Ultrastructural localization of acid phosphatase in cultured cells ofDaucus carota

Acid phosphatase localization has been studied, using the lead salt method, in suspension-cultured cells of the wild carrot. Enzyme activity in most of the cells was restricted to the walls and vacuoles. However, in some senescent cells activity was also seen in the nucleus, at one face of the dictyosomes, and in nearby dictyosome-derived vesciles.The activity in the walls was closely associated with the central portion of the wall which ultimately disintegrates in auxin-containing media. However, the large vesicles which accumulate in this portion of the wall as it breaks down never showed acid phosphatase activity, nor did the multivesicular bodies which appear to transfer vesicular material into the wall space. Although multivesicular bodies in plant cells resemble the multivesicular lysosomes of animal cells, no evidence could be obtained in this study for the presence in such bodies of hydrolytic enzymes.