Blue Light Inhibition of Tuberization in a Day-Neutral Potato

In tests on the effects of light quality on potato tuberization, continuous blue light was found to consistently inhibit tuberization of tissue-cultured plantlets of Solanum tuberosum ssp. tuberosum cv. ??Norland??. Other tested cultivars, including sports of ??Norland??, formed tubers under continuous blue light. Microarrays identified BL, GA7ox, and Nudix genes as exhibiting altered expression in response to blue light treatment. Quantitative RT-PCR (qRT-PCR) showed that GA7ox RNA increased in ??Norland?? but not in ??Sangre?? plantlets in blue light compared to darkness. RNA levels of genes identified in the literature as having roles in potato tuberization were also measured using qRT-PCR. Levels of GA20o1x, but not GA2ox, RNA increased in response to blue light in ??Norland?? plantlets. BEL5 RNA content was greater under blue light compared to darkness for both ??Norland?? and ??Sangre?? plants. Levels of FT were not significantly different in blue light compared to dark-treated ??Norland?? plants, but were low in blue light-treated compared to dark-treated ??Sangre?? plants. Addition of ancymidol to ??Norland?? plants exposed to blue light overcame blue light inhibition of tuberization. Ancymidol prevents the oxidation of ent-kaurene to ent-kaurenoic acid, thus inhibiting gibberellin biosynthesis. These data suggest that blue light may increase GA accumulation in ??Norland?? plants, as has been shown to occur in Arabidopsis plants. The novel effect of blue light in inhibiting tuberization of ??Norland?? plants suggests that this system could be a useful tool in further elucidating the mechanisms of day-neutral potato tuberization.     

Differential responses to different light spectral ranges of violaxanthin de-epoxidation and accumulation of Cbr,an algal homologue of plant early light inducible proteins,in two strains of Dunaliella

Unicellular green algae of the genus Dunaliella, similar to higher plants, respond to light stress by enhanced de-epoxidation of violaxanthin and accumulation of Cbr, a protein homologous to early light inducible proteins (Elips) in plants. These proteins belong to the superfamily of chlorophyll a/b binding proteins. Two Dunaliella strains, D. bardawil and D. salina, were compared for these two responses under light in the UVA, blue, green and red spectral ranges. In D. bardawil, the two stress responses were similarly induced under UVA, blue or red light and to a lesser extent under green light. In D. salina, a similar spectral range dependence was exhibited for violaxanthin de-epoxidation. However, Cbr accumulated only under UVA or blue light but not under green or red light. A strong synergistic effect of a low dose of blue light superimposed on red light resulted in Cbr accumulation. These results reveal strain-specific differences in spectral range requirements of the two light-stress responses. In the two strains, violaxanthin de-epoxidation is triggered under photosynthetically-active spectral ranges but at least in D. salina, Cbr accumulation appears to require a specific light signal additionally to a signal(s) generated by light stress.     

Street lamp light does not delay autumnal leaf colouration of Betula pendula

Developing leaves of several mature Betula pendula trees planted for landscaping turned red when a sudden cold period occurred during the high light conditions of Spring. At the same time the leaves of other trees remained green. The effect of street lamp light on leaf colouration of the B. pendula trees with Springtime red- and green-emerging leaves was studied in the cool Autumn weather. The result suggests that the chlorophyll a and b, and carotenoid degradation of B. pendula leaves was not delayed by the street lamp light. The intensity of light and the amount of red and far-red light of the white lamp light was obviously very low to delay autumnal leaf colouration of B. pendula.     

Exquisite Light Sensitivity of Drosophila melanogaster Cryptochrome

Drosophila melanogaster shows exquisite light sensitivity for modulation of circadian functions in vivo, yet the activities of the Drosophila circadian photopigment cryptochrome (CRY) have only been observed at high light levels. We studied intensity/duration parameters for light pulse induced circadian phase shifts under dim light conditions in vivo. Flies show far greater light sensitivity than previously appreciated, and show a surprising sensitivity increase with pulse duration, implying a process of photic integration active up to at least 6 hours. The CRY target timeless (TIM) shows dim light dependent degradation in circadian pacemaker neurons that parallels phase shift amplitude, indicating that integration occurs at this step, with the strongest effect in a single identified pacemaker neuron. Our findings indicate that CRY compensates for limited light sensitivity in vivo by photon integration over extraordinarily long times, and point to select circadian pacemaker neurons as having important roles.     

Photoperiodism and photocontrol of stem elongation in two photomorphogenic mutants of Pisum sativum L.

