MODIFICATION OF CARBONIC-ANHYDRASE ACTIVITY BY ANTISENSE AND OVER-EXPRESSION CONSTRUCTS IN TRANSGENIC TOBACCO

The activity and location of carbonic anhydrase has been modified by t ransformation of tobacco with antisense and over-expression constructs . Antisense expression resulted in the inhibition of up to 99% of carb onic anhydrase activity but had no significant impact on net CO2 assim ilation. Stomatal conductance and susceptibility to water stress appea red to increase in response to the decline in carbonic anhydrase activ ity. An over-expression construct designed to increase cytosolic carbo nic anhydrase abundance resulted in a significant increase in net acti vity, a small increase in stomatal conductance but little impact on CO 2 assimilation. Chloroplastic carbonic anhydrase activity was enhanced by the expression of an additional construct which targeted the polyp eptide to the organelle. The increase in chloroplastic carbonic anhydr ase appeared to be accompanied by a concomitant increase in Rubisco ac tivity.