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Thèse de doctorat : Instrumentation et analyses avancées : Lille 1 : 2001. / N° d'ordre (Lille) : 3070. Résumé en français et en anglais. Bibliogr. p. 122-125.

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Considerable disparities in cancer survival rates exist between African Americans (AAs) and white Americans (WAs). Various factors such as differences in socioeconomic status (SES), cancer stage at time of diagnosis, and treatment - which this analysis considers primary explanatory factors - have accounted for many of these differences. An additional factor not usually considered is vitamin D. Previous studies have inversely correlated higher solar ultraviolet-B (UVB) doses and serum 25-hydroxyvitamin D (25(OH)D) concentrations with incidence and/or mortality rates for about 20 types of cancer and improved survival rates for eight types of cancer. Because of darker skin pigmentation, AAs have 40% lower serum 25(OH)D concentrations than WAs. This study reviews the literature on disparities in cancer survival between AAs and WAs. The journal literature indicates that there are disparities for 13 types of cancer after consideration of SES, stage at diagnosis and treatment: bladder, breast, colon, endometrial, lung, ovarian, pancreatic, prostate, rectal, testicular, and vaginal cancer; Hodgkin lymphoma and melanoma. Solar UVB doses and/or serum 25(OH)D concentrations have been reported inversely correlated with incidence and/or mortality rates for all of these cancers. This finding suggests that future studies should consider serum 25(OH)D concentrations in addressing cancer survival disparities through both measurements of serum 25(OH)D concentrations and increasing serum 25(OH)D concentrations of those diagnosed with cancer, leading to improved survival rates and reduced disparities.

The effect of ultraviolet-B radiation enhancement upon the competitive interactions of two species pairs was studied in the field. Wheat (Triticum aestivum L. 'Bannock') was paired with wild oat (Avena fatua L.) and jointed goatgrass (Aegilops cylindrica Host) to represent competition between species pairs in agricultural situations. Specially modulated ultraviolet lamp systems provided either low ultraviolet-B enhancement (simulation of a 16 % ozone layer reduction based upon the generalized plant action spectrum), high ultraviolet-B enhancement (40 % ozone reduction) or control (ambient solar ultraviolet-B) irradiance. Ultraviolet-B radiation enhancement significantly altered the competitive interactions of the species pairs. However, ultraviolet-B enhancement did not affect total shoot biomass production 1n the mixtures or shoot biomass production of the species 1n monoculture. The direction 1n which competitive interactions were altered appeared to be dependent upon the time at which the seeds were planted. Also, water stress affected some aspects of the interaction between ultraviolet-B enhancement and plant competition but the manner of this effect was inconsistent. Reproductive effort of the species was generally not affected by ultraviolet-B enhancement, except in wild oat plants under interspecific competition.

Tropical regions currently receive the highest global levels of solar ultraviolet-B radiation (UV-B, 280-320 nm) even without ozone depletion. Thus, the influence of natural, present-day UV-B irradiance in the tropics was examined for five tropical species, including three native rainforest tree species and two economically important species. Solar UV-B radiation conditions were obtained vi using either a UV-B excluding plastic film or a near-ambient UV-B transmitting film in a small clearing on Barro Colorado Island (BCI), Panama (9 ° N). Significant differences were often exhibited as increased foliar UV-B absorbing compounds, increased leaf mass per area, and reduced leaf blade length for plants receiving solar UV-B radiation. Plant height was typically reduced under solar UV-B, but some variation among species in response was seen. Biomass and photosystem II function using chlorophyll fluorescence were generally unaffected. The results of this study provide strong evidence that tropical vegetation, including native rainforest species, responds to the present level of natural solar UV-B. This suggests that even a small increase in UV-B radiation with ozone depletion may have biological implications.

The severity of stratospheric ozone depletion in the temperate and polar latitudes has raised concerns about the sensitivity of terrestrial vegetation and ecosystems to solar ultraviolet (UV-B) radiation. This dissertation examined the responses of plants and microbes to solar UV-B for 3 years in Tierra de! Fuego, Argentina (55° S). This region is under the influence of the Antarctic "ozone hole" during the austral spring. Additionally, a quantitative review of the UV-B literature was conducted using a set of statistical techniques known as meta-analysis. For the field studies in Tierra de! Fuego, plots were established in a Sphagnum moss peatland and a Carexsedge fen during the spring of 1996. These plots received either near-ambient solar UV-B (90% of ambient) or reduced UV-B (20% of ambient) using specially designed plastic films. At the end of the first field season, no effects of the solar UV-B treatments were apparent on the growth and pigmentation of the plant species in either community The height growth of the moss Sphagnum mageffanicum was less under near-ambient solar UV-B than reduced UV-B during the second and third growing seasons. In contrast, volumetric density of the moss was greater under nearambient UV-B. The growth of the vascular plants did not respond to the solar UV-B treatments even after 3 years although UV-B-absorbing compounds were greater under near-ambient UV-B in some species. Populations of testate amoebae (i.e., shelled amoebae) inhabiting S. magellanicum had greater numbers under near-ambient UV-B than reduced UV-B throughout the 3 years. This response may be an indirect effect of solar UV-B mediated by the direct effect of UV-Bon S. mageffanicum height growth. Fungi on the leaf surfaces of the tree Nothojagus antarctica appeared to be directly inhibited by solar UV-B. The quantitative literature review of plant field studies simulating stratospheric ozone depletion assessed the effects of elevated UV-B on 10 plant response variables from papers published between 1976 and mid-1999. Modest significant inhibitions of leaf area, aboveground biomass, and plant height were apparent due to increased UV-B using meta-analysis. An increase in UV-B-absorbing compounds appears to be the most robust general response to increased UV-B radiation.

Abiotic stresses cause extensive loss to agriculture production worldwide. Cowpea is an important legume crop grown widely in tropical and subtropical regions where high temperature, ultraviolet-B (UVB) radiation and drought are the common stress factors limiting production. Various vegetative, physiological, biochemical and reproductive plant attributes were assessed under a range of UVB radiation levels in Experiment I and in a combination with two doses of each carbon dioxide concentration [CO2], temperature, and UVB radiation and their interactions in Experiment II by using six cowpea genotypes and sunlit plant growth chambers. The dynamics of photosynthesis and fluorescence processes were assessed in 15 cowpea genotypes under drought condition in Experiment III in pot-grown plants under sunlit conditions. A distinct response pattern was not observed in cowpea in response to UVB radiation form 0 to 15 kJ; however, plants grown under elevated UVB showed reduced photosynthesis resulting in shorter plants and produced smaller flowers and lower seed yield. Increased phenolic compounds appeared to be a defense response to UVB radiation. The growth enhancements observed by doubling of [CO2] were not observed when plants were grown in combination with elevated UVB or temperature which also showed the most detrimental effects on plant growth and seed yield. Results form Experiment I and II revealed that cowpea reproductive traits were highly sensitive to abiotic stresses compared to the vegetative growth and development. A total stress response index (TSRI) technique, derived from all vegetative and reproductive parameters, was used to screen genotypes for their stress tolerance to UVB or combination of stresses. An increase in water use efficiency while maintaining higher rate of photosynthesis was an important drought tolerance mechanism in tolerant cowpea genotypes. Using principal component analysis technique, four groups of the genotypes were identified for their drought tolerance. Evaluating same genotypes across stress conditions revealed that no single genotype has the absolute tolerance characters to all stress conditions. The identified diversity for abiotic stress tolerance among cowpea genotypes and associated traits can be used to develop tolerant genotypes suitable for an agro-ecological niche though traditional breeding or genetic engineering methods.

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