The photomorphogenic mutation lv in the garden pea (Pisum sativum L.), which appears to reduce the response to light-stable phytochrome, has been isolated on a tall, late photoperiodic genetic background and its effects further characterised. Plants possessing lv have a reduced flowering response to photoperiod relative to wild-type plants, indicating that light-stable phytochrome may have a flower-inhibitory role in the flowering response of long-day plants to photoperiod. In general, lv plants are longer and have reduced leaf development relative to Lv plants. These differences are maximised under continuous light from fluorescent lamps (containing negligible far-red (FR) light), and decrease with addition of FR to the incident light. Enrichment of white light from fluorescent lamps with FR promotes stem elongation in the wild type but causes a reduction in elongation in the lv mutant. This “negative” shade-avoidance response appears to be the consequence of a strong inhibitory effect of light rich in FR, revealed in lv plants in the absence of a normal response to red (R) light. These results indicate that the wild-type response to the R: FR ratio may be comprised of two distinct photoresponses, one in which FR supplementation promotes elongation by reducing the inhibitory effect of R, and the other in which light rich in FR actively inhibits elongation. This hypothesis is discussed in relation to functional differentiation of phytochrome types in the light-grown plant. Gene lw has been reported previously to reduce internode length and the response to gibberellin A₁, and to delay flowering. The present study shows that the lw mutation confers an increased response to photoperiod. In all these responses the lw phenotype is superficially “opposite” to the lv phenotype. The possibility that the mutation might primarily affect light perception was therefore considered. The degree of dwarfing of lw plants was found to depend upon light quality and quantity. Dwarfing is more extreme in plants grown under continuous R light than in those grown in continuous FR or blue light or in darkness. Studies of the fluence-rate response show that the lw mutation imparts a lower fluence requirement for inhibition of elongation by white light from fluorescent lamps. Dark-grown lw plants are more strongly inhibited by a R pulse than are wild-type plants but, as in the wild type, this inhibition remains reversible by FR. Light-grown lw plants show an exaggerated elongation response to end-of-day FR light. Taken together, these findings indicate that the lw mutant may be hypersensitive to phytochrome action.     

New photoresponses of phycomyces

The influence of light on asexual fruiting and mycelial growth of Phycomyces blakesleeanus Burgeff was studied by means of fruiting body counts and size measurements in cultures on solid media under varied incubation conditions. Five types of photoresponses were shown by ATCC Strain 8743a: (a) photoinduction of giant sporangiophores; (b) interference by light with an endogenous system that otherwise induces fruiting when the mycelium approaches the rim of the Petri dish; (c) inhibition of mycelial growth rates by light; (d) inhibition of dwarf sporangiophore induction by light; and (e) postponement by light of death in clones maintained by serial transfer at low temperature. A second strain, designated G5, showed responses comparable to (a), (b), and (d). The magnitudes of the responses were greatly affected by temperature of incubation and available nitrogen (asparagine) supply. The photoinduction of giant sporangiophores could be demonstrated with light of wavelengths between 380 and 480 nanometers but not with 520 nanometers or above. At 480 nanometers, light doses as small as 40 ergs per square centimeter were effective in inducing giant sporangiophores in strain 8743a.     

Transplantation of marine sponges to different conditions of light and current

Transplantation was employed to determine how marine sponges grow in different in situ conditions of light and current. The growth of Verongia aerophoba (Schmidt), which contained symbiotic cyanobacteria. was enhanced in light, particularly when sediment was excluded by a clear shield. V. cavernicola Vacelet and Chondrosia reniformis Nardo. which did not contain cyanobacteria, grew preferentially in the shade and were inhibited by light. The growth of Petrosia ficiformis (Poirct) and Chondrilla nucula Schmidt, which may or may not contain cyanobacteria. did not appear to be favoured by either light or shade. The growth of sponges in lower current speeds was considerably reduced ; this reduction was. however, partially reversed in those sponges with cyanobacteria when grown in the light. Presumably symbiotic cyanobacteria are beneficial to sponges growing in the light because they transfer photosynthetically fixed nutrient and shield the underlying tissue. Significant morphological differences were observed in sponges grown under different environmental conditions.     

