Inorganic phosphate accumulation and phosphatase activity in the nucleus of maize embryo root cells

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Abstract
The nucleus of growing root cells of Zea mays contains a high concentration of inorganic phosphate. In order to verify whether this high nuclear Pt concentration is correlated with the metabolic activity of the nucleus, the P1 has been visualized in root cells of maize embryos at the electron-microscope level during 2 different periods which are both characterized by a spectacular reactivation of the nuclear metabolism, i.e. the early germination and the period of recovery following a thermal treatment given to the seeds after 48 h of germination. In both situations the P1 concentration increased in the nucleus during its reactivation. To verify whether the high nuclear P1 concentration could be of endogenous origin, the phosphatase activities were measured in crude extracts of root tissues during nuclear reactivation. The specific activity was optimal at pH 4·5 and was shown to increase with cellular reactivation. The ultrastructural localization of acid phosphatase activity showed that P1 may be produced at 3 distinct sites: plasmalemma, vacuoles and most probably nucleus itsef. High acid phosphatase activities were found in nuclei displaying a high metabolism. Taking these results and previous data into account, we suggest that a correlation may exist between the rate of nuclear transcription, the level of nuclear acid phosphatase activity and the nuclear P1 accumulation.