Abscisic acid (ABA) or stress hormone or dormin is present in all vascular plants as well as in some mosses, some green algae and some fungi. The copletely absent in bacteria. It is commonly formed inside chloroplast either from mevalonic acid or xanthophyll like violoxanthin. Chloroplasts in leaves contain the carotenoids from which ABA arises, whereas in certain other parts like roots, fruits, seeds, etc necessary carotenoids are in other tissues chromoplasts, leucoplasts or proplastids.