to more than 60% of the original on the 62nd day. Grana in chloroplasts remained normal in clinostat. There were few starch grains in chloroplasts after 30 d in clinostat, and almost none on the 62nd day, but numerous globular objects of low electronic density were observed. These were probably related to the adaptative changes of photosynthesis. Cell division in meristematic cells of root cap ceased after 30 d in clinostat, and then resumed to attain a rate even higher than that in the control plant on 62nd day, Further the length of the tap root was more than double that in the control plants. Some of the meristematic cells in the root cap under clinstatic condition transformed into statocyst cells, which senesced and were not transformed into secretory cells. No exocytosis was observed in plant in clinostatic condition, albeit the cell wall was broken from abrasion during root growth, resulting in pseudo-exocytosis, and from which the exudates acted as lubricants for the free extension of the root tip during root growth.

Key words: Spathiphyllum sp., Simulated microgravity, Pseudo-exocytosis, Photo- synthetic rate, Chloroplast