  We consider first-order bosonic string theory, perturbed by the primary
operator, corresponding to deformation of the target-space complex structure.
We compute the effective action in this theory and find that its consistency
with the world-sheet conformal invariance requires necessarily the
Kodaira-Spencer equations to be satisfied by target-space Beltrami
differentials. We discuss the symmetries of the theory and its reformulation in
terms of the vielbein background fields.
