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Photosynthetic oxygen exchange in C 4 grasses: the role of oxygen as electron acceptor
Author(s) -
SIEBKE K.,
GHANNOUM O.,
CONROY J. P.,
BADGER M. R.,
VON CAEMMERER S.
Publication year - 2003
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2003.01112.x
Subject(s) - photosynthesis , panicum , biology , compensation point , botany , photosystem ii , c4 photosynthesis , transpiration
C 4 grasses of the NAD‐ME type ( Astrebla lappacea , Eleusine coracana , Eragrostis superba , Leptochloa dubia , Panicum coloratum , Panicum decompositum ) and the NADP‐ME type ( Bothriochloa bladhii, Cenchrus ciliaris, Dichanthium sericeum , Panicum antidotale , Paspalum notatum , Pennisetum alopecuroides , Sorghum bicolor ) were used to investigate the role of O 2 as an electron acceptor during C 4 photosynthesis. Mass spectrometric measurements of gross O 2 evolution and uptake were made concurrently with measurements of net CO 2 uptake and chlorophyll fluorescence at different irradiances and leaf temperatures of 30 and 40 °C. In all C 4 grasses gross O 2 uptake increased with increasing irradiance at very high CO 2 partial pressures ( p CO 2 ) and was on average 18% of gross O 2 evolution. Gross O 2 uptake at high irradiance and high p CO 2 was on average 3.8 times greater than gross O 2 uptake in the dark. Furthermore, gross O 2 uptake in the light increased with O 2 concentration at both high CO 2 and the compensation point, whereas gross O 2 uptake in the dark was insensitive to O 2 concentration. This suggests that a significant amount of O 2 uptake may be associated with the Mehler reaction, and that the Mehler reaction varies with irradiance and O 2 concentration. O 2 exchange characteristics at high p CO 2 were similar for NAD‐ME and NADP‐ME species. NAD‐ME species had significantly greater O 2 uptake and evolution at the compensation point particularly at low irradiance compared to NADP‐ME species, which could be related to different rates of photorespiratory O 2 uptake. There was a good correlation between electron transport rates estimated from chlorophyll fluorescence and gross O 2 evolution at high light and high p CO 2 .