White Light Treatment Research Articles

Seed germination and early development in seedlings of Noveloa coulteriana (Podostemaceae)

Unlike other aquatic plants, in Podostemaceae sexual reproduction is the primary mode of reproduction. Thus, germination and seedling establishment are essential processes in the life history of these plants, as they determine their distribution, survival, and abundance. Few studies have examined germination and early seedling development of the Mexican species of this family. In this paper, we experimentally evaluated the influence of light quality (white, red, far red, and darkness), storage time (three months, six months, and 10 years) and temperature (constant 25°C and alternate 15–25°C) on Noveloa coulteriana germination. Seeds were positive photoblastic, and showed high germination capacity in white and red light treatments (>80%). In contrast to previously studied Mexican podostemads, N. coulteriana seeds are recalcitrant. Seeds were also thermoblastic; germination rate was slower in alternate temperature compared to constant temperature. Additionally, using electron microscopy, we observed ex situ seedling development during one month (until its senescence). Micromorphologically, N. coulteriana seedlings showed the characteristic developmental pattern of the subfamily Podostemoideae, where the embryonic shoot and root meristems are lost. Our results indicate that environmental factors such as light quality or temperature fluctuation modify seed germination of N. coulteriana and may play an important role in the reestablishment of natural populations.

Modulation of environmental light alters reception and production of visual signals in Nile tilapia

Signal reception and production form the basis of animal visual communication, and are largely constrained by environmental light. However, the role of environmental light in producing variation in either signal reception or production has not been fully investigated. To chart the effect of environmental light on visual sensitivity and body colouration throughout ontogeny, we measured spectral sensitivity, lens transmission and body pattern reflectance from juvenile and adult Nile tilapia held under two environmental light treatments. Spectral sensitivity in juveniles reared under a broad-spectrum light treatment and a red-shifted light treatment differed mostly at short wavelengths, where the irradiance of the two light treatments differed the most. In contrast, adults held under the same two light treatments did not differ in spectral sensitivity. Lens transmission in both juveniles and adults did not differ significantly between environmental light treatments, indicating that differences in spectral sensitivity of juveniles originated in the retina. Juveniles and adults held under the two environmental light treatments differed in spectral reflectance, and adults transferred to a third, white light treatment differed in spectral reflectance from their counterparts held under the two original treatments. These results demonstrate that environmental light plays a crucial role in shaping signal reception in juveniles and signal production throughout ontogeny, reinforcing the notion that environmental light has the capacity to influence animal communication, and suggesting that the characteristics of environmental light should be considered in models of ecological speciation.

Applications of xerophytophysiology in plant production—LED blue light as a stimulus improved the tomato crop

Recent research using Arabidopsis has shown that blue light stimulates the plant through the receptor protein and induces regulations physiologically and morphologically. It is important to know whether the theory can be used in food crop production. In the present study blue light emitted from light-emitting diodes (LED) was used as a stimulus to tomato crop canopy after sunset for 2h to induce xerophytophysiological regulations. Blue (450nm), white and red (660nm) LED lamps, all with a properties of 0.48W, 24V, and 45μmolm2s−1 at 10cm over the lamp, were compared with non-illumination control. A 2×4 two factor experiment was conducted in a randomized split block design with the two cultivars as the main block. Results showed that the osmotic potential in the symplasm at full turgor was lower and the leaf turgor potential at full turgor was higher in tomato leaves in blue light treatment. The water fraction in the symplasm in the leaf was larger or the apoplastic water fraction was smaller in leaf of blue light irradiated plants. Both osmotic potential and relative water content at the point of incipient plasmolysis were lower in tomato leaves in blue light treatment. More leaf water was lost by stomatal transpiration and less leaf water was lost by cuticular transpiration in leaves of blue light treated tomato plants. Fruit color was improved and redder in blue light treatment. Fruit yield was increased by all light illumination treatments. The damage of fruit caused by Helicoverpa armigera worms was more severely in red light treatment and less severely in blue and white light treatments compared with the control. The leaf blight index was lower in blue and white light illumination treatments than the red light treatment and the control. Both cultivars showed LED illumination responses similar to each other although fruit yield was lower and leaf blight was severer in ‘Baiju’ than in ‘Myoko’. In conclusion, illumination treatment with blue light from LED as a stimulus was effective in fruit yield increase and quality improvement as well as improvement in disease resistance of the tomato crop.

