THE FUNCTIONAL-ROLE OF 23 KD AND 24 KD POLYPEPTIDES OF THYLAKOID IN MG2+-INDUCED CHANGE OF EXCITATION-ENERGY DISTRIBUTION BETWEEN 2 PHOTOSYSTEMS IN THE CHLOROPLASTS FROM CODIUM-FRAGILE

In contrast to the chloroplasts from higher plants, Mg2+-induced PS-II fluorescence intensity increase does not relate to Mg2+-induced surface charge density decrease of thylakoid in the chloroplasts from Codium fragile. The extraction of the green alga chloroplasts with Ca2+ to remove the 30-31kD polypeptide (Q(B) protein) on the thylakoid surface does not affect the above Mg2+-induced phenomena. If the Ca2+-treated chloroplasts are further digested by trypsin to remove the 23kD and 24kD polypeptides on the membrane surface, the Mg2+-induced fluorescence effect will completely disappear whereas the property of Mg2+-induced surface charge density changes remains unchanged. These results not only show that the 23kDa and 24kDa polypeptides on the thylakoid surface are the specific acting sites of the cation that induce Chla fluorescence change, but also demonstrate that the cation-induced change of excitation energy distribution between two photosystems is not controlled by the electrostatic property of thylakoid surface in the chloroplasts of Codium fragile.