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Plant Physiology Preview Published on December 7, 2007; 10.1104/pp.107.110924
OPEN ACCESS ARTICLE
Received October 14, 2007 The contribution of photosynthesis to the red light response of stomatal conductance
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia * Corresponding author; email: Susanne.Caemmerer{at}anu.edu.au.
To determine the contribution of photosynthesis on stomatal conductance, we contrasted the stomatal red light response of wild type tobacco (Nicotiana tabacum L. cv W38) with that of plants impaired in photosynthesis by antisense reductions in the content of either cytochrome b 6 f 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 b 6 f content, but there was little effect on stomatal conductance and 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 (LL and 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 non-significant at either growth irradiance. Irrespective of plant genotype, stomatal density in the two leaf surfaces was two-fold higher in ML than in LL-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.
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