On visual adaptation: II. The electroretinogram and the bipolar cells

First a model for theb-wave of the electroretinogram is given. The essential part of the model is the diffusion into the rod-bipolar synapse of a transmitter substance, followed by the induction of an inhibitor. Making use of this model, adaptation to an illumination too weak to cause of significant decrease in the concentration of visual pigment is interpreted as due to a decreased effectiveness of the rod impulse in exciting the bipolar cell. The disparity between threshold changes for very small test spots and for relatively large spots is explained simply, without invoking any additional physiological mechanisms. This research was supported in part by the United States Air Force through the Air Force Office of Scientific Research of the Air Research Development Command under Contract No. AF(638)-414 and in part by the United States Public Health Service Training Grant 2G-833.     

Daily and circadian variation in the electroretinogram of the domestic fowl: effects of melatonin

Visual and circadian function are integrally related in birds, but the precise nature of their interaction is unknown. The present study determined whether visual sensitivity measured electroretinographically (ERG) in 7-week-old cockerels varies over the time of day, whether this rhythm persists in constant darkness (DD) and whether exogenous melatonin affects this ERG rhythmicity. ERG b-wave amplitude was rhythmic in LD and persisted in DD with peak amplitude during mid- to late afternoon in LD and mid-subjective day in DD, indicating that the ERG rhythm is endogenously generated. No daily or circadian variation in a-wave amplitude was observed, and ERG component latency and durations were not rhythmic. Intramuscular injection of 10 g/kg melatonin at ZT10 in LD significantly decreased b-wave amplitude but had no effect on a-wave. Intraocular injection of 600 pg melatonin, however, had no effect on any aspect of the ERG. These data indicate that a circadian clock regulates ocular sensitivity to light and that melatonin may mediate some or all of this effect. The level at which melatonin modulates retinal sensitivity is not known, but the present data suggest a central site rather than a direct effect of the hormone in the eye.Abbreviations DD constant darkness - ERG electroretinography - EW Edinger-Westphal nuclei - IMEL iodomelatonin - IO isthmooptic nucleus - LD light-dark cycle - SCG superior cervical ganglion - SCN suprachiasmatic nuclei - vSCN visual suprachiasmatic nucleus     

Adaptation in Skate Photoreceptors

Receptor potentials were recorded extracellularly from the all-rod retina of the skate after the application of sodium aspartate. This agent suppresses the responses of proximal elements, but leaves relatively unaffected the electrical activity of the photoreceptors (a-wave) and pigment epithelium (c-wave). Since the latter develops too slowly to interfere with the receptor response, it was possible to isolate receptor potentials and to compare their behavior in light and dark adaptation with earlier observations on the S-potential, b-wave, and ganglion cell discharge. The results show that the photoreceptors display the full complement of adaptational changes exhibited by cells proximal to the receptors. Thus, it appears that visual adaptation in the skate is governed primarily by the photoreceptors themselves. Of particular interest was the recovery of sensitivity in the presence of background fields that initially saturate the receptor potential. Analysis of this recovery phase indicates that a gain-control mechanism operates within the receptors, at a distal stage of the visual process.     

Seasonal changes in daily metabolic patterns of Lacerta viridis

Summary Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T _b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T _a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm.Oxygen consumption measured at various T_as shows significant seasonal differences at T _as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T _as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.Abbreviations ANOVA analysis of variance - LD long day (16 h light) - SD short day (8 h light) - T _a ambient temperature - T _b body temperature     

Photophysics of the carotenoids associated with the xanthophyll cycle in photosynthesis

Green plants use the xanthophyll cycle to regulate the flow of energy to chlorophylla within photosynthetic proteins. Under conditions of low light intensity violaxanthin, a carotenoid possessing nine conjugated double bonds, functions as an antenna pigment by transferring energy from its lowest excited singlet state to that of chlorophylla within light-harvesting proteins. When the light intensity increases, violaxanthin is biochemically transformed into zeaxanthin, a carotenoid that possesses eleven conjugated double bonds. The results presented here show that extension of the conjugation of the polyene lowers the energy of the lowest excited singlet state of the carotenoid below that of chlorophylla. As a consequence zeaxanthin can act as a trap for the excess excitation energy on chlorophylla pigments within the protein, thus regulating the flow of energy within photosynthetic light-harvesting proteins.     