Prevention of quality-of-life deterioration with light therapy is associated with changes in fatigue in women with breast cancer undergoing chemotherapy.

During chemotherapy, women with breast cancer not only experience poor quality of life (QOL), they also have little exposure to bright light, which has been shown to be associated with depression, fatigue, and poor sleep in other chronic illnesses. This study examined whether increased light exposure would have a positive effect on QOL. Thirty-nine women with stage I-III breast cancer scheduled to receive ≥ 4 cycles of chemotherapy were randomized to a bright white light (BWL, n = 23) or dim red light (DRL, n = 16) treatment group. Data were collected before (baseline) and during cycles 1 and 4 of chemotherapy. Light was administered via a light box (Litebook(®), Ltd.). QOL was assessed with the Functional Assessment of Cancer Therapy-Breast (FACT-B) and the Functional Outcomes of Sleep Questionnaire (FOSQ). Compared with baseline, the DRL group demonstrated significant decline in QOL during the treatment weeks of both cycles (all ps < 0.02), whereas the BWL group had no significant decline (all ps > 0.05). Mixed model analyses revealed that there was a group-by-time interaction for FOSQ at the treatment week of cycle 4, and this interaction was mediated by fatigue. The data suggest that increased exposure to bright light during chemotherapy may prevent the decline in QOL via preventing the increase in fatigue.

식물생장조절제 및 광원처리에 따른 헛개나무 줄기와 경정유래 신초의 기내증식

This study was conducted to examine effects of plant growth regulators and light resources on the formation of multiple shoot and plant regeneration of Hovenia dulcis var. koreana Nakai. Stem and shoot tip were cultured on MS medium or WPM supplemented with various plant growth regulators. At the single treatment, the highest shoot formation was obtained when stem explants were cultured on WPM supplemented with kinetin 1.0㎎ · L^-1. MS medium containing NAA 0.1 and TDZ 0.1 ㎎·L^-1 gave the best results for shoot induction rate and shoot growth in combination treatments. Of the BAP and kinetin tested, BAP 0.5 ㎎·L^-1 on WPM was found to be more effective for shoot growth from shoot tip. Under white fluorescent light treatment, shoot growth was much higher than blue, red LED treatments. Root induction from in vitro growth of plantlet was the best on WPM supplemented with 1.0㎎ · L^-1 IBA. The results suggest that selection of plant growth regulators and light resources could be important factor to achieve an efficient in vitro growth.

Development of the Casparian strip is delayed by blue light in pea stems.

To understand the regulatory mechanisms involved in tissue development by light, the kinetics of regulation of Casparian strip (CS) development in garden pea stems was studied. We found that short-term irradiation with white light delayed the development of the CS and used this delay to assess the quantitative effect of light on CS development. We examined the effect of the duration and fluence rates of white light treatment on CS development and observed a significant relationship between fluence and the delay in CS development indicating that the Bunsen-Roscoe law of reciprocity holds for this response. The effect of white light irradiation was not inhibited in the presence of a photosynthetic inhibitor, DCMU, or a carotenoid biosynthesis inhibitor, Norflurazon, indicating that the delay in CS development by light is a photomorphogenetic response rather than a subsidiary effect mediated by photosynthetic activity. An action spectrum for the response displayed a major peak in the blue-light region, suggesting a dominant role for blue-light receptors. A minor peak in the red-light region also suggested the possible involvement of phytochromes. Although phytochromes are known to contribute to blue-light responses, phytochrome-deficient mutants showed a normal delay of CS development in response to blue light, indicating that the response is not mediated by phytochrome and suggesting a role for one or more specific blue-light receptors.

