PHOTOSYNTHETIC SHUTDOWN IN CHLORELLA NC64A ASSOCIATED WITH THE INFECTION CYCLE OF PARAMECIUM-BURSARIA CHLORELLA VIRUS-1

The effects of the algal Virus Paramecium bursaria Chlorella virus-1 o n the photosynthetic physiology of its host, Chlorella NC64A, was stud ied by observing changes in Chi fluorescence quenching and 0(2) exchan ge. Metabolic changes were calibrated against electron microscopic ana lysis of the morphological changes that occur during the infection cyc le. It takes approximately 10 h from attachment of the virus to final lysis of the host cell, so a complete infection cycle can be observed continuously in one experiment. During the early stages of the infecti on cycle many rapid changes occurred in the host cell's metabolism and these were reflected in changes of photosynthetic and respiratory rat es. The dramatic inhibition of photosynthesis in Chlorella NC64A cells by P. bursaria Chlorella virus-1 has facilitated the use of fluoresce nce quenching as an accurate measure of the first phase of viral infec tion (attachment and penetration of the host cell) and the extent to w hich a population of host cells is infected. Effects of temperature an d cation requirement of the infection cycle are described. The relevan ce of our observations to the events observed during viral infection o f higher plants is discussed.