PHOTOSYNTHETIC ACTIVITY AND CHLOROPHYLL FLUORESCENCE PARAMETERS IN AUREA AND GREEN FORMS OF NICOTIANA-TABACUM

Differences between photosynthetic characteristics of chlorophyll (Chl ) b-deficient aurea mutant (Su/su) and the green (su/su) variety of Ni cotiana tabacum were tested. Fully mature leaves of 3-5-month-old plan ts grown in potted soil were investigated. Main differences were found as follows: Respective Chl a and b contents were 3 and 5 times lower in aurea plants, while xanthophylls and carotenes contents per unit of Chl were higher. The content of light-harvesting complex (LHC) was lo wer and LHC composition differed in aurea mutant. PS 1 activity calcul ated per unit of Chl content was higher in aurea mutant. The green var iety showed the lower photosynthetic rates (P(N)) at saturating irradi ances whether calculated on the Chl or leaf area basis. At excessive l ight P(N) declined with green plants. Carboxylation efficiency (CE) (C O2 response slope of P(N) at low CO2 concentrations) was higher for au rea mutant. Time-integrated intercellular CO2 concentrations derived f rom C-13 discrimination were higher for aurea mutant (304 cm3 m-3) tha n for green plants (283 cm3 m-3), Which together with higher mean stom atal conductance in aurea matched CE differences.