Production of high-value crops is often performed under protected cultivation. In recent years various spectral modifications have been made in greenhouse covers. Two of the main reasons to modify the spectral characteristics of greenhouse covers have been to suppress the proliferation of several foliar diseases and to protect crops from insects and insect-borne virus diseases of greenhouse-grown crops. These goals were achieved by complete or partial absorption of solar UV radiation, which interrupts the life cycle of several fungal pathogens and alters the visual behavior of many insects. Examples of these management strategies are described in this article.

Methylene Blue (MB) has well-established photochemical properties and has been used in a variety of photochemical applications including photodynamic therapy. Despite the fact that most of MB's cytotoxic effects in cells are attributed to mitochondrial damage, the interactions of this dye with mitochondria and the consequent effects on photochemical properties have not yet been fully determined. We monitored MB binding, aggregation and its ability to release singlet oxygen (¹O₂) on irradiation when interacting with mitochondrial suspensions. MB actively binds to mitochondria and enters the matrix in a manner stimulated by the mitochondrial proton potential and by the increase in mitochondrial concentrations. The greater accumulation of MB in mitochondria with elevated proton potentials or those treated with high concentrations of MB results in the formation of MB dimers, previously shown to be less effective generators of ¹O₂. Accumulation of MB within mitochondria with high membrane potentials also results in the reduction of MB to the photochemically inactive leuco-MB. Indeed, irradiation of mitochondria with high proton potentials in the presence of MB results in the generation of approximately half the quantity of ¹O₂ compared with ¹O₂ generated in mitochondria with low proton potentials. These differences in photochemical properties should influence the cytotoxic effects of photodynamic treatment in the presence of MB.

The effect of pH on inhibition and enhancement of luminol–H₂O₂–CO² chemiluminescence (CL) by 18 phenolic compounds and 20 amino acids was studied. It was found that most of the tested compounds showed an inhibiting effect at lower pH and an enhancing effect at higher pH. At a midrange pH, for some phenolic compounds with two ortho-position –OH, both an inhibiting and an enhancing peak were simultaneously observed. UV–visible spectra of the tested phenolic compounds at different pH values were studied. The mechanism for CL inhibition and enhancement was proposed. It is likely that the competition of the –OH or the –NH₂ group and other reducing groups in the molecules with luminol for O₂^·− led to the CL inhibition. A reaction of –COO⁻ and quinone or ketone formed by phenolic compounds at higher pH via deprotonation with O₂^·− also resulted in the CL enhancement.

Structural modifications of photosensitizers (changes in protonation, ionic state and aggregation state) under different environmental conditions should be precisely determined to understand the interaction of the photosensitizers with biological systems. In the present study partition coefficients of hematoporphyrin IX (HpIX), disulfonated meso-tetra-phenylporphine, meso-tetra(3-hydroxyphenyl)porphine (mTHPP) and meso-tetra(3-hydroxyphenyl)chlorin in the 1-octanol–phosphate buffer system were determined in the pH region 4.0–8.0. Only the partition coefficients of HpIX and mTHPP were found to be pH dependent. Computer processing of fluorimetric titration data was applied to estimate pK_a values of the imino nitrogens of mTHPP. Monoprotonated species of mTHPP seem to be unstable or nonexistent. The possibility that both imino nitrogens of this dye are protonated according to a common pK_a is proposed. The pK_a value of the imino nitrogens of mTHPP was found to be 2.99 ± 0.04 after the application of a model taking aggregation of the drug into account. The contributions of various aqueous ionic species of mTHPP as functions of pH were calculated and compared with partition coefficients.

This article describes the results of a combined photophysical and photobiological study aimed at understanding the phototoxicity mechanism of the antimalarial drugs quinine (Q), quinacrine (QC) and mefloquine (MQ). Photophysical experiments were carried out in aqueous solutions by stationary and time-resolved fluorimetry and by laser flash photolysis to obtain information on the various decay pathways of the excited states of the drugs and on transient species formed on irradiation. The results obtained showed that fluorescence and intersystem crossing account for all the adsorbed quanta for Q and MQ (quantum yield of about 0.1 and 0.9, respectively) and only for 24% in the case of QC, which has a negligible fluorescence quantum yield (0.001). Laser flash photolysis experiments evidenced, for QC and MQ, the occurrence of photoionization processes leading to the formation of the radical cations of the drugs. The effects of tryptophan and histidine on the excited states and transient species of the three drugs were also investigated. In parallel, the photoactivity of the antimalarial drugs was investigated under UV irradiation on various biological targets through a series of in vitro assays in the presence and in the absence of oxygen. Phototoxicity on 3T3 cultured fibroblasts and lipid photoperoxidation were observed for all the drugs. The photodamage produced by the drugs was also evaluated on proteins by measuring the photosensitized cross-linking of spectrin. The combined approaches were proven to be useful for understanding the mechanism of phototoxicity induced by the antimalarial drugs.

