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The functional significance of C 3 –C 4 intermediate traits in Heliotropium L. (Boraginaceae): gas exchange perspectives
Author(s) -
VOGAN PATRICK J.,
FROHLICH MICHAEL W.,
SAGE ROWAN F.
Publication year - 2007
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.1365-3040.2007.01706.x
Subject(s) - boraginaceae , photosynthesis , stomatal conductance , botany , biology , mole , biochemistry
ABSTRACT We demonstrate for the first time the presence of species exhibiting C 3 –C 4 intermediacy in Heliotropium (sensu lato), a genus with over 100 C 3 and 150 C 4 species. CO 2 compensation points ( Γ ) and photosynthetic water‐use efficiencies (WUEs) were intermediate between C 3 and C 4 values in three species of Heliotropium : Heliotropium convolvulaceum ( Γ = 20 µ mol CO 2 mol −1 air), Heliotropium racemosum ( Γ = 22 µ mol mol −1 ) and Heliotropium greggii ( Γ = 17 µ mol mol −1 ). Heliotropium procumbens may also be a weak C 3 –C 4 intermediate based on a slight reduction in Γ (48.5 µ mol CO 2 mol −1 ) compared to C 3 Heliotropium species (52–60 µ mol mol −1 ). The intermediate species H. convolvulaceum , H. greggii and H. racemosum exhibited over 50% enhancement of net CO 2 assimilation rates at low CO 2 levels (200–300 µ mol mol −1 ); however, no significant differences in stomatal conductance were observed between the C 3 and C 3 –C 4 species. We also assessed the response of Γ to variation in O 2 concentration for these species. Heliotropium convolvulaceum , H. greggii and H. racemosum exhibited similar responses of Γ to O 2 with response slopes that were intermediate between the responses of C 3 and C 4 species below 210 mmol O 2 mol −1 air. The presence of multiple species displaying C 3 –C 4 intermediate traits indicates that Heliotropium could be a valuable new model for studying the evolutionary transition from C 3 to C 4 photosynthesis.