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GROWTH ASPECTS OF 

 PLANT VIRUS INFECTIONS 



Glenn S, Pound 



UNIVERSITY OF WISCONSIN 



The self-replication of plant viruses is one of the least understood and 

 most intriguing phenomena of biological growth. Plant viruses are re- 

 produced only in living cells and apparently by the living cells. Their 

 synthesis results from an aberration of nucleoprotein metabolism, the 

 alteration being initiated by the presence of the virus, the nucleic acid 

 of which presumably serves as a template for xdrus duplication. There- 

 fore, the growth aspects of \'irus infections, embracing both the host 

 and the pathogen, are those of the physiology of the infected plants. 

 One short paper cannot give consideration to all aspects of such growth. 

 This paper will deal only with anatomical and physiological aspects of 

 virus-infected plants and with the relation of certain environmental 

 factors to host growth and virus synthesis. It does not purport to con- 

 sider every aspect of these areas of growth but only the more common 

 phenomena. 



Virus effects on host anatomy 



When one looks at the anatomy of virus-infected plants, he sees 

 the same basic pathological efiFects characteristic of other plant dis- 

 eases: namely, hypoplasia (underdevelopment), hypertrophy (over- 

 growth due to excessive cell size), hyperplasia (overgrowth due .to 

 excessive cell division), and necrosis (death of tissue). These are not 

 always evident as single effects but in most cases occur in combinations. 



Viruses causing "mosaic" diseases are generally found in all tissues 

 of the host, but their anatomical efiFects are primarily related to paren- 

 chyma tissue. They characteristically cause a reduction in the number 



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