Initiation of the synthesis of 'stress' ABA by (+)-[2 H6 ]ABA infiltrated into leaves of Commelina communis.

The 'fettered' fraction of abscisic acid (ABA) that is held within the chloroplasts of unwilted bean and Commelina communis leaves is released when the leaves wilt and it is this 'free' ABA that is now proposed to cause the stomata to close within 2 or 3 min, well before the rise in total ABA can be detected. The large increase in 'stress' ABA begins 2-3 h later. The fettered ABA in a centrifuged homogenate is released by hyperosmotic solutions of mannitol (0.

The pathway of biosynthesis of abscisic acid in vascular plants: a review of the present state of knowledge of ABA biosynthesis.

The pathway of biosynthesis of abscisic acid (ABA) can be considered to comprise three stages: (i) early reactions in which small phosphorylated intermediates are assembled as precursors of (ii) intermediate reactions which begin with the formation of the uncyclized C40 carotenoid phytoene and end with the cleavage of 9'-cis-neoxanthin (iii) to form xanthoxal, the C15 skeleton of ABA. The final phase comprising C15 intermediates is not yet completely defined, but the evidence suggests that xanthoxal is first oxidized to xanthoxic acid by a molybdenum-containing aldehyde oxidase and this is defective in the aba3 mutant of Arabidopsis and present in a 1-fold acetone precipitate of bean leaf proteins. This oxidation precludes the involvement of AB-aldehyde as an intermediate.

beta-Carotene-15,15'-dioxygenase (EC 1.13.11.21) isolation reaction mechanism and an improved assay procedure.

beta-Carotene-15,15'-dioxygenase (EC 1.13.11.