PHYSIOLOGY AND BIOCHEMISTRY OF RESISTANCE TO PINE RUSTS 473 



to 5) appeared around susceptible slash primary tissue but not around 

 resistant slash secondary needles or shortleaf primary tissue. Suscep- 

 tibility was therefore correlated with ability to lower the pH of agar by 

 diffusion from intact tissue and induce direct germination and germ-tube 

 growth. Water and organic solvent extracts also promoted direct germina- 

 tion, in this case without affecting pH. Miller (1968) found that extracts 

 from slash and loblolly needles stimulated direct germination of C. 

 fusi forme basidiospores on agar. Nighswander and Patton (1965) obtained 

 direct germination of C. quercuum basidiospores on water agar by including 

 a decoction of oak or pine foliage. 



BIOCHEMISTRY OF PROMOTERS AND INHIBITORS 



Anthocyanin pigments extracted from red-stemmed cold-grown slash pine 

 seedlings which were partially resistant promoted direct germination and 

 germ-tube growth at less than 1 ppm. They inhibited both processes at 

 slightly higher concentrations (Hare, 1970) . Water-soluble vacuole pig- 

 ments were much more effective than lipid fractions and chloroplast 

 pigments. Diffusates of intact seedlings shaken in water were more 

 effective than aqueous homogenates, perhaps due to enzyme inactivation by 

 phenols released from ruptured cells. High activity of acetone powder 

 extracts and instability to heat also suggest enzyme participation. 



The neutral fraction from ethyl acetate-buffer partitioning of 

 alcoholic extracts was most active in inducing direct germination and 

 germ-tube growth on agar. Some fractions from slash pine seedlings 

 promoted long, thin-walled germ tubes; the same fractions from shortleaf 

 either gave no germination or germ tubes were thick-walled, branched, and 

 septate (cf. Patton and Nicholls, 1966). While there were great differ- 

 ences in the effects of various extract fractions, correlation with 

 resistance was lower than with water diffusates from intact tissues. 



PROTEIN AND ISOZYME PATTERNS ASSOCIATED WITH RESISTANCE 



Differences in proteins and enzymes would be expected between rust- 

 susceptible and rust-resistant tissues. First, heritable resistance 

 factors depend on genes which code for specific enzymes that ultimately 

 prevent establishment of infection (Shaw, 1963). Second, various enzymes, 

 particularly oxidases, have been associated with resistance mechanisms 

 against many fungal diseases. Many workers have shown that the activity 

 of certain enzymes rises in response to infection, especially in resistant 

 plants (Metlitskii and Ozeretskovskaya, 1968) . Many of the newly formed 

 proteins are new isozymes of enzymes already present, particularly PPO, 

 peroxidase, malic and succinic dehydrogenases, and acid and alkaline 

 phosphatases. These new isozymes may be more resistant to fungal break- 

 down than the original enzyme or they may increase the effectiveness of 

 fungitoxic substances. 



Differences in proteins and isozymes have been associated with resis- 

 tance to a number of plant diseases (Kiraly and Farkas, 1957; Kedar, 1959; 

 Heitefuss et at. , 1960; Rudolph and Stahmann, 1964; Rubin, Ivanova, and 

 Davydova, 1964; Andreev and Shaw, 1965; Fehrmann and Dimond, 1967; 

 Sokolova and Zvyagintseva, 1968; Macko, Woodbury, and Stahmann, 1968). 

 Other workers have not reported electrophoresis-pattern differences 

 associated with resistance to tree rusts, but Koenigs (1966) reported 

 cytochemical analyses for dehydrogenases in blister-rust infected P. 

 montioola and Eibes. 



