Altered growth of transgenic tobacco lacking leaf cytosolic pyruvate kinase

Previously, we reported that transformation of tobacco (Nicotiana tabacum L.) with a vector containing a potato cytosolic pyruvate kinase (PK(c)) cDNA generated two plant lines specifically lacking leaf PK(c) (PK(c)-) as a result of co-suppression. PK(c) deficiency in these primary transformants did not appear to alter plant development, although root growth was not examined. Here we report a striking reduction in root growth of homozygous progeny of both PK(c)- lines throughout development under moderate (600 mu E m(-2) s(-1)) or low (100 mu E m(-2) s(-1)) light intensities. When both PK(c)- lines were cultivated under low light, shoot and flower development were also delayed and leaf indentations were apparent. Leaf PK activity in the transformants was significantly decreased at all time points examined, whereas root activities were unaffected. Polypeptides corresponding to PK(c) were undetectable on immunoblots of PK(c)- leaf extracts, except in 6-week-old low-light-grown PK(c)- plants, in which leaf PK(c) expression appeared to be greatly reduced. The metabolic implications of the kinetic characteristics of partially purified PK(c) from wild-type tobacco leaves are discussed. Overall, the results suggest that leaf PK(c) deficiency leads to a perturbation in source-sink relationships.