Public concern about the safety of many forms of industrial technology are known to be linked to a range of factors including a perceived lack of confidence in regulatory decision making.1 The use of transgenic plants in agriculture may be seen as an issue that could generate similar concern. Criticism has been made about the completeness of knowledge on the potential for aberrant behaviour of genetically manipulated organisms (GMO's) in release environments, and the adequacy of existing pre‐release screening and assessment methodologies (Goldberg & Tjaden, 1990). Such comments are important because any perceived shortcomings in the pre-release assessment of GMO safety may lead to decreased public support of the technology -‐and the industry itself...
Abstract Mixtures and monocultures of wheat ( Triticum aestivum ) and wild oat ( Avena fatua ), a common weedy competitor of wheat, were exposed to enhanced solar UV‐B radiation simulating a 20% reduction in stratospheric ozone to assess the timing and seasonal development of the UV‐B effects on light competition in these species. Results from two years of field study revealed that UV‐B enhancement had no detectable effect on the magnitude or timing of seedling emergence in either species. End‐of‐season measurements showed significant UV‐B inhibition of leaf insertion height in wild oat in mixture and monoculture in the second year (irrigated year) but not in the first year (drought year). Leaf insertion height of wheat was not affected by UV‐B in either year. The UV‐B treatment had no detectable effect on monoculture or total (combined species) mixture LAI but did significantly increase (5–7%) the fractional contribution of wheat to the mixture LAI after four weeks of growth in both years. In addition, the UV‐B treatment had subtle effects on LAI height profiles with early season mixtures showing significant reductions in wild oat LAI in lower canopy layers in both years while midseason Year 2 mixtures showed significant reductions in wild oat LAI in upper canopy layers. The changes in canopy structure were found to significantly increase (6–7%) the proportional simulated clear sky canopy photosynthesis and light interception of wheat in mixture. These findings, and others, indicate that the effects of UV‐B enhancement on competition are realized very early in canopy development and provide additional support for the hypothesis that UV‐B enhancement may shift the balance of competition between these species indirectly by altering competitive interactions for light.
Broad‐band UV‐B radiation inhibited hypocotyl elongation in etiolated tomato ( Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by < 3 μmol m −2 s −1 of UV‐B radiation provided against a background of white light (> 620 μmol m −2 s −1 between 320 and 800 nm), and was similar in wild‐type and phytochrome‐1‐deficient aurea mutant seedlings. These observations suggest that the effect of UV‐B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m −2 s −1 of monochromatic UV radiation against a while light background (63 μmol m −2 s −1 showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV‐B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN, and phenylacetic acid) largely abolished the inhibitor) effect of broad‐hand UV‐B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10 −4 M , which have been shown in vitro to be effective in quenching the triplet excited stales of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV‐A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation evened by UV‐B. Kl applied after UV‐B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system invoked in UV‐B perception by tomato seedlings during de‐etiolation may be a flavin.
The relationship between nuclear DNA content and chromosome number was investigated in Andropogon gerardii. The distribution of cytotypes in a natural population of this grass was also examined. Nuclear DNA content was determined using flow cytometry rather than the traditional method of Feulgen microphotometry. Our results demonstrate the increased accuracy and speed of this new method in the detection and study of polyploidy. Nuclear DNA content is strongly correlated to chromosome number in Andropogon gerardii (r = 0.971, P <0.01). The natural population of this grass was found to consist of plants with 2N = 60 chromosomes (hexaploid cytotype) and 2N = 80 chromosomes (octoploid cytotype), in equal proportions. Intermediate cytotypes were lacking in the natural population, although three progeny plants grown in the greenhouse from wild-collected seed show intermediate values of nuclear DNA content and have 2N = 70 chromosomes. The two coexisting cytotypes are intermingled and show no difference in microhabitats. The absence of septaploids in the natural population suggests that the two cytotypes are probably reproductively isolated. Key words: polyploidy, DNA contents, flow cytometry, polymorphism.