Under a high-pressure mercury lamp (HPML) and using an exposure time of 4 h, the photoproduction of hydroxyl radicals (•OH) could be induced in an aqueous solution containing humic acid (HA). Hydroxyl radicals were determined by high-performance liquid chromatography using benzene as a probe. The results showed that •OH photoproduction increased from 1.80 to 2.74 μM by increasing the HA concentration from 10 to 40 mg L⁻¹ at an exposure time of 4 h (pH 6.5). Hydroxyl radical photoproduction in aqueous solutions of HA containing algae was greater than that in the aqueous solutions of HA without algae. The photoproduction of •OH in the HA solution with Fe(III) was greater than that of the solution without Fe(III) at pH ranging from 4.0 to 8.0. The photoproduction of •OH in HA solution with algae with or without Fe(III) under a 250 W HPML was greater than that under a 125 W HPML. The photoproduction of •OH in irradiated samples was influenced by the pH. The results showed that HPML exposure for 4 h in the 4–8 pH range led to the highest •OH photoproduction at pH 4.0.

Damage to the skin extracellular matrix (ECM) is the hallmark of long-term exposure to solar UV radiation. The aim of our study was to investigate the changes induced in unexposed human skin in vivo after single or repeated (five times a week for 6 weeks) exposure to 1 minimal erythemal dose (MED) of UV solar-simulated radiation. Morphological and biochemical analyses were used to evaluate the structural ECM components and the balance between the degrading enzymes and their physiologic inhibitors. A three-fold increase in matrix metalloproteinase 2 messenger RNA (mRNA) (P < 0.02, unexposed versus exposed) was observed after both single and repeated exposures. Fibrillin 1 mRNA level was increased by chronic exposure (P < 0.02) and unaltered by a single MED. On the contrary, a single MED significantly enhanced mRNA levels of interleukin-1α (IL-1α), IL-1β (P < 0.02) and plasminogen activator inhibitor-1 (P < 0.05). Immunohistochemistry demonstrated a significant decrease in Type-I procollagen localized just below the dermal–epidermal junction in both types of exposed sites. At the same location, the immunodetected tenascin was significantly enhanced, whereas a slight increase in Type-III procollagen deposits was also observed in chronically exposed areas. Although we were unable to observe any change in elastic fibers in chronically exposed buttock skin, a significant increase in lysozyme and alpha-1 antitrypsin deposits on these fibers was observed. These results demonstrate the existence of a differential regulation, after chronic exposure compared with an acute one, of some ECM components and inflammatory mediators.

Recent developments in optical technologies have the potential to improve the speed and accuracy of screening and diagnosis of curable precancerous lesions and early cancer, thereby decreasing the costs of detection and management of epithelial malignancies. The development of molecular-specific contrast agents for markers of early neoplastic transformation could improve the detection and molecular characterization of premalignant lesions. In the oral cavity, epidermal growth factor receptor (EGFR) overexpression has been identified in early stages of premalignant lesions of the oral squamous cell carcinoma; therefore, real-time assessment of EGFR expression could serve as a biomarker for oral neoplasia. The purpose of our study was to develop a molecular-specific optical contrast agent targeted against EGFR for in vivo assessment of epithelial neoplasia using a monoclonal antibody and the far-red fluorescent dye, Alexa Fluor® 660 streptavidin. In addition to demonstrating the specificity of the contrast agent for EGFR in cell lines, we document the ability to achieve penetration through 500 μm thick epithelial layers using multilayer tissue constructs and permeability-enhancing agents. Finally, using the fluorescence intensity of the contrast agent on fresh oral cavity tissue sections, we were able to distinguish abnormal from normal oral tissue. This contrast agent should have important clinical applications for use in conjunction with fluorescence spectroscopy or imaging (or both) to facilitate tumor detection and demarcation.

