The methyl esterases are perhaps the first to act upon pectin to expose host and 

 pathogen to a low methoxy pectin compound similar to citrus pectin. Upon further 

 activity, a compound void of methyl groups (represented by pectic acid) may be released. 

 Both pine cells and rust mycelium responded negatively to such products. Pine paren- 

 chymatous cells began browning when exposed to a 0.1 percent concentration of citrus 

 pectin, with all explants becoming brown at 0.5 percent. These cells were even more 

 sensitive to pectic acid, becoming brown when exposed to 0.05 percent concentrations 

 and showing complete color change and inhibition of proliferation with the 0.1 percent 

 concentration. Apparently, the rust fungus can tolerate greater concentrations of 

 these compounds than can its host because although growth of the rust was severely 

 suppressed by the 1-percent concentrations, no symptoms of death, such as lysis or 

 color change, were evident. The same responses were noted in the polygalacturonic 

 acid treatment of the rust, i.e., growth was restrained and indicators of death were 

 not evident. 



The life of pine cells and fungus isolates was least affected by the highly 

 water soluble sodium polypectate. The host cells showed a tendency toward color 

 changes from green to brown only in the treatment with the highest concentration 

 (0.5 percent). Increase in pine cell culture size was almost absent. This implies 

 that the polygalacturonic chain may be detrimental to cell proliferation, but also 

 may be beneficial in prolonging the life of cells, possibly as a pH buffer or as an 

 exchange matrix for other molecules. The rust mycelium was the least affected by 

 sodium polypectate in comparison to the other pectin compounds; however, growth rates 

 and total growth were different from those achieved in control treatments. When 

 compared to no treatment, the slow-growing isolate was slightly suppressed and the 

 fast growing isolate apparently received some benefit. 



The pectic compounds tested suppressed growth of both pine host cells and rust 

 mycelium in culture. In this study, the hosts' cells succumbed at lower concentrations 

 of pectic compounds and were more sensitive as the complexity of the pectic compounds 

 decreased than were the rust cells. Deductively, then, in the host -parasite inter- 

 actions between western white pine and the blister rust fungus, the survival of the 

 fungus is dependent upon the tolerance limits of the host. It seems that, regardless 

 of whether the pectinases orignated from host or fungus, control of their activities 

 is mediated through the physiologic status of the parasitized pine cells. 



4 



