Approach on Flower and Pollen Development of Brassica parachinesis Under Microgravity and Simulated Microgravity

Plants have usually evolved under the surface gravity and have acquired the ability to gravistumili to regulate their growth and development. Space experiments show that the plant morphogenesis and growth responses are highly influenced by the gravity level. In the present study, flower and pollen development of {\it Brassica parachinese} under microgravity on board the Chinese SJ-8 recoverable satellite and under simulated microgravity on a 3D clinostat condition, respectively, were studied. Flower opening is due to the rapid growth and the movements of petals, which are accompanied by a high rate of cell expansion. The period of flower bud development and opening in
space were about 18 h significantly increased in comparison with 5 h under 1 g control conditions. The experimental results of the 3D clinostat rotation also showed the similar results, that plants under clinostat rotation produced flowers with smaller petals and shorter stamens in comparison with the usually controlled plants, but no other attributes were apparently affected. In this case, significant reduction of the pollen was also observed in the flowers. The influences of altered gravity on the arrays of microtubules in pollen cells during microspore nuclear migration and the asymmetrical mitosis were also observed. Based on our knowledge, the present space experiment is the first one to use the live imaging analysis to study the influence of the microgravity condition on the flower expansion and opening.