PLANT PHYSIOLOGY , Vol 101, Issue 2 493-497, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Response of Photochemical Processes of Photosynthesis to Dinitrogen Fixation in Soybean
P. Maury, S. Suc, M. Berger and C. Planchon
Ecole Nationale Superieure Agronomique, Institut National Polytechnique, 145, Avenue de Muret, F-31076 Toulouse Cedex, France
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.