Abscisic AcidLocalization andMetabolism inBarley Aleurone

Akeurone layers ofHordeum vUlgare, cV.'Himalaya' tookup114CIabscisic acid (ABA)whenincubated forvarious times. Radioactivity accumulated withtime inalowspeed, DNA-containing pellet accounting for 1.6to2.3%oftheradioactivity recovered insubcellular fractions at18 hours. Thinlayer chromatography ofethanolic ormethanolic extracts of thecytosol, which contained greater than 95%oftheradioactivity taken up bylayers, revealed that labeled ABAwasmetabolized tophaseic acid (PA) and4-dihydrophaseic acid (DPA)andthree polar metabolites Mxl,Mx2, andMx3.ABA wasnotmetabolized byendosperm, incubated under conditions usedforlayers, indicating that metabolism wastissue-specific. Layers metabolized I3HIDPA toMxlandMx2.ABA,PA,andDPA-methyl ester andepi-DPA-methyl ester inhibited synthesis ofa-amylase bylayers incubated foreither 37or48hours. Theselayers converted themethyl DPAandepi-methyl-DPA esters totheir respective acids. DPA didnot inhibit Lactuca sativa germination orrootandcoleoptile elongatio of germinating Hordewn vudgar seeds, orcoleoptile elongation ofgerminating Zeanmays seeds.