The Effect of an Antiserum to Plastocyanin on Various Chloroplast Preparations

Abstract

A monospecific antiserum to tobacco plastocyanin agglutinates stroma-free swellable chloroplasts from wild type tobacco, (Nicotiana tobacum var. John William's Broadleaf) from the tobacco aurea mutant Su/su2, (Nicotiana tabacum var. Su/su2) from Antirrhinum majus and spinach (Spinacia oleracea). In this condition the antiserum inhibits linear photosynthetic electron flow in tobacco and spinach chloroplasts. This inhibition of electron transport as well as the agglutination are not observed if the chloroplasts have been sonicated prior to antiserum addition. This is due to the fact that plastocyanin is removed by ultasonication. The antiserum stimulates a number of photophosphorylation reactions in tobacco chloroplasts. This stimulation is always larger in the aurea mutant chloroplasts from yellow leaf patches of a variegated tobacco mutant (N. tabacum, var. NC 95) than in the green type chloroplasts. The stimulation appears to be a consequence of the inhibition of linear electron transport. The antiserum does not affect PMS-mediated cyclic photophosphorylation in tobacco chloroplasts from the wild type whereas the reaction appears stimulated in the tobacco mutant chloroplasts. However, menadione-mediated cyclic photophosphorylation is inhibited upon addition of the antiserum. The same is true for noncyclic photophosphorylation coupled to electron transport in the aerobic system diaminodurene/ascorbate leads to methylviologen in the presence of N-tetraphenyl-p-phenylenediamine in spinach chlorplasts. If the lamellar system of Antirrhinum and spinach has lost is swellability neither agglutination nor inhibition of electron transport is observed. However, also in this state antibodies to plastocyanin are specifically adsorbed onto the surface to the thylakoid membrane. This state which is characterized by a morphologically well preserved lamellar system is realized in chloroplast preparations from Antirrhinum and spinach and is termed stroma-freed chloroplasts. In both states of the molecular structure of the thylakoid membrane, plastocyanin is located in the outer surface of the thylakoid. However, it cannot be excluded that functioning plastocyanin is also located in the interior of the thylakoid membrane.