Photosynthetic Reactions of Chloroplasts with Unusual Structures

Photosynthetic reactions of whole leaves and isolated chloroplasts from various mutants of Nicotiana tabacum have been correlated to the lamellar structure seen in electron micrographs of the chloroplasts. In this way it could be established that a fully active photosystem I can be associated with single unfolded thylakoids. The complete photosynthetic electron transport system including the oxygen evolving apparatus of photosystem II, on the other hand, appears to require a close packing of at least 2 thylakoids. The unusual high capacity for photosynthesis observed earlier for leaves of certain aurea mutants is reflected by a correspondingly high activity of the isolated chloroplasts in the Hill reaction. These chloroplasts contain extended areas where 2 thylakoids touch by forming simple lamellar overlappings instead of the familiar stacks of lamellar discs.