PLANT PHYSIOLOGY , Vol 101, Issue 2 363-371, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Green Roots: Photosynthesis and Photoautotrophy in an Underground Plant Organ
H. E. Flores, Yr. Dai, J. L. Cuello, I. E. Maldonado-Mendoza and V. M. Loyola-Vargas
Plant Pathology Department, Graduate Program in Plant Physiology and Biotechnology Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (H.E.F., J.L.C., Y.-r.D.)
The potential for photosynthetic and photoautotrophic growth was studied in
hairy root cultures of Asteraceae and Solanaceae species. Upon transfer to
light, initially heterotrophic root cultures of Acmella oppositifolia and
Datura innoxia greened rapidly, differentiated chloroplasts, and developed
light-dependent CO2 fixation in the cortical cells. Photosynthetic
potential was expressed in root cultures of all the Asteraceae genera
examined (Acmella, Artemisia, Rudbeckia, Stevia, and Tagetes). Hairy roots
of A. oppositifolia and D. innoxia were further adapted to photoautotrophy
by growing in the presence of light and added CO2 (1-5%) and by direct or
sequential transfers into media containing progressively lower sugar
concentrations. The transition to photoautotrophy was accompanied by an
increase in CO2 fixation and in the specific activity of
1,5-ribulose-bisphosphate carboxylase/ oxygenase (Rubisco). During the
adaptation of A. oppositifolia roots to photoautotrophy, the ratio of
Rubisco to phosphoenolpyruvate carboxylase increased significantly,
approaching that found in the leaves. The levels and patterns of alkaloids
and polyacetylenes produced by Solanaceae and Asteraceae hairy roots,
respectively, were dramatically altered in photomixotrophic and
photoautotrophic cultures. Photoautotrophic roots of A. oppositifolia have
been mainitained in vitro for over 2 years.
