PHOTOSYNTHETIC CHARACTERISTICS OF C3-C4 INTERMEDIATE FLAVERIA SPECIES .3. REDUCTION OF PHOTORESPIRATION BY A LIMITED-C4 PATHWAY OF PHOTOSYNTHESIS IN FLAVERIA-RAMOSISSIMA

The initial products of photosynthesis by the C3 species F. cronquistii, the C4 species F. trinervia and the C3-C4 intermediate species F. ramosissima were determined using a pulse-chase technique with 14CO2-12CO2. The intermediate species F. ramosissima incorporated at least 42% of the total soluble 14C fixed into malate and aspartate after 10 s of photosynthesis in 14CO2, as compared with 90% for the C4 species F. trinervia and 5% for the C3 species F. cronquistii. In both F ramosissima and F. trinervia, turnover of labeled malate and asparate occurred during a chase period in 12CO2, although the rate of turnover was slower in the intermediate species. Relative to F. cronquistii, F. ramosissima showed a reduced incorporation of radioactivity into serine and glycine during the pulse period. A functional C4 pathway of photosynthesis is apparently operating in F. ramosissima which can account for its reduced level of photorespiration. This species is a true biochemical intermediate between C3 and C4 plants.