Characterization of a Light-Induced Oxygen-Uptake in Tobacco Protoplasts

Protoplasts prepared from the wild type tobacco N. tabacum var. John William’s Broadleaf ex­ hibit photosynthetic oxygen-evolution if the suspension medium is supplemented with bicarbonate. In the absence of bicarbonate no steady state oxygen-evolution is observed with such prepara­ tions. Instead, an appreciable uptake which is mainly insensitive to DCMU and which persists over hours, and therefore is no mduction phenomenon, is seen. Protoplasts of the tobacco aurea mutant Su/su, which is a plant with an exceptionally high photorespiration, show an oxygen con­ sumption in the light which is 4 to 5 times higher per protoplast than in the wild type. Again, the uptake is practically insensitive to DCMU which means that the effect is to be associated with pho­ tosystem I. This is further substantiated by the fact that protoplasts prepared from yellow leai sec­ tions of the variegated tobacco mutant NC 95 also show the light induced uptake. As reported ear­ lier, the yellow leaf sections of this mutant exhibit only photosystem I reactions. The action spectrum for this oxygen-uptake yields the spectrum of chlorophyll. Consequently, this uptake is an inherent property of the chloroplast and has nothing to do with earlier described, light-dependent oxygen consumptions, which were mainly driven by blue light and hence used some yellow pigment as the photoreceptor. No effect or contribution of yellow pigments such as carotenoids is seen since the action spectrum with the yellow tobacco mutants which have an up to 4 fold higher carotenoid/chlorophyll ratio than the wild type is identical to that of the wild type.