Über die wirkung des phytochroms beim laubmooskallus II. Sauerstoffmetabolismus und acetylcholinwirkung

Abstract

The oxygen metabolism is a good parameter for the determination of rapid responses of green moss callus to light. We measured the oxygen uptake with the Warburg method and polarographically with a Clark electrode and the YSI-oxygen monitor. The exposure of dark grown moss callus to red light (5–20 min) induced a rapid increase in O 2 -uptake after switching off the light. The respiration change depends on the exposure duration and the light intensity. During the first 2 or 3 h after irradiation with red light and with red-far red light, the rates of the O 2 -uptake show no differences but after this lag-phase the 2 curves are splitting. The respiration of the red irradiated cells remained higher over a period of 23 h compared to the red — far red irradiated cells. In the latter case the respiration reached the value of the dark control after 20 h. We could reverse the red effect of the rapid respiration change immediately with far red, using an irradiation apparatus with a rhythm of 0.45 s red — far red without a dark-phase. The acetylcholine (ACh) interactions with these light qualities were very complex. ACh was only physiologically active when the cofactor ascorbic acid was present. ATP is an additional cofactor for the ACh action with red — far red induced processes. There are great differences between ACh effects in long time experiments (like our Warburg tests) and in short time ones. ACh had no effect on the oxygen output or uptake when the cells were irradiated with red light, in contrast to the effect occuring with quick alternating red — far red illumination. In this case ACh promotes the oxygen output. This effect is inhibited by eserine. The complex manner of ACh effects is indicated by the results which we got from Warburg experiments. The application of ACh together with the onset of red irradiation has no effect independent of the ATP content of the substrate. We got the opposite results in experiments were we applied the hormone after the red illumination. In this case ACh mimicked a far red effect. ATP in the substrate nullified the ACh-action. We got exactly antagonistic ACh-effects with red — far red light treatments. In this case we had to apply the hormone with the onset of the irradiation. Then ACh mimicked a red light effect but only with ATP as cofactor. The physiological effects of red irradiations in moss callus grown in darkness or in continuous far red light cannot be mimicked by ACh. ACh becomes active after or during the irradiation. Light is necessary for ACh effects. Therefore, we think one cannot consider this hormone as being a special phytochrome hormone.