Localization of wheat-germ agglutinin in developing wheat embryos and those cultured in abscisic acid

The time course of appearance of wheat-germ agglutinin (WGA) in the various embryonic tissues during embryogenesis in Triticum aestivum L. was studied by sensitive immunofluorescence and peroxidase-antiperoxidase detection systems. The radicle, root cap and coleorhiza first accumulated WGA in early Stage II (8-10 d post-anthesis) prior to the main period of embryo growth, while WGA was found in the epiblast and coleoptile in early and late State III, respectively. Stage III is characterized by maximum embryo growth, followed by desiccation which occurs in Stage IV. When Stage-II embryos were precociously germinated in the absence of abscisic acid (ABA) no WGA was detected in the coleoptile and epiblast of the young seedlings. In the presence of ABA, Stage-II embryos did not germinate but WGA precociously accumulated in the coleoptile and epiblast. The levels and distribution of WGA in the resulting embryo resembled those in a fully mature, dry embryo (Stage V). Barley possesses a seed lectin similar to WGA, but it is never detected in coleoptiles. Some but not all of the barley cultivars tested were found to accumulate lectin in this organ of mature embryos when treated with ABA. Thus, ABA appears to be involved in the highly regulated temporal and spatial expression of WGA during embryogenesis in cereals.