Hi there!

As you must be aware of, tapetum - the innermost layer of the anther wall is chiefly a nourishing layer. It provides nourishment for the growing microspores.

Microspores are formed after microsporogenesis. The resultant microspores are held together by callose in a tetrad condition. The tapetum releases callase enzyme which dissolves the callose in the tetrad and the microspores thus get separated. 

The tapetum now releases the pro-ubisch bodies which further modifies into Ubisch bodies. They interact with sporopollenin and get deposited over the microspore wall forming the exine layer of the pollen wall. 

Thanks