Carboxylesterase activities during the establishment of the procambium and procortex in embryos of pisum sativum L.

A cytochemical and electrophoretic analysis of alpha-naphthyl and naphthol AS-D acetate esterases from the radicles of pea seeds germinated for 24, 36 and 48 h permitted the detection of the loss of activity from the procortex with time after germination, but a stability of this activity in the prostele. Inhibitor studies showed the procambial enzyme as a single band of carboxylesterase activity the remainder being acetylesterase activity. The procambial carboxylesterase which is present in the more mature root apex corresponds to that of the 48-h embryo (separating at Rf 0·74).     

Cytochemical and autoradiographic studies of the localization and turnover of chromatin and nucleolar associated phospholipids in plant and animal tissues

The localization of chromatin-associated phospholipids has been demonstrated on chromosomes and on chromatin of interphase nuclei by cytochemical methods either in plant and in animal tissues. Three methods of fixation are suggested which can be combined which two cytochemical methods for phospholipids detection. An additional method is represented by autoradiographic technique after incorporation of a radioactive precursor such as [3H] ethanolamine. This method has been used with good results in nuclei of lateral root apices of Vicia faba on 1 micron thick section, thus avoiding any possible contamination by nuclear membrane. In these nuclei the phospholipids appear associated with the chromatin and more intensely with the nucleolar regions. The positivity of the cytochemical reaction disappears after extraction of fixed tissue with acidified methanol chloroform and after treatment of unfixed sections with phospholipase D. The use of phospholipid precursor has allowed the study of chromatin-phospholipids synthesis in root apices of Vicia faba with respect to timings of the cell cycle. The results show that there is a strong case for a pattern of chromatin phospholipid synthesis which operates during S phase. Concerning the role of phospholipids it is suggested that they may be linked to acidic protein and may have a structural function, particularly on the nucleoli.     

Hepatocyte euploidization is a typical mammalian physiological specialization

1. Quantitative cytochemical studies of hepatocytes from a variety of species representing the various sub-classes of mammals have shown that euploidization of hepatocytes is a typical feature of mammalian livers. 2. Euploidization occurs during early development and frequently involves a large proportion of the hepatocyte population. 3. Comparison with livers from birds and diploid fish indicates that euploidization is a special mammalian feature.     

Synthesis of chromatin phospholipids

The presence of a phospholipid fraction associated with chromatin has been demonstrated by biochemical technique in rat hepatocytes. The composition of this fraction determined by chromatography with respect to that of the nuclei is characterized by low content of phosphatidylserine and high content in phosphatidylethanolamine. Also the synthesis and turnover studied after injection of [32P]O4(2-) show a different behaviour: the peak of activity is after 6 hrs in nuclei and microsomes, whereas in chromatin it occurs after 9 hrs. A second peak is evident after 24 hrs in chromatin and microsome phospholipids. Differences have been also shown by analyzing the single phospholipid radioactivity in time. The behaviour of chromatin phospholipids has also been studied during DNA premitotic synthesis in regenerating liver. It has been shown that there is no difference in synthesis in relation to that of DNA in nuclear phospholipids, whereas the specific activity of chromatin phospholipids begins to increase twelve hours after hepatectomy and continues throughout the period of the first mitotic wave, thus bringing to a summation with the beginning of the second wave. The role of this phospholipid fraction in relation to DNA synthesis and gene expression is discussed.     

Agrobacterium tumefaciens Ribonucleic Acid Synthesis in Tomato Cells and Crown Gall Induction

Purified Agrobacterium tumefaciens deoxyribonucleic acid (DNA) does not produce crown gall tumors in growing plants, conditioned by wounding, as the living bacteria do. Purified bacterial DNA migrates in the plant and replicates, but it is not transcribed in our experimental conditions. On the contrary, when DNA is released naturally from bacteria into plant cells, a bacterial ribonucleic acid (RNA) can be found in these cells. There seems to be a direct relation between the appearance of A. tumefaciens RNA in the plant cells and the induction of the tumor.