Spectra Of Pigments Research Articles

Evaluation of biophysical and optical determinations of light absorption by photosystem II in phytoplankton

Fast repetition rate (FRR) fluorescence can provide highly resolved estimates of light absorption by photosystem II (PSII), a variable that is critical to bio‐optical determinations of phytoplankton productivity. We compared estimates of chlorophyll a‐specific light absorption by PSII, achlPSII, using both biophysical (FRR) and optical (chlorophyll a‐specific light absorption coefficient, achl) techniques on cultures of phytoplankton from diverse taxa. Biophysical determinations of achlPSII were obtained from the product of the effective light absorption cross‐section of PSII (σPSII), measured by FRR fluorescence, and the ratio of PSII reaction centers to chlorophyll a (nPSII), measured by oxygen flash yields. Both parameters were highly variable between individual taxa. In mixtures of algae, the estimates of σPSII were largely determined by the taxon that dominated fluorescence intensity. Independent optical estimates of achlPSII were obtained by weighting the light absorption spectra of photosynthetic pigments by the fluorescence excitation spectra. The biophysical and optical estimates of achlPSII were highly correlated (r2 = 0.94) with a slope that was not significantly different from 1 and an intercept of 0. Estimates of productivity using biophysical or optical absorption measurements should therefore be comparable when the latter are adjusted to account for the proportion of light provided for photochemistry into both photosystem I and II. Finally, we show how simultaneous measurements of σPSII and achlPSII can be used to derive nPSII where flash‐yield measurements are impractical, as is almost universally the case in field measurements.

H2O2-induced inhibition of photosynthetic O2 evolution by Anabaena variabilis cells.

Hydrogen peroxide inhibits photosynthetic O2 evolution. It has been shown that H2O2 destroys the function of the oxygen-evolving complex (OEC) in some chloroplast and Photosystem (PS) II preparations causing release of manganese from the OEC. In other preparations, H2O2 did not cause or caused only insignificant release of manganese. In this work, we tested the effect of H2O2 on the photosynthetic electron transfer and the state of OEC manganese in a native system (intact cells of the cyanobacterium Anabaena variabilis). According to EPR spectroscopy data, H2O2 caused an increase in the level of photooxidation of P700, the reaction centers of PS I, and decreased the rate of their subsequent reduction in the dark by a factor larger than four. Combined effect of H2O2, CN-, and EDTA caused more than eight- to ninefold suppression of the dark reduction of P700+. EPR spectroscopy revealed that the content of free (or loosely bound) Mn2+ in washed cyanobacterial cells was ~20% of the total manganese pool. This content remained unchanged upon the addition of CN- and increased to 25-30% after addition of H2O2. The content of the total manganese decreased to 35% after the treatment of the cells with EDTA. The level of the H2O2-induced release of manganese increased after the treatment of the cells with EDTA. Incubation of cells with H2O2 for 2 h had no effect on the absorption spectra of the photosynthetic pigments. More prolonged incubation with H2O2 (20 h) brought about degradation of phycobilins and chlorophyll a and lysis of cells. Thus, H2O2 causes extraction of manganese from cyanobacterial cells, inhibits the OEC activity and photosynthetic electron transfer, and leads to the destruction of the photosynthetic apparatus. H2O2 is unable to serve as a physiological electron donor in photosynthesis.

Fuzzy logic for identifying pigments studied by Raman spectroscopy.

Fuzzy logic and linguistic variables are used for the automatic interpretation of Raman spectra obtained from pigments found in cultural heritage art objects. Featured bands are extracted from a Raman spectrum of a reference pigment and the methodology for constructing the library is illustrated. An unknown spectrum is then interpreted automatically and a process for identifying the corresponding pigment is described. A reference library consisting of 32 pigments was built and the effectiveness of the algorithm was tested by the Raman spectroscopic analysis of 10 pigments that are known to have been extensively used in Byzantine hagiography. Binary mixtures of these pigments were also tested. The algorithm's level of identification was good even though extra peaks, noise, and background signals were encountered in the spectra.

