Chapter 4 – SOLAR UV IRRADIATION AND THE GROWTH AND DEVELOPMENT OF HIGHER PLANTS

OF NATURAL SOLAR ULTRAVIOLET RADIATION ... 253 Introduction: Plant Responses to Solar Ultraviolet Radiation . 253 Effect of Solar Ultraviolet Radiation Exclusion on the Alpine Plant in Its Natural Habitat 254 Microenvironment Beneath the Test and Control Filters 254 Leaf Elongation, Shoot Yield, and Change in Area Cover 255 Frequency of Flowering . . 256 Effect of an Abrupt Change in the Ultraviolet Radiation Regime . . 258 Conclusions Concerning the Removal of UV on the Tundra . .258

Solar Ultraviolet Radiation as an Ecological Factor for Alpine Plants

The increased use of UV radiation as a drinking water treatment technology has instigated studies of the repair potential of microorganisms following treatment. This study challenged the repair potential of an optimally grown nonpathogenic laboratory strain of Escherichia coli after UV radiation from low- and medium-pressure lamps. Samples were irradiated with doses of 5, 8, and 10 mJ/cm(2) from a low-pressure lamp and 3, 5, 8, and 10 mJ/cm(2) from a medium-pressure UV lamp housed in a bench-scale collimated beam apparatus. Following irradiation, samples were incubated at 37 degrees C under photoreactivating light or in the dark. Sample aliquots were analyzed for up to 4 h following incubation using a standard plate count. Results of this study showed that E. coli underwent photorepair following exposure to the low-pressure UV source, but no repair was detectable following exposure to the medium-pressure UV source at the initial doses examined. Minimal repair was eventually observed upon medium-pressure UV lamp exposure when doses were lowered to 3 mJ/cm(2). This study clearly indicates differences in repair potential under laboratory conditions between irradiation from low-pressure and medium-pressure UV sources of the type used in water treatment.

Potential Repair of Escherichia coli DNA following Exposure to UV Radiation from Both Medium- and Low-Pressure UV Sources Used in Drinking Water Treatment

Ancient civilizations understood that sunlight provides visibility, warmth, health and vitality. Their understanding of how sunlight provides these life-sustaining influences was immersed in mythology and cultural traditions. Offspring, dissatisfied with the intellectual power of their ancestors’ explanations, sought new mythologies in their search for a better understanding of the cosmos and their relationship with it. Starting in the late 17th century, a new mythology arose in Europe that was based on scientific principles and provided the basis for a more reliable understanding of the relationship between humans and sunlight. By the start of the 19th century, the application of these principles led to the realization that sunlight is not a single stimulus but, rather, a collection of stimuli of different wavelengths (e.g. infrared, visible, ultraviolet). This realization inspired additional studies aimed at determining whether different wavelengths might be responsible for the different effects of sunlight. As this review documents, indeed they are. This review focuses primarily on studies before 1920 that were involved in the discovery of UV radiation, its properties and its influences on living organisms. After 1920, the number of UVrelated publications grew rapidly, reaching at least 275 for the years 1920–1927 alone (1). Between 1960 and 2001, there are 37 466 publications on the subject ‘‘ultraviolet radiation’’ listed in PUBMED, a U.S. government-supported computer database of health-related research. Due to the extent of the literature, this review covers only the most important studies between 1920 and 2001. The selection of these studies was made solely by the author, and any omissions and shortcomings are his responsibility. There are a number of excellent reviews on UV photobiology written between 1920 and 2001, and these should be consulted for more in-depth analyses (cf. [1–20]). We begin with the discovery of UV radiation, its properties and relationship with sunlight. These discoveries were unveiled through a series of serendipitous observations coupled with improvements in instrumentation and careful experimentation. This is followed by a more detailed discussion of the evidence linking sunlight and UV radiation with physiological and pathological changes in humans, nonhuman animals and microorganisms. Each group has its own unique narrative relating it to UV radiation. A recurring theme is that UV radiation has both beneficial and harmful effects depending upon the type of organism, wavelength region (UVA, UVB or UVC) and irradiation dose (intensity 3 duration).

A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms¶

Effect of photochemical treatment in the preservation of fresh tomato (Lycopersicon esculentum cv. Capello) by delaying senescence

. Microscopic observations show that growth delay and division delay occur on nutrient agar after Escherichia coli B has been irradiated at 3341 A. These effects also occur in nutrient broth.

