Growth and Photosynthetic Responses of Wheat Plants

Crowth and photosynthesis of wheat (Triticum aestivum 1. cv Super DwarO plants grown onboard the space shuttle Discovery for 10 d were examined. Compared to ground control plants, the shoot fresh weight of space-grown seedlings decreased by 25%. Postflight measurements of the O, evolution/photosynthetic photon flux density response curves of leaf samples revealed that the C0,-saturated photosynthetic rate at saturating light intensities in space-grown plants declined 25% relative to the rate in ground control plants. l h e relative quantum yield of C0,-saturated photosynthetic O, evolution measured at limiting light intensities was not significantly affected. In space-grown plants, the light compensation point of the leaves increased by 33%, which likely was dueto an increase (27%) in leaf dark-respiration rates. Related experiments with thylakoids isolated from space-grown plants showed that the light-saturated photosynthetic electron transport rate from H,O through photosystems I1 and I was reduced by 28%. These results demonstrate that photosynthetic functions are affected by the microgravity environment.