Photosynthesis

The u s e of t r a c e r carbon, a s carbon-14, h a s m a d e possible consider-able p r o g r e s s in the mapping of the routes taken by the carbon a t o m f r o m CO into plant substances. The techniques of separation and identification t h a t h a v e made this p r o g r e s s possible lie largely in the region of chromatography and radioautography involving fractional g a m m a amounts of material. Most of the e a r l i e r steps of carbon incorporation a r e now known and will b e described. In addition, a number of the l a t e r steps on the routes to amino acids and proteins and other plant substances a r e now under investigation. A s a r e s u l t of the recognition of the e a r l i e r stages of carbon incorporation, a number of proposals have been postulated about the photochemical a c t itself. These proposals have led to the development of d i r e c t physical t e s t s of their validity and some r e s u l t s of these will b e described. The remaining principal a r e a of investigation involving the route of oxygen a t o m s f r o m water t o molecular oxygen i s largely unexplored, but the u s e of new methods of analyzing f o r the heavy isotopes of oxygen may m a k e m o r e p r o g r e s s in this a r e a possible.