G. Dean Price1, Susanne von Caemmerer, John R. Evans, Katharina Siebke, Jan M. Anderson, Murray R. Badger
1Australian National University,
Tóm tắt
We have used transgenic tobacco (Nicotiana tabacum L.
cv. W38) plants expressing an antisense gene directed against the transcript
of the Rieske FeS protein of the chloroplast bf complex
to examine the effect a reduction in chloroplast Rieske FeS content on leaf
gas exchange and photosynthetic metabolite pools. Plants with chloroplast
Rieske FeS protein content ranging from 5 to 80% of wild-type were
analysed. CO2 assimilation rate declined linearly with
the reduction in Rieske FeS content when expressed on a leaf area basis. In
contrast to photosynthesis, there was no change in stomatal conductance except
for plants with less than 10% of wild-type Rieske FeS content. There
was a close correlation between Rieske FeS content and cytochrome
f content, showing that the reduction in Rieske FeS
content lead to a similar reduction in other components of the cytochrome
bf complex. While lower Rieske FeS content was
associated with declines in chlorophyll content, ATPδ subunit and
ribulosebisphosphate carboxylase–oxygenase (Rubisco) contents, these
declines were considerably smaller than the reduction in cytochrome
bf content. As Rieske FeS content was reduced, there was
a slight lowering of the chlorophyll a/b ratio. Lower
CO2 assimilation rates at ambient
CO2 and high light were associated with dramatic
reductions in ribulose bisphosphate (RuBP) and modest declines in 3-
phosphoglycerate (PGA). Rubisco carbamylation declined to 40–50%
in plants with Rieske FeS content lower than 20% of wild-type. We
conclude that, at high light, a reduction in chloroplast Rieske FeS protein
content leads to inhibition of CO2 assimilation rate via
reductions in the rate of RuBP regeneration caused by a restriction in
electron transport and via effects on in vivo Rubisco activity.