Deuteration of enone - mechanism? What happens when the above compound is mixed with D2O (deuterated water)? 
As a result of tautomerism, I'd expect the 4H atoms, one alpha to carbonyl carbon, and three at gamma position; to be replaced with deuterium. 

However, I'm not clear about the mechanism that'd be followed to achieve the same. 

My thoughts:
The first step should involve formation of carbanion by abstraction of hydrogen gamma to carbonyl group. The carbanion is stabilised by extended conjugation, and has three resonance structures. 

Now, how does the reaction exactly proceed? Could someone please provide a detailed mechanism, it'd be really helpful. Thanks a lot.
As TAR86 mentioned, you seem to understand where deuteration occurs in crotonaldehyde. The process is usually conducted under alkaline conditions. All of the steps are reversible and need not occur in the same order as in the diagram. For instance, enolate 2 can deuterate at the &alpha;-position prior to &gamma;-deuteration. Hope this helps.