Microgravity seems to impose stress on the photosynthetic apparatus according to a new American study. Seeds of rape, Brassica rapa, were germinated in growth chambers on board a space shuttle that during 14 days flight took several loops around Earth in microgravity. Growth conditions were monitored and replicated to control plants grown at the Kennedy Space Center. Microgravity did not seem to influence growth and biomass accumulation, but the chlorophyll a/b ratio increased from 2.4 in ground controls to 3.5 in space grown plants. Mainly photosystem I was affected, having a reduced number of complexes and a 30% decrease of photochemical activity. Microgravity also led to altered chloroplast ultrastructure as shown by transmission electron micrographs.
Read full article here: Jiao et al (October 2004) Physiologia Plantarum 122: 281-290