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1981 (2)
1Author    GeorgH. Schmid, KlausP. Bader, Richard Gerster, Christian Triantaphylides, Marcel AndréRequires cookie*
 Title    Dependence of Photorespiration and Photosynthetic Unit Sizes on Two Interdependent Nuclear Gene Factors in Tobacco  
 Abstract    A new set of tobacco mutants was obtained by selfing a single variegated plant which emerged in a seed lot of Nicotiana tabacum var. Consolation. The seeds obtained from this mutant give rise to four phenotypes: variegated, yellow, yellow-green, and green seedlings. The green, yellow-green and yellow characters are due to two interdependent nuclear gene factors. The yellow-green phenotype is the homozygous (aabb) true breeding condition, whereas the green and the yellow phenotype are heterozygous (AaBb) with respect to both nuclear factors, the difference in the yellow and green phenotype being the addition of a labile gene factor pair, Cc, in the yellow condition. If photorespiration is measured as the Warburg effect or as 180 2-consumption by mass spectrometry it appears that the heterozygous green phenotype is the defective condition with high photorespiration. The three phenotypes differ with respect to chlorophyll content and photosynthetic unit sizes, the photosynthetic unit size in the yellow phenotype being approxi­ mately 1/10 of that of the green type. The gene expression for photorespiration (measured as 180 2-uptake for example) in the heterozygous green type is suppressed by the addition of the labile gene factor pair Cc in heterozygous condition which leads to the yellow phenotype. In the yellow and green phenotype the photosynthetic unit size is different but not the ratio of photosys­ tem I/photosystem II activity. Moreover, from the present studies it appears that the Warburg effect i. e. an increase of photo­ synthetic rate upon anoxia, can only partly be due to an inhibition of ribulose 1,5-biphosphate oxygenase or glycolate oxidase. 
  Reference    Z. Naturforsch. 36c, 662—671 (1981); received March 23 1981 
  Published    1981 
  Keywords    Photorespiration, Mass Spectrometry, Photosynthetic Units, Tobacco Mutants 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0662.pdf 
 Identifier    ZNC-1981-36c-0662 
 Volume    36 
2Author    Ryuichi Ishii, GeorgH. SchmidRequires cookie*
 Title    The Kok Effect and Its Relationship to Photorespiration in Tobacco  
 Abstract    The Kok effect of photosynthesis was investigated in different tobacco mutants. It was found that the breaks in the light intensity curve were always at or around 1000 lux in all plants tested regardless o f the unit sizes which differed by a factor of 10. It was concluded that the photo­ receptor responsible for the effect must be present in the wild type and the chlorophyll deficient mutants in the same amount and is probably not chlorophyll. Due to the fact that the light dependency of the Hill reaction in isolated tobacco chloroplasts also shows a break at or around the "Kok intensity" it was concluded that probably a structural change of the photochemical apparatus around 1000 lux contributes to the effect. Measurement of 180 2-uptake by mass spectrometry at low light intensity shows at low C 0 2-concentration an enhancement of 180 2-uptake again at/around 1000 lux indicating that photorespiration starts to function at the "Kok intensity". Due to the fact that 180 2-uptake remains constant at high C 0 2-concentrations the break in the photosynthetic light intensity curve cannot be due to an inhibition o f "dark respiration" at low light intensities. 
  Reference    Z. Naturforsch. 36c, 450 (1981); received February 26 1981 
  Published    1981 
  Keywords    Kok Effect, Tobacco Mutants, 180 2-Uptake, Mass Spectrometry 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0450.pdf 
 Identifier    ZNC-1981-36c-0450 
 Volume    36