Absorption of light by metarhodopsin modifies the effect of a conditioning light on the barnacle photoreceptor

We show that the effect of an adapting light on the sensitivity of barnacle photoreceptors depends on the direction of net pigment transfer [rhodopsin (R) to metarhodopsin (M) or reverse] occasioned by the adapting light. For stimuli giving no net pigment transfer the state of the pigment appears irrelevant, R R having the same effect as M M. With respect to these, R M gives enhanced facilitation and M R depressed facilitation. This suggests a correlation with the prolonged depolarising after-potential (PDA) and the anti-PDA, which follow R M and M R stimuli respectively. These effects appear mainly in less sensitive cells and for higher amounts of conditioning light — but still well within the physiological range and well below the threshold for PDA and anti-PDA induction. The special interest of these results is that they appear to be interpretable only by assuming that absorption of light by metarhodopsin exerts an effect on the stimulus coincident response (LRP), the first demonstration of such an effect.Based on material presented at the European Neurosciences Meeting, Florence, September 1978     

Growth of a photosynthetic bacterium anaerobically in darkness,supported by “oxidant-dependent” sugar fermentation

Rhodopseudomonas capsulata can obtain energy for growth from light (anaerobically) and can also grow heterotrophically in darkness using alternative energy conversion modes, namely, aerobic respiration or an unusual type of anaerobic catabolism of sugars. Dark anaerobic growth with fructose as sole carbon and energy source is dependent on the presence of an accessory oxidant such as trimethylamine-N-oxide, is accompanied by production of lactate and other classical fermentation products, and yields cells with a high content of photosynthetic pigments and polyhydroxybutyrate.Abbreviation Used TMAO trimethylamine-N-oxide - DMSO dimethyl sulfoxide - EMP Embden-Meyerhof-Parnas - ED Entner-Doudoroff - PHB polyhydroxybutyrate     

Rapid photomodulation of stem extension in light-grownSinapis alba L.

Treatment of the whole of aSinapis alba plant with supplementary far-red light (FR), in back-ground white light (WL), induces a rapid increase in stem extension rate. This rapid increase is regulated by the light environment of the stem itself. Supplementary FR to the stem increases extension rate after a lag period of 10–15 min. A lag period of 3–4 h follows FR irradiation of the leaf, before an increase in extension rate is detectable. When the stem is given supplementary FR, the change in extension rate which is induced increases with increasing FR fluence rate, and with decreasing phytochrome photoequilibrium. There is no difference between the effects of supplementary FR _max 719 nm and supplementary FR _max 739 nm for these relationships. The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R). These data indicate that the response is controlled by phytochrome photoequilibrium.Abbreviations B blue light - FR far-red light - R red light - WL white light - Pfr far-red absorbing form of phytochrome - Pr red absorbing form of phytochrome - P_tot total phytochrome level (=Pr+Pfr); -Pfr/Ptot, measured - ER difference in stem extension rate, before and after treatment     

An enzyme to degrade lettuce endosperm cell walls. Appearance of a mannanase following phytochrome- and gibberellin-induced germination

Summary Lettuce seeds (Lactuca sativa L. cv. Grand Rapids) stimulated to germinate by gibberellin and red light produce large amounts of endo--mannanase. This enzyme increases markedly following radicle emergence and is capable of degrading mannose-containing polysaccharides, which are the major components of the endosperm cell wall. Non-germinated seeds contain little enzyme and under conditions where gibberellin- or red light-stimulated germination is prevented (eg. by abscisic acid or prolonged far red light) enzyme levels remain low. Cycloheximide inhibits the increase in enzyme levels when supplied to germinating seeds, but the enzyme once produced is stable in vivo in the presence of this inhibitor for at least 24h. The majority of the extractable mannanase activity is located in the endosperm and we propose that the function of this enzyme is to mobilise the endosperm cell wall polysaccharides as a nutrient source for the growing embryo.Abbreviations ABA abscisic acid - BA benzyladenine - GA gibberellic acid     

A new approach for optical assessment of directional anisotropy in turbid media

A study of polarized light transport in scattering media exhibiting directional anisotropy or linear birefringence is presented in this paper. Novel theoretical and experimental methodologies for the quantification of birefringent alignment based on out‐of‐plane polarized light transport are presented here. A polarized Monte Carlo model and a polarimetric imaging system were devised to predict and measure the impact of birefringence on an impinging linearly polarized light beam. Ex‐vivo experiments conducted on bovine tendon, a biological sample consisting of highly packed type I collagen fibers with birefringent property, showed good agreement with the analytical results.