On the relation between the photoactivation energy and the absorbance spectrum of visual pigments

We relate the collected experimental data on the minimum energy for photoactivation ( E a) to the wavelengths of peak absorbance ( λ max) of 12 visual pigments. The E a values have been determined from the temperature-dependence of spectral sensitivity in the long-wavelength range. As shown previously, the simple physical idea E a=const.×(1/ λ max) (here termed the Stiles–Lewis–Barlow or SLB relation) does not hold strictly. Yet there is a significant correlation between E a and 1/λ max (r 2=0.73) and the regression slope obtained by an unbiased fit is 84% of the predicted value of the best SLB fit. The correlation can be decomposed into effects of A1→A2 chromophore change and effects of opsin differences. For a chromophore change in the same opsin, studied in two A1/A2 pigment pairs, the SLB relation holds nearly perfectly. In seven pigments having different opsins but the same (A2) chromophore, the correlation of E a and 1/ λ max remained highly significant ( r 2=0.87), but the regression coefficient is only 72% of the best SLB fit. We conclude that (1) when the chromophore is exchanged in the same opsin, the λ max shift directly reflects the difference in photoactivation energies, (2) when the opsin is modified by amino acid substitutions, λ max and E a can be tuned partly independently, although there is a dominant tendency for inverse proportionality. In four (A1) rhodopsins with virtually the same λ max, E a varied over a 4.5 kcal/mol range, which may be taken as a measure of the freedom for independent tuning. Assuming that low E a correlates with high thermal noise, we suggest that the leeway in λ max− E a coupling is used by natural selection to keep E a as high as possible in long-wavelength-sensitive pigments, and that this is why the opsin-dependent E a(1/ λ max)-relation is shallower than predicted.

On the relation between the photoactivation energy and the absorbance spectrum of visual pigments

We relate the collected experimental data on the minimum energy for photoactivation ( E a ) to the wavelengths of peak absorbance ( λ max ) of 12 visual pigments. The E a values have been determined from the temperature-dependence of spectral sensitivity in the long-wavelength range. As shown previously, the simple physical idea E a =const.×(1/ λ max ) (here termed the Stiles–Lewis–Barlow or SLB relation) does not hold strictly. Yet there is a significant correlation between E a and 1/λ max (r 2 =0.73) and the regression slope obtained by an unbiased fit is 84% of the predicted value of the best SLB fit. The correlation can be decomposed into effects of A1→A2 chromophore change and effects of opsin differences. For a chromophore change in the same opsin, studied in two A1/A2 pigment pairs, the SLB relation holds nearly perfectly. In seven pigments having different opsins but the same (A2) chromophore, the correlation of E a and 1/ λ max remained highly significant ( r 2 =0.87), but the regression coefficient is only 72% of the best SLB fit. We conclude that (1) when the chromophore is exchanged in the same opsin, the λ max shift directly reflects the difference in photoactivation energies, (2) when the opsin is modified by amino acid substitutions, λ max and E a can be tuned partly independently, although there is a dominant tendency for inverse proportionality. In four (A1) rhodopsins with virtually the same λ max , E a varied over a 4.5 kcal/mol range, which may be taken as a measure of the freedom for independent tuning. Assuming that low E a correlates with high thermal noise, we suggest that the leeway in λ max − E a coupling is used by natural selection to keep E a as high as possible in long-wavelength-sensitive pigments, and that this is why the opsin-dependent E a (1/ λ max )-relation is shallower than predicted.

Assessing the role of race in quantitative measures of skin pigmentation and clinical assessments of photosensitivity

