title: Response of Photochemical Processes of Photosynthesis to Dinitrogen Fixation in Soybean.
abstract: Symbiotic N2 fixation activity brings about changes in the photochemical processes of photosynthesis in soybean (Glycine max L. Merr.). For a potential photochemical efficiency ([phi]Po) similar to that obtained with an exclusively mineral nutrition, soybean, at full bloom stage (R2) with a moderate N2 fixation activity, had a better electron transfer quantum yield ([phi]PSII) and a higher photochemical quenching. At the beginning seed stage (R5), corresponding to more intense N2 fixation, the same phenomena were enhanced; in addition, an effect on the photochemical (k2b) and nonphotochemical (Kn-k22) transfer rates and an earlier activation of the electron transfer chain were characterized using a new parameter, the relative induction time of PSII fluorescence (Ap/Fm). The response of the photochemical parameters was related to the N2 fixation level (performance of the host plant-microsymbiont association): the energetic cost of symbiotic N2 fixation appeared to be met by a better photochemical efficiency of photosynthesis coupled with a decrease in thermal dissipation (kn - k22), by faster thylakoid energization, and by faster reopening of photosystem II centers at the time of fluorescence induction, as shown by decreased Ap/Fm.
authors.affiliation: Ecole Nationale Superieure Agronomique, Institut National Polytechnique, 145, Avenue de Muret, F-31076 Toulouse Cedex, France.
authors.forename: P.
authors.initials: P
authors.lastname: Maury
authors.forename: S.
authors.initials: S
authors.lastname: Suc
authors.forename: M.
authors.initials: M
authors.lastname: Berger
authors.forename: C.
authors.initials: C
authors.lastname: Planchon