Broad Range Of Light Intensities Research Articles

Light regulation of the Arabidopsis respiratory chain. Multiple discrete photoreceptor responses contribute to induction of type II NAD(P)H dehydrogenase genes.

Controlled oxidation reactions catalyzed by the large, proton-pumping complexes of the respiratory chain generate an electrochemical gradient across the mitochondrial inner membrane that is harnessed for ATP production. However, several alternative respiratory pathways in plants allow the maintenance of substrate oxidation while minimizing the production of ATP. We have investigated the role of light in the regulation of these energy-dissipating pathways by transcriptional profiling of the alternative oxidase, uncoupling protein, and type II NAD(P)H dehydrogenase gene families in etiolated Arabidopsis seedlings. Expression of the nda1 and ndc1 NAD(P)H dehydrogenase genes was rapidly up-regulated by a broad range of light intensities and qualities. For both genes, light induction appears to be a direct transcriptional effect that is independent of carbon status. Mutant analyses demonstrated the involvement of two separate photoreceptor families in nda1 and ndc1 light regulation: the phytochromes (phyA and phyB) and an undetermined blue light photoreceptor. In the case of the nda1 gene, the different photoreceptor systems generate distinct kinetic induction profiles that are integrated in white light response. Primary transcriptional control of light response was localized to a 99-bp region of the nda1 promoter, which contains an I-box flanked by two GT-1 elements, an arrangement prevalent in the promoters of photosynthesis-associated genes. Light induction was specific to nda1 and ndc1. The only other substantial light effect observed was a decrease in aox2 expression. Overall, these results suggest that light directly influences the respiratory electron transport chain via photoreceptor-mediated transcriptional control, likely for supporting photosynthetic metabolism.

Measurements of capture velocity in a magneto-optical trap for a broad range of light intensities

We use a dark-spot Zeeman-tuned slowing technique to measure the capture velocity in a sodium magneto-optical trap as a function of the trapping laser intensity. We expand on previous work by measuring the capture velocity over a broad range of light intensities. We observe that the capture velocity reaches a maximum value and then decreases with increasing light intensities, which might imply a minimum in the trap-loss rate. This observation supports a recently published explanation of the dependence of the trap-loss rates, at low intensities, based mainly on the escape velocity.

Light acclimation maintains the redox state of the PS II electron acceptor Q(A) within a narrow range over a broad range of light intensities.

Chrysanthemum inducum-hybrid 'Coral Charm', Hibiscus rosa-sinensis L. 'Cairo Red' and Spathiphyllum wallisii Regel 'Petit' were grown in natural light in a greenhouse at three levels of irradiance using permanent shade screens. Light acclimation of photosynthesis was characterized using modulated chlorophyll a fluorescence of intact leaves. A close correlation was found between the degree of reduction of the primary electron acceptor Q(A) of Photosystem II (PS II) approximated as the fluorescence parameter 1-q(P), and light acclimation. The action range of 1-q(P) was 0-0.4 from darkness to full irradiance around noon, within the respective light treatments in the greenhouse, indicating that most PS II reaction centres were kept open. In general, the index for electron transport (ETR) measured by chlorophyll fluorescence was higher for high-light (HL) than intermediate-(IL) and low-light (LL) grown plants. However, HL Chrysanthemum showed 40% higher ETR than HL Hibiscus at light saturation, despite identical redox states of Q(A). The light acclimation of the non-radiative dissipation of excess energy in the antenna, NPQ, varied considerably between the species. However, when normalized against q(P), a strong negative correlation was found between thermal dissipation and ETR measured by chlorophyll fluorescence. To be able to accommodate a high flux of electrons through PS II, the plants with the highest light-saturated ETR had the lowest NPQ/q(P). The possibility of using chlorophyll fluorescence for quantification of the energy balance between energy input and utilization in PS II in intact leaves is discussed.

Foraging modes of chinstrap penguins:contrasts between day and night

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 165:161-172 (1998) - doi:10.3354/meps165161 Foraging modes of chinstrap penguins: contrasts between day and night John K. Jansen*, Peter L. Boveng, John L. Bengtson National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration, 7600 Sand Point Way N.E., Building 4, Seattle, Washington 98115-0070, USA *E-mail: john.jansen@noaa.gov Penguins rely on vision to travel and hunt at sea. Vision in marine predators, particularly those hunting phototactic prey under a broad range of light intensities, must be better understood to realize how these species respond to changes in their environment. We studied the effects of daily cycles in light intensity on visual predators by examining the duration and timing of chinstrap penguins' Pygoscelis antarctica foraging trips and the size, composition, and timing of their meals. We used radio telemetry and stomach-contents sampling to study adult penguins that were provisioning chicks during the summers of 1993 and 1994 at Seal Island, Antarctica. The penguins rarely initiated or terminated foraging trips at night, but otherwise varied the timing and duration of trips to sea. Cluster analyses using departure and arrival times revealed 5 distinct modes of foraging: 3 were strictly diurnal (early, mid-, and late) and 2 were partly nocturnal (overnight and extended). Durations of diurnal trips (4 to 11 h) were shorter than overnight (13 to 14 h) and extended trips (18 to 22 h). Early and mid-diurnal trips and extended trips were significantly shorter in 1993 than in 1994; late diurnal and overnight trip durations did not differ between years. Diurnal foraging was most common in 1993, whereas overnight foraging predominated in 1994. Shortened diurnal foraging in 1993 appears to have increased the frequency of diurnal foraging by allowing more parent birds to alternate diurnal trips within a single day and by reducing the incidence of birds extending diurnal foraging through the night. That penguins foraged more frequently by day when permitted by shorter trip durations (in 1993) suggests that they opted to forage diurnally whenever possible. Returning diurnal and overnight foragers had greater than 99 and 74% Antarctic krill Euphausia superba by weight in their stomachs, respectively. However, overnight foragers also returned with significant amounts of highly digested remains of pelagic fish, suggesting birds were in offshore waters taking fish during the night. In contrast, only 1 out of 40 diurnal foragers from both years combined had evidence of fish. Thus, the daily light cycle affected both the timing and duration of chinstrap penguin foraging as well as the type of prey consumed during trips to sea. Diel activity patterns · Diet composition · Foraging trip duration · Myctophid fish · Ecological monitoring · Pygoscelis antarctica · Euphausia superba Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 165. Publication date: May 07, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Regulation of sensitivity in vertebrate rod photoreceptors by calcium

