FLUORESCENCE STUDIES OF NUCLEOPROTEINS 127 



MEissEL: In all the expoi'inicnts on fluoniclifotiiina: sliowii Iu-it \ital or siipra\i(ivl 

 staining was performed. 



marcovich: What was the concentration of the acridine orange? Did the staining 

 of the medium occur? How many generations of the yeast cells did you observe 

 at the concentration used? 



MEISSEL: Acridine orange diluted 1:100,000 or 1:50,000 in physiological saline 

 or in the medium for animal cell cultures was used. Acridine orange blocks cell 

 structures which results in inhibition of the normal division of the yeast cells. 

 When the concentration of the stain is not very high, the vitally fluorochromed 

 yeast cell, being transferred to a fresh culture mefliinn, would first of all free its 

 structures from fluorochrome, excrete the stain and only afterwards begin its 

 mviltiplication. 



SHABADASH : According to your microphotographs radiation effects, as evidenced 

 by autofluorescence. are found both in radioresistant (kidney) as well as in radio- 

 sensitive (haemopoietic organ) cells. Can we conclude that all the cell types in the 

 body are radiosensitive? When absoriDtion and fluorescence in the ultraviolet 

 light of the kidney culture cells is studied mitochondria are discernible which 

 also show autofluorescence. There is an increase of this effect following irradiation. 

 How should we consider the part which ribonucleoproteins play in the overall 

 cytoplasmic reaction? 



MEISSEL : Tissue culture cells are somewhat more radiosensitive than similar cells 

 in the body. Here we showed cells that had received doses of 2,000 r. Strictly 

 speaking all cells are radiosensitive, but they differ as to the degree of their 

 sensitivity. 



I believe that among those cell nucleoproteins which begin to show bright 

 fluorescence in the ultraviolet region following irradiation, there are mito- 

 chondrial ribonucleoproteins. but probably also some other types of the cyto- 

 plasmic RNA as well as nucleotides. 



TOBIAS : Did you observe any changes in these same cells under the microscope 

 some time after exposure? Did not the photodynamic effect of the acridine orange 

 manifest itself in the cells ? What changes occur there when you expose them to 

 light for a long time while taking the photographs. 



MEISSEL: In our work we tried to achieve vital fluorescence of the cell. For this 

 purpose fluorescence of the cells fluorochromed with acridine orange was excited 

 not by ultraviolet, but by blue-violet light, which is much less dangerous than 

 ultraviolet. Apart from this, much depends on the exposure during observation 

 and taking j^hotographs. ExjDosure in our work was short, and no distinguishable 

 changes caused by induced fluorescence were observed. W^hen observation was 

 carried out for a longer time distinct photodynamic reactions manifested them- 

 selves in the cells. 



ZEiTLiN: Did any changes occur in the absorption in the short wave ultraviolet 

 region following formation of the complex acridine orange +nucleic acid? 



MEISSEL : The fact is that acridine orange absorbs ultraviolet light in the same 

 region as nucleic acids. As to whether there are changes in the absorption and 

 fluorescence due to complex formation: nucleic acid — diaminoacridine — this is a 

 problem we are studying at present. Important data on this problem have been 



