Leaf Anatomy of <italic>Raphanus sativus</italic> Exposed to Space Shuttle/ISS Temperature Profiles

A series of experiments was initiated to characterize plant growth at the elevated temperatures typically observed in the space shuttle and the International Space Station (ISS) to allow for subsequent isolation of temperature effects from those of microgravity. Plants were grown in temperatures ranging from 18-30°C in anticipated flight conditions of light intensity, photoperiod, and CO₂ concentration. The effects of these environmental variables on leaf development and anatomy were examined. Results indicate that leaf anatomy is significantly effected by elevated temperature. Leaf thickness decreased with increasing temperature and showed an equal reduction in the thickness of the palisade and spongy mesophyll. Shoot fresh and dry weight/unit leaf area increased with increasing temperature and chlorophyll content was reduced. These results indicate that increased temperature lead to a reduction in intercellular air spaces within the leaf.