Chapter 3 Action spectroscopy of photomovement

Foster, Kenneth W.

doi:10.1016/s1568-461x(01)80007-7

Cited by 15 publications

(15 citation statements)

References 119 publications

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“…The analog must activate the opsin directly by being incorporated into the available binding site. As a short chromophore with only two conjugated double bonds, the analog has an action spectrum ( The spectra are shown on the same relative sensitivity scale, and the scales are in a standard proportion, where a 1-eV shift is the same length as 2 log sensitivity units (12).…”

Section: Resultsmentioning

confidence: 99%

“…Peranema rhodopsin joins the growing list of nonanimal eukaryotic rhodopsins, including those identified in dinoflagellates by the evaluation of protein sequences (30) and action spectral analysis (11,12,18), in cryptophytes by action spectra (9,12) and protein sequence evaluation (22), in fungi by shifted action spectra (34) and protein sequence evaluation (3), and in green algae by shifted action spectra (16) and protein sequence evaluation (20,38). Two other probable groups with rhodopsins suggested by action spectra are the ciliates (12,25) and foramins (12). The rhodopsins of fungi and green algae show the greatest similarity to each other and then to archaeal sensory rhodopsin IIs compared to cyanobacterial rhodopsins.…”

Section: Discussionmentioning

confidence: 99%

“…Plot of action spectra. The threshold action spectra for native rhodopsin and n-hexenal-opsin were plotted as previously described (12,34). In brief, the threshold for each stimulating wavelength was obtained by linear extrapolation of its log-intensity linear-response curve (see Fig.…”

Section: Saranak and Foster Eukaryot Cellmentioning

confidence: 99%

“…While Shettles did not make any particular hypothesis about the nature of the receptor, the photore-ceptor rhodopsin has been found in several evolutionary branches that diverged early from animals, including green algae (16) and fungi (34). Replotting of Shettles's data (35,36) yielded an action spectrum which fit reasonably well with the rhodopsin standard curve (12) if one considers that the technology used did not provide sufficiently narrow-wavelength bands of light. These overly broad bands of light resulted in a flattened action spectrum.…”

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confidence: 99%

“…Since the available evidence suggests that rhodopsin might be the photoreceptor responsible for enhancing curling in Peranema, we used our established techniques for the identification of photoreceptors (12,16,34) to show here that rhodopsin is indeed the photoreceptor for the curling behavior of Peranema. We also confirm unusual features of the light/dark adaptation and link rhodopsin activation to calcium ions and channels during curling behavior.…”

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Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins

Saranak

Foster

2005

Eukaryot Cell

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When it is gliding, the unicellular euglenoid Peranema trichophorum uses activation of the photoreceptor rhodopsin to control the probability of its curling behavior. From the curled state, the cell takes off in a new direction. In a similar manner, archaea such as Halobacterium use light activation of bacterio-and sensory rhodopsins to control the probability of reversal of the rotation direction of flagella. Each reversal causes the cell to change its direction. In neither case does the cell track light, as known for the rhodopsin-dependent eukaryotic phototaxis of fungi, green algae, cryptomonads, dinoflagellates, and animal larvae. Rhodopsin was identified in Peranema by its native action spectrum (peak at 2.43 eV or 510 nm) and by the shifted spectrum (peak at 3.73 eV or 332 nm) upon replacement of the native chromophore with the retinal analog n-hexenal. The in vivo physiological activity of n-hexenal incorporated to become a chromophore also demonstrates that charge redistribution of a short asymmetric chromophore is sufficient for receptor activation and that the following isomerization step is probably not required when the rest of the native chromophore is missing. This property seems universal among the Euglenozoa, Plant, and Fungus kingdom rhodopsins. The rhodopsins of animals have yet to be studied in this respect. The photoresponse appears to be mediated by Ca 2؉ influx.Since rhodopsins sharing sequence similarities are found in bacteria, archaea, eukaryotic microorganisms, and animals, it is possible to gain insight into the evolutionary progression and diversification leading to the receptor proteins of human visual photoreceptors as well as other photoreceptors. As part of this continuing project on the evolution and mechanisms of visual systems, the light-dependent responses of Peranema have been studied with respect to behavior, action spectra, the mechanism of activation, and signaling to the cell.Peranema trichophorum is a colorless eukaryotic phagotroph of the Euglenophyta that lives in fresh water (8). It does not have a chloroplast but rapidly deforms in shape and is very effective at capturing and eating prey (41). Peranema voraciously takes any particles into its body by phagocytosis (1). This "feeding behavior" is clearly and commonly observed under the microscope. Its life cycle is not well studied, but from light microscopic observations Peranema appears to have several distinct stages of growth. After the cells are put into fresh medium, which is initially low on waste products, one sees small round cells of about 10 to 15 m in diameter. These cells elongate into oval cells that swim freely in solution and fast in a helical euglenoid motion. Over 2 weeks, these cells elongate further to 25 to 70 m in length, remaining 10 m wide, and are seen to glide forward on a surface pulled by their leading anterior cilium, which is about the length of the cell body. (We use the word "cilium" rather than "eukaryotic flagellum" to describe the leading appendage that enables the cell to glide to e...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Saranak and Foster Eukaryot Cellmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins

Saranak

Foster

2005

Eukaryot Cell

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An electro‐optic monitor of the behavior of Chlamydomonas reinhardtii cilia

Josef

Saranak

Foster

2005

Cell Motil. Cytoskeleton

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The unicellular green alga Chlamydomonas reinhardtii steers through water with a pair of cilia (eukaryotic flagella). Long-term observation of the beating of its cilia with controlled stimulation is improving our understanding of how a cell responds to sensory inputs. Here we describe how to record ciliary motion continuously for long periods. We also report experiments on the network of intracellular signaling that connects the environment inputs with response outputs. Local spatial changes in ciliary response on the time scale of the underlying biochemical dynamics are observed. Near-infrared light monitors the cells held by a micropipette. This condition is tolerated well for hours, not interfering with ciliary beating or sensory transduction. A computer integrates the light stimulation of the eye of Chlamydomonas with the ciliary motion making possible long-term correlations. Measures of ciliary responses include the beating frequency, stroke velocity, and stroke duration of each cilium, and the relative phase of the cis and trans cilia. The stationarity and dependence of the system on light intensity was investigated. About 150,000,000 total beat cycles and up to 8 h on one cell have been recorded. Each beat cycle is resolved so that each asynchronous beat is detected. Responses extend only a few hundred milliseconds, but there is a persistence of momentary changes that last much longer. Interestingly, we see a response that is linear with absolute light intensity as well as different kinds of response that are clearly nonlinear, implying two signaling pathways from the cell body to the cilia.

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Ciliary behavior of a negatively phototactic Chlamydomonas reinhardtii

Josef¹,

Saranak²,

Foster³

2005

Cell Motil. Cytoskeleton

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With an instrument that can record the motion of both cilia of the unicellular alga Chlamydomonas reinhardtii for many hours, the behavioral differences of its two cilia have been studied to determine their specific role in phototaxis. The organism was held on a fixed micropipette with the plane of ciliary beating rotated into the imaging plane of a quadrant photodetector. The responses to square-wave light patterns of a wide range of temporal frequencies were used to characterize the responses of each cilium. Eighty-one cells were examined showing an unexpectedly diverse range of responses. Plausible common signals for the linear and nonlinear signals from the cell body are suggested. Three independent ciliary measures--the beat frequency, stroke velocity, and phasing of the two cilia--have been identified. The cell body communicates to the cilia the direction of phototaxis the cell desires to go, the absolute light intensity, and the appropriate graded transient response for tracking the light source. The complexity revealed by each measure of the ciliary response indicates many independent variables are involved in the net phototactic response. In spite of their morphological similarity, the two cilia of Chlamydomonas respond uniquely. Probably the signals from the cell body fan out to independent pathways in the cilia. Each cilium modifies the input in its own way. The change in the pattern of the effective and recovery strokes of each cilium associated with negative phototaxis has been demonstrated and its involvement in phototactic turning is described.

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Chapter 3 Action spectroscopy of photomovement

Cited by 15 publications

References 119 publications

Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins

Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins

An electro‐optic monitor of the behavior of Chlamydomonas reinhardtii cilia

Ciliary behavior of a negatively phototactic Chlamydomonas reinhardtii

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