Thermo-optically Induced Reorganizations in the Main Light Harvesting Antenna of Plants. II. Indications for the Role of LHCII-only Macrodomains in Thylakoids

We have investigated the circular dichroism spectral transients associated with the light-induced reversible reorganizations in chirally organized macrodomains of pea thylakoid membranes and loosely stacked lamellar aggregates of the main chlorophyll a/b light harvesting complexes (LHCII) isolated from the same membranes. These reorganizations have earlier been assigned to originate from a thermo-optic effect. According to the thermo-optic mechanism, fast local thermal transients due to dissipation of the excess excitation energy induce elementary structural changes in the close vicinity of the dissipation [Cseh et al. (2000) Biochemistry 39: 15250–15257]. Here we show that despite the markedly different CD spectra in the dark, the transient (light-minus-dark) CD spectra associated with the structural changes induced by high light in thylakoids and LHCII are virtually indistinguishable. This, together with other close similarities between the two systems, strongly suggests that the gross short-term, thermo-optically induced structural reorganizations in the membranes occur mainly, albeit probably not exclusively, in the LHCII-only domains [Boekema et al. (2000) J Mol Biol 301: 1123–1133]. Hence, LHCII-only domains might play an important role in light adaptation and photoprotection of plants.     

Inhibition of bovine α-chymotrypsin by cyclic trypsin inhibitor SFTI-1 isolated from sunflower seeds and its two acyclic analogues

Summary Trypsin inhibitor SFTI-1 isolated from sunflower seeds (comprising 14 amino acid residues and two cycles: head-to-tail cyclisation and disulfide bridge) is the smallest naturally occurring plant serine proteinase inhibitor. In our recent paper we have shown that the elimination head-to-tail cyclisation did not change trypsin inhibitory activity as judged by measured by association equilibrium constants K _a . The removal of disulfide bridge produced 2.4-fold lower activity. In the present paper we described chymotrypsin inhibitory activity. SFTI-1 inhibits significantly lower bovine α-chymortypsin (K _a =(5.20±1.56)×10⁶ M⁻¹). The activity of the analogue with disulfide bridge only was practically the same, whereas the K _a value determined for homodetic peptide was almost 3-fold lower. Considering the results obtained and the recent literature data we postulate the lower inhibitory activity against both enzymes of the analogue with head-to-tail cyclisation only reflect its lower proteolytic stability.     

Inhibition of endogenous trypsin- and chymotrypsin-like activities in transgenic lettuce expressing heterogeneous proteinase inhibitor SaPIN2a

SaPIN2a, a proteinase inhibitor II from American black nightshade (Solanum americanum Mill.) is highly expressed in the phloem and could be involved in regulating proteolysis in the sieve elements. To further investigate the physiological role of SaPIN2a, we have produced transgenic lettuce (Lactuca sativa L.) expressing SaPIN2a from the CaMV35S promoter by Agrobacterium-mediated transformation. Stable integration of the SaPIN2a cDNA and its inheritance in transgenic lines were confirmed by Southern blot analysis and segregation analysis of the R₁ progeny. SaPIN2a mRNA was detected in both the R₀ and R₁ transformants on northern blot analysis but the SaPIN2a protein was not detected on western blot analysis using anti-peptide antibodies against SaPIN2a. Despite an absence of significant inhibitory activity against bovine trypsin and chymotrypsin in extracts of transgenic lettuce, the endogenous trypsin-like activity in each transgenic line was almost completely inhibited, and the endogenous chymotrypsin-like activity moderately inhibited. Our finding that heterogeneously expressed SaPIN2a in transgenic lettuce inhibits plant endogenous protease activity further indicates that SaPIN2a regulates proteolysis, and could be potentially exploited for the protection of foreign protein production in transgenic plants.Abbreviations CaMV cauliflower mosaic virus - cDNA complementary DNA - NOS nopaline synthase - PAGE polyacrylamide gel electrophoresis - PI proteinase inhibitor - SaPIN2a Solanum americanum proteinase inhibitor IIa - SDS sodium dodecyl sulphate - T-DNA transferred DNA     

Thylakoid protein phosphorylation during State 1—State 2 transitions in osmotically shocked pea chloroplasts

In osmotically shocked pea chloroplasts illuminated with modulated blue-green light (light 2), phosphorylation of the light-harvesting chlorophyll $\text{a}\text{b-}\text{protein}$ complex (LHCP) accompanies the slow decrease in modulated fluorescence that indicates adaptation to light absorbed predominantly by Photosystem II (State 2). On subsequent additional illumination with continuous far-red light (absorbed predominantly by Photosystem I; light 1) both effects are reversed: modulated chlorophyll fluorescence emission increases (indicating adaptation towards State 1) and LHCP is dephosphorylated. Net phosphorylation and dephosphorylation of LHCP induced by light 2 and excess light 1, respectively, occur on the same time scale as the ATP-dependent chlorophyll fluorescence changes indicative of State 2 and State 1 transitions. The phosphatase inhibitor NaF (10 mM), stimulates the effect of blue-green light on fluorescence and prevents the effect of far-red light. These results provide a demonstration that light of different wavelengths can control excitation energy distribution between the two photosystems via the plastoquinol-activated LHCP phosphorylation mechanism suggested previously (Allen, J.F., Bennett, J., Steinback, K.E. and Arntzen, C.J. (1981) Nature 291, 25–29; and Horton, P. and Black, M.T. (1980) FEBS Lett. 119, 141–144).     

