380 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



by their antibiotic production is unknown, as is their effect on crop 

 plants. 



An American audience may well be interested in the comments 

 coming from a leading Russian scientist on this fundamental subject. 



We enriched the soil artificially with actinomycetes — producers of strepto- 

 mycin, and we grew in this soil plants — peas and wheat. The sap of such plants 

 was tested for its bactericidal effect on Bac. mycoides and Staph, aureus. 

 Death of the bacterial cells in the sap of the experimental plants followed after 

 8-12 hours, and in the sap of the control plants which were grown in soil not 

 enriched with actinomycetes, there was only suppression of growth, but death 

 of the bacteria was not observed. 



The extrapolation of these results to nature is expressed by 

 Krasil'nikov as a very intriguing hypothesis of plant immunity ! 



Actinomycetes, bacteria, and fungi which produce antibiotic substances grow 

 in the soil in the rhizosphere of plants [rhizosphere means in the immediate 

 vicinity of the roots]. They saturate this zone or microfoci in the soil with 

 the products of their metabolism, including antibiotics. The latter enter the 

 plants through the roots and exert their action there. It is self-evident that the 

 concentration of antibiotics in soil, when formed under natural conditions, will 

 be lower than the concentrations ci'eated upon artificial introduction. How- 

 ever, under natural conditions these substances are constantly formed and there- 

 fore one would assume that their entrance into plants is not stopped during the 

 whole vegetative period. 



Having entered the plant tissues substances protect them against the penetra- 

 tion of microbial parasites, suppress the growth of those that have already 

 invaded, produce or elevate the toxicity of the plant sap, and thus elevate to a 

 larger or smaller extent the immunological properties of the plant. 



In other words, microbial agents are factors which increase the resistance and 

 insusceptibility of plants to infection." 



In this article, I have deliberately selected items of botanical interest 

 in the field of antibiotic research and development. It is not too 

 generally appreciated that the source of most of these remarkable 

 drugs has been lower plants whose structure, life history, natural 

 occurrence, isolation, and identification have been the concern of 

 botanists. Other specialists, including the bacteriologists, engineers, 

 chemists, druggists, agriculturists, nutritionists, veterinarians, clini- 

 cians, and medical doctors, have each made their unique and great 

 contributions to the discovery, development, and use of antibiotics. 



One is sobered on reflection that these natural products, which 

 assuage man's suffering and increase his food supply, came into his 

 keeping in an era of cruel wars and unprecedented population upsurge. 



" N, A. Krasirnikov, Soil Microorganisms and Higher Plants, p. 385, 1961. 



