Fig. 4. Northern blot analysis with the strand-specific omt antisense riboprobe to detect endogenous OMT mRNA steady state levels. (A) The five A-group T₁ plants that maintained low OMT activity through the 7-wk stage. Third youngest leaf was sampled. The 1.7-kb band is the endogenous OMT mRNA and is not visible in the transgenic plants but shows a strong band in the control. (B) B-group T₁ plants sampled at the flag-leaf stage. The 1.7-kb band is strongly present in the controls and bm17-B3, which behaved as a control as it had lost the antisense omt. The endogenous 1.7-kb band is present at a reduced level in some transgenics and is not visible in others. The blot was sequentially hybridized with the strand-specific maize antisense omt riboprobe and the 28S rDNA probe. The reduced expression of the endogenous OMT suggests that antisense omt expression may promote instability of the endogenous OMT mRNA. The 1.3 kb unknown RNA has strand-specific binding with the omt antisense probe. That RNA did not hybridize when an omt cDNA probe or the sense riboprobe was used. A bm in the plant designation indicates that T₀ parent had the brown midrib phenotype. Each plant family is generated from an independent event.