Ratios of chlorophyll fluorescence induced by ultraviolet (UV) and bluegreen (BG) radiation [F(UV)/F(BG)] were determined with a Xe‐PAM fluorometer to test the utility of this technique as a means of non‐intrusively assessing changes in the pigmentation and optical properties of leaves exposed to varying UV exposures under laboratory and field conditions. For plants of Vicia faba and Brassica campestris , grown under controlled‐environmental conditions, F(UV‐B)/F(BG) was negatively correlated with whole‐leaf UV‐B‐absorbing pigment concentrations. Fluorescence ratios of V. faba were similar to, and positively correlated with (r 2 =0.77 [UV‐B]; 0.85 [UV‐A]), direct measurements of epidermal transmittance made with an integrating sphere. Leaves of 2 of 4 cultivars of field‐grown Glycine max exposed to near‐ambient solar UV‐B at a mid‐latitude site (Buenos Aires, Argentina, 34° S) showed significantly lower abaxial F(UV‐B)/F(BG) values (i.e., lower UV‐B epidermal transmittance) than those exposed to attenuated UV‐B, but solar UV‐B reduction had a minimal effect on F(UV‐B)/F(BG) in plants growing at a high‐latitude site (Tierra del Fuego, Argentina, 55° S). Similarly, the exotic Taraxacum officinale did not show significant changes in F(UV‐B)/F(BG) when exposed to very high supplemental UV‐B (biologically effective UV‐B=14–15 kJ m −2 day −1 ) in the field in Tierra del Fuego, whereas a native species, Gunnera magellanica , showed significant increases in F(UV‐B)/F(BG) relative to those receiving ambient UV‐B. These anomalous fluorescence changes were associated with increases in BG‐absorbing pigments (anthocyanins), but not UV‐B‐absorbing pigments. These results indicate that non‐invasive estimates of epidermal transmittance of UV radiation using chlorophyll fluorescence can detect changes in pigmentation and leaf optical properties induced by UV‐B radiation under both field and laboratory conditions. However, this technique may be of limited utility in cold environments where UV and low temperatures can stimulate the production of BG‐absorbing pigments that interfere with these indirect measurements of UV‐transmittance.
This paper describes the work performed with a pure metal thermal interface material (TIM) for the sole purpose to improve the transfer of heat from the die to the metal cover case. A flux-less reflow process is employed in order to reflow the indium TIM material. This operation is performed in a vacuum furnace utilizing heat, vacuum, and pressure in a specific sequence in order to wet the metal lid and the backside of the flip chip die. The initial objective was to demonstrate minimal voiding of the TIM and subsequently limited flow out of molten solder from and along the sides of the die. A series of experiments were employed where acceptance criteria is evaluated by a) X-Ray, b) scanning acoustical microscopy (SAM), and c) cross-section. Acceptance criteria consists of 1) indium wetting of both lid to indium interface and indium to silicon interface die, 2) indium bond line (BLT) thickness, 3) lid tilt, and 4) lid shear strength. Acceptance is determined after a subsequent 4X ball grid array (BGA) reflow in a conventional belt reflow furnace with minimal voiding, no popcorn or blistering of the laminate substrate, and TIM thickness and solder flow out at sides of the die within the acceptable limits of the above mentioned criteria.
Brief (1-100 min) irradiations with three different ultraviolet-B (UV-B) and ultraviolet-C (UV-C) wave bands induced increases the UV-absorbing pigments extracted from cucumber (Cucumis sativus L.) and Arabidopsis. Spectra of methanol/1% HCl extracts from cucumber hypocotyl segments spanning 250-400 nm showed a single defined peak at 317 nm. When seedlings were irradiated with 5 kJ m(-2) UV-B radiation containing proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm; full-spectrum UV-B, FS-UVB), tissue extracts taken 24 h after irradiation showed an overall increase in absorption (91% increase at 317 nm) with a second defined peak at 263 nm. Irradiation with 1.1 kJ m(-2) UV-C (254 nm) caused similar changes. In contrast, seedlings irradiated with 5 kJ m(-2) UV-B including only wavelengths longer than 290 nm (8% of UV-B between 290 and 300 nm; long-wavelength UV-B, LW-UVB) resulted only in a general increase in absorption (80% at 317 nm). The increases in absorption were detectable as early as 3 h after irradiation with FS-UVB and UV-C, while the response to LW-UVB was first detectable at 6 h after irradiation. In extracts from whole Arabidopsis seedlings, 5 kJ m(-2) LW-UVB caused only a 20% increase in total absorption. Irradiation with 5 kJ m(-2) FS-UVB caused the appearance of a new peak at 270 nm and a concomitant increase in absorption of 72%. The induction of this new peak was observed in seedlings carrying the fah1 mutation which disrupts the pathway for sinapate synthesis. The results are in agreement with previously published data on stem elongation indicating the existence of two response pathways within the UV-B, one operating at longer wavelengths (>300 nm) and another specifically activated by short wavelength UV-B (<300 nm and also by UV-C).
