The Expression of Light-Regulated Genes in the High-Pigment-1 Mutant of Tomato1

Three light-regulated genes, chlorophyll a/b-binding protein (CAB), ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit, and chalcone synthase (CHS), are demonstrated to be up-regulated in the high-pigment-1 (hp-1) mutant of tomato (Lycopersicon esculentum Mill.) compared with wild type (WT). However, the pattern of up-regulation of the three genes depends on the light conditions, stage of development, and tissue studied. Compared with WT, the hp-1 mutant showed higher CAB gene expression in the dark after a single red-light pulse and in the pericarp of immature fruits. However, in vegetative tissues of light-grown seedlings and adult plants, CAB mRNA accumulation did not differ between WT and the hp-1 mutant. The ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit mRNA accumulated to a higher level in the hp-1 mutant than WT under all light conditions and tissues studied, whereas CHS gene expression was up-regulated in de-etiolated vegetative hp-1-mutant tissues only. The CAB and CHS genes were shown to be phytochrome regulated and both phytochrome A and B1 play a role in CAB gene expression. These observations support the hypothesis that the HP-1 protein plays a general repressive role in phytochrome signal transduction.

Reduction of Light-Induced Anthocyanin Accumulation in Inoculated Sorghum Mesocotyls1 : Implications for a Compensatory Role in the Defense Response

Sorghum (Sorghum bicolor L. Moench) accumulates the anthocyanin cyanidin 3-dimalonyl glucoside in etiolated mesocotyls in response to light. Inoculation with the nonpathogenic fungus Cochliobolus heterostrophus drastically reduced the light-induced accumulation of anthocyanin by repressing the transcription of the anthocyanin biosynthesis genes encoding flavanone 3-hydroxylase, dihydroflavonol 4-reductase, and anthocyanidin synthase. In contrast to these repression effects, fungal inoculation resulted in the synthesis of the four known 3-deoxyanthocyanidin phytoalexins and a corresponding activation of genes encoding the key branch-point enzymes in the phenylpropanoid pathway, phenylalanine ammonia-lyase and chalcone synthase. In addition, a gene encoding the pathogenesis-related protein PR-10 was strongly induced in response to inoculation. The accumulation of phytoalexins leveled off by 48 h after inoculation and was accompanied by a more rapid increase in the rate of anthocyanin accumulation. The results suggest that the plant represses less essential metabolic activities such as anthocyanin synthesis as a means of compensating for the immediate biochemical and physiological needs for the defense response.

An AU-box motif upstream of the SD sequence of light-dependent psbA transcripts confers mRNA instability in darkness in cyanobacteria

The psbA2 gene of a unicellular cyanobacterium, Microcystis aeruginosa K-81, encodes a D1 protein homolog in the reaction center of photosynthetic Photosystem II. The expression of the psbA2 transcript has been shown to be light-dependent as assessed under light and dark (12/12 h) cycling conditions. We aligned the 5′-untranslated leader regions (UTRs) of psbAs from different photosynthetic organisms and identified a conserved sequence, UAAAUAAA or the ‘AU-box’, just upstream of the SD sequences. To clarify the role of 5′-upstream cis-elements containing the AU-box for light-dependent expression of psbA2, a series of deletion and point mutations in the region were introduced into the genome of heterologous cyanobacterium Synechococcus sp. strain PCC 7942, and psbA2 expression was examined. A clear pattern of light-dependent expression was observed in recombinant cyanobacteria carrying the K-81 psbA2 –38/+36 region (which includes the minimal promoter element and a light-dependent cis-element with the AU-box), +1 indicating the transcription start site. A constitutive pattern of expression, in which the transcripts remained almost stable under dark conditions, was obtained in cells harboring the –38/+14 region (the minimal element), indicating that the +14/+36 region with the AU-box is important for the observed light-dependent expression. Point mutations analyses within the AU-box also revealed that changes in number, direction and identity (as assayed by adenine/uridine nucleotide substitutions) influenced the light-dependent pattern of expression. The level of psbA2 transcripts increased markedly in CG- or deletion-box mutants in the dark, strongly indicating that the AU- (AT-) box acts as a negative cis-element. Furthermore, characterization of transcript accumulation in cells treated with rifampicin suggests that psbA2 5′-mRNA is unstable in the dark, supporting the view that the light-dependent expression is controlled at the post-transcriptional level. We discuss various mechanisms that may lead to altered mRNA stability such as the binding of factor(s) or ribosomes to the 5′-UTR and possible roles of the AU-box motif and the SD sequence.

Influence of light on DNA content of Helianthus annuus Linnaeus.

