Chlorella was used to study the effects of
dehydration on photosynthetic activities. The use of unicellular green algae assured that the extent of
dehydration was uniform throughout the whole cell population during the course of desiccation. Changes in the activities of the cells were monitored by measurements of fluorescence induction kinetics. It was found that inhibition of most of the photosynthetic activities started at a similar level of cellular water content. They included CO2 fixation, photochemical activity of
Photosystem II and electron transport through
Photosystem I. The blockage of electron flow through
Photosystem I was complete and the whole transition occurred within a relative short time of
dehydration. On the other hand, the suppression of
Photosystem II activity was incomplete and the transition took a longer time of
dehydration. Upon
rehydration, the inhibition of
Photosystem II activity was fully reversible when samples were in the middle of the transition, but was not thereafter. The electron transport through
Photosystem I was also reversible during the transition, but was only partially afterward.