ACTION OF ULTRAVIOLET RADIATION ON PROTOPLASM

Abstract

The main object of this review is to assess present knowledge of the fundamental action of u.-v. upon protoplasm. The general effects summarized include bactericidal, fungicidal, viricidal, photolethal in plants, photolethal in animals, harmful effects on culture media, sensitization to heat, retardation of cell division, acceleration of cell division, retardation of growth in tissue culture, impairment of N metabolism, impairment of carbohydrate uptake, impairment of adaptive enzyme formation, stimulation of endogenous metabolism, impairment of exogenous metabolism, changes in fermentation, activation of eggs, stimulation of muscle contraction, impairment of motility, impairment of excitability of nerve. They indicate that the cell is affected at the surface, in the nucleus, and in the cytoplasm. Other effects, upon respiration, excitability and growth probably involve the entire cell. Action spectra, comparing the efficiency of various wavelengths of the u.-v. spectrum, are discussed because they are believed to give approx. the absorption spectrum of the compound which mediates the u.-v. effect, though in no case is perfect agreement obtained between action spectra and absorption by any of the compounds known to exist in protoplasm. However, in most studies the action spectra resemble absorption by proteins and nucleic acid. Hence the author analyzes the effects of radiations on proteins and nucleic acid or nucleoproteins. The sensitization of cells to heat by a preceding exposure to u.-v. is discussed as analogous to similar sensitization of proteins. Finally, the very recently discovered phenomenon of photoreactivation (reversal of u.-v. damage by illumination with visible light) opens up a fresh field for harvesting evidence on the nature of u.-v. damage to protoplasm.