Premium
Oxygen consumption during leaf nitrate assimilation in a C 3 and C 4 plant: the role of mitochondrial respiration
Author(s) -
COUSINS A. B.,
BLOOM A. J.
Publication year - 2004
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 - 10.1111/j.1365-3040.2004.01257.x
Subject(s) - photorespiration , photosynthesis , respiration , nitrogen assimilation , assimilation (phonology) , nitrogen , nitrate , oxygen , chemistry , botany , biology , horticulture , linguistics , philosophy , organic chemistry
Measurements of net fluxes of CO 2 and O 2 from leaves and chlorophyll a fluorescence were used to determine the role of mitochondrial respiration during nitrate (NO 3 – ) assimilation in both a C 3 (wheat) and a C 4 (maize) plant. Changes in the assimilatory quotient (net CO 2 consumed over net O 2 evolved) when the nitrogen source was shifted from NO 3 – to NH 4 + (Δ AQ ) provided a measure of shoot NO 3 – assimilation. According to this measure, elevated CO 2 inhibited NO 3 – assimilation in wheat but not maize. Net O 2 exchange under ambient CO 2 concentrations increased in wheat plants receiving NO 3 – instead of NH 4 + , but gross O 2 evolution from the photosynthetic apparatus ( J O2 ) was insensitive to nitrogen source. Therefore, O 2 consumption within wheat photosynthetic tissue (ΔΟ 2 ), the difference between J O2 and net O 2 exchange, decreased during NO 3 – assimilation. In maize, NO 3 – assimilation was insensitive to changes in intercellular CO 2 concentration ( C i ); nonetheless, ΔΟ 2 at low C i values was significantly higher in NO 3 – ‐fed than in NH 4 + ‐fed plants. Changes in O 2 consumption during NO 3 – assimilation may involve one or more of the following processes: ( a ) Mehler ascorbate peroxidase (MAP) reactions; ( b ) photorespiration; or ( c ) mitochondrial respiration. The data presented here indicates that in wheat, the last process, mitochondrial respiration, is decreased during NO 3 – assimilation. In maize, NO 3 – assimilation appears to stimulate mitochondrial respiration when photosynthetic rates are limiting.