Immunoelectron-microscopy localization of abscisic acid with colloidal gold on Lowicryl-embedded tissues of Chenopodium polyspermum L

Further study on the localization of abscisic acid (ABA) has been undertaken at the ultrastructural level in Chenopodium polyspermum L. Axillary-bud-bearing nodes on the main axis were fixed with soluble 1-(3-dimethylaminopropyl)-3 ethyl carbodiimide, then postfixed with paraform-aldehyde and embedded in Lowicryl K4M at -20° C. Ultrathin sections mounted on grids were successively incubated with rabbit anti-ABA antibodies and with gold-labelled goat anti-rabbit antibodies (40 nm particle size). Control sections treated with preimmune rabbit serum and ABA-preabsorbed antibodies were devoid of label. The background staining was very low with this technique. Quantitative analysis of the immunolabelling showed that two main sites of ABA accumulation could be defined: first, plastids in cortical cells and vascular parenchyma cells associated with sieve elements and xylem vessels; second, the cell cytoplasm and nucleus in the axillary bud tip and in procambial strands. In vascular bundles, the cambial cells showed no immunoreactivity. These observations support the hypothesis for the cytoplasmic synthesis of ABA which is subsequently trapped in plastids as cells mature.