The science behind chilling hours requirement for temperate fruit trees ?

A number of temperate climate fruit trees (apples, pears, …) and vegetables require chilling hours to flower / bear fruits.

https://en.m.wikipedia.org/wiki/Vernalization
https://en.m.wikipedia.org/wiki/Chilling_requirement
So, what’s going on at the biochemistry level ? What does the chilling hours (1000, 500, …) requirement translate to at a cellular level ?

It is right there in your first link:

My bad - thank you