The brown-colored sulfur bacterium Chlorobium (Cb.) phaeobacteroides 1549 (new name, Chlorobaculum limnaeum 1549) contains many kinds of carotenoids as well as bacteriochlorophyll (BChl) e. These carotenoids were identified with C₁₈-high-performance liquid chromatography, absorption, mass and proton nuclear magnetic resonance spectroscopies and were divided into two groups: the first is carotenoid with one or two ϕ-end groups such as isorenieratene and β-isorenieratene and the second is carotenoid with one or two β-end groups such as β-zeacarotene, β-carotene and 7,8-dihydro-β-carotene. The latter 7,8-dihydro-β-carotene was found to be a novel carotenoid in nature. OH-γ-Carotene glucoside laurate and OH-chlorobactene glucoside laurate were also found as minor components. The distribution of BChl e homologs in Cb. phaeobacteroides cultivated under various light intensities did not change, but the carotenoid to BChl e ratio changed markedly: carotenoid with the ϕ-end group maintained the same ratio to BChl e, whereas that with the β-end group increased with increasing light intensity. The cells cultured under low-light intensity contained more ϕ-end carotenoids than β-end. In Cb. phaeobacteroides the wavelength of the Qy band of BChl e aggregates did not change. We suggested that Cb. phaeobacteroides photoadapts to light intensity by changing the carotenoid composition.

DNA repair plays a central role in the cellular response to UV. In this work we have studied the response of skin cells (i.e. fibroblasts and keratinocytes) from the same or from different individuals after both ultraviolet-B (UV-B) and ultraviolet-C (UV-C) irradiations using the comet assay to characterize the specific cellular response to UV-induced DNA damage. Cells were irradiated with increasing doses of UV-B or UV-C. To study the UV dose dependency of initial steps of DNA repair, namely recognition and incision at DNA damage level, the comet assay was performed, under alkaline conditions, 60 min after UV irradiation to allow detection of DNA strand breaks. Comparative analysis of tail moment values after UV exposure of cells from the same or from different individuals showed interexperimental and interindividual variations, implying that repeated assays are necessary to characterize the individual DNA repair capacity. With increasing doses of UV in keratinocytes, a plateau was rapidly reached after irradiation, whereas in fibroblasts a linear dose–effect relationship was observed. These interindividual variations associated with cellular specificity in DNA response may be of significance in skin cell and individual susceptibility toward UV-induced carcinogenesis.

The effects of acid and alkali treatment on the light absorption, energy transfer and protein secondary structure of the photosystem II core antenna CP43 and CP47 of spinach were investigated by the absorption spectra, fluorescence emission spectra and circular dichroism spectra. It has been found that acid treatment caused the appearance of absorption characteristic of pheophytin a (Pheo a), whereas alkali treatment induced a new absorption peak at 642 nm. The energy transfer between β-carotene and chlorophyll a (Chl a) in CP43 was easily disturbed by alkali, whereas in CP47 was readily affected by acid. As to the effects on the secondary structure of proteins in CP43 and CP47, effects of acid were far less than those of alkali. Both acid and alkali disturbed the microenvironment of Chl a and interfered exciton interaction between Chl a molecules. It was suggested that acid and alkali affect the light absorption, energy transfer and protein secondary structure of CP43 and CP47 in a different way. H can permeate into the internal space of α-helix, change Chl a into Pheo a and disturb the microenvironment of pigments without damaging the secondary structure of protein, whereas OH⁻ can induce the protein unfolding at first, then saponify Chl a to chlorophyllide and disturb the microenvironment of pigments.

It is well established that for successful photoinactivation (PI) of gram-negative bacteria a cationic photosensitizer is required. This requirement suggests a charge-dependent interaction between the photosensitizer and the gram-negative bacterium, which may be influenced by the presence of ions in the suspending medium. The aim of the present study was to investigate the effect of cations Na and Ca² on the efficacy of the PI of the gram-negative Pseudomonas aeruginosa and the gram-positive Staphylococcus aureus. The bacteria were suspended in buffer containing either meso-tetra(N-methyl-4-pyridyl)-porphyrin or meso-mono-phenyl-tri(N-methyl-4-pyridyl)-porphyrin as photosensitizer and various concentrations of Na or Ca² . The cell suspensions were exposed to a broadband light dose of 9 J/cm². In buffer without added cations, P. aeruginosa and S. aureus were equally sensitive to PI. Addition of cations strongly decreased the sensitivity of both bacteria to PI, with the PI of P. aeruginosa being much more decreased than that of S. aureus, and Ca² being more effective than Na . The decreased sensitivity was accompanied by a reduced binding of the photosensitizers to the bacteria.