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Photosynthetic oxygen evolution within Sesbania rostrata stem nodules
Author(s) -
James Euan K.,
Minchin Frank R.,
Oxborough Kevin,
Cookson Alan,
Baker Neil R.,
Witty John F.,
Crawford Robert M.M.,
Sprent Janet I.
Publication year - 1998
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1998.00003.x
Subject(s) - photosynthesis , chloroplast , cortex (anatomy) , spongy tissue , botany , biology , biophysics , nodule (geology) , chemistry , biochemistry , palisade cell , paleontology , neuroscience , gene
The tropical wetland legume, Sesbania rostrata Brem. forms N 2 ‐fixing nodules along its stem and on its roots after infection by Azorhizobium caulinodans . The N 2 ‐fixing tissue is surrounded by a cortex of uninfected cells which, in the stem nodules (but not the root nodules), contain chloroplasts. The photosynthetic competence of these chloroplasts was assessed through a novel technique involving image analysis of chlorophyll a fluorescence. Calculation of the quantum efficiency of photosystem II (PS II) photochemistry from these images indicated that most of the chloroplasts with potential for non‐cyclic photosynthetic electron transport were concentrated within the mid‐ and inner‐cortex, close to the edge of the N 2 ‐fixing tissue. PS II activity in the cortical cells was confirmed in vivo using O 2 ‐specific microelectrodes which showed that the concentration of O 2 (pO 2 ) in the outer cortex could rise from less than 1% up to 23.4% upon increased irradiance of the nodule, but that the pO 2 of the inner cortex and infected tissue remained less than 0.0025%. Nitrogenase activity of stem nodules, as measured using a flow‐through acetylene reduction assay (no H 2 evolution was evident), showed a reversible increase of 28% upon exposure of the nodules to supplemental light. This increase resembled that obtained with stem nodules upon their exposure to an external pO 2 of 40%.