Background: Given the increasing demographic diversity in America, clarifying the relationship between race, color, ethnicity, and disease processes in epidemiological settings is critical.Objectives: To examine the correlation between objective measures of skin pigmentation with the subject’s racial identification, physician-rated, and subject-rated phototype.Setting: Dermatology Branch of the National Cancer Institute, NIH.Participants: 558 employees (76 non-white) were evaluated using standard AAD cancer screening materials. Skin pigmentation of a subset was determined by taking spectrometric readings and digital photography of the upper inner arm.Design: Melanin and erythema indices (M, E) of spectrometry were compared to the red, green, and blue components (R, G, B) of color determined by computer analysis of digital photographs. All five measurements were compared to both physician-assessed Fitzpatrick Skin Phototype (PSPT) and self-reported Skin Phototype (SSPT). Self-identified race (white, black, Hispanic, and other) was compared to all seven measures of skin pigmentation using statistical methods.Results: Among the methods of assessing skin pigmentation, PSPT diagnosis exhibits the highest level of association with race, albeit of moderate strength (R-square = 0.548, P < 0.01, 2-tailed). Self-assessed phototype (SSPT) and objective measures using colorimetry and spectrometry all correlate poorly with race (R-square = 0.283; −0.314 < R-square < −0.235; 0.385 < R-square < 0.404; P < 0.01). The association between race and PSPT strengthens toward the darker spectrum of pigmentation as determined by PSPT (R-square = 0.139 for PSPT I-III and R-square = 0.616 for PSPT III-VI, P < 0.01) and SSPT (R-square = 0.244 for SSPT I-II; R-square = 0.403 for SSPT I-III and R-square = 0.598 for SSPT ≥ III, P < 0.01).Conclusions: (1) Objective measures for the determination of skin pigmentation are necessary for correct assessment of photosensitivity and the risk for skin cancer. (2) Among lighter individuals (PSPT I-III), race correlates poorly with PSPT and does not correlate with SSPT. Background: Given the increasing demographic diversity in America, clarifying the relationship between race, color, ethnicity, and disease processes in epidemiological settings is critical. Objectives: To examine the correlation between objective measures of skin pigmentation with the subject’s racial identification, physician-rated, and subject-rated phototype. Setting: Dermatology Branch of the National Cancer Institute, NIH. Participants: 558 employees (76 non-white) were evaluated using standard AAD cancer screening materials. Skin pigmentation of a subset was determined by taking spectrometric readings and digital photography of the upper inner arm. Design: Melanin and erythema indices (M, E) of spectrometry were compared to the red, green, and blue components (R, G, B) of color determined by computer analysis of digital photographs. All five measurements were compared to both physician-assessed Fitzpatrick Skin Phototype (PSPT) and self-reported Skin Phototype (SSPT). Self-identified race (white, black, Hispanic, and other) was compared to all seven measures of skin pigmentation using statistical methods. Results: Among the methods of assessing skin pigmentation, PSPT diagnosis exhibits the highest level of association with race, albeit of moderate strength (R-square = 0.548, P < 0.01, 2-tailed). Self-assessed phototype (SSPT) and objective measures using colorimetry and spectrometry all correlate poorly with race (R-square = 0.283; −0.314 < R-square < −0.235; 0.385 < R-square < 0.404; P < 0.01). The association between race and PSPT strengthens toward the darker spectrum of pigmentation as determined by PSPT (R-square = 0.139 for PSPT I-III and R-square = 0.616 for PSPT III-VI, P < 0.01) and SSPT (R-square = 0.244 for SSPT I-II; R-square = 0.403 for SSPT I-III and R-square = 0.598 for SSPT ≥ III, P < 0.01). Conclusions: (1) Objective measures for the determination of skin pigmentation are necessary for correct assessment of photosensitivity and the risk for skin cancer. (2) Among lighter individuals (PSPT I-III), race correlates poorly with PSPT and does not correlate with SSPT.

Spectral responses of melanin to ultraviolet A irradiation.

The purpose of this investigation was to study the ultraviolet A-induced effects on melanin pigmentation both in an in vitro model system and in vivo. Ultraviolet-Vis absorbance spectra of L-3,4-dihydroxyphenylalanine-melanin solutions at different concentrations were measured before and after ultraviolet A exposure (10-120 J per cm2). The difference spectra reveal that following ultraviolet A exposure the absorbance increases exponentially from 800 nm to 450 nm accompanied by a prominent decrease of absorbance in the ultraviolet A range. This change of spectral features depends on both ultraviolet A doses and melanin concentrations. The photo-bleaching effect observed in the ultraviolet A range also depends on oxygen. Human subjects were irradiated with ultraviolet A (40-80 J per cm2) on their back and diffuse reflectance spectra were collected at both irradiated and untreated sites. The absorption spectra of ultraviolet A-induced pigment were calculated as the difference of the two. The ultraviolet A-induced pigment in vivo has similar spectral characteristics and dose dependency as the in vitro system. Photo-oxidation of pheomelanin solutions presents distinctively different spectral and dose-response characteristics from eumelanin. After ultraviolet A irradiation pheomelanin absorbance decreases both in the visible and the ultraviolet A range. We conclude that irradiation with ultraviolet A induces significant photochemical alterations in the skin witnessed by increased photoprotection in the visible spectral range and reduced protection in the ultraviolet A range. We suggest that soluble melanin plays an important part in ultraviolet A-induced pigment in skin and two distinct absorption mechanisms of melanin may be involved in ultraviolet A photo-oxidation. We also propose that eumelanin and pheomelanin could be differentiated according to their spectral responses to ultraviolet A irradiation.