Light treatment prevents fatigue in women undergoing chemotherapy for breast cancer

Fatigue is one of the most disturbing complaints of cancer patients and is often the reason for discontinuing treatment. This randomized controlled study tested the hypothesis that increased morning bright light, compared to dim light, would result in less fatigue in women with breast cancer undergoing chemotherapy. Thirty-nine women newly diagnosed with stage I-III breast cancer were randomized to either bright white light (BWL) or dim red light (DRL) treatment and were instructed to use the light box for 30 min every morning throughout the first four cycles of chemotherapy. The Multidimensional Fatigue Symptom Inventory was administered prior to the start of chemotherapy (baseline), during the chemotherapy treatment week of cycle 1 (C1TW), the last week (recovery week) of cycle 1 (C1RW), the chemotherapy treatment week of cycle 4 (C4TW), and the last week (recovery week) of cycle 4 (C4RW). The DRL group reported increased fatigue at C1TW (p = 0.003) and C4TW (p < 0.001) compared to baseline, while there was no significant change from baseline in the BWL group. A secondary analysis showed that the increases in fatigue levels in the DRL group were not mediated through nor associated with changes in sleep or in circadian rhythms as measured with wrist actigraphy. The results of this study suggest that morning bright light treatment may prevent overall fatigue from worsening during chemotherapy. Although our hypothesis that overall fatigue would improve with bright light treatment was not supported, the lack of deterioration in total fatigue scores suggests that bright morning light may be a useful intervention during chemotherapy for breast cancer.

A Randomized, Double-Blind, Placebo-Controlled Study of Light Therapy for Antepartum Depression

Affective disorder during pregnancy is a common condition requiring careful judgment to treat the depression while minimizing risk to the fetus. Following up on promising pilot trials, we studied the efficacy of light therapy. Twenty-seven pregnant women with nonseasonal major depressive disorder according to DSM-IV (outpatients, university polyclinic) were randomly assigned to 7,000 lux fluorescent bright white or 70 lux dim red (placebo) light administered at home in the morning upon awakening for 1 h/d in a 5-week double-blind trial carried out between October 2004 and October 2008. Clinical state was monitored weekly with the 29-item Structured Interview Guide for the Hamilton Depression Rating Scale (HDRS) with Atypical Depression Supplement (SIGH-ADS). Changes of rating scale scores over time were analyzed with the general linear model. Differences from baseline of SIGH-ADS and 17-item HDRS scores at every time point were the dependent variables, time was the within-subjects factor, and treatment was the between-subjects factor. The model also included baseline score of depression and gestational age at intervention start. The superiority of bright light over dim light placebo was shown for both SIGH-ADS (R² = 0.251; F(3,23) = 3.91; P < .05) and HDRS (R² = 0.338; F(3,23) = 5.42; P < .01) when analyzing the week-by-week change from baseline, and HDRS scores showed a significant interaction of treatment with time (F(4,92) = 2.91; P < .05). Categorical analysis revealed that the response rate (HDRS ≥ 50% improvement) at week 5 was significantly greater for bright light (81.3%, n = 16) than for placebo light (45.5%, n = 11) (P < .05). Remission (final score ≤ 8) was attained by 68.6% versus 36.4%, respectively (P < .05). Expectation ratings did not differ significantly between groups. Bright white light treatment for 5 weeks improved depression during pregnancy significantly more than placebo dim red light. The study provides evidence that light therapy, a simple, cost-effective antidepressant modality with minimal side effects for the mother and no known risk for the unborn child, may be a useful nonpharmacologic approach in this difficult situation. clinicaltrials.gov Identifier: NCT01043289.

Bright Light Treatment of Depression for 28 Adolescents

Background: Bright light therapy, an effective therapeutic option for depressive adults, could provide safe, economic, and effective rapid recovery also in adolescents. Method: This was a randomized cross-over trial, i.e. that 14 patients received first dim white light (50 lux) one hour a day for one week and then Bright light therapy (2500 Lux) for one week. 14 patients received first Bright light therapy and then dim white light. For assessment of depressive symptoms, Beck depression inventory scales were administered 1 week before and one day before dim white light treatment, on the day between dim white light and bright white light treatment, on the day after bright white light treatment and one week after bright white light treatment. Saliva melatonin and cortisol samples were collected at 08:00 a.m. and 08:00 p.m., 1 week before and one day before dim white light treatment, on the day between dim white light and bright white light treatment, on the day after bright white light treatment and one week after bright white light treatment and assayed for melatonin and cortisol to observe any change in circadian timing. Results: 28 volunteers, between 14 and 17 years old, completed the study. Beck depression inventory scores improved significantly. The assays of morning saliva melatonin showed significant differences between Bright white light and dim white light (p = 0.005), those of evening saliva melatonin and saliva cortisol did not show significant differences. No significant adverse reactions were observed. Conclusion: Antidepressant response to bright light treatment in this age group was statistically superior to dim white light