Top view geometry of the in‐plane ( a ) and the out‐of‐plane ( b ) detection. Letter C indicates the location of the detection arm.     

Investigations of the polarity of the photo-induced electrical signal of chloroplast suspensions

This paper reports data and considerations relevant to the question of what determines the polarity of the voltages induced between electrodes in a suspension of chloroplasts when irradiated with a flash of light from a laser or flash-lamp. We found positive polarity (electrode nearest the light source positive) with excitation by ns pulses at 694, 539 and 530 nm wavelength. This and the earlier finding (Meszéna et al. (1988) Studia Biophysica 126:77–86), confirmed in this work, of negative polarity at 420 nm confirm, in part, the action spectrum reported by Gräber and Trissl (1981 FEBS Let 123:95–99) using 50 s flashes. Gräber and Trissl also showed that swelling the chloroplasts can reverse the polarity.Negative polarity is expected on the basis of a simple light-gradient in the sample together with what is known about photosynthetic charge movements. The cause of positive polarities has eluded explanation. Duration of flash was suspected. We tried a random series of short flashes averaging about 10 s apart and found that all simply duplicated the first flash. If there is any effect of light following the first flash it must occur in less than about 10 s.We suggest that the polarity is determined by a complicated interference pattern of the light in the chloroplast which can focus it onto different parts, front or back, depending upon the wavelength of the light and the structure of the chloroplast.Abbreviations DCMU 3-(3, 4-dichlorophenyl)-1, 1 dimethylurea - PSII photosystem II, the oxygen emitting system in green plant photosynthesis - EDTA ethylenediaminetetraacetic acid - Hepes N-2-Hydroxyethylpiperazine-N'-2-ethanesulfonic acid     

The relationship between phytochrome-photoequilibrium and Development in light grown Chenopodium album L.

Chenopodium album seedlings were grown in light environments in which supplementary far-red light was mixed with white fluorescent light during various parts of the photoperiod. Both the logarithmic rate constant of stem extension and the leaf dry weight: stem dry weight ratio were linearly related to estimated phytochrome photoequilibrium () in each treatment regime. These data are taken to be indicative of a functional link between phytochrome and development in the green plant. A layer of chlorophyllous tissue only affected the linearity between calculated and the logarithmic stem extension rate at high chlorophyll concentrations, whilst even low concentrations-equivalent to the levels found in stem tissue-caused a significant shift in measured . End-of-day supplementary far-red (FR) light induced between 0–35 per cent of the response elicited by all-day supplementary FR, whilst daytime supplementary FR (with a white fluorescent light end-of-day treatment) induced approximately 90 per cent. The ecological significance of this difference is discussed with respect to shade detection.Paper 7 in the series The function of phytochrome in the natural environment [for paper 6 see McLaren, J.S., Smith, H., Plant, Cell and Environment 1, 61–67, 1978]     

Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

The control by phytochrome of hypocotyl elongation of light-grown Cucumis sativus L. after a white-light period was examined. The farred-absorbing form of phytochrome inhibits hypocotyl elongation. The response to phytochrome photostationary state () is not linear; all values of from 0.004 to 0.13 promote growth maximally, in the range of values of from 0.13 to 0.22 there is a linear growth response, between values of of 0.22 and 0.35 there is again no differential effect, and for values above 0.35 there is a strong (near linear) effect of on elongation. A kinetic examination of events following the white-light period shows that the major recovery from the photoperiod requires 8.5 h of darkness. End-of-day far-red treatment produces a very different response pattern, with a minor growth stimulation within 28 min of treatment followed by a major effect after 80 to 90 min. Three hours after far-red treatment there is a transient decline in growth rate which persists for about 2 h. Over the whole time course there is a great stimulation of growth rate compared with the controls. A similar growth-rate pattern also occurs if the end-of-day is 0.48, although the magnitude of the growth stimulation is less. Two components are affected by end-of-day , namely the time at which growth recovers and the subsequent growth rate. In the long term, the latter accounts for most of the differences in elongation growth. The dark recovery when only the hypocotyl is irradiated requires 4 h, but end-of-day far-red treatment reduces this to about 1.5 h. The persistence of the far-red-absorbing form of phytochrome for many hours in darkness in these light-grown plants is also demonstrated.Abbreviations and symbols D darkness - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - WL white light (from fluorescent lamps) - photostationary state of phytochrome - _c calculated      

Induction of embryogenicTriticum aestivum L. calli. II. Quantification of organic addenda and other culture variable effects

Nine experiments were conducted to determine effects of various culture medium addenda on induction of embryogenic calli from immature embryos of a responsiveTriticum aestivum L. genotype (PCYT 10). Effects were quatified by counting somatic embryos (embryoids) per callus. Optimal auxin concentrations to induce and maintain somatic embryogenesis were 3.62 M 2,4-dichlorophenoxyacetic acid (2,4-D) or 9.05 M 3,6-dichloro-o-anisic acid (dicamba). In general, dicamba permitted formation of significantly more embryoids than 2,4-D. Kinetin (6-furfurylaminopurine) at 2.56 M or 4.65 M significantly increased percentage scutellar callus when added to 2,4-D or dicamba-containing medium, respectively. Kinetin at 4.65 M signficantly increased the numbers of embryoids formed when added to medium containing either synthetic auxin. Significantly fewer embryoids formed when cultures were incubated under diffuse light (16-h photoperiod). Casein hydrolysate (200 mgl^-1) or L-arginine (0.23 mM) had no effect on numbers of embryoids formed, whereas L-tryptophan (0.20 mM) enhanced such formation with 2,4-D and decreased such formation with dicamba. Two additional experiments generally demonstrated that response to auxin source in the genotypes ND 7532, PCYT 20, Yaqui 50, and Oasis was similar to that in PCYT 10. The higher molar concentration of dicamba required to induce embryogenic callus coupled with more evident embryoid precocious germination and a more rapid rate of tissue necrosis upon extended incubation without subculture suggests that dicamba is metabolized more rapidly than 2,4-D inT. aestivum callus cultures.This study was supported by NASA-Ames Cooperative Agreement No. NCC2-139. Contribution of the Utah Agricultural Experiment Station, Utah State University, Logan, UT, Journal Paper No. 3359.     

Wide‐field hyperspectral 3D imaging of functionalized gold nanoparticles targeting cancer cells by reflected light microscopy

We present a new hyperspectral reflected light microscopy system with a scanned broadband supercontinuum light source. This wide‐field and low phototoxic hyperspectral imaging system has been successful for performing spectral three‐dimensional (3D) localization and spectroscopic identification of CD44‐targeted PEGylated AuNPs in fixed cell preparations. Such spatial and spectral information is essential for the improvement of nanoplasmonic‐based imaging, disease detection and treatment in complex biological environment. The presented system can be used for real‐time 3D NP tracking as spectral sensors, thus providing new avenues in the spatio‐temporal characterization and detection of bioanalytes.

3D image of the distribution of functionalized AuNPs attached to CD44‐expressing MDA‐MB‐231 human cancer cells.     

Methodological problems in evolutionary biology V. The import of supervenience

Rosenberg has rightly argued that fitness is supervenient. But he has wrongly assumed that this makes The fittest survive nontautologous. Supervenience makes strict reduction impossible. It sheds light on disputes concerning the testability of evolutionary theory.     

