PLANT PHYSIOLOGY , Vol 110, Issue 3 801-806, Copyright © 1996 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Growth and Photosynthetic Responses of Wheat Plants Grown in Space
B. C. Tripathy, C. S. Brown, H. G. Levine and A. D. Krikorian
National Aeronautics and Space Administration, Mail Code MD-RES (B.C.T.), and The Dynamac Corporation, Mail Code DYN-3 (C.S.B., H.G.L.), Kennedy Space Center, Cape Canaveral, Florida 32899
Growth and photosynthesis of wheat (Triticum aestivum L. cv Super Dwarf)
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 O2
evolution/photosynthetic photon flux density response curves of leaf
samples revealed that the CO2-saturated photosynthetic rate at saturating
light intensities in space-grown plants declined 25% relative to the rate
in ground control plants. The relative quantum yield of CO2-saturated
photosynthetic O2 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 due to 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 H2O through photosystems II and
I was reduced by 28%. These results demonstrate that photosynthetic
functions are affected by the microgravity environment.
