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Carbonic anhydrase and C 4 photosynthesis: a transgenic analysis
Author(s) -
VON CAEMMERER S.,
QUINN V.,
HANCOCK N. C.,
PRICE G. D.,
FURBANK R. T.,
LUDWIG M.
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.1365-3040.2003.01157.x
Subject(s) - carbonic anhydrase , photosynthesis , bicarbonate , cytosol , assimilation (phonology) , enzyme , chemistry , biochemistry , carbon dioxide , complementary dna , enzyme assay , botany , biology , gene , ecology , linguistics , philosophy , organic chemistry
Carbonic anhydrase (CA, EC 4.2.1.1) catalyses the first reaction in the C 4 photosynthetic pathway, the conversion of atmospheric CO 2 to bicarbonate in the mesophyll cytosol. To examine the importance of the enzyme to the functioning of the C 4 photosynthetic pathway, Flaveria bidentis (L.) Kuntze, a C 4 dicot, was genetically transformed with an antisense construct in which the cDNA encoding a putative cytosolic CA (CA3) was placed under the control of a constitutive promoter. Some of the primary transformants had impaired CO 2 assimilation rates and required high CO 2 for growth. The T 1 progeny of four primary transformants were used to examine the quantitative relationship between leaf CA activity and CO 2 assimilation rate. CA activity was determined in leaf extracts with a mass spectrometric technique that measured the rate of 18 O exchange from doubly labelled 13 C 18 O 2 . Steady‐state CO 2 assimilation rates were unaffected by a decrease in CA activity until CA activity was less than 20% of wild type when they decreased steeply. Transformants with less than 10% of wild‐type CA activity had very low CO 2 assimilation rates and grew poorly at ambient CO 2 partial pressure. Reduction in CA activity also increased the CO 2 partial pressure required to saturate CO 2 assimilation rates. The present data show that CA activity is essential for the functioning of the C 4 photosynthetic pathway.