Immunohistochemical localization of glutamine synthetase in developing maize kernels

Abstract

Antibodies to spinach (Spinacia oleracea) leaf glutamine synthetase (GS) cross-reacted with all forms of GS from the tissues of the maize (Zea mays L.) kernel. Phycoerythrin-conjugated anti-rabbit IgG was used to detect sites of anti-GS binding in paraformaldehyde-fixed cryostat sections of whole maize kernels from 8 to 32 days after pollination. A positive GS signal was found in the vascular tissue of the kernel base, the pericarp, and lower endosperm cells at all stages examined. Embryo staining increased from none to heavy throughout development and was uniform throughout the embryo. Staining increased throughout the endosperm up to 24 days after pollination, then remained intense in the lower endosperm while decreasing in the upper endosperm. Staining was very weak in the basal endosperm transfer cells, suggesting that GS is not directly involved in the uptake of amino acids into the endosperm. The distribution of GS in the pedicel region is consistent with a possible role of GS in the unloading of amino acids from the phloem. Key words: amino acids, immunofluorescence, seed development, Zea mays.