Inhibition ofd-alanyl-d-alanine ligase in different bacterial species by amino phosphonic acids

A comparative study was performed on the kinetic properties and the specificity ofd-alanyl-d-alanine ligases fromPseudomonas aeruginosa, Streptococcus faecalis, andStaphylococcus aureus, using some aminophosphonic acids and related compounds.dl-I-Aminoethylphosphonic acid was shown to be a competitive inhibitor of theP. aeruginosa andS. faecalis ligases; assuming ad-form stereospecificity, its activity was nearly equal to that ofd-cycloserine. 2-Aminoethylphosphonate was found to be a weak inhibitor of the ligases, in contrast to the carboxylic analog, β-alanine. γ-Aminobutyric acid and phosphoethanolamine also exhibited some inhibitory properties.     

Correspondences in the Behavior of the Electroretinogram and of the Potentials Evoked at the Visual Cortex

Electrical potentials from the eye (ERG) and from the contralateral visual cortex were recorded in response to flashes of white and of colored light of various intensities and durations. The evoked potentials were found to parallel the behavior of the ERG in several significant respects. Selective changes in the ERG brought about by increasing the light intensity and by light adaptation led to parallel selective changes in the cortical responses. The dual waves (b₁, b₂) of the ERG were found to have counterparts in two cortical waves (c₁, c₂) which, in respect to changes in light intensity and to light adaptation, behaved analogously to the two retinal components. The responses evoked at high intensity showed only the diphasic c₁-potential. As stimulus intensity was lowered the c₁-wave decreased in magnitude and a delayed c₂-component appeared. The c₂-potential increased in amplitude as light intensity of the flash was further reduced. Eventually the c₂-wave, too, decreased as stimulus reduction continued. There was no wave length specificity in regard to either the duplex b-waves or duplex cortical waves. Both appeared at all wave lengths from 454 mµ to 630 mµ. The two cortical waves evoked by brief flashes of colored light showed all the behavior to changes in stimulus intensity and to light adaptation that occurred with white light.     

Effects of light on cyanide‐resistant respiration and alternative oxidase function in Arabidopsis seedlings

Mitochondrial alternative oxidase (AOX), the unique respiratory terminal oxidase in plants, catalyzes the energy wasteful cyanide (CN)‐resistant respiration and plays a role in optimizing photosynthesis. Although it has been demonstrated that leaf AOX is upregulated after illumination, the in vivo mechanism of AOX upregulation by light and its physiological significance are still unknown. In this report, red light and blue light‐induced AOX (especially AOX1a) expressions were characterized. Phytochromes, phototropins and cryptochromes, all these photoreceptors mediate the light‐response of AOX1a gene. When aox1a mutant seedlings were grown under a high‐light (HL) condition, photobleaching was more evident in the mutant than the wild‐type plants. More reactive oxygen species (ROS) accumulation and inefficient dissipation of chloroplast reducing‐equivalents in aox1a mutant may account for its worse adaptation to HL stress. When etiolated seedlings were exposed to illumination for 4 h, chlorophyll accumulation was largely delayed in aox1a plants. We first suggest that more reduction of the photosynthetic electron transport chain and more accumulation of reducing‐equivalents in the mutant during de‐etiolation might be the main reasons.     

Photoperiodic responses ofXanthium strumarium L. (Compositae) introduced and indigenous in eastern asia

Photoperiodic responses among populations ofXanthium strumarium L. in eastern Asia from Vladivostok, USSR, to Hong Kong and Taiwan include a wide range of adaptation. Among indigenous populations of thestrumarium morphological complex, responses range from near day neutrality (Vladivostok) to approximately a night length requirement of 9.5 hr (Hong Kong). Introduced populations in Japan include a night length requirement of 9.75 hr in theitalicum morphological complex and of 10.25–10.5 hr in thechinense morphological complex. The range of photoperiodic adaptation is nearly as wide as among populations of North America.     

cPPB‐aE is discovered from photosynthetic benthic dinoflagellates

Although chlorophyll degradation pathways in higher plants have been well studied, little is known about the mechanisms of chlorophyll degradation in microalgae. In this article, we report the occurrence of a chlorophyll a derivative that has never been discovered in photosynthetic organisms. This chlorophyll derivative emits no fluorescence and has a peculiar absorbance peak at 425, 451, 625, and 685 nm. From these features, it was identified as 13²,17³‐cyclopheophorbide a enol (cPPB‐aE), reported as a degradation product of chlorophyll a derived from prey algal cells in heterotrophic protists. We discovered cPPB‐aE in six benthic photosynthetic dinoflagellates that are phylogenetically separated into four clades based on SSU rDNA molecular phylogeny. This is the first report of this chlorophyll derivative in photosynthetic organisms and we suggest that the derivative is used to quench excess light energy.     

