Tapetum is most important layer as it produces hormone auxin and enzyme callase which degrades callose wall of microspore tetrad. It forms pro ubisch's body which gets coated with sporopollenin to form ubsich's body which form outer wall exine of pollen grain. It also secretes pollen kit which makes pollen grain sticky and protects pollen grain from UV rays. Tapetum provides nutrition to developing pollen but does not play any role in release of Pollen.