| Abstrakt: |
In order to investigate the effects of photosynthesis on nitrogen fixing nodules, gas exchanges of shoot and nodulated-root were measured under continuous exposure of the nodulated root to 10 % C2H2during 24 h. This exposure to C2H2induced inhibitions of photosynthesis (P) and nodule C2H2reduction activity (ARA), the latter differing from the well-known short-term C2H2-induced decline of nitrogenase by a longer lag before ARA decreased. Photosynthesis, transpiration and ARA were inhibited by 50, 25 and 20 %, respectively, 2, 4 and 6 hours after the beginning of the exposure to C2H2. The inhibition of P was also observed with 5 and 2 % C2H2, and with 50μL L-1C2H4, but in these cases there was no subsequent inhibition of nodule ARA. On the other hand, inhibition of P by C2H2was also observed with non-nodulated plants. These results suggest that C2H2may have a C2H4-hormone-like action, although with a 2 × 103times lower efficiency than C2H4, and that the inhibition of ARA was not a direct consequence of the inhibition of P. It is suggested that the ARA assay under C2H2concentrations as low as 5 % may be one way to avoid the above described inhibition of in vivonitrogenase activity. |
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