THE STIMULATING EFFECT OF A COLD, DARK PRETREATMENT ON THE ETIOPLAST/CHLOROPLAST TRANSFORMATION OF ANGIOSPERMS–II. SYNERGISM BETWEEN RED-LIGHT and COLD PRETREATMENT ON THE CO2- and O2-GAS-EXCHANGE OF WHEAT LEAVES

Abstract— Recently we reported on the stimulating effect of a cold, dark pretreatment on the processes of greening of dark-grown angiosperms under continuous white light (Schönbohm et al., 1988; Physiol. Plant. 72 ,541–546). These effects could be nullified by a subsequent second dark phase (25°C) which precedes the white light period. Our analysis was now focused on the effect of cold, dark pretreatments (with or without red-preirradiation) on the gas exchange (O₂; CO₂) of etiolated primary leaves of wheat during a subsequent white light period. The following results were obtained: (1) The net-O₂-consumption under continuous white light decreased much more quickly after a cold than after a warm pretreatment. (2) This effect was enhanced by red-preirradiation. (3) The O₂-compensation point was reached more quickly during the de-etiolation period when the leaves had been subjected to a cold instead to a warm pretreatment. (4) The “cold-effect” could be nullified by a subsequent warm, dark pretreatment (in this material the compensation point could not be reached within 8 h). (5) Cold treated material which had also been exposed to red light showed during the first 30 min of de-etiolation an extremely strong ^“out-burst” of CO₂. No correlation was apparent between the O₂-uptake and this high CO₂-release. (6) A cold, dark pretreatment induces a decrease of CO₂-release during the second half of the de-etiolation period. This effect could be nullified by a secondary warm, dark treatment given after the cold, dark pretreatment. Our experiments indicate that red-preirradiation and cold, dark pretreatment stimulate chlorophyll synthesis (Schonbohm et al., 1988) and also photosynthetic O₂-evolution and CO₂-uptake. We also assume that this pretreatment causes CO₂ release that is neither directly related to the respiratory electron transport chain nor to the photorespiration.