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The pathway of photosensory transduction in Physarum polycephalum
cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
365
THE PATHWAY OF PHOTOSENSORYTRANSDUCTION IN PHYSARUM POLYCEPHALUM K. E. Wohlfarth-Bottermann and I. Block Institute of Cytology, University of Bonn 61 a D-5300 Bonn 1, Ulrich-Haberland-Str. Federal Republic of Germany ABSTRACT Irradiation of the plasmodia of Ph2rsarum with blue and white light results in a transient change of their oscillatory contraction frequency. This reaction to light decreases with increasing distance from the illuminated area (Block and Wohlfarth-Bottermann, 19Sl). The first local appearance of light response in nonilluminated parts of the plasmodia was used to analyse the sensory pathway of the light stimulus modulating the Different experimental assays recontractile apparatus. vealed that the direction of photosensory transduction is determined by the momentary direction of protoplasmic The endoplasmic flow carries the sigshuttle streaming. nal responsible for photosensory transduction and light reaction to the force generating ectoplasmic tube. INTRODUCTION In unicellular organisms and undifferentiated cells, the link between light stimulus reception, stimulus transduction and reaction, i.e., the complete sequence of sensory processes connecting stimulus reception and physiological response is largely unknown (Senger, 1980). For an analysis of the pathway of phototransduction,the plasmodial stage of Physarum polycephalum offers the experimental advantage of large distances (in cm range) between the sites of perception on the one hand and reaction on the other hand, whereas special differentiations for signal transfer are completely lacking. For this function, only biomembranes and the undifferentiated cytoplasm can be considered. Phototaxis leads the plasmodia of myxomycetes to the sites of fruit dispersal, whereas a negative taxis keeps Physarum in the nutritional environment (Rakoczy, in (1981) deSenger, 1980). Block and Wohlfarth-Bottermann monstrated that blue light induces without measurable time lag a transient frequency decrease of oscillatory contraction automaticity. This blue light reaction 0 1981 Academic
Press Inc. (London)
Ltd.
366
Cell Biology International
Reports, Vol. 5, No. 4, April 1981
decreases with increasing distance from the irradiated area. The response could be registered immediately after onset of illumination also in non-irradiated areas within a distance of up to 3 cm from the site of light perception. Therefore, further experiments were devoted to the analysis of the pathway of the signal transmission, as an example for photo-signal transmission in "undifferentiated cells". MATERIALS AND METHODS Physarum polycephalum was cultured in the dark and starved at least for 12 hours before protoplasmic strands together with their substrate were excised under red light and used for tensiometric registration of radial 1977; contraction activity in situ (Wohlfarth-Bottermann, Block and Wohlfarth-Bottermann, 1981). Only for the "weighing" experiments (Fig. 3), the strands were partially removed from their substrate. The results of this communication.are based on the-investigation of 140 proIO-26O C. Dimensions toplasmic strands. Room temperature of the isolated specimens and irradiation program: see Legends to the diagrams. Illumination: cold light source KL 150 B (Schott Comp., Mainz). RESULTS The physiology of blue light reception and its sensory transduction is of importance for many cell types. There is a considerable variety of responses in different organisms, but the mechanisms are largely unknown (Schmidt, 1980). Because our previous experiments with 1981) were blue light (Block and Wohlfarth-Bottermann, in favour of the assumption that the transmission of the stimulus to other areas of the plasmodium and the subsequent modulation of the contractile machinery could be performed by the endoplasmic shuttle streaming, we focussed our interest on finding experimental arrangements 1, 3 and 7 show suitable to test this assumption. Figs. diagrammatically our apparative procedures which finally
la
Cell Biology International
Reports, Vol. 5, No. 4, April 1981
revealed the pathway of signal the results of our experiments
367
We present transmission. at the end of each Legend.
arrangements during irraFiq. 1: Diagrams of different 1 and 2 = diation and registration of photo-response. tension transducers registering the radial contraction activities at different sites of a protoplasmic strand bars = light protecting screens: (dotted) ; solid vertical solid horizontal black bars = carbon filter paper (subsolid horizontal white bar: strate of the plasmodium); agar substrate. Moist chamber to prevent drying of the object by evaporation not shown. The double arrows indicate the sites of irradiation. 0.7-l .O mm; length: 25-100 mm. strand diameter: %adiation: 15-30 min (water filter)4400 lux blue light length; 496 nm; irradiated area: 15 mm of the strand distance of registration No. 2 from the irradiated area: 2-25
mm.
