Ratio Of Sunlight Research Articles

Seasonal Differences in the UVA/UVB Ratio of Natural Sunlight Influence the Efficiency of the Photoisomerization of (6-4) Photoproducts into their Dewar Valence Isomers.

The UVA and UVB components of sunlight can produce three classes of bipyrimidine DNA photolesions [cyclobutane pyrimidine dimers (CPDs), pyrimidine (6‐4) pyrimidone photoproducts (6‐4PPs) and related Dewar valence isomers (DewarPPs)]. The UVA/UVB ratio of sunlight is high in winter and low in summer in the Northern Hemisphere. Since UVB radiation produces 6‐4PPs and UVA radiation converts them into DewarPPs through photoisomerization, it is expected that there may be differences in the photoisomerization of 6‐4PPs between summer and winter, although that has never been documented. To determine that, isolated DNA was exposed to natural sunlight for 8 h in late summer and in winter, and absolute levels of the three classes of photolesions were quantified using calibrated ELISAs. It was found that sunlight produces CPDs and 6‐4PPs in DNA at a ratio of about 9:1 and converts approximately 80% of 6‐4PPs into DewarPPs within 3 h. Moreover, photoisomerization is more efficient in winter than in late summer after sunlight irradiation for the same duration, at similar solar UV doses and with the same induction level of CPDs. These results demonstrate that seasonal differences in the UVA/UVB ratio influence the efficiency of the photoisomerization of 6‐4PPs into DewarPPs.

The shade-avoidance syndrome: multiple signals and ecological consequences.

Plants use photoreceptor proteins to detect the proximity of other plants and to activate adaptive responses. Of these photoreceptors, phytochrome B (phyB), which is sensitive to changes in the red (R) to far-red (FR) ratio of sunlight, is the one that has been studied in greatest detail. The molecular connections between the proximity signal (low R:FR) and a model physiological response (increased elongation growth) have now been mapped in considerable detail in Arabidopsis seedlings. We briefly review our current understanding of these connections and discuss recent progress in establishing the roles of other photoreceptors in regulating growth-related pathways in response to competition cues. We also consider processes other than elongation that are controlled by photoreceptors and contribute to plant fitness under variable light conditions, including photoresponses that optimize the utilization of soil resources. In examining recent advances in the field, we highlight emerging roles of phyB as a major modulator of hormones related to plant immunity, in particular salicylic acid and jasmonic acid (JA). Recent attempts to manipulate connections between light signals and defence in Arabidopsis suggest that it might be possible to improve crop health at high planting densities by targeting links between phyB and JA signalling.

木漏れ日に着目した単木落葉樹の日射遮蔽に関する数値解析

In order to create more attractive urban spaces by greening, we need to take into account the various effects of greenery, for example solar shading of tree crown and cooling effect by transpiration, when designing green urban spaces. The purpose of this study is to develop numerical tree model of a deciduous tree for simulating the effects of solar shading by tree crown on the surface temperature, brightness distribution and illuminance distribution under tree crown. As a fundamental study, this paper investigates relationship between tree geometry and solar transmittance using the CG tree model. The solar transmittance ratio is determined as the ratio of sunlight through a tree into the tree shadow. Several tree species and variation are created by a CGsoftware. Hourly the solar transmittance ratio is calculated by the ray-tracing method using the CG model. The relationship between the tree geometry depending on tree species and the solar transmittance ratio is analyzed. The result shows that the solar transmittance ratio of Prunus x yedoensis and Platanus x acarifolia have no relationship to these factors, although the ratio of Zelkova serrata, which has similar geometry type to plant community, is depended on LAI. These indicate that a tree model for solar transmittance need several parameters such as LAI, size of leaf and density of branch.

Illuminated behaviour: phytochrome as a key regulator of light foraging and plant anti‐herbivore defence

In many ecological scenarios, the success of an individual plant is defined by the behavioural decisions that it makes when confronted with the risks of competition with other plants, and biomass losses to insect herbivores. These decisions involve expression of shade avoidance responses and induced chemical defences. Because these responses are costly, they frequently engender resource allocation dilemmas. In this review, I discuss the mechanisms that trigger adaptive responses to competitors and herbivores, highlighting the role of phytochromes as central organizers of the overall resource allocation strategy of plants. Phytochromes sense the reduction in the red to far-red (R : FR) ratio of sunlight caused by the proximity of other plants. Shade-intolerant plants respond to low R : FR ratios with shade avoidance behaviours and reduced investment in defence. Pfr depletion leads to increased stability of growth-promoting phytochrome-interacting factors (PIFs), and results in the production of auxins and gibberellins, degradation of DELLA proteins, which are repressors of PIFs, and reduced sensitivity to jasmonates. Thus, phytochrome appears to fulfil its organizational role by regulating the relative strength of the signalling circuits controlled by growth-related and defence-related hormones. I point out cases of signalling redundancy and discuss the significance of recent work on hormone signalling for our understanding of the mechanisms that control adaptive plant behaviour.

Stratospheric aerosol observations from a balloon-borne polarimetric experiment

This paper documents a balloon-borne experiment vis-a-vis the observation of the radiance and polarization ratio of sunlight scattered by the stratospheric aerosol at near-infrared wavelengths. Described are the results and preliminary analysis of the first flight, on 15 Dec. 1983, at an altitude of 20 km. The observations, particularly the polarization features, are consistent with single scattering calculations for spherical particles with a mean radius of ~0.3 μm and with a refractive index of 1.45 at 0.85 μm; thus, the presence of sulfuric acid aerosol is corroborated.