Acquisition of Tomato yellow leaf curl virus enhances attraction of Bemisia tabaci to green light emitting diodes

The light sensitivity of insects varies in response to different wavelengths of light. The change of light responses of vector insects plays an important role in the method of transmission and propagation of plant viruses. Here, we investigated whether the light attraction behaviors of whiteflies are altered by virus acquisition. Firstly, the light attraction rates of whiteflies were determined using LED light bulbs exhibiting different wavelengths in the visible and UV spectra. Whiteflies, Bemisia tabaci and Trialeurodes vaporariorum, were mostly attracted to green LEDs (526 nm). The attraction rate to green LED light was higher in B. tabaci than in T. vaporariorum, whereas it did not significantly differ between the B- and Q-biotypes of B. tabaci. Secondly, we investigated whether or not the green light attraction behavior of B. tabaci is influenced by the acquisition of Tomato yellow leaf curl virus (TYLCV). The attraction rate to green LED light was 2.5–3 times higher in TYLCV-infected whiteflies than in TYLCV-free whiteflies. However, this difference disappeared when the distance from the light source was greater than 0.5 m. Our results show that B. tabaci favors green light and its attraction is highly enhanced by the acquisition of the plant virus, TYLCV.     

The effect of light quality on leaf production and development of in vitro-cultured plants of Alternanthera brasiliana Kuntze

We investigated the influence of light quality on the leaf development of Alternanthera brasiliana Kuntze (Amaranthaceae) grown in vitro. Growth parameters including specific leaf mass, thickness, and leaf density were lowest in plants grown under red light. Blue light induced the largest number of leaves/plant, and the largest thickness and area of the leafblade. Green and red lights induced the smallest leaf areas. The thickness of the abaxial-face epidermis and spongy parenchyma of the plants was significantly reduced in plants grown under red light. The thickness of the palisade parenchyma and upper epidermis were significantly increased in plants grown under blue light, compared to the other fluorescent-light treatments. The specific spectral band also influenced the differentiation of mesophyll cells. In the dark and under red light, the mesophyll was homogenous; and in the dark and under green light, the leaves were more compact. Under blue light, the cells displayed the characteristic palisade morphology. The results showed that the increase of a specific parenchyma type was related to a specific spectral band. All spectral-quality treatments reduced the numbers of stomata and trichomes. The results for green light were in some respects similar to those for red light, and in other respects similar to those for blue light, probably because phytochromes and cryptochromes are green-light receptors. This study indicated that Alternanthera plants have strong morphological plasticity induced by light. The results suggest that high-quality Alternanthera can be achieved by culturing the plants in vitro under a combination of blue and red light.     

Diatom Phytochromes Reveal the Existence of Far-Red-Light-Based Sensing in the Ocean

The absorption of visible light in aquatic environments has led to the common assumption that aquatic organisms sense and adapt to penetrative blue/green light wavelengths but show little or no response to the more attenuated red/far-red wavelengths. Here, we show that two marine diatom species, Phaeodactylum tricornutum and Thalassiosira pseudonana, possess a bona fide red/far-red light sensing phytochrome (DPH) that uses biliverdin as a chromophore and displays accentuated red-shifted absorbance peaks compared with other characterized plant and algal phytochromes. Exposure to both red and far-red light causes changes in gene expression in P. tricornutum, and the responses to far-red light disappear in DPH knockout cells, demonstrating that P. tricornutum DPH mediates far-red light signaling. The identification of DPH genes in diverse diatom species widely distributed along the water column further emphasizes the ecological significance of far-red light sensing, raising questions about the sources of far-red light. Our analyses indicate that, although far-red wavelengths from sunlight are only detectable at the ocean surface, chlorophyll fluorescence and Raman scattering can generate red/far-red photons in deeper layers. This study opens up novel perspectives on phytochrome-mediated far-red light signaling in the ocean and on the light sensing and adaptive capabilities of marine phototrophs.     

Control of the Photosynthetic Apparatus of Acetabularia mediterranea by Blue Light : Analysis by Light-Saturation Curves

During growth, Acetabularia mediterranea requires the action of blue light to maintain high rates of photosynthesis. In the present study, blue light-dependent alterations of the photosynthetic apparatus, which can be detected by analysis of light-saturation curves and by measurements of partial reactions of the photosynthetic electron transport chain, are described. Light-saturation curves of photosynthesis in vivo were measured with a new closed oxygen electrode system after culture of Acetabularia in continuous red or blue light. These curves were compared to those of 2,6-dichlorophenol-indophenol reduction by isolated chloroplast membranes. The analysis lead to the following statements: (a) only one reaction limits electron transport rates in vitro (dichlorophenol-indophenol reduction) at all light intensities irrespective of the light quality during growth, and (b) the limiting step is light driven and located in the reaction center of photosystem II. Presumably, this same reaction determines the flow of electrons under low light intensities in vivo in cells from white, blue, and red light. In addition to photosynthesis, the rates of dark respiration changed due to the action of blue light. Concomitantly, the light compensation point of apparent photosynthesis was shifted during monochromatic irradiations.     