0.7-1.1 mm; length: 50-80 mm. strand diameter: b: 10 secrY26000 lux white light; irradiated frradiation: of registrations from the irraarea: 25 mm; distance diated area: 2-3 mm. arrangement as in Fig. lb. Upper Fig. 2: Experimental original registration of radial contraction acticurves: 1 and 2. Ordinate: radial activity revities at sites gistered in millipond; abscissa: time course of experiment in min. The lower curve represents the corresponding frequency evaluation. Ordinate: period duration in min; abscissa: time course of the experiment in min. Result : There is a unilateral immediate onset of light response (increase in period duration).
Fig. 3: Symbols as in Fig. 1. The second transducer acts as an electrobalance to register the momentary streaming direction by weighing continuously the inout-flow of endoplasm at this side of the strand
(2) or
Cell Biology
368
International
Reports,
Vol. 5, No. 4, April
1981
(Wohlfarth-Bottermann, 1979). . strand diameter: 0.8-1.3 mm: length : 45'90 mm. %radiation: 30 secd26000 lux white light; irradiated between irradiated area and regiarea: 10 mm; distance stration site No. 1: 2-3 mm. strand diameter: 0.9-1.1 mm; length: 65-75 mm. b: Irradiation: 30-45 secd26000 lux white light: irradiated area: IO mm; distance of registration Do. 1: 2-3 mm. arrangement as in Fig. 3a. Unner Fig. 4: Experimental curves: weight registration of shuttle streaming -by transducer 2 and of radial activity by transducer 1. evaluation of radial activity. Lower curve: frequency Arrows: onset and termination of irradiation. During the protoplasmic flow was directed toward irradiation, transducer 1 (as indicated by the decrease in weight). Note the increased period duration following irradiation. of the unilateResult: The response, i.e., the direction ral period increase is identical with the momentary direction of endoplasmic flow during the time span of irradiation.
2.0
5
10 15 mm as in Fig. 5: As in Fig. 4, but with an arrangement was performed when protoplasmic Fig. 3b. Irradiation flow was directed toward transducers 1 and 2. Result: as in Fig. 4. Fig. 3b). Control: Fig. 6: As in Fig. 5 (arrangement Protoplasmic flow direction was opposite to direction in direction of the illuminated area. in Fig. 5, i.e., This means that during and immediately after illumination, no irradiated endoplasm came into contact with the measuring point of transducer 1. Result: There is no increase in period duration in the control experiment.
