Planta (1983) 158: 54-62 Planta 9 Springer-Verlag 1983 The blue-light reaction in plasmodia of Physarumpolycephalum is coupled to respiration W. Korohoda*, Z. Shraideh**, Z. Baranowski*** and K.E. Wohlfarth-Bottermann**** Institut fiir Cytologic der Universit~it, Ulrich-Haberland-Strasse 61 a, D-5300 Bonn 1, Federal Republic of Germany Abstract. The influence of inhibitors of energy me- tabolism (2-deoxy-D-glucose, monoiodoacetate, KCN) as well as various substrates for respiration (sodium acetate, glycine, glutamine, e-ketoglutar- ate, pyruvate) were investigated with respect to the effect of blue light (450 nm) on contractile behav- iour of plasmodial strands of Physarum polycepha- lure. When the energy metabolism is not experi- mentally modified, blue light induces a prolonga- tion of the period of the contraction-relaxation cy- cle. This effect appears within 2-3 min and seems to represent the primary reaction of this organism to blue light. Inhibition of respiration by KCN completely abolished this response to blue-light ir- radiation. In contrast, an impediment of glycolysis enhanced the effect. This indicates that the reaction to blue light is related to respiration, i.e., to the function of mitochondria. Among different sub- strates for respiration only ~-ketoglutarate com- bined with pyruvate and applied in the presence of inhibitors of glycolysis showed an enhancement of the photoresponse, i.e., a prolongation of the period and an increase of the amplitude of the force oscillations. This indicates that the pyruvate and ~-ketoglutarate-dehydrogenase complexes functioning in mitochondrial respiration are in- volved in the primary blue-light reaction of plas- modia of Physarum polycephalum. * Supported by the Deutsche Forschungsgemeinschaft as Visiting professor at the University of Bonn. Permanent address: Institute of Molecular Biology, Jagiellonian Uni- versity, Cracow, Poland ** Supported by a fellowship from the Deutscher Akade- mischer Austauschdienst *** Supported by a fellowship from the Alexander yon Hum- boldt Stiftung. Permanent address: Nencki-Institute of Experimental Biology, Polish Academy of Sciences, Warszawa, Poland **** To whom correspondence should be addressed Abbreviations: 2dGlc=2-deoxy-D-glucose; MIA=monoiodo- acetate; ekG = c~-ketoglutarate; PA = pyruvic acid Key words: Blue-light reaction - Glycolysis - Pho- totaxis - Phototransduction - Physarum - Respira- tion. Introduction Initial observations concerning the effects of light irradiation on protoplasmic shuttle streaming in plasmodia of acellular slime molds were reported 70 years ago by Vouk (1913). The author described irregularities in the shuttle-streaming periodicity as a consequence of daylight illumination. In small plasmodia, streaming in the direction of the front area coincides with the contraction phase of the posterior strand network. Vouk (1913) described that this ~ progressive" streaming phase has a lon- ger duration compared with the "regressive" streaming duration. A velocity analysis of both phases (Vouk 1913, Fig. 3) showed an irregularity in the sinusoidal form only in the "progressive" phase, most likely identical to the contraction phase mentioned above. This means that both a longer duration and an irregular course of the con- traction phase (Baranowski et al. 1982) can be traced back to early observations of shuttle- streaming phenomena as described by Vouk (1913). The light reaction of plasmodial strands, ex- cised from the multinuclear plasmodia and irradi- ated with blue (450 nm) and blue-green (496 nm) light, is a tensiometrically measurable, transient prolongation of the periods immediately following the onset of illumination (Block and Wohlfarth- Bottermann 1981). The signal transduction from the irradiated areas to non-illuminated regions is performed by the endoplasmic shuttle stream which contains an as yet unknown transmitting factor (Wohlfarth-Bottermann and Block 1981). As in other cells, the nature of the photoreceptor