Photosynthetic Characteristics of C 3 -C 4 Intermediate Flaveria Species

Abstract

Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C3-C4 plants based on leaf anatomy, photosynthetic CO2 compensation point, O2 inhibition of photosynthesis, and activities of C4 enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C4 species F. trinervia, while the other C3-C4 intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO2 compensation points of these intermediates at 30°C were very low relative to those of C3 plants, ranging from 7 to 14 microliters per liter. In contrast to C3 plants, net photosynthesis by the intermediates was not sensitive to O2 concentrations below 5% and decreased relatively slowly with increasing O2 concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O2 varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C3 species. The inhibition of carboxylation efficiency by 21% O2 varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C4 (2% for F. trinervia) and C3 (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C4 enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C4 photosynthesis. It appears that these Flaveria species may be true biochemical C3-C4 intermediates.