The relationship between CO2-assimilation rate, Rubisco carbamylation and Rubisco activase content in activase-deficient transgenic tobacco suggests a simple model of activase action.
Transgenic tobacco (Nicotiana tabacum L. cv. W38) plants with an antisense gene directed against the mRNA of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) activase were used to examine the relationship between CO2-assimilation rate, Rubisco carbamylation and activase content. Plants used were those members of the r1progeny of a primary transformant with two independent T-DNA inserts that could be grown without CO2supplementation. These plants had from < 1% to 20% of the activase content of control plants. Severe suppression of activase to amounts below 5% of those present in the controls was required before reductions in CO2-assimilation rate and Rubisco carbamylation were observed, indicating that one activase tetramer is able to service as many as 200 Rubisco hexadecamers and maintain wild-type carbamylation levels in vivo. The reduction in CO2-assimilation rate was correlated with the reduction in Rubisco carbamylation. The anti-activase plants had similar ribulose-1,5-bisphosphate pool sizes but reduced 3-phosphoglycerate pool sizes compared to those of control plants. Stomatal conductance was not affected by reduced activase content or CO2-assimilation rate. A mathematical model of activase action is used to explain the observed hyperbolic dependence of Rubisco carbamylation on activase content.
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia.
Colleen J
CJ
Mate
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia. susanne@rsbs-central.anu.edu.au.|Director's Research Group, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia. susanne@rsbs-central.anu.edu.au.
Susanne
S
von Caemmerer
Environmental Biology Group, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia.
John R
JR
Evans
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia.|Cooperative Research Centre for Plant Sciences, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia.
Graham S
GS
Hudson
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia.|Cooperative Research Centre for Plant Sciences, Research School of Biological Sciences, Australian National University, PO Box 475, 2601, Canberra, ACT, Australia.
T John
TJ
Andrews
Activase (Rubisco); Nicotiana (transgenic); Photosynthesis (C3); Ribulose-1,5-bisphosphate carboxylase/oxygenase; Transgenic tobacco