DETECTION OF A 10 KDA BREAKDOWN PRODUCT CONTAINING THE C-TERMINUS OF THE D1-PROTEIN IN PHOTOINHIBITED WHEAT LEAVES SUGGESTS AN ACCEPTOR SIDE MECHANISM

Photoinhibition of intact leaves of wheat generates a 10 kDa breakdown product which is clearly observed both at 4-degrees-C and 25-degrees-C. Selective immunoblotting has shown that the 10 kDa fragment contains the C-terminus of the D1-protein and, under the conditions employed, supports an acceptor side mechanism for photoinhibition in vivo. Although a corresponding 23 kDa N-terminal D1-fragment was not detected our results are consistent with the argument that the primary cleavage site is in the loop joining putative transmembrane segments IV and V.