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BIOENERGETICS AND PHOTOSYNTHESIS

The Contribution of Photosynthesis to the Red Light Response of Stomatal Conductance^1,[OA]

Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia

To determine the contribution of photosynthesis on stomatal conductance, we contrasted the stomatal red light response of wild-type tobacco (Nicotiana tabacum ‘W38’) with that of plants impaired in photosynthesis by antisense reductions in the content of either cytochrome b₆f complex (anti-b/f plants) or Rubisco (anti-SSU plants). Both transgenic genotypes showed a lowered content of the antisense target proteins in guard cells as well as in the mesophyll. In the anti-b/f plants, CO₂ assimilation rates were proportional to leaf cytochrome b₆f content, but there was little effect on stomatal conductance and the rate of stomatal opening. To compare the relationship between photosynthesis and stomatal conductance, wild-type plants and anti-SSU plants were grown at 30 and 300 µmol photon m^–2 s^–1 irradiance (low light and medium light [ML], respectively). Growth in ML increased CO₂ assimilation rates and stomatal conductance in both genotypes. Despite the significantly lower CO₂ assimilation rate in the anti-SSU plants, the differences in stomatal conductance between the genotypes were nonsignificant at either growth irradiance. Irrespective of plant genotype, stomatal density in the two leaf surfaces was 2-fold higher in ML-grown plants than in low-light-grown plants and conductance normalized to stomatal density was unaffected by growth irradiance. We conclude that the red light response of stomatal conductance is independent of the concurrent photosynthetic rate of the guard cells or of that of the underlying mesophyll. Furthermore, we suggest that the correlation of photosynthetic capacity and stomatal conductance observed under different light environments is caused by signals largely independent of photosynthesis.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Susanne von Caemmerer (susanne.caemmerer{at}anu.edu.au).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.110924

^* Corresponding author; e-mail susanne.caemmerer{at}anu.edu.au.

Received October 14, 2007; accepted December 2, 2007; published December 7, 2007.

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