Cell Biology
International
Reports,
Vol. 5, No. 4, April
7981
369
microscope Fig. 7: Symbols as in Fig. 1. IM = inverted for the observation of the momentary streaming direction of endoplasm (red light illumination). Strand diameter: 0.1-0.3 mm; length: 40-120 mm. Irradiation: 20-45 secN nm; di26000 lux white light; irradiated area: lo-18 stance of registration: 2-3 mm. observation Arrangement as in Fig. 7. The direct reveals an immediate period increase in the w streaming direction toward which the protoplasmic flow was directed The transducer on the other side during illumination. (dotted curves) registered the corresponding reaction only with a considerable time lag. Often even a decrease in period duration can be observed at this side. Result: The direct observation of streaming before, during and after irradiation proves the thesis that streaming determines the direction of propagation of the photo-induced signal, i.e., the information transfer runs via protoplasmic streaming. DISCUSSION The average period of shuttle streaming in mediun sized plasmodia (diameter 10 cm) at room temperature on non-nutrient agar is 1.47 min (Hiilsmann and WohlfarthBottermann, 1978). This corresponds with the period duration of radial contraction rhythmicity, which was found to be 1.34 min according to tensiometric registrations 1977). As the immediate nhoto(Wohlfarth-Bottermann, response, we registered a 6 to 38 % increase of-the duration of the first radial contraction period following the onset of illumination. The velocity of streaming with values of&l mm/set is rapid enough to serve as a carrier
370
Cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
for the signal responsible for phase s:rnchronization of contraction activity (Yoshimoto and Kaniya, 1978; Achen1981). Thus, all available bath and Wohlfarth-Bottermann, data are in accordance with the presented finding that the endoplasmic stream represents the pathway of signal transmission during the transduction of a photo-induced signal. Fig. 9: Diagram of endoplasmic shuttle 9 streaming in a protoplasmic strand of Physarum. Straight arrows: endoplasmic BE z Z-E streaming; curved arrows: streamlets the ectoplasmic tube (dotted) ~~~:,:‘:$P~44%+~ a<2 <,?a leaving during its contraction (upper side) or *o entering the ectoplasmic tube during its =)t Q ;'Ly< '2 dilation (lower side). White and black thick arrows:alternating stages during shuttle streaming. There is a permanent partial exchange of endoplasm and ectoplasm during each contraction cycle via openings of the circular invagination system limiting the borderline between endoplasmic core and ectoplasmic tube (Hiilsmann and b?ohlfarth-Bottermann, 1978).
The information transfer via endoplasm to the responsive areas of non-illuminated regions of ectoplasm is based on the general presence of endoplasm,-ectoplasm interconversion sites along the longitudinal axis of the 1974). On an plasmodial strands (Wohlfarth-Bottermann, the mixing of endoplasn and ectoplasm can amount average, to 30 % of the volume of the ectoplasmic wall during one 1978). The contraction cycle (Grebecki and Cieslawska; a suitable pathendoplasmic stream (Fig. 9) represents way by which the photo-induced signal is transported to to the contractile machinery the site of response, i.e., within the ectoplasmic tube. The difficulty with experiments of weighing the streaming pattern and simultaneously registering radial activity (Figs.3-6) lies in the fact that frequently the streaming is too irregular. In all experiments with a regular shuttle streaming (Figs.4-6) we found that the direction of streaming and of signal propagation was identical. The direct microscopic observation of the direction of shuttle streaming (Figs.7-8) gave conclusive evidence that the message transfer runs via endoplasmic streaming. The endoplasmic pathway of transmission of the photosignal suggests a chemical transduction of the photostimulus from the perceptive site to the responsive site. An electrical transduction via the plasmalemma can apparently be excluded, corresponding to the experience that an electrical coupling is also not responsible for the
Cell Biology International
Reports. Vol. 5, No. 4, April 198 1
371
transmission of the phase synchronizing signal (Achenbach and Wohlfarth-Bottermann, 1981). Whereas for phase synchronization a mechanical coupling cannot be ruled out, it appears reasonable to interpret the photo-transduction as a mechanism of chemical coupling: a light activated the photoreceptor molecules are either disensor, i.e., rectly transducted via the endoplasmic stream or the perceptive molecules influence .unkn,own~$ndoplasmic carriers (second messengers). Movement of Ca ~ and other ions may be involved'in the-early light-dependent reactions (Daniel and J&lfors, 1972). ,The.most simple explanation would be that a flavine type receptor molecule (Schmidt, in press) bound to ectoplas1980; Schreckenbach et al., mic and/or endoplasmic membranes and related to energy production transiently modulates the oscillatory energy production cycle. The photo-stimulation would then lead to a temporal retardation of the clock. Schreckenbach et al. (in press) describe a photo-induced reversible inhibition of glucose consumption. A local photo-induced temporal lag of oscillators could represent a chemical signal that becomes diluted with increasing distance from the irradiated area (Block and Wohlfarth-Bottermann,l981), namely, by the increasing mixing of irradiated endoplasm with non-irradiated ectoplasm (Fig. 9). A tentative chain of events: Photo-induced inhibition of respiration (Daniel, 1965) or Retardation of energy supply and of the oscillatory cycle by decreased glucose breakdown (Schrekkenbach et al., in press),--+ Increased period duration (Block and Wohlfarth-Bottermann, 1981)-Local phase shifts of contraction rhythms -Propagated waves (Hejnowicz and Wohlfarth-Bottermann, 1980) and changes in streaming direction (Achenbach and Wohlfarth-Bottermann, 1981)----Increased local efflux of protoplasm = photophobic response. The identification of an endoplasmic pathway of signal transfer for photo-transduction may be an aid in further experiments to analyse the molecular link between stimulus reception and its physiological response in distant areas. Obviously, so-called undifferentiated cells are able to transmit signals modulating their chemomechanical energy transformation (and thus their locomotion behaviour) not only by a conventionally assumed bioelectric transduction along plasmalemmal structures: In the future, the "humoral" (i.e., cytoplasmic) transmission of signals via cytoplasmic streaming must be considered additionally when analysing the reaction mechanism of cells upon external and internal stimuli.