There are close links between solar UV radiation, climate change, and plastic pollution. UV-driven weathering is a key process leading to the degradation of plastics in the environment but also the formation of potentially harmful plastic fragments such as micro- and nanoplastic particles. Estimates of the environmental persistence of plastic pollution, and the formation of fragments, will need to take in account plastic dispersal around the globe, as well as projected UV radiation levels and climate change factors. UV radiation, climate change, and plastic pollution are closely interlinked. Existing studies on the persistence of plastics do not fully consider these linkages, challenging global assessments of plastic dispersal, persistence, and weathering. Recently, an Intergovernmental Negotiating Committee was tasked with developing an international binding agreement to end plastic pollution. In response, the UNEP Environmental Effects Assessment Panel assessed effects of UV radiation and interacting climate change factors on plastics, focusing on the durability of products as well as the production and dispersal of micro- and nano-plastic pollutants in the environment. Annual global production of plastics was estimated at 400 million metric tonnes in 2022 (Plastics Europe, 2023). A substantial fraction of these plastics ultimately ends up in the natural environment as unmanaged and ubiquitous contaminants. Plastics are highly diverse in composition and properties. Further, their formulations typically include additives, such as dyes, flame retardants, and plasticizers, resulting in variations in chemical composition, functional and structural properties, and persistence in the environment. The environmental accumulation of plastics has led to concerns about the effects of macro- (>5 mm), micro- (<5 mm), and nano- (<0.1 μm) plastics on the health of humans and other organisms. Consequently, there is a need to better understand the environmental fate of plastic debris and especially its degradation and fragmentation into micro- and nanoplastics that can be inhaled or ingested (Abdolahpur Monikh et al., 2023). Solar UV radiation drives free-radical mediated photo-oxidation reactions that render plastics brittle and can lead to fragmentation following exposure to mechanical forces (Jansen et al., 2024) (Figure 1). Naturally occurring dissolved organic matter can further facilitate the degradation of plastics via the production of reactive oxygen species. Because of the larger surface to volume ratio of fragments, UV also accelerates the leaching of potentially toxic additives. The extent of UV-induced degradation of plastics in the environment depends on temperature and the intensity and spectral composition of solar UV radiation. Typically, UV-B wavelengths (280–315 nm) are more effective in oxidizing and embrittling common plastics compared to more prevalent UV-A (315–400 nm) or visible (400–700 nm) wavelengths (Zepp et al., 2023). Biological plastic degradation and/or fragmentation has also been reported, yet the global importance of this process remains to be demonstrated in natural environments. The Montreal Protocol on Substances that Deplete the Ozone Layer, and its Amendments (hereafter referred to as the "Montreal Protocol"), have prevented widespread loss of stratospheric ozone and consequent increases in surface UV-B radiation. Without the Montreal Protocol, rates of UV-B-driven photodegradation of plastics, and consequent fragmentation, would have increased in recent decades. Correspondingly, the lifetime of plastic products exposed to solar radiation would have decreased (with associated economic and environmental costs), as would the persistence of macroplastic debris in the environment (Jansen et al., 2024). In addition to protecting the biosphere from UV-B radiation, the Montreal Protocol provides climate change mitigation benefits through reduced emissions of ozone-depleting substances (ODS), many of which are also potent greenhouse gases (Velders et al., 2007). Furthermore, complex interactive effects between UV radiation and global climate change depend on factors such as consumer behavior, land-use (e.g., increased use of evaporation-reducing plastic films), wildfires and cloudiness (e.g., affecting local UV irradiance), dissolved organic matter in the water column (e.g., affecting UV penetration and formation of reactive oxygen species) and air and ocean currents (e.g., affecting global plastic dispersal). Furthermore, some feedstocks for plastic production are ODS that are currently exempted from the Montreal Protocol (Andersen et al., 2021). If these substances escape during plastic production, they potentially affect UV radiation, the global climate and hence the persistence of environmental plastic pollution. It is expected that the complex, interactive effects of UV radiation and climate change, together with changes in feedstocks, will make plastic weathering less predictable in the future. Global effects of UV radiation and climate change on plastic debris