Regulation of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase by
Carbamylation and
2-Carboxyarabinitol 1-Phosphate in Tobacco:
Insights from Studies of Antisense Plants Containing Reduced
Amounts of Rubisco Activase1
Edward T. Hammond,
T. John Andrews, and
Ian E. Woodrow*
School of Botany, The University of Melbourne, Parkville, Victoria
3052, Australia (E.T.H., I.E.W.); and Research School of Biological
Sciences, Australian National University, Canberra, ACT 2601, Australia
(T.J.A.)
The regulation of
ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity by
2-carboxyarabinitol 1-phosphate (CA1P) was investigated using
gas-exchange analysis of antisense tobacco (Nicotiana
tabacum) plants containing reduced levels of Rubisco activase.
When an increase in light flux from darkness to 1200 µmol quanta
m
2 s1 was followed, the slow increase in
CO2 assimilation by antisense leaves contained two phases:
one represented the activation of the noncarbamylated form of Rubisco,
which was described previously, and the other represented the
activation of the CA1P-inhibited form of Rubisco. We present evidence
supporting this conclusion, including the observation that this second
phase, like CA1P, is only present following darkness or very low light
flux. In addition, the second phase of CO2 assimilation was
correlated with leaf CA1P content. When this novel phase was resolved
from the CO2 assimilation trace, most of it was found to
have kinetics similar to the activation of the noncarbamylated form of
Rubisco. Additionally, kinetics of the novel phase indicated that the
activation of the CA1P-inhibited form of Rubisco proceeds faster than
the degradation of CA1P by CA1P phosphatase. These results may be
significant with respect to current models of the regulation of Rubisco
activity by Rubisco activase.
1
This work was supported by grants from the
Australian Research Council and the University of Melbourne. E.T.H.
received an Australian Postgraduate Award from the Australian Research
Council and a Collaborative Research Scholarship from the Australian
National University. I.E.W. was supported by a Senior Research
Fellowship from the Australian Research Council.
*
Corresponding author; e-mail i.woodrow{at}botany.unimelb.edu.au;
fax 61-3-9347-5460.
Plant Physiol. (1998) 118: 1463-1471
Copyright Clearance Center: 0032-0889/98/118//09
© 1998 American Society of Plant Physiologists
