A micromethod for the determination of the nucleic acids.

This paper describes a micro modification of the Schneider method (1) for determination of the nucleic acids in tissues. This modification has been applied successfully to 1 to 3 mg. (wet weight) samples of pollen mother cell material from plant anthers, the samples containing from 1.6 to 15.1 y of desoxyribose nucleic acid and from 8.6 to 58.0 y of ribose nucleic acid per mg. (wet weight). The original method was devised for animal tissue; the present modification extends its usefulness to certain plant material and to tissues of which only very small samples are available. Fig. 1 illustrates the micro equipment devised for the method. Samples are removed and placed on the bottom of the pestle of the micro PotterElvehjem homogenizer in a moist chamber to prevent evaporation of water prior to weighing on the micro balance. If it is possible to separate the tissue into discrete cells, as was the case in the plant material, a separate aliquot may be weighed for cell count, and the results of the analysis expressed per cell or per 10,000 cells, rather than per unit wet weight of tissue. The samples weighed as above are homogenized for 1 minute with 0.03 ml. of cold distilled water, with a stirring motor revolving at 1500 R.P.M. Following this, the pestle is moved a short way up the tube, another 0.03 ml. of cold distilled water is added, and is sucked below the pestle by again moving it upward a short distance. Two 0.08 ml. portions of cold 10 per cent trichloroacetic acid are then added similarly and the washed pestle is removed from the tube. A stirring thorn is assigned to each tube at this point and is used to mix the tube contents at this and each subsequent washing. Fig. 2 illustrates a cold centrifuge block by means of which the micro tubes were centrifuged for 15 minute periods at O-5” in a Sorvall model G angle head centrifuge without the use of a cold room. The t.richloroacetic acid-precipitated material is washed twice in the cold with 0.10 ml. portions of 10 per cent trichloroacetic acid and once in the cold with a 0.10 ml. portion of 5 per cent trichloroacetic acid prior to heat-