present a double-edged sword: solar UV radiation and higher temperatures enhance the degradation of macroplastic debris but also lead to the generation of potentially hazardous micro- and nanoplastic particles. At present, the contribution of UV-driven weathering on the global load of micro- and nanoplastics cannot be reliably quantified due to a lack of data on rates of photo-oxidation and fragmentation in natural ecosystems. These rates are likely to be high for airborne plastics exposed to stronger UV irradiances, moderate for plastics on soil and near water surfaces, and low for plastics deeper in the water column or buried in soil where photodegradation will not occur due to the absence of UV. Future estimates of plastic persistence in the environment need to be based on existing projections of global UV radiation levels, and growing knowledge of dispersal of plastic around the globe. Such assessments will also inform the design and use of new plastics with durability matching the functional life of products, and that will mineralize into CO2 and other gases. MAKJ, ALA, PWB, RB, LER, JFB: conceptualization, investigation, and writing—original draft. All other authors: conceptualization, investigation, and writing—review and editing. The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency. LER conducts collaborative research with Clinuvel Pharmaceuticals Ltd and Mitsubishi Tanabe Pharma Inc. on the development of photoprotective agents. All other authors declare no conflicts of interest. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.
The ecological and photobiological communities lost a leader, a pioneer, and a beloved mentor recently with the death of Martyn M. Caldwell, who passed away January 24, 2021, in Washington, DC, after an extended battle with Parkinson's and Lewy body disease. While Martyn was instrumental in the development of the field of ultraviolet (UV) environmental photobiology, he was foremost a renowned plant physiological ecologist who played a leading role in the advancement of this discipline throughout the world. After receiving his Ph.D. from Duke University, where he studied with W. Dwight Billings, Martyn spent his academic career (41 years) as a Professor in the Rangeland Resources Department at Utah State University (USU). Later he would serve as Director of USU's Ecology Center and several terms as a Program Director for the US National Science Foundation. Martyn's research examining the effects of solar UV radiation on plants and ecosystems began with his dissertation research in the Colorado alpine. These field studies sought to understand the ecological role of UV radiation in influencing plants growing in naturally high UV, alpine environments. This research was summarized and published in Ecological Monographs (Caldwell, 1968) and is now considered a classic in the ecological literature. Even though Martyn's lab would go on to explore many aspects of the UV photobiology of higher plants, he would remain committed to advancing knowledge that emphasized the ecological significance of this small, but important part of the solar spectrum. Soon after his dissertation research was published, Martyn compiled a number of plant UV responses to produce a “generalized” plant action spectrum (Caldwell, 1971) that, for many years, would serve as the standard biological UV spectral weighting function (BSWF) used in plant UV research. He maintained a keen interest in the development and testing of polychromatic action spectra throughout his career (e.g., Flint & Caldwell, 2003) as he understood the fundamental importance of BSWFs in conducting ecologically relevant plant UV photobiological research and in assessment of the environmental effects of increases in solar UV-B radiation (280–315 nm) resulting from stratospheric ozone depletion (Caldwell & Flint, 2006). The ambitious field campaign undertaken by Martyn, his student, Ronald Robberecht, together with Dwight Billings, that documented the natural latitudinal gradient in solar UV-B radiation, which exists from high-latitude, low-elevation sites in the Arctic to low-latitude, high elevations in the tropical alpine, is particularly noteworthy (Caldwell et al., 1980). These studies, and others, compared the sensitivity and protective responses of Arctic and alpine ecotypes and species to UV-B radiation and provided compelling evidence for a significant evolutionary role of solar UV-B in driving plant adaptation across this gradient (Barnes et al., 1987; Caldwell et al., 1982; Robberecht et al., 1980). Martyn's contribution to understanding the potential ecological effects of increased solar UV-B radiation resulting from stratospheric ozone depletion began soon after the reports of the possible catalytic destruction of ozone by nitrogen oxides and chlorofluorocarbons in the early 1970s. Initially, the research in his lab examined the detrimental effects of increased UV-B radiation exposure on photosynthesis and growth (e.g., Dickson & Caldwell, 1978; Sisson & Caldwell, 1976). However, it soon became clear