It also stimulates the storage of shoot derived nutrients. Perhaps even the gases are stored. It also stimulates the storage of root derived materials, for future scarcity. It also attempts to increase shoot derived materials, by bolting. This bolting, perhaps brings the plant into better atmosphere and better light.
ABA is made by any nonmeristematic cell faced with a lack of root derived nutrients.
ABA also adjusts root and shoot size in order to increase water and mineral consumption. Also, ABA releases stores of needed root derived materials and may stimulate a form of root bolting. It is released when there is no significant external threat from extreme temperature, disease, physical trauma such as wind or insects, or toxins of various biological or man made sources. It is also made only in meristematic cells. It promotes a generalized storing of all nutrients, balancing this with growth.