ADENOSINE 5-TRIPHOSPHATE CONTENT AND ENERGY CHARGE DURING PHOTOMORPHOGENESIS OF THE MUSTARD SEEDLING SIN APIS ALBA L.

Abstract— The contents of ATP, ADP and AMP (enzymatic assay) and the rate of respiration (output of CO₂ per h, continuously measured with an infrared CO₂ analyzer) were determined in long-term experiments with intact dark-grown and far-red-light-grown mustard ( Sinapis alba L.) seedlings. While there is a strong effect of far-red light treatment on the respiratory rate (inhibition as well as promotion, depending on the onset of light), an effect on the contents of adenosine nucleotides, and therewith on energy charge, is hardly detectable. At most, there is a tendency that long-term far-red light slightly lowers ATP levels and energy charge. The results suggest that the adenylate system (and therewith the energy charge) in the mustard seedling is controlled by endogenous homoeostasis even under intense phytochrome-mediated photomorphogenesis. It is unlikely that the levels of adenosine nucleotides or the energy charge are links in any causal chain originating from P_fr and leading to phenomena of photomorphogenesis.