Synthesis of 8,16-Ethanoretinals and Their Interactions with Apoprotein of Phoborhodopsin from Natronobacterium pharaonis

Several 8,16-Ethanoretinals 3 were synthesized from cyclohexanones. From the binding experiments of these analogs with apoprotein of phoborhodopsin, it was found that retinal was incorporated as 6s-trans conformation in the protein and the fine structure in absorption spectra of pigments were dependent on the coplanarity of the conjugated polyene structure in the chromophore. Keywords: ethanoretinal, retinal analog, phoborhodopsin, chromophore, s-trans conformation

Absorption spectrum of phytoplankton pigments derived from hyperspectral remote-sensing reflectance

For a data set collected around Baja California with chlorophyll- a concentration ((chl- a)) ranging from 0.16 to 11.3 mg/m 3, hyperspectral absorption spectra of phytoplankton pigments were independently inverted from hyperspectral remote-sensing reflectance using a newly developed ocean-color algorithm. The derived spectra were then compared with those measured from water samples using the filter-pad technique, and an average difference of 21.4% was obtained. These results demonstrate that the inversion algorithm worked quite well for the coastal waters observed and suggest a potential of using hyperspectral remote sensing to retrieve both chlorophyll- a and other accessory pigments.

Structural investigations on betacyanin pigments by LC NMR and 2D NMR spectroscopy

Four betacyanin pigments were analysed by LC NMR and subjected to extensive NMR characterisation after isolation. Previously, low pH values were applied for NMR investigations of betalains resulting in rapid degradation of the purified substances thus preventing extensive NMR studies. Consequently, up to now only one single 13C NMR spectrum of a betalain pigment, namely that of neobetanin (=14,15-dehydrobetanin), was available. Because of its sufficient stability under highly acidic conditions otherwise detrimental for betacyanins, this pigment remained an exemption. Since betalains are most stable in the pH range of 5–7, a new solvent system has been developed allowing improved data acquisition through improved pigment stability at near neutral pH. Thus, not only 1H, but for the first time also partial 13C data of betanin, isobetanin, phyllocactin and hylocerenin isolated from red-purple pitaya [ Hylocereus polyrhizus (Weber) Britton & Rose, Cactaceae] could be indirectly obtained by gHSQC– and gHMQC–NMR experiments.

Absorption spectra of reconstituted visual pigments of a nocturnal prosimian, Otolemur crassicaudatus

Absorption spectra of visual pigments characterize animal vision. The association between absorption spectra and amino acid (aa) sequences of pigments has been well established for the middle- to-long-wave-sensitive (M/LWS) class of cone visual pigments of vertebrates, known as the “five-sites” rule where amino acid residues at the 180th, 197th, 277th, 285th, and 308th sites mostly determine the spectra. For primate M/LWS pigments, however, applicability of the rule is not clear because of the scarcity of absorbance data collected directly from purified pigments. In particular, no prosimian pigment has been examined in vitro. In this study, we reconstituted visual pigments of a nocturnal prosimian, the greater galago ( Otolemur crassicaudatus), which has the M/LWS cone and the rod visual pigments in its retina. The five residues of the galago M/LWS pigment are Ala, His, Tyr, Ala, and Ala, respectively, and its peak absorption spectra ( λ max) was measured to be 539 nm, which is virtually identical to the expected value from the rule (538 nm), showing that the five-sites rule holds for this prosimian. The λ max of the rod visual pigment was measured as 502 nm. Accurate estimate of λ max values is essential in establishing the molecular basis of visual pigment evolution.