Effect of hot air, UV-C, white light and modified atmosphere treatments on expression of chlorophyll degrading genes in postharvest broccoli ( Brassica oleracea L.) florets

Several treatments were applied in order to delay postharvest degreening in broccoli florets and investigate their effects on genes associated with chlorophyll catabolism. Degradation of chlorophylls is the most evident visual manifestation of broccoli postharvest deterioration, occurring rapidly due to the immature stage in which the material is harvested. Treatments such as storage in modified atmosphere, exposure to hot air, UV-C and white lamps were employed in the current work to induce a delay in degreening and chlorophyll degradation. Expression of genes possibly related to chlorophyll catabolism was analyzed in these samples and discussed. Chlorophyllases, the enzymes traditionally believed to remove the phytol side chain from chlorophyll appear to have a gene expression that was not regulated by postharvest treatments. Pheophytinase, a recently discovered new enzyme in this metabolic pathway, correlated chlorophyll loss accurately in heat, UV-C and white-light treatments, but not in modified atmospheres. Results presented in this work indicate that postharvest treatments that delay chlorophyll degradation have a higher effect on the expression of pheophytinase rather than on chlorophyllase genes.

低溫及LED光質處理對阿魏菇(Pleurotus eryngii var. ferulae)原基誘導之影響

Mycelia of Pleurotus eryngii var. ferulae cultured on PDA with 25℃ dark condition, then moved to 15℃ with red, yellow, blue, green, and white light irradiation (12 hr light/12 hr dark). After two months, no primordia appeared under constant dark, red and yellow light; primordia appearance of blue and white light treatment were 83.3% and 75%, respectively. Low mycelial growth temperature had significant effects on indeces such as days of primordia appearance, days of 90% primordia appearance, days of major primordia appearance, percentage of plate with primordia appearance, and number of primordia per plate. The mechanical treatment increased the number of primordia per plate. The optimal conditions for inducing primordia of P. eryngii var. ferulae were that mycelia cultured at 25℃ without mechanical treatment and then incubated at 15℃, the next was mechanical treated 30℃ incubated mycelia cultured incubated at 15℃. Among low temperature treatments, the primordia were poorly or not induced at temperature higher than 20℃. The dual temperature treatment decreased the percentage of plate with primordia appearance and was not able to reduce the days of primordia appearance.

Effects of Monochromatic Light on Proliferation Response of Splencyte in Broilers

To investigate the effects of various monochromatic lights on splenocyte proliferation responses, a total of 260 Arbor Acre male broilers on P1 (post-hatching day 1) were exposed to blue light (BL), green light (GL), red light (RL) and white light treatments by light emitting diode system for 7 weeks, respectively. All light sources were equalized on the intensity of 15 lx and light period of 23 h daily. Morphological change of spleen and response of splenocyte proliferation were assessed by using histochemistry staining and colorimetric test in cultures of purified splenic cells. The results were as follows: (1) At P21, GL increased significantly the spleen weight by 163.6% and spleen index by 118.8% compared with RL (P < 0.05). Until P49, BL enhanced significantly the spleen weights by 42.2% compared with RL (P < 0.05), but no significant difference was found in the spleen index among four light-treated groups (P > 0.05). (2) Compared with RL, GL increased significantly the diameter of splenic nodule and area of periarterial lymphatic sheath at P21 by 87.2 and 58.1%, respectively (P < 0.05); BL increased significantly the diameter of splenic nodule and area of periarterial lymphatic sheath at P49 by 64.4 and 50.5%, respectively (P < 0.05). (3) At P21, GL enhanced spleen lymphocytes proliferation in response to concanavalin A compared with RL by 50.0% (P < 0.05). Until P49, the mitogenic response in BL was significantly higher (29.4%) than that of RL (P < 0.05). (4) The interleukin-2 (IL-2) bioactivity was significantly increased to 34.3% in GL than in RL at P21 (P < 0.05). Until P49, the IL-2 bioactivity in BL was significantly higher (62.2%) than that of RL (P < 0.05). (5) There was no significant difference in the nitric oxide (NO) concentration of splenocyte among RL, GL and BL groups at P21 (P > 0.05), but the concentration in RL group at P49 was significantly increased, 59.0 and 63.7% compared to that of GL and BL groups, respectively (P < 0.05). These results suggested that the monochromatic light affected splenocyte proliferation mainly because of alterations in IL-2 bioactivity and NO production in splenocyte of broiler. In early stage of broiler growth, the action of GL was obvious, while the response of BL was stronger in later stage.

