PLANT PHYSIOLOGY , Vol 111, Issue 3 921-929, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Synthesis and Turnover of Cell-Wall Polysaccharides and Starch in Photosynthetic Soybean Suspension Cultures
V. V. Lozovaya, O. A. Zabotina and J. M. Widholm
University of Illinois, Department of Crop Sciences, Edward R. Madigan Laboratory, 1201 West Gregory, Urbana, Illinois 61801 (V.V.L., J.M.W.)
Soybean (Glycine max [L.] Merr.) suspension cultures grown under
photoautotrophic and photomixotrophic (1% sucrose) culture conditions were
used in 14CO2 pulse-chase experiments to follow cell-wall polysaccharide
and starch biosynthesis and turnover. Following a 30-min pulse with 14CO2,
about one-fourth of the 14C of the photoautotrophic cells was incorporated
into the cell wall; this increased to about 80% during a 96-h chase in
unlabeled CO2. Cells early in the cell culture cycle (3 d) incorporated
more 14C per sample and also exhibited greater turnover of the pectin and
hemicellulose fractions as shown by loss of 14C during the 96-h chase than
did 10- and 16-d cells. When the chase occurred in the dark, less 14C was
incorporated into the cell wall because of the cessation of growth and
higher respiratory loss. The dark effect was much less pronounced with the
photomixotrophic cells. Even though the cell starch levels were much lower
than in leaves, high 14C incorporation was found during the pulse,
especially in older cells. The label was largely lost during the chase,
indicating that starch is involved in the short-term storage of
photosynthate. Thus, these easily labeled and manipulated photosynthetic
cells demonstrated extensive turnover of the cell-wall pectin and
hemicellulose fractions and starch during the normal growth process.