Bilirubin and S-nitrosothiols interaction: evidence for a possible role of bilirubin as a scavenger of nitric oxide

Bilirubin (BR), the final product of heme catabolism, plays a crucial role in the defense against reactive oxygen species in various cell types. In this study, we addressed the hypothesis that BR can act as a physiological scavenger of nitric oxide (NO), a gaseous mediator involved in many cellular functions and able to trigger the formation of reactive nitrogen species with pro-oxidant activity. We found that S-nitrosocysteine (SNOC) and S-nitrosoglutathione (GSNO), which have a half-life of 0.52±0.07 hr and 38±5 hr and release NO at a constant rate of 1.42±0.2 hr −1 and 0.018±0.002 hr −1, respectively, were able to decrease BR half-life in a concentration-dependent manner under physiological conditions. This effect appears to be dependent on NO formation as l-cysteine and GSH did not affect BR consumption and nitrite was four to five times less efficient than SNOC in reducing BR half-life. Oxyhemoglobin, a well-known scavenger of NO, protected BR from SNOC-mediated degradation. In addition, the reaction between SNOC/GSNO and BR modified the absorption spectrum of the bile pigment showing a gradual increase in the absorbance at 316 nm. This change in the BR spectrum indicates that the bile pigment could be a target for N-nitrosation reactions, since it resembles the modifications occurred when other molecules such as di-peptides and uric acid are nitrosated. Taken together, these data suggest that BR should not be considered only as an endogenous antioxidant but also as a molecule with the potential ability to counteract intracellular nitrosative stress reactions.

Retinal counterion switch in the photoactivation of the G protein-coupled receptor rhodopsin.

The biological function of Glu-181 in the photoactivation process of rhodopsin is explored through spectroscopic studies of site-specific mutants. Preresonance Raman vibrational spectra of the unphotolyzed E181Q mutant are nearly identical to spectra of the native pigment, supporting the view that Glu-181 is uncharged (protonated) in the dark state. The pH dependence of the absorption of the metarhodopsin I (Meta I)-like photoproduct of E181Q is investigated, revealing a dramatic shift of its Schiff base pKa compared with the native pigment. This result is most consistent with the assignment of Glu-181 as the primary counterion of the retinylidene protonated Schiff base in the Meta I state, implying that there is a counterion switch from Glu-113 in the dark state to Glu-181 in Meta I. We propose a model where the counterion switch occurs by transferring a proton from Glu-181 to Glu-113 through an H-bond network formed primarily with residues on extracellular loop II (EII). The resulting reorganization of EII is then coupled to movements of helix III through a conserved disulfide bond (Cys110-Cys187); this process may be a general element of G protein-coupled receptor activation.

Molecular basis of spectral tuning in the newt short wavelength sensitive visual pigment.

Previously we reported the sequence of the member of the short wavelength sensitive 2 (SWS2) family of vertebrate visual pigments from the retina of the Japanese common newt, Cynops pyrrhogaster[Takahashi, Y. et al. (2001) FEBS Lett. 501, 151-155]. Now we have expressed the apopigment and regenerated it with A1 retinal. Its absorption maximum, 474 nm, is greatly red shifted compared to other known SWS2 pigments (418-455 nm). To determine the amino acid residues that control its spectral tuning, we replaced the residues that were near the chromophore and which differed between the newt and the bullfrog (lambda(max) = 430 nm) wild-type SWS2 pigments: Pro91Ser, Ser94Ala, Ile122Met, Cys127Ser, Ser211Cys, Tyr261Phe, and Ala292Ser. Each of these site-directed mutants led to blue shifts of the newt pigment with five of them causing substantial shifts; their sum was about equal to the difference between the absorption maximum of the bullfrog and newt pigments, 44 nm. The 32 nm shift of the absorption maximum of the multiple seven-residue mutant to 442 nm is fairly close to that of the wild-type bullfrog pigment. Thus, the seven amino acid residues that we replaced are the major cause of the red shift of the newt SWS2 pigment's spectrum. Two of the residues, 91 and 94, have not previously been identified as wavelength regulating sites in visual pigments. One of these, 91, probably regulates color via a new mechanism: altering of a hydrogen bonding network that is connected via a water to the chromophore, in this case its counterion, Glu113.

The infrared microspectroscopic and energy dispersive X-ray analysis of paints removed from a painted, medieval sculpture of Saint Wolfgang

A spectroscopic study of paints removed from a 15th century sculpture depicting Saint Wolfgang, which is housed in the Ball State Museum of Art, was performed. Infrared spectra on the minute paint samples were obtained using a microscope accessory in the transmission mode, and the spectra were compared to reference spectra of known art pigments and materials. In addition, energy dispersive X-ray spectra were obtained using a scanning electron microscope source. Although many of the pigments found are relatively modern pigments, the first application of paint is composed of materials consistent with the sculpture's medieval date. Pigments identified include brass gilding, calcium carbonate, China clay, lac dye, orpiment, Prussian blue, satin ochre, ultramarine blue and red, and zinc chromate. A zinc tungate finish was also identified.