Over the past decade and a half, there have been great advances in our understanding of how light is transduced into electrical signals by the retina; rod and cone photoreceptors in vertebrates. One essential feature of these sensory neurons is their ability to adapt to background illumination, which allows them to function over a broad range of light intensities. This adaptatio appears to arise mostly from negative feedback on phototransduction that is mediated by calcium ions. Recent work has suggested that this feedback is fairly complex, and involves several pathways directed at different components of phototransduction. From direct measurements of these feedback pathways in rods, it is possible to evaluate their relative contributions to the overall sensitivity of the cell. At the same time, these feedback mechanisms, as currently known, appear to be sufficient for explaining the change in sensitivity of rods during adaptation to light.

The light-harvesting complex II (B800-850) of Rhodobacter sulfidophilus: Characterization and formation under different growth conditions

The photosynthetic bacterium Rhodobacter sulfidophilus is able to grow chemotrophically and phototrophically at a broad range of light intensities. In contrast to other facultative phototrophs, R. sulfidophilus synthesizes reaction center and light-harvesting (LH) complexes, B870 (LHI) and B800–850 (LHII) even under full aerobic conditions in the dark. The content of bacteriochlorophyll (BChl) varied from 3.8 μg Bchl per mg cell protein when grown at high light intensity (20 000 lux) to 60 μg Bchl per mg cell protein when grown at low light intensities (6 lux). After a shift from high light to low light conditions, the size of the photosynthetic unit increased by a factor of 4. Chromatographie analysis of the LHII complex, isolated and purified from cells grown phototrophically (at high and low light intensities) and chemotrophically, could resolve only one type of a and one type of β polypeptide in the purified complex, of which the N-terminal sequences have been determined.

Modelling some effects of behavior on larval settlement in a turbulent boundary layer

Abstract A one-dimensional model of larval concentration and settlement flux in a turbulent boundary layer was used to consider how some aspects of larval behavior in the plankton or on the bottom might affect settlement rates. The focus was on behavioral modifications of two terms in the model—the vertical (fall) velocity ( w f ), a composite measure of swimming and gravitational sinking, and the probability of settlement per unit time ( p ) for larvae interacting with the bottom. Depth-independent changes in vertical speed can increase the settlement rate by up to an order of magnitude. Such changes might be produced by negative phototactic responses that induce passive sinking of larvae throughout the water column during daylight, by photonegative swimming responses that may occur in relatively shallow or clear water (where swimming responses are fairly uniform throughout the water column), or by photonegative swimming responses that are of similar magnitude over a broad range of light intensities. In addition to increasing the long-term average settlement rate, negative phototactic responses should increase temporal variability in settlement at time scales of ≦24 h, as long as larvae are responding to changes in light intensity at depth. This prediction, coupled with results from Gross et al . [(1992) Journal of Marine Research , 50 , 611–642], suggests that for larvae that respond to light there may be two sources of substantial (order-of-magnitude) temporal variability in settlement that operate at time scales of 24 h or less— diel periodicity in light intensity and semi-diurnal or diurnal tidal periodicity in boundary shear stress and turbulence intensity. The additional effect of phase shift between tidal and light cycles introduces substantially less variability to the average (>24 h) settlement rate than do individual effects of the two forcings. Behavioral responses that produce a depth dependence in vertical speed can affect the settlement rate only if w f varies roughly by a factor of 2 or more very close to the bottom (i.e. within a few percent of total boundary layer thickness for tidal boundary layers). Phototactic or barokinetic responses of larvae are not likely to produce depth gradients in vertical speed strong enough to affect settlement rates. However, such gradients might be produced by a recent contact with a potential settlement site, by effects of velocity gradients near the bottom on larval orientation, or by larval responses to chemical cues associated with the bottom. Behavioral responses to fluid forces exerted on larvae on the bottom can alter the settlement rate by an order of magnitude or more. However, the settlement rate is predicted to be most sensitive to effects of weak, rather than strong, flow on the settlement probability. Thus, understanding larval responses to weak flows may be especially important to predicting settlement rates.