372
Cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
The authors thank Dr. R. L. Snipes (Giessen) for reading the manuscript and Dr. R. Stiemerling (Bonn) preparation of the diagrams.
for
ACKNOWLEDGEXENTS
REFERENCES Achenbach, U. and Wohlfarth-Bottermann, K.E. (1981) Synchronization and signal transmission in protoplasmic strands of Physarum. The endoplasmic streaming as a pacemaker and the importance of phase deviations for the control of streaming reversal. Planta (submitted). Block, I. and Wohlfarth-Bottermann, K.E. (1981) Blue light as a medium to influence oscillatory contraction frequency in Physarum. Cell Biology International Reports (in press). Control of respiration by light duDaniel, J.W. (1965) ring the sporulation and growth of a myxomycete. Journal of Cell Biology 3, 23A-24A. Daniel, chanJ.W. and Jarlfors, U. (1972) Light-induced ges in the ultrastructure of a plasmodial myxonycete. Tissue and Cell 4, 405-426. Grebecki, A. and Cieslawska, II. (1978) Dynamics of the ectoplasmic walls during pulsation of plasmodial veins of Physarum polycephalum. Protoplasma 97, 365-371.
Hejnowicz, Z. and Wohlfarth-Bottermann, K.E. (1980) Propagated waves induced by gradients of physiological factors within plasmodia of Physarum polycephalum. Planta 150, 144-152. Hiilsmann, N. and Wohlfarth-Bottermann, K.E. (1978) Spatio-temporal relationships between protoplasmic streaming and contraction activities in plasmodial veins of Physarum polycephalum. Cytobiologie -17, 317-334."
Schmidt, W. (1980) Physiological blue light reception. IN: Structure and Bonding, vol. 41 (eds. J.D. Dunitz Springer,Heidelberg. et al.), p. l-44, Schreckenbach, T., Walckhoff, B. and Verfuerth, C. (in press) Blue light receptor in a white mutant of Physarum polycephalum mediates inhibition of spherulation and regulation of glucose metabolism. Proceedings National Academy of Sciences (USA). The blue light syndrome. Springer, Senger, H. (1980) Berlin. Wohlfarth-Bottermann, K.E. (1974) Plasmalemma invaginations as characteristic constituents of plasmodia of Physarum polycephalum. Journal of Cell Science 16, 23-37.
Cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
373
Oscillating contractions Wohlfarth-Bottermann, K.E. (1977) in protoplasmic strands of Physarum: Simultaneous tensiometry of longitudinal and radial rhythms, periodicity analysis and temperature dependence. Journal of Experimental Biology 67, 49-59. Wohlfarth-Bottermann, K.E. (1979) Oscillatory contraction activity in Physarum. Journal of Experimental Biology 81, 15-32. Yoshimoto, Y. and Kamiya, N. (1978) Studies on contraction rhythm of the plasmodial strand. III. Role of endoplasmic streaming in synchronization of local rhythms. Protoplasma 95, 111-121.