Induction of embryogenic Triticum aestivum L. calli. II. Quantification of organic addenda and other culture variable effects

Nine experiments were conducted to determine effects of various culture medium addenda on inducation of embryogenic calli from immature embryos of a responsive Triticum aestivum L. genotype (PCYT 10). Effects were quantified by counting somatic embryos (embryoids) per callus. Optimal auxin concentrations to induce and maintain somatic embryogenesis were 3.62 M 2,4-dichlorophenoxyacetic acid (2,4-D) or 9.05 M 3,6-dichloro-o-anisic acid (dicamba). In general, dicamba permitted formation of significantly more embryoids than 2,4-D. Kinetin (6-furfurylaminopurine) at 2.56 M or 4.65 M significantly increased percentage scutellar callus when added to 2,4-D or dicamba-containing medium, respectively. Kinetin at 4.65 M significantly increased the numbers of embryoids formed when added to medium containing either synthetic auxin. Significantly fewer embryoids formed when cultures were incubated under diffuse light (16-h photoperiod). Casein hydrolysate (200 mg1^-1) or L-arginine (0.23 mM) had no effect on numbers of embryoids formed, whereas L-tryptophan (0.20 mM) enhanced such formation with 2,4-D and decreased such formation with dicamba. Two additional experiments generally demonstrated that response to auxin source in the genotypes ND 7532, PCYT 20, Yaqui 50, and Oasis was similar to that in PCYT 10. The higher molar concentration of dicamba required to induce embryogenic callus coupled with more evident embryoid precocious germination and a more rapid rate of tissue necrosis upon extended incubation without subculture suggests that dicamba is metabolized more rapidly than 2,4-D in T. aestivum callus cultures.This study was supported by NASA-Ames Cooperative Agreement No. NCC2-139. Contribution of the Utah Agricultual Experiment Station, Utah State University, Logan, UT, Journal Paper No. 3358.     

Inside Cover: Investigation of the source‐detector separation in near infrared spectroscopy for healthy and clinical applications (J. Biophotonics 11/2019)

Near infrared spectroscopy (NIRS) neuroimaging sensors use light source and detector pairs placed over scalp to measure underlying neurophysiology. Source detector separation (SDS) is a critical design parameter and should aim a balanced trade‐off for detected light intensity and sensitivity to brain tissue. In this study, we used multi‐layer digital head models to systematically evaluate the role of SDS on NIRS spatial sensitivity profiles within both healthy and clinical conditions. Further details can be found in the article by Lei Wang, Hasan Ayaz, and Meltem Izzetoglu ( e201900175 ).

     

Fluence-response curves and action spectra for promotion and inhibition of seed germination in wildtype and long-hypocotyl mutants of Arabidopsis thaliana L.

The fluence-response curves of wildtype and long-hypocotyl mutants of Arabidopsis thaliana L. for induction and inhibition of seed germination, expressed as percentage germination on probit scale against logarithm of fluence, are very different in shape. The mutants show reduced photoinhibition of hypocotyl growth in white light compared with wildtype, suggesting they are either mutated in phytochrome, the blue/UV-absorbing photosystem or some other red-absorbing photosystem. Calculations of the amount of the far-red-absorbing form of phytochrome (Pfr), by a given fluence have been made taking into account pre-existing Pfr in the seeds. This pre-existing Pfr can change dramatically the slope of a fluence-response curve. Other factors such as an overriding factor, stimulating germination by a non-phytochrome-related process, the total phytochrome content, the range of normal distribution of logarithm of Pfr requirement of individuals in the population and differential screening can influence the form and-or position of a fluence-response curve. Action spectra calculated for germination induction and for the inhibition of induction for the different genotypes are qualitatively the same, having peaks of effectiveness at 660 nm and 730 nm respectively. In the blue region of the spectrum very little activity is seen in comparison with that of red light. Differences in bandwidth of effectiveness for induction of germination are attributed to different amounts of screening pigments in the seed batches. The long-hypocotyl mutants therefore have a normal phytochrome system operative in the control of seed germination, by short-term irradiation and no other photosystem appears to be involved.Abbreviations and symbols FR far-red light - P phytochrome - Pfr far-red-absorbing form of P - Pr red-absorbing form of P - R red light - SD standard deviation of logarithm Pfr around - logarithm Pfr required for 50% germination - aparent molar conversion cross section - maximum Pfr/Ptot established by a given wave-length - ₀ initial Pfr     

