IMMUNOLOCALIZATION OF A UNIQUE FORM OF MAIZE KERNEL GLUTAMINE-SYNTHETASE USING A MONOCLONAL-ANTIBODY

The pedicel (basal maternal tissue) of maize (Zea mays L.) kernels con tains a physically and kinetically unique form of glutamine synthetase (GS(p1)) that is involved in the conversion of transport forms of nit rogen into glutamine for uptake by the developing endosperm (M.J. Muhi tch [1989] Plant Physiol 91: 868-875). A monoclonal antibody has been raised against this kernel-specific GS that does not cross-react eithe r with a second GS isozyme found in the pedicel or with the GS isozyme s from the embryo, roots, or leaves. When used as a probe for tissue p rinting, the antibody labeled the pedicel tissue uniformly and also la beled some of the pericarp surrounding the lower endosperm. Silver-enh anced immunogold staining of whole-kernel paraffin sections revealed t he presence of GS(p1) in both the vascular tissue that terminates in t he pedicel and the pedicel parenchyma cells, which are located between the vascular tissue and the basal endosperm transfer cells. Light sta ining of the subaleurone was also noted. The tissue-specific localizat ion of GS(p1) within the pedicel is consistent with its role in the me tabolism of nitrogenous transport compounds as they are unloaded from the phloem.