Regulation of 5-Aminolevulinic Acid (ALA) Synthesis in Developing Chloroplasts : II. Regulation of ALA-Synthesizing Capacity by Phytochrome

When dark-grown cucumber (Cucumis sativus L.) seedlings previously exposed to white light for 20 hours were returned to darkness, the ability of isolated chloroplasts to synthesize 5-aminolevulinic acid dropped by approximately 70% within 1 hour. The seedlings were then exposed to light, and the synthetic ability of the isolated chloroplasts was determined. Restoration of the synthetic capacity was promoted by continuous white or red light of moderate intensity. Intermittent red light was also effective. Blue and far-red light did not restore the synthetic capability. Blue light given after a red pulse did not enhance the effect of the red light. Far-red light given immediately after each red pulse prevented the stimulation due to intermittent red light. Restoration of the biosynthetic activity by in vivo light treatments was inhibited by cycloheximide indicating the requirement for translation on 80 S ribosomes for the in vivo light response. These findings suggest that the majority of the plastidic 5-aminolevulinic acid synthesis is under phytochrome regulation.     

Enhancement of the Stomatal Response to Blue Light by Red Light, Reduced Intercellular Concentrations of CO(2), and Low Vapor Pressure Differences

The effects of environmental parameters on the blue light response of stomata were studied by quantifying transient increases in stomatal conductance in Commelina communis following 15 seconds by 0.100 millimole per square meter per second pulses of blue light. Because conductance increases were not observed following red light pulses of the same or greater (30 seconds by 0.200 millimole per square meter per second) fluences, the responses observed could be reliably attributed to the specific blue light response of the guard cells, rather than to guard cell chlorophyll. In both Paphiopedilum harrisianum, which lacks guard cell chloroplasts, and Commelina, the blue light response was enhanced by 0.263 millimole per square meter per second continuous background red light. Thus, the blue light response and its enhancement do not require energy derived from red-light-driven photophosphorylation by the guard cell chloroplasts. In Commelina, reduction of the intercellular concentration of CO₂ by manipulation of ambient CO₂ concentrations resulted in an enhanced blue light response. In both Commelina and Paphiopedilum, the blue light response was decreased by an increased vapor pressure difference. The magnitude of blue-light-specific stomatal opening thus appears to be sensitive to environmental conditions that affect the carbon and water status of the plant.     

Effect of light and substratum complexity on microhabitat selection and activity of the ophiuroid Ophiopholis aculeata

We evaluated the effect of light intensity and substratum complexity on habitat preference and displacement speed of the ophiuroid Ophiopholis aculeata. The ophiuroid strongly preferred reduced light and to a lesser extent complex substrata. Further, displacement speed increased with light intensity and decreased with substratum complexity (ophiuroids were virtually immobile on darkened complex substrata). In the field, the density of exposed ophiuroids, with the disk out of a crevice, was always low, irrespective of the intensity of solar radiation. However, the extent to which they extended their arms (to feed) was inversely related to light intensity, as the number of suspension-feeding arms was low under direct sunlight, intermediate under indirect light and high at night. Field observations showed that the response to light was not modified when UV radiation was eliminated with a filter, and a laboratory experiment showed that white light intensity alone produced patterns similar to those observed in the field. O. aculeata may reduce arm extension with increasing light intensity to reduce the threat of visual predators, whose foraging efficiency increases with light intensity. However, visual predators are rare in our study site. We hypothesize that the large-scale larval dispersion of O. aculeata (due to the long pelagic phase) prevents ophiuroids from adapting to local conditions so that its response to light reflects adaptation to visual predators in other locations.     

Exposing broiler eggs to green,red and white light during incubation

Previous work has shown that exposing broiler eggs to white light during incubation can improve hatchability and post-hatch animal welfare. It was hypothesized that due to how different wavelengths of light can affect avian physiology differently, and how pigmented eggshells filter light that different monochromatic wavelengths would have differential effects on hatchability and post-hatch animal welfare indicators. To determine, we incubated chicken eggs (n=6912) under either no light (dark), green light, red light or white light; the light level was 250 lux. White and red light were observed to increase hatch of fertile (P<0.05) over dark and green light incubated eggs. White, red and green light exposure during incubation improved (P<0.05) the proportion of non-defect chicks over dark incubated eggs. Post-hatch 45-day weight and feed conversion was not affected by light exposure of any wavelength (P>0.05). Fear response of during isolation and tonic immobility was reduced (P<0.05) in broilers incubated under white or red light when compared with either green or dark broilers. Broilers incubated with white or red light had lower (P<0.05) composite asymmetry scores and higher (P<0.05) humoral immunity titers than dark incubated broilers, however, green light broilers did not differ (P>0.05) from dark incubated broilers. All light incubated broilers had lower (P<0.05) plasma corticosterone and higher (P<0.05) plasma serotonin concentrations than dark incubated broilers. These results indicate that white light and red light that is a component of it are possibly the key spectrum to improving hatchability and lower fear and stress susceptibility, whereas green light is not as effective. Incubating broiler eggs under these spectrums could be used to improve hatchery efficiency and post-hatch animal welfare at the same time.     