A near u.v. action spectrum for growth delay in nutrient broth has been obtained. It shows a single peak at 3380 A and is indistinguishable from the action spectrum for photo-protection from far u.v. (2537 A) killing in the same organism. Furthermore, photoprotected cells show a much greater growth delay than cells that have not been photoprotected. These, as well as kinetic data, suggest that the essential action of a photoprotection treatment consists in the induction of a growth-division delay. This delay would presumably permit more time for intracellular recovery systems to operate on the far u. v. damage to nucleic acids.

Liquid holding recovery (effected by holding cells in phosphate buffer after far u. v. irradiation) shows complete overlap with photoprotection. It is concluded that photoprotection and liquid holding recovery operate on the same far u. v. damage. As with photoprotection, it is probable that the essential action of a liquid holding treatment is the induction of a growth-division delay.

No photoprotection is observed of intracellular T2 bacteriophage or of E. coli Bs-l (Hill).

Delay in growth and division induced by near ultraviolet radiation in escherichia coli b and its role in photoprotection and liquid holding recovery

Summary Survival after far ultraviolet irradiation can be greatly increased in most cells by a posttreatment with near ultraviolet or violet-blue radiation (photoreactivation) or, in some cells, by a pretreatment with near ultraviolet radiation (photoprotection). In addition, many cells recover from some lethal far ultraviolet damage by posttreatments not involving light (dark recovery), and it seems likely that considerable recovery of this type occurs even under ‘normal’ postirradiation conditions that do not involve any special ‘treatments’. In this paper, three aspects of photoreactivation of lethal damage are considered: (1) the nature of photoreactivable damage, including the possibility of cytoplasmic and RNA, as well as DNA, damage; (2) the mechanism of direct (photoenzymatic) photoreactivation, with special reference to dose-rate saturation and temperance dependence; and (3) relations among photoprotection, dark recovery, and photoreactivation, with particular reference to the phenomenon of ‘indirect photoreactivation’, which is similar in mechanism to photoprotection. The general approach is broad, an attempt being made to point out some gaps and inconsistencies in our knowledge of these phenomena.

Photoreactivation and photoprotection

Summary

Photoprotection from biological damage by ultraviolet radiation of 2537 A has been sought in a variety of microorganisms. Its taxonomic occurrence is spotty and it is clearly not as general a phenomenon as photoreactivation.



The action spectrum has been determined for bacteria from two different taxonomic orders and found to be the same, lying in the range 3100–4000 A, with a single peak at 3400 A. These spectra are much narrower than those for photoreactivation and are confined to the near ultraviolet region. Their similarity suggests that only one chromophore is utilized in bacterial photoprotection.



Photoprotection is found to require, at an ultraviolet survival level of 2 per cent, about three times as much radiation energy as photoreactivation.



Consideration of absorption and action spectra, as well as a direct test with transforming principle, indicates that the chromophore probably is not nucleic acid. The action spectra suggest reduced diphosphopyridine nucleotide.

Biological and physical ranges of photoprotection from ultraviolet damage in microorganisms

— The action spectrum and dose-rate dependence for photoreactivation of mutation to prototrophy in late-lag-phase cultures of Escherichia coli H3r30 (which lacks active photo-reactivating enzyme) are roughly similar to those for photoprotection from killing in other strains. It is suggested that photoreactivation of this mutation in H/r30 is an indirect effect, similar in mechanism to photoprotection. The action spectrum and dose-rate dependence for photoreactivation of mutation to prototrophy in late-lag-phase cultures of E. coli H3r30-R (which possesses active photoreactivating enzyme) are roughly similar to those for photoreactivation of killing in most other strains. It is suggested that photoreactivation of this mutation in H/r30-R is a direct effect at long wavelengths, but that there is an indirect component at short wavelengths. A quite different interpretation of these data is noted. Finally, it is found that, under the conditions of these experiments, indirect photoreactivation of killing in H/r30 and H/r30-R is weak or nonexistent.

Action spectra for photoreactivation of mutation to prototrophy in strains of escherichia coli possessing and lacking photoreactivating‐enzyme activity*

Photoprotection from Far Ultraviolet Effects in Cells

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