Date of Award


Degree Type


University or Center

Atlanta University (AU)

Degree Name




First Advisor

Dr. E.L. Stevenson


The isoenzyme patterns of three enzymes and the ultrastructural changes of Rutgers tomato plants were determined after infection with Potato Spindle Tuber Viroid. Electrophoresis of the protein extract in polyacrylamide gels fol lowed by staining for malate dehydrogenase, esterase, and peroxidase showed that only peroxidase was affected by the infection. Two new bands of the isoenzyme were detected in protein extracts of infected tissues. It is suggested that these bands represent the molecular symptoms of the disease.

Thin sections of diseased tissues examined with the electron microscope revealed cytopathic modifications such as the interruptions of the nuclear membrane, increased vacuolation of diseased cells, increased production of peroxisomes, the formation of paramural bodies, and the reduction of starch granules in the chloroplast.

Increased vacuolation of diseased cells suggests that PSTV infection speeds up the aging process in the tissues.The increased production of peroxisomes might contribute to the extrasynthesis of peroxidase. The formation of paramural bodies suggests a host response to the invading pathogen and may function as a mechanism to block further spread of the pathogen to other cells. And finally it is possible that the reduction in starch granules could result from an inhibi tion of starch synthesis or the increased translocation of this photosynthetic product out of the chloroplast.

Included in

Biology Commons