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The Kok effect in V icia faba cannot be explained solely by changes in chloroplastic CO 2 concentration
Author(s) -
Buckley Thomas N.,
Vice Heather,
Adams Mark A.
Publication year - 2017
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.14775
Subject(s) - photosynthesis , vicia faba , oxygen , chemistry , photorespiration , darkness , respiration , limiting oxygen concentration , botany , quantum yield , horticulture , biology , fluorescence , physics , organic chemistry , quantum mechanics
Summary The Kok effect – an abrupt decline in quantum yield ( QY ) of net CO 2 assimilation at low photosynthetic photon flux density ( PPFD ) – is widely used to estimate respiration in the light ( R ), which assumes the effect is caused by light suppression of R . A recent report suggested much of the Kok effect can be explained by declining chloroplastic CO 2 concentration ( c c ) at low PPFD . Several predictions arise from the hypothesis that the Kok effect is caused by declining c c , and we tested these predictions in Vicia faba . We measured CO 2 exchange at low PPFD , in 2% and 21% oxygen, in developing and mature leaves, which differed greatly in R in darkness. Our results contradicted each of the predictions based on the c c effect: QY exceeded the theoretical maximum value for photosynthetic CO 2 uptake; QY was larger in 21% than 2% oxygen; and the change in QY at the Kok effect breakpoint was unaffected by oxygen. Our results strongly suggest the Kok effect arises largely from a progressive decline in R with PPFD that includes both oxygen‐sensitive and ‐insensitive components. We suggest an improved Kok method that accounts for high c c at low PPFD .