Estimation of the light distribution between photosystems I and II in intact wheat leaves by fluorescence and photoacoustic measurements

Usisng intact leaves, the extent of the decrease in chlorophyll a fluorescenece caused by the addition of continuous 710 nm light superimposed on modulated (20 Hz) 550 nm light was used to determine the distribution of this absorbed light between photosystems I () and II (). The F_o and F_m levels, which defined the total variable fluorescenece, were taken as equal to those obtained with excess 710 nm light and with saturating blue-green light, respectively.An analogous procedure was used with a photoacoustic detector, saturating white light defining a base line for oxygen yield, the levels with an without 710 nm light being used to define and respectively.The two methods gave similar values for the distribution of light between the two photosystems for the experimental conditions used, averaging 0.55 for a range of Triticum genotypes and Brachypodium sylvaticum grown in high or low light.     

NMR of bicelles: orientation and mosaic spread of the liquid-crystal director under sample rotation

Model-membrane systems composed of liquid-crystalline bicellar phases can be uniaxially oriented with respect to a magnetic field, thereby facilitating structural and dynamics studies of membrane-associated proteins. Here we quantitatively characterize a method that allows the manipulation of the direction of this uniaxial orientation. Bicelles formed from DMPC/DHPC are examined by ³¹P NMR under variable-angle sample-spinning (VAS) conditions, confirming that the orientation of the liquid-crystalline director can be influenced by sample spinning. The director is perpendicular to the rotation axis when (the angle between the sample-spinning axis and the magnetic field direction) is smaller than the magic angle, and is parallel to the rotation axis when is larger than the magic angle. The new ³¹P NMR VAS data presented are considerably more sensitive to the orientation of the bicelle than earlier ²H studies and the analysis of the sideband pattern allows the determination of the orientation of the liquid-crystal director and its variation over the sample, i.e., the mosaic spread. Under VAS, the mosaic spread is small if deviates significantly from the magic angle but becomes very large at the magic angle.     

L'azione dei raggi U.V. sul Grano

Summary

In order to study a side of the influence of ultra-violet light on plants, the A. has harvested, 10 days after fertilisation, 1040 plants of Triticum vulgare Vill. and made many groups of them; then he sheared differently the ears and screened them partially from light so as to obtain, from the same subject, treated and untreated grains. Such ears he treated for different times of exposure with the light of a quarzlamp giving almost only ultra-violet rays. For the present, are here reported only results concerning the influence of ultra-violet light upon both germinating energy and power:

• ultra-violet light stimulates the germinating power of grains, born from subjects treated no longer than 240 hours at a distance of 1 m from the lamp; longer treatments abate germinating power;

• ultra-violet light stimulates, the germinating energy of grains born from subjects treated no longer than 120 hours; treatments during 120–240 hours don't notably modify it; treatments of over 240 hours reduce it very much;

• according to the conditions in which this work has been done, a 10 days-irradiation seems to be, under every point of view, for the best. A 71/2 — days irradiation seems to be insufficient, a 121/2 — days one excessive, and hence prejudicial;

• glumes are strong screening-organ for ultra-violet light;

• ultra-violet light gives late appearing effects.

Since great difficulties usually occur whenever tests such as the present one are undertaken, the A. proposes some leading ways to previously settle the U.V.-rays dosimetry fit for every plant, in order to avoid wast of time and to get data of general value.     

