| Popis: |
Summary The induction phase of C02 fixation of intact attached bean leaves was examined at 25°C under two different photon flux densities (242 and 833 μmol photons m−2 s−1) and after dark periods of different durations (0. 5, 1, 3, 6, 12, and 24 h). During a 50 minute time period following the dark/light change, the transient of the C02 fixation was analysed. The values used were IVmax (= the maximal induction velocity) and Γt (= the time compensation point). Γt rose with the duration of the dark period from about 98 s to about 360 s. IVmax decreased under the same conditions from 0.034 to 0.003 μmol C02 m−2 s−2 under strong light, and from 0.002 to 0.006 μmol C02 m−2 s−2 under moderate light. These results suggest that Γt and IV-max are related to different metabolic patways. Γt seems to be correlated to the activation of the Calvin cycle. IVmax is basically determined by the supply of assimilatory power created by the given light conditions and is modified by the adaptation velocity of the pool sizes of appropriate Calvin cycle intermediates. A second result of these examinations is that plants start C02 fixation faster than expected if the duration of the dark period equals the duration of the cultivation period. A very long dark period of 24 h leads to an injury of the photosynthetic apparatus. A very slow increase of the C02 fixation can be noticed. |
