PHOSPHATASE ACTIVITY AND CELLULAR DIFFERENTIATION IN PHLEUM ROOT MERISTEM

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Abstract
Using 9 different organic phosphate substrates as alternatives in a standardized 5′‐nucleotidase histochemical test system, enzyme activity patterns were recorded for timothy grass root epidermis. At least 4 different phosphatases were distinguished on the bases of substrate specificity, reaction rate, tissue distribution, and response to inhibitors. Except with adenosine‐3′‐monophosphate, all activities were restricted to the 300‐mμ‐long root tip meristem. These enzyme activities were associated with the earliest phases of differentiation of the epidermal hair and hairless cell initials. The distribution of activities was not associated with the same cell type in each part of the meristem. Little activity was found with most substrates in the undifferentiated cells of the 0‐100μ zone; alternating active hairless and inactive hair cell initials predominated in the 100‐200μ segment; and active hair–inactive hairless sister cells formed the principal pattern in the 200‐300μ segment of the meristem. The data showed that a particular enzyme activity was associated with a specific cell type only in relation to that cell's position along the differentiation gradient of the entire tissue. But, within a meristem segment, a specific cell type might act differently from its neighbors, depending on its mitotic capacity. This complex of physiological dependence and independence of a cell type on tissue ontogeny was cited as a characteristic of the phenomenon of cellular differentiation superimposed on tissue differentiation gradients.
Funding Information
  • National Science Foundation (G–12903)