Light and nutrient availability affect the size-scaling of growth in phytoplankton

Communities of marine phytoplankton consist of cells of many different sizes. The size-structure of these communities often varies predictably with environmental conditions in aquatic systems. It has been hypothesized that physiological differences in nutrient and light requirements and acquisition efficiencies contribute to commonly observed correlations between phytoplankton community size structure and resource availability. Using physiological models we assess how light and nutrient availability can alter the relative growth rates of phytoplankton species of different cell sizes. Our models predict a change in the size dependence of growth rate depending on the severity of limitation by light and nutrient availability. Under conditions of growth-saturated resource supply, phytoplankton growth rate (mol C ) scales with cell volume with a size-scaling exponent of ; light limitation reduces the size-scaling exponent to approximately , and nutrient limitation decreases the exponent to as a consequence of the size-scaling of resource acquisition. Exponents intermediate between and occur under intermediate availability of light and nutrients and depend on the size-scaling of pigment photoacclimation and the size range examined.     

Division,growth, and branch formation in protonema of the mossPhyscomitrium turbinatum: Studies of sequential cytological changes in living cells

Summary Elongating caulonemal tip cells ofPhyscomitrium turbinatum were cultivated on mediumcoated cover slips and periodically observed with Nomarski differential interference contrast optics. Tip cells exhibit apical growth and an average growth rate of 27.5 m/h. During cell elongation the nucleus migrates forward in the tip cell, but this movement slowly decreases so that there is a gradual increase in the distance between the nucleus and cell tip. Minimum length cells contain small vacuoles adjacent to the basal wall which coalesce during subsequent cell elongation to form a solitary large basal vacuole.An increase in chloroplasts during cell elongation is due to the presence of a population of proliferating chloroplasts located between the cell tip and the nucleus resulting in a gradient in chloroplast number and shape. The zone of chloroplast proliferation shifts progressively forward during cell elongation from a peri-nuclear position to a region closer to the cell tip. During division of the apical cell a perpendicular metaphase plate is formed. Reorientation movements of the phragmoplast-cell plate during telophase, and early stages of the following interphase produce a 35–40° cross wall. This rotation of the spindle axis positions the daughter nuclei temporarily adjacent to the lateral walls on opposite sides of the cell with the sub-apical nucleus on the side nearest the light source. It subsequently migrates across the cell to become situated on the wall farthest from the light source. Sub-apical cells form branches at the distal (= apical) end of the cell on the lateral wall closest to the light source. Branch development is accompanied by changes in chloroplast shape, number, and position.     

Locomotor response of the goldfish to polarized light and itse-vector

Summary The locomotor orientation of eleven goldfish, 20–25 cm long, was monitored during periods varying between 24 hours and 8 1/2 days, to verify the response to a depolarized and polarized sky, 100 cm in diameter, and to abrupt 90 ° degree rotation of thee-vector. The monitor consisted of a cylindrical tank with 16 peripheral compartments (Fig. 1) to which the fish had free access. Entry into and exit from each compartment was electronically recorded. The distribution of entries, which had no cyclical relationship with the compartments in depolarized light, became significantly symmetrical and bimodal in polarized light with the preferred compartments oriented parallel with thee-vector. Abrupt 90 ° rotation of the vector counter clockwise maintained this relationship during the entire duration of the recordings (up to 17 hours) (Fig. 2). The mean of the orientation angles of the fish on leaving compartments aligned with thee-vector were significantly higher than those from the remaining compartments (Fig. 3). This behavior tended to keep the locomotor orientation parallel with thee-vector as the fish moved between compartments. A strong cyclical relationship between these orientation angles and the compartments of origin was present in polarized but absent in depolarized light. Counter clockwise 90 ° rotation of thee-vector maintained the cyclic behavior of angles but the relationship between the larger means and thee-vector shifted over one or two compartments. This shift disappeared in clockwise rotation. This phenomenon may be due to one of these directions being unnatural. The results demonstrate a pronounced sensitivity and response toe-vector orientation in the goldfish. The sensory mechanism remains unknown.The authors are greatly indebted to Dr. T. H. Waterman for a critical review and discussion of the results here presented.