UV-induced Fluorescence Research Articles

Variation of UV-induced fluorescence along wheat leaves

UV-excitation of green leaves induces a red fluorescence (RF) and a blue-green fluorescence (BGF) emitted by chlorophyll and hydroxycinnamic acids (HCA), respectively. The potential use of BGF for crop remote sensing requires the precise knowledge of molecular and anatomical origins of BGF during plant development. In this study, we investigated how cell age and the leaf stage of development influence the BGF signature. We measured the UV-induced fluorescence along the three leaves of 15-days old wheat plants (Triticum aestivum L.) using a UV-PAM fluorimeter. Then, the BGF was described and quantified along the leaves by microscopic fluorescence imaging. The HCA origin of BGF was verified by comparing alkali-induced changes of leaf BGF to pH-induced variation of ferulic acid fluorescence spectra. The decrease of RF from the base towards the tip of all leaves showed that UV-absorbers accumulated as cell aged. Except for the oldest leaf, there was no similar decrease in BGF, which therefore could emanates from leaf surface. We showed that BGF emanates from the wall of each epidermal cell type and from the trichome protoplast. We verified that all these structures contain HCA. Lignified cell wall of sclerenchyma bands contributed also to BGF. Among the three leaves, the oldest one emitted the lowest BGF which was related to the lowest density of trichomes. However, the decrease of BGF along this leaf can not be explained by a reduction in trichomes density. The significance of BGF signatures is discussed considering the spatial distribution of blue-green fluorophores and UV-absorbers

Evidence from action and fluorescence spectra that UV-induced violet-blue-green fluorescence enhances leaf photosynthesis.

We assessed the contribution of UV-induced violet-blue-green leaf fluorescence to photosynthesis in Poa annua, Sorghum halepense and Nerium oleander by measuring UV-induced fluorescence spectra (280-380 nm excitation, 400-550 nm emission) from leaf surfaces and determining the monochromatic UV action spectra for leaf photosynthetic O2-evolution. Peak fluorescence emission wavelengths from leaf surfaces ranged from violet (408 nm) to blue (448 nm), while excitation peaks for these maxima ranged from 333 to 344 nm. Action spectra were developed by supplementing monochromatic radiation from 280 to 440 nm, in 20 nm increments, to a visible nonsaturating background of 500 mumol m-2 s-1 photosynthetically active radiation and measuring photosynthetic O2-evolution rates. Photosynthetic rates tended to be higher with the 340 nm supplement than with higher or lower wavelength UV supplements. Comparing photosynthetic rates with the 340 nm supplement to those with the 400 nm supplement, the percentage enhancement in photosynthetic rates at 340 nm ranged from 7.8 to 9.8%. We suspect that 340 nm UV improves photosynthetic rates via fluorescence that provides violet-blue-green photons for photosynthetic energy conversion because (1) the peak excitation wavelength (340 nm) for violet-blue-green fluorescence from leaves was also the most effective UV wavelength at enhancing photosynthetic rates, and (2) the magnitude of photosynthetic enhancements attributable to supplemental 340 nm UV was well correlated (R2 = 0.90) with the apparent intensity of 340 nm UV-induced violet-blue-green fluorescence emission from leaves.

An ultraviolet absorbing pigment causes a narrow-band violet receptor and a single-peaked green receptor in the eye of the butterfly Papilio.

The distal photoreceptors in the tiered retina of Papilio exhibit different spectral sensitivities. There are at least two types of short-wavelength sensitive receptors: an ultraviolet receptor with a normal spectral shape and a violet receptor with a very narrow spectral bandwidth. Furthermore, a blue receptor, a double-peaked green receptor and a single-peaked green receptor exist. The violet receptor and single-peaked green receptor are only found in ommatidia that fluoresce under ultraviolet illumination. About 28% of the ommatidia in the ventral half of the retina exhibit the UV-induced fluorescence. The fluorescence originates from an ultraviolet-absorbing pigment, located in the most distal 70 microns of the ommatidium, that acts as an absorption filter, both for a UV visual pigment, causing the narrow spectral sensitivity of the violet receptor, and for a green visual pigment, causing a single-peaked green receptor.

Classification and quantification of polycyclic aromatic hydrocarbons on quartz sand particles by direct Fourier transform imaging fluorescence

A new method for analysis of PAH contamination deposited on quartz sand was developed. It is based on direct observation of the UV-induced fluorescence using a microscope and a specially designed imaging spectrometer which provides full fluorescence spectra at each pixel. The method is fast and requires no sample preparation. Linear calibration plots were obtained for monocomponent contaminations and for simple PAH mixtures. Absolute detection limits of a few pg are reported, which correspond to bulk concentrations in the μg g −1 range. In addition to concentrations, the method provides microscopic chemical images of the contaminants, which may provide useful source characterization.

Corneal epithelium and UV-protection of the eye.