Heat shock and light activation of aChlamydomonas HSP70 gene are mediated by independent regulatory pathways

Induction ofHSP70 heat shock genes by light has been demonstrated inChlamydomonas. Our aim was to establish whether this induction by light is mediated by the heat stress sensing pathway or by an independent signal chain. Inhibitors of cytoplasmic protein synthesis revealed an initial difference. Cycloheximide and other inhibitors of protein synthesis preventedHSP70A induction upon illumination but not during heat stress. Analysis ofHSP70A induction in cells that had differentiated into gametes revealed a second difference. While heat shock resulted in elevatedHSP70A mRNA levels, light was no longer able to serve as an inducer in gametes. To identify the regulatory sequences that mediate the response of theHSP70A gene to either heat stress or light we introduced a series of progressive 5′ truncations into its promoter sequence. Analyses of the levels of mRNA transcribed from these deletion constructs showed that in most of them the responses to heat shock and light were similar, suggesting that light induction is mediated by a light-activated heat shock factor. However, we show that theHSP70A promoter also containscis-acting sequences involved in light induction that do not participate in induction by heat stress. Together, these results provide evidence for a regulation ofHSP70A gene expression by light through a heat shock-independent signal pathway.     

Biogenesis and light regulation of the major light harvesting chlorophyll-protein of diatoms

The apoprotein of the major light harvesting pigment-protein complex from the diatom Phaeodactylum tricornutum (UTEX 646) is composed of two similar polypeptides of 17.5 and 18.0 kilodaltons (kD). The in vivo synthesis of these polypeptides is inhibited by the 80s protein synthesis inhibitor cycloheximide, but not by the 70s ribosome inhibitor chloramphenicol. When total poly(A)⁺ RNA was used in in vitro protein synthesis, a number of polypeptides were synthesized with a dominant product at 22 kD. When the polypeptides were immunoprecipitated with monospecific antibodies to the 17.5 and 18.0 polypeptides, a single protein zone of 22 kD was detected. Immunoprecipitation with preimmune serum failed to precipitate detectable levels of protein at any relative molecular weight (M_r). These findings indicate that the two apoprotein polypeptides of the diatom light harvesting pigment-protein are translated from polyadenylated message on cytoplasmic ribosomes as either a single or two (or more) similar M_r precursor proteins. These findings also suggest that this protein is encoded in the nucleus.

Photosynthetic light adaptation features of P. tricornutum UTEX 646 indicate that it responds to low light by increasing cell size and numbers of photosystem I and II reaction centers per cell, but does not change photosynthetic rate per cell or photosynthetic unit sizes significantly. When low light cells are exposed to higher photon flux densities, the in vivo incorporation of label into the apoprotein of the light harvesting complex decreases. In contrast, high light grown cells show rapid (<3 hour) increases in apoprotein synthesis when exposed to low light levels. This is the first demonstration of a specific role of photon flux density in regulating the synthesis of a major light harvesting pigment-protein during photosynthetic light adaptation.

     

Electrophysiological Properties of Cells in the Median Ocellus of Limulus

Two types of photoreceptors are found in the median ocellus of Limulus. One type is maximally sensitive to ultraviolet (UV) light, the other to green light; they are called UV and VIS cells, respectively. Biphasic receptor potentials, consisting of a small initial hyperpolarizing phase and a later slow depolarizing phase, can be recorded from both receptor types. These biphasic responses are elicited in UV cells in response to long-wavelength light, and in VIS cells in response to ultraviolet light. Another type of hyperpolarizing response can be recorded in UV cells: after a bright ultraviolet stimulus, the cell remains depolarized; long-wavelength light rapidly returns the membrane potential to its value preceding ultraviolet illumination (this long-wavelength-induced potential change is called a "repolarizing response"). Also, a long-wavelength stimulus superimposed during a UV stimulus elicits a sustained repolarizing response. A third cell type (arhabdomeric cell) found in the median ocellus generates large action potentials and is maximally sensitive to UV light. Biphasic responses and repolarizing responses also can be recorded from arhabdomeric cells. The retina is divided into groups of cells; both UV cells and VIS cells can occur in the same group. UV cells in the same group are electrically coupled to one another and to an arhabdomeric cell.