Phenotypic and phenological plasticity of an aquatic macrophyteMenyanthes trifoliata L.

Phenotypic and phenological properties ofMenyanthes trifoliata L. were investigated within and outside of aPhragmites australis (Cav.) Trin. ex. Steud. canopy in a floating peat mat in Mizorogaike Pond, Central Japan. Under theP. australis canopy,M. trifoliata adjusted its phenotypic properties to the conditions of decreased light by increasing leaf blade area, decreasing leaf blade thickness and elongating petioles. The earlier expansion of leaves ofM. trifoliata within theP. australis community than outside the community was advantageous in terms of allowing the plant in the mixed community to produce as much dry matter as possible before the foliage ofP. australis could overgrow it. Despite the harmful effect ofP. australis onM. trifoliata's vegetative growth and reproduction, the latter species can persist in aP. australis community by changing its phenotypic and phenological properties.     

Sinusoidal and delta function responses of visual cells of the Limulus eye

Dynamic responses of visual cells of the Limulus eye to stimuli of sinusoids and narrow pulses of light superimposed on a nonzero mean level have been obtained. Amplitudes and phase angles of averaged sinusoidal generator potential are plotted with respect to frequency of intensity modulation for different mean levels of light adaptation. At frequencies above 10 CPS, generator potential amplitudes decrease sharply and phase lag angle increases. At frequencies below 1 CPS, amplitude decreases. A maximum of amplitude in the region of 1 to 2 CPS is apparent with increased mean intensity. The generator potential responses are compared with those of differential equation models. Variation of gain with mean intensity for incremental stimuli is consistent with logarithmic sensitivity of the photoreceptor. Frequency response of the photoreceptor derived from narrow pulses of light predicts the frequency response obtained with sinusoidal stimuli, and the photoreceptor is linear for small signals in the light-adapted state.     

STATE TRANSITIONS AND NONPHOTOCHEMICAL QUENCHING DURING A NUTRIENT‐INDUCED FLUORESCENCE TRANSIENT IN PHOSPHORUS‐STARVED DUNALIELLA TERTIOLECTA1

Assessments of nutrient‐limitation in microalgae using chl a fluorescence have revealed that nitrogen and phosphorus depletion can be detected as a change in chl a fluorescence signal when nutrient‐starved algae are resupplied with the limiting nutrient. This photokinetic phenomenon is known as a nutrient‐induced fluorescence transient, or NIFT. Cultures of the unicellular marine chlorophyte Dunaliella tertiolecta Butcher were grown under phosphate starvation to investigate the photophysiological mechanism behind the NIFT response. A combination of low temperature (77 K) fluorescence, photosynthetic inhibitors, and nonphotochemical quenching analyses were used to determine that the NIFT response is associated with changes in energy distribution between PSI and PSII and light‐stress‐induced nonphotochemical quenching (NPQ). Previous studies point to state transitions as the likely mechanism behind the NIFT response; however, our results show that state transitions are not solely responsible for this phenomenon. This study shows that an interaction of at least two physiological processes is involved in the rapid quenching of chl a fluorescence observed in P‐starved D. tertiolecta: (1) state transitions to provide the nutrient‐deficient cell with metabolic energy for inorganic phosphate (P_i)‐uptake and (2) energy‐dependent quenching to allow the nutrient‐stressed cell to avoid photodamage from excess light energy during nutrient uptake.     

Concept of energy in biological systems

Beside the concept of material inputs and outputs of components of the representation of biological systems given to us by Rosen, the concept of energy is incorporated. The interaction of material and energy is represented by a cartesian product; and separate material and energetical mappings are considered as the new representation of components. These developments generate aMα category, and it is shown thatMα is isomorphic to theM category of previous developments.     

A specialised transducing phage of P22 for which the ability to form plagues is associated with transduction of the proAB region

Summary The multisite mutantproAB47 has been used to isolate specialised transducing phages of P22 for theproA andproB genes. Several of the preparations contain phages that form small plaques, and many of the properties of these suggest that the small plaques are formed by the transducing phages. Preliminary studies on the transduction of theproAB region by one such phage suggest that it forms fairly stable heterogenotes, both from apro point mutant and fromproAB47. The fact that the latter mutant is missing the phage attachment site results in a delay in integration of the specialised transducing phage.