Consequences of Warburg Effect Conditions on Growth Parameters and CO₂-Exchange Rates in Tobacco Mutants

Abstract

If photorespiration is studied as increase in dry weight per plant under Warburg effect conditions, the following results are obtained with the tobacco mutant set derived from N. tabacum var. Consolation: The green phenotype exhibits approximately 30% more Warburg effect than the yellow-green phenotype. Treatment with 2% O₂ reduces the rate of the leaf area expansion in both phenotypes. If the O₂-effect is referred to unit leaf area, the relative Warburg effects are practically the same in both phenotypes. This phenomenon is due to the fact that under normal O₂-conditions the green phenotype exhibits a higher rate of photosynthesis than the yellow-green phenotype and the increase in leaf area under 2% O₂ is inhibited more strongly in the yellow-green phenotype than in the green one. If, in the short experimental period, the increase of dry weight or increase in leaf area under 2% O₂-partial pressure is taken as a criterion of photorespiration, the yellow phenotype shows practically no effect. However, the yellow phenotype reacts very unfavorably upon exposure to 2% O₂. This treatment inhibits its ability to perform photosynthesis, apparently irreversibly. A prolonged period of exposure to 2% O₂ also damages the photosynthetic apparatus in the green and yellow-green phenotypes. This damage, however, seems to be partly reversible. Evidently the defective plants are characterized by the genetic condition which belongs to the green and yellow phenotypes.