STORAGE AND IMMOBILIZATION OF PHOTOSYSTEM-II REACTION CENTERS USED INAN ASSAY FOR HERBICIDES

Significant improvements in a previously described method for detectio n of herbicides at nanogram per milliliter concentrations are describe d. The activity of photosystem II reaction centers from spinach thylak oids was extended from hours to over 6 months by rapid freezing and st orage at -70 degrees C in appropriate cryoprotection media. Freeze-dri ed reaction centers were also stable for at least 3 months at 4 degree s C. Reaction centers immobilized in calcium alginate gels retained ac tivity for 1 week at 4 degrees C, and immobilization permitted optical and chemical interference by milli samples to be eliminated.