Photosynthesis and carbon partitioning in transgenic tobacco plants deficient in leaf cytosolic pyruvate kinase
Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco (Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PKc-). PKc- plants cultivated under a low light intensity (100 &mgr;mol m-2 s-1) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PKc (PKc+). PKc- and PKc+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed 14CO2 during photosynthesis. However, during growth under low light the nighttime, export of previously fixed 14CO2 by fully expanded PKc- leaves was 40% lower, whereas concurrent respiratory 14CO2 evolution was 40% higher than that of PKc+ leaves. This provides a rationale for the reduced root growth of the PKc- plants grown at low irradiance. Leaf photosynthetic and export characteristics in PKc- and PKc+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PKc in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low.
Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada N1G 2W1 (B.G., J.J.).
B
Grodzinski
J
Jiao
VL
Knowles
WC
Plaxton