Photosynthetic and Photorespiratory Characteristics of Flaveria Species

Abstract

The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C3, C3-C4, C4-like, and C4 plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C3-C4 intermediates showed an inverse continuum in level of photorespiration and development of the C4 syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C4 photosynthesis to F. Among the intermediates, the photosynthetic C02 compensation points at 300C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C4-like species varied from 3 to 6 microbars, similar to those measured for the C4 species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypynrvate reductase, and serine hydroxymethyltransferase decreased progressively from C3 to C3-C4 to C4-like and C4 species. On tlh other hand, most intermediates had higher levels of phosphenaIhuvate carboxylase and NADP-malic enzyme than C3 species, but generally lower activities compared to C4-like and C4 species. The levels of these C4 enzymes are correlated with the degree of C4 photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C4 syndrome in C3-C4 Flaveria species was their intermediate chlorophyll a/b rafos. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C4 photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C4 pathway. In the progression from C3 to C4 species in Flaveria, the CO2 compensation point decreased more rapidly than did the decrease in 02 inhibition of photosynthesis or the increase in the degree of C4 photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO2 and prior to substantive reduction in 02 inhibition and development of the C4 syndrome. However, further reduction in 03 inhibition in some intermediates and C4-like species is considered primarily due to the development of the C4 syndrome. Thus, the evolution of C3-C4 intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO2 concentration first via refixation of photorespired C02, followed by development of the C4 syndrome.

Modification of Photosystem I Light Harvesting of Bundle-Sheath Chloroplasts Occurred during the Evolution of NADP-Malic Enzyme C4 Photosynthesis

“…1). Our values of r from Flaveria agree with previously published data (Holaday et al, 1984;Ku et al, 1991). On this basis, we can compare the new results achieved here with the known characteristics for the different Flaveria species.…”

Degree of C4 Photosynthesis in C4 and C3-C4Flaveria Species and Their Hybrids

“…Variable degrees of development of C4 photosynthesis have been described for C3-C4 and C4-like species in the genus Flaveria (6,8,9,[16][17][18]20 …”

“…

ABSTRACTenzyme activities and compartmentation, anatomy, and coordination of the carbon accumulation (mesophyll metabolism) and reduction (bundle sheath metabolism) portions of the C4 cycle (9,16,19).A large number of interspecific Flaveria hybrids between photosynthetic types have been made, and these plants also exhibit variable degrees of C4 photosynthesis (1, 2, 4, 5, 7, 11). In a companion paper (4), we described the 14CO2 assimilation and turnover of photosynthetic metabolites along with CO2 exchange and 613C of four such hybrids involving Flaveria trinervia (C4), Flaveria brownii (C4-like), and Flaveria linearis (C3-C4).

…”

“…Photosynthesis of several C4 species was inhibited 79 to 98% by 1 mnvm DCDP (13). Brown et al (3) found that 1 mi DCDP inhibited photosynthesis of F. trinervia by 72 to 80%, and they used the inhibitor to assess the degree of C4 photosynthesis in C3-C4 intermnediate species of Flaveria, Panicum, Moricandia, and Neurachne.Variable degrees of development of C4 photosynthesis have been described for C3-C4 and C4-like species in the genus Flaveria (6,8,9,[16][17][18]20 …”

“…enzyme activities and compartmentation, anatomy, and coordination of the carbon accumulation (mesophyll metabolism) and reduction (bundle sheath metabolism) portions of the C4 cycle (9,16,19).…”