To study UV-absorption and UV-induced fluorescence in the bovine corneal epithelium. Spectrophotometry and spectrofluorimetry. The corneal epithelium absorbs UV-B radiation mainly owing to its content of protein, RNA, and ascorbate. Some of the absorbed energy is transformed to the less biotoxic UV-A radiation by fluorescence. RNA and ascorbate reduce tissue fluorescence. The corneal epithelium acts as a UV-filter, protecting internal eye structures through three different mechanisms: (1) Absorption of UV-B roughly below 310 nm wavelength. (2) Fluorescence-mediated ray transformation to longer wavelengths. (3) Fluorescence reduction. The extremely high ascorbate concentration in the corneal epithelium has a key role in two of these processes.

Burn Depth Estimation Using Indocyanine Green Fluorescence

Expedient primary excision of deep dermal and full-thickness burn wounds with subsequent skin grafting is the standard of care in most burn institutions, but differentiating full-thickness from partial-thickness burns is often difficult. Because accurate early assessment of burn depth may improve care, a variety of technical methods have attempted to measure burn depth but these methods have had limited success. We describe a new technique to determine burn depth that uses infrared (840- to 850-nm) fluorescence emission from intravenously administered indocyanine green following excitation with infrared (780 nm) and UV light (369 nm). Full-thickness and partial-thickness burns in hairless rat skin were distinguished based on the infrared-induced and UV-induced fluorescence intensity ratios relative to normal, unburned skin immediately after the burn and on post-burn days 1 through 3 and 7. Dual-wavelength excitation of indocyanine green infrared fluorescence can delineate full-thickness from partial-thickness burns at an early date, allowing prognosis, surgical planning, and early primary excision and grafting.

Burn depth estimation using indocyanine green fluorescence

• Expedient primary excision of deep dermal and full-thickness burn wounds with subsequent skin grafting is the standard of care in most burn institutions, but differentiating full-thickness from partial-thickness burns is often difficult. Because accurate early assessment of burn depth may improve care, a variety of technical methods have attempted to measure burn depth but these methods have had limited success. We describe a new technique to determine burn depth that uses infrared (840- to 850-nm) fluorescence emission from intravenously administered indocyanine green following excitation with infrared (780 nm) and UV light (369 nm). Full-thickness and partial-thickness burns in hairless rat skin were distinguished based on the infrared-induced and UV-induced fluorescence intensity ratios relative to normal, unburned skin immediately after the burn and on post-burn days 1 through 3 and 7. Dual-wavelength excitation of indocyanine green infrared fluorescence can delineate full-thickness from partial-thickness burns at an early date, allowing prognosis, surgical planning, and early primary excision and grafting. (<i>Arch Dermatol.</i>1992;128:43-49)

A simple, combined fluorogenic and chromogenic method for the assay of proteases in gingival crevicular fluid

Substrate impregnated paper discs were prepared using peptidyl derivatives of 7-amino-4-trifluoromethylcoumarin (AFC). After incubation with test solutions, the green, UV-induced fluorescence of AFC liberated by enzyme activity was distinguishable from the blue-violet fluorescence of the substrates. The AFC could then be coupled with p-dimethylaminocinnamaldehyde to form a colored Schiff base. Semi-quantiative assessments of disc fluorescence and color were made by comparison with AFC/substrate standards. Assays with discs impregnated with MeOSuc-Ala-Ala-Pro-Val-AFC, Z-Gly-Gly-Arg-AFC and Ala-Pro-AFC for elastase-, trypsin-, and dipeptidyl peptidase (DPP) IV-like activities respectively were evaluated using purified DPP IV and 100 eluates of crevicular fluid collected on filter paper strips from 10 gingivitis and periodontitis patients. The results showed that, within their working ranges, scores of disc fluorescence and color were reasonably accurate and reliable by comparison with enzyme activities measured in parallel quantitative fluorimetric assays with the same substrates. Using disc color, which was more sensitive than fluorescence, it was generally possible to measure all three enzyme activities in crevicular fluid samples from 5 periodontitis patients with varying degrees of gingival inflammation and pocketing. Disc color assays require no special apparatus and could be used for enzyme estimations in the clinical setting.

A microcomputer-based image analysis system and applications to chlorophyll fluorescence studies

An IBM-PC based software system to quantify images of biological sytems is presented. To illustrate the potential of the imaging system described, UV light-induced chlorophyll fluorescence of Chlorella vulgaris cells was monitored using a video camera interfaced to a microscope. The photoinhibitor, DCMU (30 μM) inhibited the UV-induced fluorescence decay in heterotrophically grown cells but not in autotrophically grown cells. Algal cells were also incubated in various concentrations of ascorbic acid (500, 250, 100, 50, 10 and 0 mM) prior to UV light exposure. In the presence of 500, 250 and 100 mM ascorbic acid, the decay of chlorophyll fluorescence was significantly delayed in both heterotrophically and autotrophically grown cells. Heterotrophically grown cells were more sensitive to ascorbic acid than autotrophically grown cells since 10 nM ascorbic acid delayed fluorescence decay in heterotrophic cultures.