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

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.