474 ROBERT C. HARE 



Hare (1970) compared extracts from fusiform rust-resistant and 

 -susceptible tissues for protein and isozyme patterns (zymograms) of 14 

 enzymes, by polyacrylamide-gel-disc electrophoresis. The purpose was to 

 find a protein or isozyme that is always associated with resistance or 

 susceptibility. Such a substance might be used as a genetic marker and, 

 if identified as a specific enzyme, might provide a clue to a resistance 

 mechanism. 



Similar organs of all southern pines yield remarkably similar protein 

 patterns, but several bands differ between similar susceptible and 

 resistant tissues, e.g., the eastern and western loblolly seed source 

 differences already described. Protein patterns from older resistant 

 slash seedlings more closely resemble patterns from young resistant 

 shortleaf than those from young susceptible slash. 



Zymograms tend to vary more than protein patterns, perhaps because 

 enzyme stains are frequently more sensitive than protein stains. Oxidases 

 that may be important in disease-resistance mechanisms include IAAO, PPO, 

 ascorbic acid oxidase, and peroxidase (Hare, 1966). Zymogram differences 

 in all of these except IAAO have been shown between fusiform-rust resis- 

 tant and susceptible southern pines (Hare, 1970). We have not succeeded 

 in detecting the products of IAA oxidation on acrylamide gels, but this 

 enzyme is apparently a form of peroxidase (Hare, 1964) . 



The role of PPO and IAAO in resistance and gall formation has already 

 been discussed. Peroxidase may also oxidize phenols to more fungitoxic 

 quinones in the presence of organic peroxides (Fehrmann and Dimond, 1967). 

 Ascorbic acid is a strong reducing agent frequently found in the cell 

 wall (Newcomb , 1963). It prevents the browning reaction following 

 wounding by keeping the phenols reduced; thus it may decrease resistance 

 by inhibiting PPO activity. Ascorbic acid oxidase, therefore, may 

 promote resistance by its sparing action on the toxic quinones (Hare, 

 1970) . 



Several dehydrogenases have zymogram differences associated with 

 fusiform rust resistance (Hare, 1970). Glucose-6-phosphate dehydrogenase 

 participates in the pentose phosphate shunt, which is important in disease 

 resistance (Farkas and Kiraly, 1962). Zymograms of this enzyme consis- 

 tently differ depending on whether extract are from fusiform rust- 

 resistant or -susceptible southern pines. Malic and alcohol dehydro- 

 genases are also very active and have zymogram differences related to 

 rust resistance. 



LITERATURE CITED 



Allen, P. J. 1959. Physiology and biochemistry of defense, p. 435-467. 

 In J. G. Horsfall and A. E. Dimond (ed.), Plant pathology. Vol. I. 

 Academic Press, New York 674 p. 



Anderson, 0. C. 1939. A cytological study of resistance of Viking 

 currant to infection by Cronartium ribioola. Phytopathology 29: 

 26-40. 



Andreev, L. N., and M. Shaw. 1965. A note on the effect of rust infec- 

 tion on peroxidase isozymes in flax. Can. J. Bot. 43: 1479-1483. 



Barrett, R. E., and J. H. McLaughlin. 1954. Disease resistance factors 

 in wheat; electrophoretic and chromatographic analysis of protein 

 extracts of wheat seedlings. J. Agr. and Food Chem. 2: 1026-1029. 