Optimizing conditions for the extraction of pigments in cochineals (Dactylopius coccus Costa) using response surface methodology.

A simple method was developed for the extraction and determination of color pigments in cochineals (Dactylopius coccus Costa). The procedure was based on the solvent extraction of pigments in insect samples using methanol:water (65:35, v:v) as extractant. Two-level factorial design was used in order to optimize the solvent extraction parameters: temperature, time, methanol concentration in the extractant mixture, and the number of extractions. The results suggest that the number of extractions is statistically the most significant factor. The separation and determination of the pigments was carried out by high-performance liquid chromatography with UV-visible detection. Because the absorption spectra of different pigments are different in the visible region, it is convenient to use a diode array detector to obtain chromatographic profiles that allow for the characterization of the extracted pigments.

Study of Raman spectra of pigment mixtures

Raman spectroscopy provides useful information for detecting and identifying constituent materials in artworks; but due to the fact that in most cases it is not possible to obtain spectra of single pigments, an informatic tool (named Analyser of Pigments) has been developed to identify all the pigments present in the samples tested 〚M. Breitman, in: Optics and Lasers in Biomedicine and Culture, OWLS V, Springer Verlag, Berlin, 2000, pp. 127–130〛. When mixed pigments do not behave as expected, problems of identification arise. These are the cases we deal with here. A comparative study with different concentrations of two pigments (ultramarine blue and massicot) was carried out. Using our techniques for spectra analyses, it was found that, compared with the theoretical results, some Raman peaks of one pigment were not detected in most of the Raman spectra mixtures 〚M. Breitman, Análisis, Diseño e Identificación de Algoritmos para Reconocimiento de Espectros Raman. Ph.D., June 2000〛. In this work, we present the theory that when the reflection coefficient of one component is larger than the other, a contribution to the spectra of mixture may occur 〚J. Chemom. (1990) 1〛.

Molecular evolution of color vision in vertebrates

Visual systems of vertebrates exhibit a striking level of diversity, reflecting their adaptive responses to various color environments. The photosensitive molecules, visual pigments, can be synthesized in vitro and their absorption spectra can be determined. Comparing the amino acid sequences and absorption spectra of various visual pigments, we can identify amino acid changes that have modified the absorption spectra of visual pigments. These hypotheses can then be tested using the in vitro assay. This approach has been a powerful tool in elucidating not only the molecular bases of color vision, but the processes of adaptive evolution at the molecular level.

Development of Azo Pigments for High Performance Organic Photoconductors (OPC)

We developed a novel coupler, hydroxyperinone, 2- and/or 5-hydroxy-7H-benz[de]benzimidazo[2,1-a]isoquinoline-7-one and synthesized a bisazo pigment from the novel coupler. The OPC using this bisaszo pigments showed better characteristics in sensitivity and cyclic stability than the OPC using bisazo pigments derived from Naphthol AS. 13C NMR spectra of these bisazo pigments indicated that the dominant tautomer of the new bisazo pigment in the solid state was different from those of other bisazo pigments. The difference in tautomers reflects their characteristics. We designed and synthesized a unique highly sensitive unsymmetrical bisazo pigment having a large dipole moment in the excited state, on the basis of the photocarrier generation process model. Thermally stimulated current measurements were applied to elucidate factors for high sensitivity.

Anthocyanins of jack pine (Pinus banksiana) seedlings

Purpling of the needles of jack pine seedlings in forest tree nurseries in the autumn is a result of the production of at least five anthocyanin pigments: cyanidin 3-O-glucoside (~80%), delphinidin 3-O-glucoside (~8%), peonidin 3-O-glucoside (~8%), petunidin 3-O-glucoside (~3%) and malvidin 3-O-glucoside (trace). The twigs subtending the needles also produce a similar range of pigments. The entire spectrum of pigments is produced from the time of the first exposure to freezing temperatures. Proanthocyanidins are a prominent feature of the needle phenolics and the question of their possible involvement in the purpling phenomenon following exposure to sub-zero temperatures is raised. The red colour of the hypocotyl of the newly germinated seedling is also a result of a similar mixture of pigments.Key words: Pinus banksiana, Pinaceae, jack pine seedlings, anthocyanin pigmentation, hypocotyl, proanthocyanidins.