CO2, light and temperature influence senescence and protein degradation in wheat leaf segments

Effects of environmental conditions influencing photosynthesis and photorespiration on senescence and net protein degradation were investigated in segments from the first leaf of young wheat (Triticum aestivum cv. Arina) plants. The segments were floated on H2O at 25, 30 or 35 degrees C in continuous light (PAR: 50 or 150 mu mol m(-2) s(-1)) in ambient air and in CO2-depleted air. Stromal enzymes, including phosphoglycolate phosphatase, glutamine synthetase, ferredoxin-dependent glutamate synthase, phosphoribulokinase, and the peroxisomal enzyme, glycolate oxidase, were detected by SDS-PAGE followed by immunoblotting with specific antibodies. In general, the net degradation of proteins and chlorophylls was delayed in CO2-depleted air. However, little effect of CO2 on protein degradation was observed at 25 degrees C under the lower level of irradiance. The senescence retardation by the removal of CO2 was most pronounced at 30 degrees C and at the higher irradiance. The stromal enzymes declined in a coordinated manner. Immunoreactive fragments from the degraded polypeptides were in most cases not detectable. However, an insolubilized fragment of glycolate oxidase accumulated in vivo, especially at 25 degrees C in the presence of CO2. Detection of this fragment was minimal after incubation at 30 degrees C and completely absent on blots from segments kept at 35 degrees C. In CO2-depleted air, the fragment was only weakly detectable after incubation at 25 degrees C. The results from these investigations indicate that environmental conditions that influence photosynthesis may interfere with senescence and protein catabolism in wheat leaves.