Histochemical localization of nucleotide pyrophosphatase and cyclic nucleotide phosphodiesterase in seeds and shoots of Triticum.

The activities of potato nucleotide pyrophosphatase and cyclic nucleotide phosphodiesterase against a common substrate, p-nitrophenyl thymidine 5'-phosphate and its histochemical analogue, AS-BI-naphthyl thymidine 5'-phosphate, were determined with the aid of relatively specific inhibitors, NAD and 2',3'-cAMP, respectively. These inhibitors were utilized to reexamine wheat (Triticum aestivum L. cv. Mironovska 808) seeds and 3-5-d old shoots for the occurrence and histochemical localization of nucleotide pyrophosphatase, and to establish the localization of cyclic nucleotide phosphodiesterase. Nucleotide pyrophosphatase is a cytoplasmic enzyme found to be particularly active in the coleoptile epidermis and hypodermis, leaf mesophyll, as well as in developing fibres and phloem. Cyclic nucleotide phosphodiesterase is also a cytoplasmic enzyme active in the shoot vascular bundles, particularly the xylem, and in the seed. Within the seed it is highly active in the crushed cell layer adjacent to the scutellum and in endosperm cells adjacent to the aleurone layer. Within the embryo, cyclic nucleotide phosphodiesterase is most active in epithelial cells adjacent to the crushed cell layer, the suspensor, radicle and root-cap, as well as in the pro-vascular tissues of the scutellum.