Fluorescence Behavior of Euglena Photoreceptor¶

Evangelista, Valtere; Passarelli, Vincenzo; Barsanti, Laura; Gualtieri, Paolo

doi:10.1562/0031-8655(2003)0780093fboep2.0.co2

Cited by 4 publications

(7 citation statements)

References 27 publications

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“…The results of the present measurements performed with two different techniques (microspectrophotometry and digital absorption microscopy) together with those previously reported (6,7) give a detailed picture of the photochromicity of the paraflagellar swelling of Euglena . This organelle possesses a photocycle, with two stable states, state A nonfluorescent, and state B fluorescent.…”

Section: Discussionsupporting

confidence: 72%

“…4). The fluorescence spectrum of state B shows a band centered at 556–560 nm after excitation with the selected microscope filter (7). Moreover, the fluorescence of the protein in state B allows us to visualize the selective and exclusive photogeneration of the two states (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Upon photoexcitation at 365 nm state A generates state B, which can be photochemically driven back to state A, upon illumination at 436 nm. The kinetics of the photocycle was measured, digitizing at constant rate, the fluorescence images of the Euglena cell photoreceptor (6), as well as the emission fluorescence spectrum of state B (7). Only the absorption spectrum of the nonfluorescent state A of the photoreceptor was measured.…”

Section: Introductionmentioning

confidence: 99%

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In Vivo Absorption Spectra of the Two Stable States of the Euglena Photoreceptor Photocycle

Barsanti

Coltelli

Evangelista

et al. 2009

Photochem & Photobiology

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Euglena gracilis possesses a simple but sophisticated light detecting system, consisting of an eyespot formed by carotenoids globules and a photoreceptor. The photoreceptor of Euglena is characterized by optical bistability, with two stable states. In order to provide important and discriminating information on the series of structural changes that Euglena photoreceptive protein(s) undergoes inside the photoreceptor in response to light, we measured the in vivo absorption spectra of the two stable states A and B of photoreceptor photocycle. Data were collected using two different devices, i.e. a microspectrophotometer and a digital microscope. Our results show that the photocycle and the absorption spectra of the photoreceptor possess strong spectroscopic similarities with a rhodopsin-like protein. Moreover, the analysis of the absorption spectra of the two stable states of the photoreceptor and the absorption spectrum of the eyespot suggests an intriguing hypothesis for the orientation of microalgae toward light.

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Section: Discussionsupporting

confidence: 72%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In Vivo Absorption Spectra of the Two Stable States of the Euglena Photoreceptor Photocycle

Barsanti

Coltelli

Evangelista

et al. 2009

Photochem & Photobiology

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“…Gualtieri and others, based on theoretical considerations, absorption spectroscopy and gas chromatography-mass spectrometry, proposed that the photoreceptor pigment for Euglena phototaxis is a rhodopsin (James et al 1992;Barsanti et al 1993a;Gualtieri 2001). This hypothetical rhodopsin was thought to undergo a photocycle which has been analyzed by fluorescence emission spectroscopy (Evangelista et al 2003). Hydoxylamine reacts with free and opsinbound retinal.…”

Section: Earlier Results and Hypothesesmentioning

confidence: 99%

Photomovement in Euglena

Häder

Iseki

2017

Advances in Experimental Medicine and Biology

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Motile microorganisms such as the green Euglena gracilis use a number of external stimuli to orient in their environment. They respond to light with photophobic responses, photokinesis and phototaxis, all of which can result in accumulations of the organisms in suitable habitats. The light responses operate synergistically with gravitaxis, aerotaxis and other responses. Originally the microscopically obvious stigma was thought to be the photoreceptor, but later the paraxonemal body (PAB, paraflagellar body) has been identified as the light responsive organelle, located in the trailing flagellum inside the reservoir. The stigma can aid in light direction perception by shading the PAB periodically when the cell rotates helically in lateral light, but stigmaless mutants can also orient with respect to the light direction, and negative phototaxis does not need the presence of the stigma. The PAB is composed of dichroically oriented chromoproteins which is reflected in a pronounced polarotaxis in polarized light. There was a long debate about the potential photoreceptor molecule in Euglena, including carotenoids, flavins and rhodopsins. This discussion was terminated by the unambiguous proof that the photoreceptor is a 400 kDa photoactivated adenylyl cyclase (PAC) which consists of two α- and two β-subunits each. Each subunit possesses two BLUF (Blue Light receptor Using FAD) domains binding FAD, which harvest the light energy, and two adenylyl cyclases, which produce cAMP from ATP. The cAMP has been found to activate one of the five protein kinase s found in Euglena (PK.4). This enzyme in turn is thought to phosphorylate proteins inside the flagellum which result in a change in the flagellar beating pattern and thus a course correction of the cell. The involvements of PAC and protein kinase have been confirmed by RNA interference (RNAi). PAC is responsible for step-up photophobic responses as well as positive and negative phototaxis, but not for the step-down photophobic response, even though the action spectrum of this resembles those for the other two responses. Analysis of several colorless Euglena mutants and the closely related Euglena longa (formerly Astasia longa) confirms the results. Photokinesis shows a completely different action spectrum. Some other Euglena species, such as E. sanguinea and the gliding E. mutabilis, have been investigated, again showing totally different action spectra for phototaxis and photokinesis as well as step-up and step-down photophobic responses.

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“…Light microscopy allows imaging and processing of proteins and algal cells under both lab controlled conditions and natural environment (Gualtieri, ); when microscopes are coupled with special set‐ups and appropriate image analysis processing routines, they can produce five dimensional images. In fact, wavelength ( λ ) and time ( t ) add to the common three space coordinates, x , y , and z , allowing the measurement of absorption/fluorescence spectra and time lapse image sequences (Barsanti et al, ; Barsanti, Passarelli, Walne, & Gualtieri, ; Evangelista, Frassanito, Passarelli, Barsanti, & Gualtieri, ; Evangelista, Passarelli, Barsanti, & Gualtieri, ; Gualtieri, ; Gualtieri & Coltelli, ; Gualtieri, Passarelli, & Barsanti, ; Walker, Ishikawa, & Kumagai, ). Absorption and fluorescence spectra give a reliable and in vivo picture of the metabolic processes dynamics under physiological conditions and/or in response to environmental stressors (Juarez et al, ; Rodriguez et al, ).…”

Section: Introductionmentioning

confidence: 99%

Algae through the looking glass

Coltelli

Barsanti

Evangelista

et al. 2017

Microscopy Res & Technique

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Microalgae are one of the most suitable subjects for testing the potentiality of light microscopy and image analysis, because of the size of single cells, their endogenous chromaticity, and their metabolic and physiological characteristics. Microscope observations and image analysis can use microalgal cells from lab cultures or collected from water bodies as model to investigate metabolic processes, behavior/reaction of cells under chemical or photic stimuli, and dynamics of population in the natural environment in response to changing conditions. In this paper we will describe the original microscope we set up together with the image processing techniques we improved to deal with these topics. Our system detects and recognizes in-focus cells, extracts their features, measures cell concentration in multi-algal samples, reconstructs swimming cell tracks, monitors metabolic processes, and measure absorption and fluorescent spectra of subcellular compartments. It can be used as digital microscopy station for algal cell biology and behavioral studies, and field analysis applications.

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Fluorescence Behavior of Euglena Photoreceptor¶

Cited by 4 publications

References 27 publications

In Vivo Absorption Spectra of the Two Stable States of the Euglena Photoreceptor Photocycle

In Vivo Absorption Spectra of the Two Stable States of the Euglena Photoreceptor Photocycle

Photomovement in Euglena

Algae through the looking glass

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