Localization of the acid phosphatasic activity in plant cell nucleoli

We have made an ultrastructural study of the nuclear acid phosphatase localization in the different tissues of Allium cepa L. anthers, after meiosis. The enzyme is preferentially located in the fibrillar component, within the nucleolus, with a greater reaction density around the nucleolar organizing region (NOR). The specificity of the reaction was proved by contrasting the results with those obtained in two different series of anthers. One of these series was incubated in Gomori's medium with an acid phosphatasic inhibitor, and the other in Gomori's medium without substrate. In both cases the acid phosphatase reaction was negative. Some authors (Hardin and Spicer, 1970; Tandler et al., 1970; Rodríguez-García and Stockert, 1979) have observed an accumulation of inorganic cations (Ca++, Mg++, ... and Na+) within the nucleolar region where the phosphatase acid activity was detected by us. The coincidence of this localization is discussed, suggesting that these cations are probably involved in the phosphatasic activity of these nucleolar zones. Our results agree with the idea that this enzyme contributes to an increase in the amount of nuclear ortophosphate ions (Harris, 1963). On the other hand this enzyme could play a part in the successive triming of the different preribosomal RNA species that occurs during their maturation (Dalgarno and Shine, 1977).