Abstract
Summary The C 3 species Flaveria cronquistii was crossed with the C 4 species F. brownii . Crosses were performed in both directions. The reciprocal hybrids possess a Kranz-like leaf anatomy, but the concentration of bundle-sheath chloroplasts is much lower than in the C 4 parent. The CO 2 compensation concentration (Γ) at 21 % O 2 of F. brownii × F. cronquistii was the same as in the male parent (51 [μl −1 CO 2 . It was significantly lower in the reciprocal hybrid (45 μl 1 −1 ), although not intermediate. Oxygen sensitivity of CO 2 compensation concentration in the range of zero to 50 % oxygen in both hybrids did not differ significantly from that in F. cronquistii . Activities of phosphoenolpyruvate carboxylase and alanine aminotransferase in the hybrids were only slightly higher than in F. cronquistii . The activity of NADP malic enzyme is increased 6- to 8-fold in the hybrids relative to the C 3 parent, whereas the activity of NADP malate dehydrogenase in the hybrids was in the range of the C 4 parent. δ 13 C values of both hybrids are well within the range Of C 3 plants. Taken collectively, the results suggest that in these reciprocal hybrids CO 2 is mainly assimilated by the C 3 pathway of photosynthesis and the C 4 cycle is at most of only minor importance.
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