Evidence for Predominant Participation of Photosystem II_β-Units in Nitrogen Formation by Hydroxylamine-Treated Tobacco Chloroplasts : PROTEINS, ENZYMES AND METABOLISM : MEMBRANES AND BIOENERGETICS

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Relative optical cross sections for flash-induced O_2- and N_2-production with water and 1 mM NH_2OH as electron donors to PSII, respectively, as well as that for PSI-mediated O_2-uptake have been measured in tobacco chloroplasts by mass spectrometry. In the wild type tobacco these three reactions are driven by three populations of photosynthetic units different with respect to the antenna size. The antenna size of O_2-evolving units is twice as large compared to the N_2-evolving one, but both of these have the same spectral characteristics in the far red region. In contrast to the wild type, the antenna sizes of O_2- and N_2-evolving units in the chlorophyll b-deficient tobacco mutant Su/su var. Aurea are the same as the sizes of the N_2-evolving units in the wild type chloroplasts. Taking into account the data of Thielen and Van Gorkom [Biochim. Biophys. Acta (1981) 635:111] on a strong difference in the relative amounts of PSII_α and PSII_β in the mutant compared with the wild type (the ratio about 1:3 and 3:1, respectively) it is concluded that mainly the stroma-exposed PSII_β units are competent to N_2-evolution.
日本植物生理学会の論文