PLANT PHYSIOLOGY , Vol 109, Issue 1 307-317, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Regulation of Photosynthetic Induction State in High- and Low-Light-Grown Soybean and Alocasia macrorrhiza (L.) G. Don
J. P. Krall, E. V. Sheveleva and R. W. Pearcy
Section of Plant Biology, University of California, Davis, California 95616-8537
Alocasia (Alocasia macrorrhiza [L.] G. Don) and soybean (Glycine max [L.])
were grown under high or low photon flux density (PFD) conditions to
achieve a range of photosynthetic capacities and light-adaptation modes.
The CO2 assimilation rate and in vivo linear electron transport rate (Jf)
were determined over a range of PFDs and under saturating 1-s-duration
lightflecks applied at a range of frequencies. At the same mean PFD, the
assimilation rate and the Jf were lower under the lightfleck regimes than
under constant light. The activation state of two, key enzymes of the
photosynthetic carbon reduction cycle pathway, ribulose-1,5-bisphosphate
carboxylase/oxygenase (Rubisco) and fructose-1,6-bisphosphatase, and the
photosynthetic induction states (ISs) were also found to be lower under
flashing as compared to continuous PFD. Under all conditions, the IS
measured 120 s after an increase in PFD to constant and saturating values
was highly correlated with the Rubisco activation state and stomatal
conductances established in the light regime before the increase. Both the
fructose-1,6-bisphosphatase and Rubisco activities established in a
particular light regime were highly correlated with the mean Jf in that
regime. The relationships between enzyme activation state and Jf and
between IS and enzyme activation state were similar in soybean and Alocasia
and were not affected either by growth-light regime, and hence
photosynthetic capacity, or by flashing versus constant PFD. The common
relationship between the linear Jf and the activation state of key enzymes
suggests that electron transport may be the determinant of the signal
regulating IS, at least to the extent that the IS is controlled by the
activation state of key stromal enzymes.
