| Abstract: | By means of differential centrifugation, cytosol fraction and microsome were prepared from maize roots which have been grown in dark for 4 d. Highly purified plasma membranes were isolated from the microsome in two-phase aqueous system which is composed of 6.9 % (W/W) Dextran T500 and PEG 3350. The tonoplast was collected from the interface between 1% and 8% (W/W) Dextran T70 after gradient centrifugation. Electron microscopic observation and marker enzyme activities analysis proved that these fractions contained very few other membranes. Microvolume radioactivity ligand binding assay indicated that the specific binding sites of ABA in maize root microsome were mainly distributed on tonoplast and plasma membrane fractions. Their specific binding activity was 2485.4 and 1257.3 fmol/mg protein, respectively, the specific binding activity of cytosol fraction being the lowest (one order of magnitude lower). The dissociation constant (KD) of ABA-BP in plasma membrane was 1.57 nmol/L. |
