The photosynthetic electron transport capacity of chloroplasts prepared from needles of unhardened and hardened seedlings of Pinus silvestris

Abstract

1. 1. Based on an equal Chl basis, the photosynthetic electron transport capacity from water to NADP was 2.5 times lower in hardened than in unhardened seedlings of Pinus silvestris. 2. 2. Studies of the photosynthetic partial reactions and of the fluorescence kinetics at -5°C suggested that the pool size of P (probably plastoquinone) on the reducing side of PSII was rate-limiting for saturated electron transport in hardened seedlings. 3. 3. The ratios of Chl/Cyt f and Chl/Cyt b (tot.) were not influenced by the hardening process. However, there were changes between the different in vivo Cyt b forms. The hardening caused a reduction of Cyt b-559HP while Cyt b-559LP and Cyt b-6 increased. 4. 4. The temperature dependence for the electron transport from water to NADP and for the partial reactions H 2O → DPIP and Asc → NADP were studied between 0 and 30°C. Arrhenius plots of these reactions revealed no significant differences between unhardened and hardened seedlings in the activation energy for the photosynthetic electron transport.