Cytochemical techniques for the electron microscopic localization of inosine diphosphatase, thiamine pyrophosphatase, and acid phosphatase have been applied to the developing root tip of Zea mays. Following formaldehyde fixation the Golgi apparatus of most of the cells showed reaction specificity for IDPase and TPPase. Following glutaraldehyde fixation marked localization of IDPase reactivity in the Golgi apparatus was limited to the root cap, the epidermis, and the phloem. A parallelism was apparent between the sequential morphological development of the apparatus for the secretion of a polysaccharide product, the fairly direct incorporation of tritiated glucose into the apparatus to become a component of this product and the development of the enzyme reactivity.

Acid phosphatase, generally accepted as a lysosomal marker, was found in association with the Golgi apparatus in only a few cell types near the apex of the root. The localization was usually in a single cisterna at the face of the apparatus toward which the production of secretory vesicles builds up and associated regions of what may be smooth endoplasmic reticulum. Since the cell types involved were limited regions of the cap and epidermis and some initial cells, no functional correlates of the reactivity were apparent. Despite the presence of this lysosomal marker, no structures clearly identifiable as ‘lysosomes’ were found and the lack of reaction specificity in the vacuoles did not allow them to be so defined.

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