Received:
17th December 1980
Accepted: 29th December 1980
International
Reports,
Vol. 5, No. 4, April
1981
365
THE PATHWAY OF PHOTOSENSORYTRANSDUCTION IN PHYSARUM POLYCEPHALUM K. E. Wohlfarth-Bottermann and I. Block Institute of Cytology, University of Bonn 61 a D-5300 Bonn 1, Ulrich-Haberland-Str. Federal Republic of Germany ABSTRACT Irradiation of the plasmodia of Ph2rsarum with blue and white light results in a transient change of their oscillatory contraction frequency. This reaction to light decreases with increasing distance from the illuminated area (Block and Wohlfarth-Bottermann, 19Sl). The first local appearance of light response in nonilluminated parts of the plasmodia was used to analyse the sensory pathway of the light stimulus modulating the Different experimental assays recontractile apparatus. vealed that the direction of photosensory transduction is determined by the momentary direction of protoplasmic The endoplasmic flow carries the sigshuttle streaming. nal responsible for photosensory transduction and light reaction to the force generating ectoplasmic tube. INTRODUCTION In unicellular organisms and undifferentiated cells, the link between light stimulus reception, stimulus transduction and reaction, i.e., the complete sequence of sensory processes connecting stimulus reception and physiological response is largely unknown (Senger, 1980). For an analysis of the pathway of phototransduction,the plasmodial stage of Physarum polycephalum offers the experimental advantage of large distances (in cm range) between the sites of perception on the one hand and reaction on the other hand, whereas special differentiations for signal transfer are completely lacking. For this function, only biomembranes and the undifferentiated cytoplasm can be considered. Phototaxis leads the plasmodia of myxomycetes to the sites of fruit dispersal, whereas a negative taxis keeps Physarum in the nutritional environment (Rakoczy, in (1981) deSenger, 1980). Block and Wohlfarth-Bottermann monstrated that blue light induces without measurable time lag a transient frequency decrease of oscillatory contraction automaticity. This blue light reaction 0 1981 Academic
Press Inc. (London)
Ltd.
366
Cell Biology International
Reports, Vol. 5, No. 4, April 1981
decreases with increasing distance from the irradiated area. The response could be registered immediately after onset of illumination also in non-irradiated areas within a distance of up to 3 cm from the site of light perception. Therefore, further experiments were devoted to the analysis of the pathway of the signal transmission, as an example for photo-signal transmission in "undifferentiated cells". MATERIALS AND METHODS Physarum polycephalum was cultured in the dark and starved at least for 12 hours before protoplasmic strands together with their substrate were excised under red light and used for tensiometric registration of radial 1977; contraction activity in situ (Wohlfarth-Bottermann, Block and Wohlfarth-Bottermann, 1981). Only for the "weighing" experiments (Fig. 3), the strands were partially removed from their substrate. The results of this communication.are based on the-investigation of 140 proIO-26O C. Dimensions toplasmic strands. Room temperature of the isolated specimens and irradiation program: see Legends to the diagrams. Illumination: cold light source KL 150 B (Schott Comp., Mainz). RESULTS The physiology of blue light reception and its sensory transduction is of importance for many cell types. There is a considerable variety of responses in different organisms, but the mechanisms are largely unknown (Schmidt, 1980). Because our previous experiments with 1981) were blue light (Block and Wohlfarth-Bottermann, in favour of the assumption that the transmission of the stimulus to other areas of the plasmodium and the subsequent modulation of the contractile machinery could be performed by the endoplasmic shuttle streaming, we focussed our interest on finding experimental arrangements 1, 3 and 7 show suitable to test this assumption. Figs. diagrammatically our apparative procedures which finally
la
Cell Biology International
Reports, Vol. 5, No. 4, April 1981
revealed the pathway of signal the results of our experiments
367
We present transmission. at the end of each Legend.
arrangements during irraFiq. 1: Diagrams of different 1 and 2 = diation and registration of photo-response. tension transducers registering the radial contraction activities at different sites of a protoplasmic strand bars = light protecting screens: (dotted) ; solid vertical solid horizontal black bars = carbon filter paper (subsolid horizontal white bar: strate of the plasmodium); agar substrate. Moist chamber to prevent drying of the object by evaporation not shown. The double arrows indicate the sites of irradiation. 0.7-l .O mm; length: 25-100 mm. strand diameter: %adiation: 15-30 min (water filter)4400 lux blue light length; 496 nm; irradiated area: 15 mm of the strand distance of registration No. 2 from the irradiated area: 2-25
mm.
