Stomatal conductance in tobacco plants with reduced photosynthetic capacity

BAROLI, IRENE; PRICE, G DEAN; BADGER, MURRAY R; VON CAEMMERER, SUSANNE

Snowbird, Utah

Congreso; Special Meeting of the American Society of Plant Biology: The Biology of Transpiration; 2006

American Society of Plant Biologists

To determine the contribution of photosynthesis on stomatal conductance, we contrasted the stomatal red light response of wildtypetobacco (Nicotiana tabacum ?W38?) with that of plants impaired in photosynthesis by antisense reductions in the content ofeither cytochromeb6 f complex (anti-b/f plants) or Rubisco (anti-SSU plants). Both transgenic genotypes showed a lowered contentof the antisense target proteins in guard cells as well as in the mesophyll. In the anti-b/f plants, CO2 assimilation rates wereproportional to leaf cytochromeb6 f content, but there was little effect on stomatal conductance and the rate of stomatal opening. Tocompare the relationship between photosynthesis and stomatal conductance, wild-type plants and anti-SSU plants were grown at30 and 300 mmol photon m22 s21 irradiance (low light and medium light [ML], respectively). Growth in ML increased CO2assimilation 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-lightgrownplants and conductance normalized to stomatal density was unaffected by growth irradiance. We conclude that the redlight response of stomatal conductance is independent of the concurrent photosynthetic rate of the guard cells or of that of theunderlying mesophyll. Furthermore, we suggest that the correlation of photosynthetic capacity and stomatal conductanceobserved under different light environments is caused by signals largely independent of photosynthesis.