IN-SITU EVIDENCE THAT CHILLING IN THE LIGHT DOES NOT CAUSE UNCOUPLINGOF PHOTOPHOSPHORYLATION OR DETACHMENT OF COUPLING FACTOR IN CHILLING-SENSITIVE PLANTS

The potential involvement of impaired photophosphorylation in the chil ling sensitivity of photosynthesis in warm climate plant species has b een a topic of investigation for more than two decades. With recent ad vances in the analysis of photosynthetic energy transduction in intact leaves, experiments are now possible that either address or avoid imp ortant uncertainties in the significance and interpretation of earlier in vitro work. Nevertheless, different laboratories using different t echniques to analyze the effects of chilling in the light on photophos phorylation in intact cucumber (Cucumis sativus) leaves have come to v ery different conclusions regarding the role of impaired ATP formation capacity in the inhibition of net photosynthesis. In order to evaluat e these discrepancies and bring this issue to a final resolution, in t his investigation, we have made a detailed analysis of the decay of th e flash-induced electrochromic shift and changes in chlorophyll fluore scence yield in cucumber leaves before, during and after a 5 h light-c hill at chill temperatures of between 4 and 10 degrees C. We feel that our findings address the major discrepancies in both data and interpr etation as well as provide convincing evidence that photophosphorylati on is not disrupted in cucumber leaves during or after light and chill ing exposure. It follows that impaired photophosphorylation is not a c ontributing element to the inhibition of net photosynthesis that is wi dely observed in warm climate plants as a result of chilling in the li ght.