ALTERED GROWTH OF TRANSGENIC TOBACCO LACKING LEAF CYTOSOLIC PYRUVATE-KINASE

Previously, we reported that transformation of tobacco (Nicotiana taba cum L.) with a vector containing a potato cytosolic pyruvate kinase (P Kc) cDNA generated two plant lines specifically lacking leaf PKc (PKc- ) as a result of co-suppression. PKc deficiency in these primary trans formants did not appear to alter plant development, although root grow th was not examined. Here we report a striking reduction in root growt h of homozygous progeny of both PKc- lines throughout development unde r moderate (600 mu E m(-2) s(-1)) or low (100 mu E m(-2) s(-1)) light intensities. When both PKc- lines were cultivated under low light, sho ot and flower development were also delayed and leaf indentations were apparent. Leaf PK activity in the transformants was significantly dec reased at all time points examined, whereas root activities were unaff ected. Polypeptides corresponding to PKc were undetectable on immunobl ots of PKc- leaf extracts, except in 6-week-old low-light-grown PKc- p lants, in which leaf PKc expression appeared to be greatly reduced. Th e metabolic implications of the kinetic characteristics of partially p urified PKc from wild-type tobacco leaves are discussed. Overall, the results suggest that leaf PKc deficiency leads to a perturbation in so urce-sink relationships.