0.7-1.1 mm; length: 50-80 mm. strand diameter: b: 10 secrY26000 lux white light; irradiated frradiation: of registrations from the irraarea: 25 mm; distance diated area: 2-3 mm. arrangement as in Fig. lb. Upper Fig. 2: Experimental original registration of radial contraction acticurves: 1 and 2. Ordinate: radial activity revities at sites gistered in millipond; abscissa: time course of experiment in min. The lower curve represents the corresponding frequency evaluation. Ordinate: period duration in min; abscissa: time course of the experiment in min. Result : There is a unilateral immediate onset of light response (increase in period duration).
Fig. 3: Symbols as in Fig. 1. The second transducer acts as an electrobalance to register the momentary streaming direction by weighing continuously the inout-flow of endoplasm at this side of the strand
(2) or
Cell Biology
368
International
Reports,
Vol. 5, No. 4, April
1981
(Wohlfarth-Bottermann, 1979). . strand diameter: 0.8-1.3 mm: length : 45'90 mm. %radiation: 30 secd26000 lux white light; irradiated between irradiated area and regiarea: 10 mm; distance stration site No. 1: 2-3 mm. strand diameter: 0.9-1.1 mm; length: 65-75 mm. b: Irradiation: 30-45 secd26000 lux white light: irradiated area: IO mm; distance of registration Do. 1: 2-3 mm. arrangement as in Fig. 3a. Unner Fig. 4: Experimental curves: weight registration of shuttle streaming -by transducer 2 and of radial activity by transducer 1. evaluation of radial activity. Lower curve: frequency Arrows: onset and termination of irradiation. During the protoplasmic flow was directed toward irradiation, transducer 1 (as indicated by the decrease in weight). Note the increased period duration following irradiation. of the unilateResult: The response, i.e., the direction ral period increase is identical with the momentary direction of endoplasmic flow during the time span of irradiation.
2.0
5
10 15 mm as in Fig. 5: As in Fig. 4, but with an arrangement was performed when protoplasmic Fig. 3b. Irradiation flow was directed toward transducers 1 and 2. Result: as in Fig. 4. Fig. 3b). Control: Fig. 6: As in Fig. 5 (arrangement Protoplasmic flow direction was opposite to direction in direction of the illuminated area. in Fig. 5, i.e., This means that during and immediately after illumination, no irradiated endoplasm came into contact with the measuring point of transducer 1. Result: There is no increase in period duration in the control experiment.
