THE ACTION SPECTRUM OF LIGHT INDUCED AGGREGATION IN POLYSPHONDYLIUM PALLIDUM, AND A PROPOSED GENERAL MECHANISM FOR LIGHT RESPONSE IN THE CELLULAR SLIME MOLDS

¹ Department of Biological Sciences, University of Delaware, Newark, Delaware 19711

In the cellular slime mold, Polysphondylium pallidum, aggregations are induced by a brief period of light coming after a long (5 hour) dark period. The action spectrum of this response was determined by illuminating small populations of amebae with a constant sub-saturation amount of light at each of several different wavelengths and measuring the number of aggregates induced in each case. Peaks in response occurred at 475 and 675 mµ. One of these peaks falls on the absorption maximum of hexane extracted carotenoids from another cellular slime mold, Acrasis rosea, suggesting that the receptor pigment may be a carotenoid.

The light responses of the cellular slime molds are briefly reviewed. It is suggested that the events during light stimulation of aggregation and during other light induced responses may be similar to those which occur during light stimulation of the metazoan retina. In that case, the initial cellular even common to all light responses of the cellular slime molds may be the stimulation of cyclic-AMP production.