that these effects were not readily apparent under realistic UV-B exposures in the field. The research then shifted to explore UV-B effects on pollen and reproduction (Flint & Caldwell, 1984), and UV-B induced photomorphogenic responses in plants, including changes in UV-screening compounds (flavonoids) and associated changes in leaf and floral optical properties (Caldwell, Robberecht, & Flint, 1983; Flint & Caldwell, 1983). This line of research led to efforts to understand the ecological consequences of UV-induced photomorphogenic alterations in plant morphology for competition (Barnes et al., 1988; Fox & Caldwell, 1978). Following reports of decreases in stratospheric ozone over Antarctica and other parts of the world, Martyn's research branched out to explore how UV-B radiation influenced plants and ecosystems in various vegetation types around the globe, including tropical forests (Flint & Caldwell, 1998; Searles et al., 1995), cool-deserts (Belnap et al., 2008), and the wetlands, bogs, and southern beech (Nothofagus spp.) forests of Tierra del Fuego. Long-term field experiments in Tierra del Fuego, Argentina, were begun in 1996 in collaboration with Carlos Ballaré and others from the University of Buenos Aires (Ballaré et al., 2001). These studies continued for 6 years and revealed the multiple direct and indirect ways that solar UV-B radiation was impacting important ecosystem-level processes including community composition, litter decomposition, biogeochemistry, and herbivory (Pancotto et al., 2003; Robson et al., 2004; Rousseaux et al., 1998; Searles et al., 2001). Soon after the international adoption of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987, Martyn became one of the original members of the United Nations Environment Program (UNEP) Environmental Effects Assessment Panel (EEAP), which produces regular scientific assessments to policy makers on the environmental effects of stratospheric ozone depletion. He would serve on the EEAP for two decades and provide critical leadership as this assessment panel gradually progressed beyond its initial focus on UV radiation and ozone depletion to include the interactive effects of UV radiation, ozone depletion, and climate change (Caldwell et al., 1998; Caldwell et al., 2007). Martyn's penchant for conducting ecologically relevant UV research led him and his associates to develop a number of research innovations, including the first modulated UV lamp system for field UV-B supplementation studies (Caldwell, Gold, et al., 1983) and a fiber-optic inclined point-quadrat system for non-destructively measuring canopy leaf area profiles (Caldwell, Harris, & Dzurec, 1983). Throughout much of his career, Martyn employed electrical engineers in his laboratory who designed and fabricated these and other instruments (e.g., whole-plant gas exchange system and root observation periscope), and also modified commercially available instruments (e.g., UV spectroradiometers) to make them more suitable for field use. More remarkably, his UV research was only one aspect of a much broader research program in plant ecophysiology. His pioneering research in plant physiological ecology encompassed topics as varied as root growth and belowground competition for nutrients and water, hydraulic redistribution of soil water and ecohydrology, canopy architecture and light relations, ecophysiology of photosynthesis, plant responses to wind, and the composition and structure of cold-desert plant communities. Martyn was a mentor and teacher for numerous students, post-docs, and technical staff, and he graciously gave of his time to serve on a number of national and international committees and scientific editorial boards. He was elected as a fellow in the American Association for the Advancement of Science in 1986 and, in 2002, was recognized by the Institute for Scientific Information (ISI) for being in the top half-percent of the most-cited research in ecology and the environment. Martyn was fluent in German and had a special connection with the German scientific community. He was elected an honorary member of the German Ecological Society in 1993 and the German National Academy of Sciences in 1999. Martyn was kindhearted, quiet, and humble, and he was always interested and cared about the personal lives of his students and associates. He enjoyed cooking and took pleasure in hosting students, colleagues, and guests for dinner parties to show his appreciation for their contributions. Martyn was passionate about classical music and enjoyed attending the opera, symphony orchestra, and museums; he traveled widely with his spouse, Mario, visiting friends and vacationing. It is testament to Martyn's scientific insight and achievements that his research continues to serve as the benchmark for researchers looking to understand the ecological responses of plants to UV radiation. His passing is felt by a very wide and diverse circle of people around the world. Data sharing is not applicable to this article as no new data were created or analyzed in this study.