Cell Biology
International
Reports,
Vol. 5, No. 4, April
7981
369
microscope Fig. 7: Symbols as in Fig. 1. IM = inverted for the observation of the momentary streaming direction of endoplasm (red light illumination). Strand diameter: 0.1-0.3 mm; length: 40-120 mm. Irradiation: 20-45 secN nm; di26000 lux white light; irradiated area: lo-18 stance of registration: 2-3 mm. observation Arrangement as in Fig. 7. The direct reveals an immediate period increase in the w streaming direction toward which the protoplasmic flow was directed The transducer on the other side during illumination. (dotted curves) registered the corresponding reaction only with a considerable time lag. Often even a decrease in period duration can be observed at this side. Result: The direct observation of streaming before, during and after irradiation proves the thesis that streaming determines the direction of propagation of the photo-induced signal, i.e., the information transfer runs via protoplasmic streaming. DISCUSSION The average period of shuttle streaming in mediun sized plasmodia (diameter 10 cm) at room temperature on non-nutrient agar is 1.47 min (Hiilsmann and WohlfarthBottermann, 1978). This corresponds with the period duration of radial contraction rhythmicity, which was found to be 1.34 min according to tensiometric registrations 1977). As the immediate nhoto(Wohlfarth-Bottermann, response, we registered a 6 to 38 % increase of-the duration of the first radial contraction period following the onset of illumination. The velocity of streaming with values of&l mm/set is rapid enough to serve as a carrier
370
Cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
for the signal responsible for phase s:rnchronization of contraction activity (Yoshimoto and Kaniya, 1978; Achen1981). Thus, all available bath and Wohlfarth-Bottermann, data are in accordance with the presented finding that the endoplasmic stream represents the pathway of signal transmission during the transduction of a photo-induced signal. Fig. 9: Diagram of endoplasmic shuttle 9 streaming in a protoplasmic strand of Physarum. Straight arrows: endoplasmic BE z Z-E streaming; curved arrows: streamlets the ectoplasmic tube (dotted) ~~~:,:‘:$P~44%+~ a<2 <,?a leaving during its contraction (upper side) or *o entering the ectoplasmic tube during its =)t Q ;'Ly< '2 dilation (lower side). White and black thick arrows:alternating stages during shuttle streaming. There is a permanent partial exchange of endoplasm and ectoplasm during each contraction cycle via openings of the circular invagination system limiting the borderline between endoplasmic core and ectoplasmic tube (Hiilsmann and b?ohlfarth-Bottermann, 1978).
The information transfer via endoplasm to the responsive areas of non-illuminated regions of ectoplasm is based on the general presence of endoplasm,-ectoplasm interconversion sites along the longitudinal axis of the 1974). On an plasmodial strands (Wohlfarth-Bottermann, the mixing of endoplasn and ectoplasm can amount average, to 30 % of the volume of the ectoplasmic wall during one 1978). The contraction cycle (Grebecki and Cieslawska; a suitable pathendoplasmic stream (Fig. 9) represents way by which the photo-induced signal is transported to to the contractile machinery the site of response, i.e., within the ectoplasmic tube. The difficulty with experiments of weighing the streaming pattern and simultaneously registering radial activity (Figs.3-6) lies in the fact that frequently the streaming is too irregular. In all experiments with a regular shuttle streaming (Figs.4-6) we found that the direction of streaming and of signal propagation was identical. The direct microscopic observation of the direction of shuttle streaming (Figs.7-8) gave conclusive evidence that the message transfer runs via endoplasmic streaming. The endoplasmic pathway of transmission of the photosignal suggests a chemical transduction of the photostimulus from the perceptive site to the responsive site. An electrical transduction via the plasmalemma can apparently be excluded, corresponding to the experience that an electrical coupling is also not responsible for the
Cell Biology International
Reports. Vol. 5, No. 4, April 198 1
371
transmission of the phase synchronizing signal (Achenbach and Wohlfarth-Bottermann, 1981). Whereas for phase synchronization a mechanical coupling cannot be ruled out, it appears reasonable to interpret the photo-transduction as a mechanism of chemical coupling: a light activated the photoreceptor molecules are either disensor, i.e., rectly transducted via the endoplasmic stream or the perceptive molecules influence .unkn,own~$ndoplasmic carriers (second messengers). Movement of Ca ~ and other ions may be involved'in the-early light-dependent reactions (Daniel and J&lfors, 1972). ,The.most simple explanation would be that a flavine type receptor molecule (Schmidt, in press) bound to ectoplas1980; Schreckenbach et al., mic and/or endoplasmic membranes and related to energy production transiently modulates the oscillatory energy production cycle. The photo-stimulation would then lead to a temporal retardation of the clock. Schreckenbach et al. (in press) describe a photo-induced reversible inhibition of glucose consumption. A local photo-induced temporal lag of oscillators could represent a chemical signal that becomes diluted with increasing distance from the irradiated area (Block and Wohlfarth-Bottermann,l981), namely, by the increasing mixing of irradiated endoplasm with non-irradiated ectoplasm (Fig. 9). A tentative chain of events: Photo-induced inhibition of respiration (Daniel, 1965) or Retardation of energy supply and of the oscillatory cycle by decreased glucose breakdown (Schrekkenbach et al., in press),--+ Increased period duration (Block and Wohlfarth-Bottermann, 1981)-Local phase shifts of contraction rhythms -Propagated waves (Hejnowicz and Wohlfarth-Bottermann, 1980) and changes in streaming direction (Achenbach and Wohlfarth-Bottermann, 1981)----Increased local efflux of protoplasm = photophobic response. The identification of an endoplasmic pathway of signal transfer for photo-transduction may be an aid in further experiments to analyse the molecular link between stimulus reception and its physiological response in distant areas. Obviously, so-called undifferentiated cells are able to transmit signals modulating their chemomechanical energy transformation (and thus their locomotion behaviour) not only by a conventionally assumed bioelectric transduction along plasmalemmal structures: In the future, the "humoral" (i.e., cytoplasmic) transmission of signals via cytoplasmic streaming must be considered additionally when analysing the reaction mechanism of cells upon external and internal stimuli.