Mean nuclear 2C DNA content (C equaling haploid DNA per nucleus) of the first leaf of the sunflower, Helianthus annuus L., is influenced by the quality and the quantity of light. Seedlings of two inbred lines, RHA 299 and RHA 271 were germinated and grown in controlled environmental conditions. Lighting was adjusted to provide different combinations of photon flux densities and red to far red (R:FR) ratios. At R:FR = 5.8 and photon flux densities of 170 mumol.m-2.s-1, 200 mumol.m-2.s-1, and 230 mumol.m-2.s-1, DNA content remained high and relatively constant (x = 6.97 pg for RHA 271 and x = 7.32 pg for RHA 299). When the photon flux density range (R:FR = 5.8) was elevated to 350 mumol.m-2.s-1, 410 mumol.m-2.s-1, and 470 mumol.m-2.s-1, mean DNA content was reduced to 6.23 pg (RHA 271) and 6.46 pg (RHA 299). At R:FR = 1.5, mean DNA content was consistently high (7.2-7.9 pg) only at the lowest photon flux density of 170 mumol.m-2.s-1. Significant decreases in DNA content (< or = 12%) were observed at photon flux densities of 200 mumol.m-2.s-1 and 230 mumol.m-2.s-1. At the higher photon flux densities (350 mumol.m-2.s-1, 410 mumol.m-2.s-1, and 470 mumol.m-2.s-1) and R:RF = 1.5, the plants had extremely low DNA contents (mean x = 3.36 pg for RHA 271 and 3.41 pg for RHA 299) and high between-plant variance. The instability of DNA content, particularly for plants grown under light that is far red rich, suggests that phytochromes may be involved in regulating DNA content of the sunflower.

Regulation of herbivore growth by the balance of light and nutrients.

Experiments using planktonic organisms revealed that the balance of radiant energy and available nutrients regulated herbivore growth rates through their effects on abundance and chemical composition of primary producers. Both algae and herbivores were energy limited at low light/nutrient ratios, but both were nutrient limited at high light/nutrient ratios. Herbivore growth increased with increasing light intensity at low values of the light/nutrient ratio due to increases in algal biomass, but growth decreased with increasing light at a high light/nutrient ratio due to decreases in algal quality. Herbivore production therefore was maximal at intermediate levels of the light/nutrient ratio. The results contribute to an understanding of mass transfer mechanisms in ecosystems and illustrate the importance of integration of energy-based and material-based currencies in ecology.

Location of light-repressible, small GTP-binding protein of the YPT/rab family in the growing zone of etiolated pea stems.

YPT/rab proteins are ras-like small GTP-binding proteins that serve as key regulators of vesicular transport. The mRNA levels of two YPT/rab genes in pea plants are repressed by light, with the process mediated by phytochrome. Here, we examined the mRNA expression and the location of the two proteins, pra2- and pra3-encoded proteins, using monoclonal antibodies. The pra2 and pra3 mRNA levels were highest in the stems of dark-grown seedlings. The corresponding proteins were found in the cytosol and the membranes of the stems. Most of the pra2 protein was in the growing internodes, especially in the growing region, but the pra3 protein was widespread. These results suggest that the pra2 protein is important for vesicular transport in stems, possibly contributing to stem growth in the dark, and that the pra3 protein is important for general vesicular transport. The amounts of pra2 and pra3 proteins decreased with illumination. The decrease in these proteins may be related to the phytochrome-dependent inhibition of stem growth that occurs in etiolated pea seedlings.

Electrically Tunable Selective Reflection of Light from Ultraviolet to Visible and Infrared by Heliconical Cholesterics

Acknowledgements This work was supported by NSF DMR-1410378 and DMR-1121288. We thank V. Borshch for helping with preparation of illustrations, to Y. K. Kim for the help in experiments, V. A. Belyakov and S. V. Shiyanovskii for useful discussions.

Sampling scarab beetles in tropical forests: the effect of light source and night sampling periods

Light traps have been used widely to sample insect abundance and diversity, but their performance for sampling scarab beetles in tropical forests based on light source type and sampling hours throughout the night has not been evaluated. The efficiency of mercury-vapour lamps, cool white light and ultraviolet light sources in attracting Dynastinae, Melolonthinae and Rutelinae scarab beetles, and the most adequate period of the night to carry out the sampling was tested in different forest areas of Costa Rica. Our results showed that light source wavelengths and hours of sampling influenced scarab beetle catches. No significant differences were observed in trap performance between the ultraviolet light and mercury-vapour traps, whereas these two methods caught significantly more species richness and abundance than cool white light traps. Species composition also varied between methods. Large differences appear between catches in the sampling period, with the first five hours of the night being more effective than the last five hours. Because of their high efficiency and logistic advantages, we recommend ultraviolet light traps deployed during the first hours of the night as the best sampling method for biodiversity studies of those scarab beetles in tropical forests.

Identifying student and teacher difficulties in interpreting atomic spectra using a quantum model of emission and absorption of radiation

Our study sets out to identify the difficulties that high school students, teachers, and university students encounter when trying to explain atomic spectra. To do so, we identify the key concepts that any quantum model for the emission and absorption of electromagnetic radiation must include to account for the gas spectra and we then design two questionnaires, one for teachers and the other for students. By analyzing the responses, we conclude that (i) teachers lack a quantum model for the emission and absorption of electromagnetic radiation capable of explaining the spectra, (ii) teachers and students share the same difficulties, and (iii) these difficulties concern the model of the atom, the model of radiation, and the model of the interaction between them.

Crash tests of light-post thrie-beam traffic barriers. Final report.

Federal Highway Administration, Office of Research, Washington, D.C.

Transmission of light in water; an annotated bibliography

Cover title.

The effect of light truck design variables on top speed, performance, and fuel economy, 1981. Final report.

National Highway Traffic Safety Administration, Office of Research and Development, Washington, D.C.