372
Cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
The authors thank Dr. R. L. Snipes (Giessen) for reading the manuscript and Dr. R. Stiemerling (Bonn) preparation of the diagrams.
for
ACKNOWLEDGEXENTS
REFERENCES Achenbach, U. and Wohlfarth-Bottermann, K.E. (1981) Synchronization and signal transmission in protoplasmic strands of Physarum. The endoplasmic streaming as a pacemaker and the importance of phase deviations for the control of streaming reversal. Planta (submitted). Block, I. and Wohlfarth-Bottermann, K.E. (1981) Blue light as a medium to influence oscillatory contraction frequency in Physarum. Cell Biology International Reports (in press). Control of respiration by light duDaniel, J.W. (1965) ring the sporulation and growth of a myxomycete. Journal of Cell Biology 3, 23A-24A. Daniel, chanJ.W. and Jarlfors, U. (1972) Light-induced ges in the ultrastructure of a plasmodial myxonycete. Tissue and Cell 4, 405-426. Grebecki, A. and Cieslawska, II. (1978) Dynamics of the ectoplasmic walls during pulsation of plasmodial veins of Physarum polycephalum. Protoplasma 97, 365-371.
Hejnowicz, Z. and Wohlfarth-Bottermann, K.E. (1980) Propagated waves induced by gradients of physiological factors within plasmodia of Physarum polycephalum. Planta 150, 144-152. Hiilsmann, N. and Wohlfarth-Bottermann, K.E. (1978) Spatio-temporal relationships between protoplasmic streaming and contraction activities in plasmodial veins of Physarum polycephalum. Cytobiologie -17, 317-334."
Schmidt, W. (1980) Physiological blue light reception. IN: Structure and Bonding, vol. 41 (eds. J.D. Dunitz Springer,Heidelberg. et al.), p. l-44, Schreckenbach, T., Walckhoff, B. and Verfuerth, C. (in press) Blue light receptor in a white mutant of Physarum polycephalum mediates inhibition of spherulation and regulation of glucose metabolism. Proceedings National Academy of Sciences (USA). The blue light syndrome. Springer, Senger, H. (1980) Berlin. Wohlfarth-Bottermann, K.E. (1974) Plasmalemma invaginations as characteristic constituents of plasmodia of Physarum polycephalum. Journal of Cell Science 16, 23-37.
Cell Biology
International
Reports,
Vol. 5, No. 4, April
1981
373
Oscillating contractions Wohlfarth-Bottermann, K.E. (1977) in protoplasmic strands of Physarum: Simultaneous tensiometry of longitudinal and radial rhythms, periodicity analysis and temperature dependence. Journal of Experimental Biology 67, 49-59. Wohlfarth-Bottermann, K.E. (1979) Oscillatory contraction activity in Physarum. Journal of Experimental Biology 81, 15-32. Yoshimoto, Y. and Kamiya, N. (1978) Studies on contraction rhythm of the plasmodial strand. III. Role of endoplasmic streaming in synchronization of local rhythms. Protoplasma 95, 111-121.
Received:
17th December 1980
Accepted: 29th December 1980