Pigment production in Spirulina fussiformis in different photophysical conditions

The present investigation makes a comparative investigation of individual light source on the different commercially important pigments in Spirulina fussiformis in photobioreactor culture condition. Continuous culture system was carried out throughout the experimental condition. Initially, seed culture, corresponding to 0.2 g/L on dry weight basis was cultivated in Zarrouks medium with different colored light source in reactor. Maximum daily biomass productivity, 0.8 g/L, 0.75 g/L and 0.69 g/L in white light (WL), blue light (BL) and green light (GL), respectively, conditions was noticed. Pigment content during WL treatment showed the highest accumulation (5.5 μg/mL) of chlorophyll whereas, other pigments roughly remained constant without much change, implying WL intensity is better for chlorophyll synthesis. On the other hand, chlorophyll and phycocyanin content gradually increased up to 7 μg/mL and 2 mg/mL, respectively, at BL intensity. The response to GL was negative to all pigments studied except for phycocyanin; in this case a highest production (2.5 mg/mL) was seen during 18 days experimental period. Additionally, when yellow light (YL) treatment experiments were conducted, the rate of production gradually decreased from 6th day onward in all pigments demonstrating the photobleaching effect of YL. The average rate of pigments production did not show significant accumulation in red light (RL) light treatment except phycoerythrin which showed an increasing trend of production. It is worth to mention here that higher light intensity is better for production of phycocyanin and phycoerythrin in Spirulina.

Medicinally Important Secondary Metabolites and Growth of Hypericum perforatum L. Plants as Affected by Light Quality and Intensity

Hypericum perforatum L. (St. John's wort) is a traditional medicinal plant that is mainly used for the treatment of neurological disorders and depression. The present study was undertaken to investigate the effects of different light quality, including blue, white, and red light, in combination with two light intensities, 250 and 500 μmol m-2s-1 photosynthetic photon flux (PPF) on the concentrations of medicinally important secondary metabolites in the leaf tissues and growth of H. perforatum plants. The results revealed that growth was greatest in those plants grown under white and red light with 500 μmol m-2s-1 PPF. The hypericin and pseudohypericin contents of the plants grown under red light with 250 μmol m-2s-1 PPF were 1.9 and 1.9 times higher, respectively, than those grown under red light with 500 μmol m-2s-1 PPF. The differences in contents between blue and white light treatment were not significant for plants grown with 250 μmol m-2s-1 PPF. Our result revealed that the contents of medicinally important secondary metabolites in the tissues of H. perforatum plants can be altered by controlling the light environment.

A biochemical comparison of Octaplas with a universally applicable development product (Uniplas) and single-donor fresh-frozen plasmas subjected to methylene-blue dye and white-light treatment

The aim of this study was to perform an extensive biochemical comparison of the pharmaceutically licensed coagulation active plasma Octaplas with an identical, but universally applicable, development product (Uniplas) and single-donor fresh-frozen plasma (FFP) units subjected to a medical device treatment using a combination of methylene-blue dye and subsequent white-light exposure (MB plasma).

A biochemical comparison of a pharmaceutically licensed coagulation active plasma (Octaplas ®) with a universally applicable development product (Uniplas) and single-donor FFPs subjected to methylene-blue dye and white-light treatment

The strive for more standardised and highly efficacious products is one of the important mainstays in modern haemotherapy. Coagulation active plasma for transfusion is the product of choice when treating hereditary or acquired isolated or complex coagulopathies, when no specific concentrate is available. The aim of this study was to perform an extensive biochemical comparison of the pharmaceutically licensed coagulation active plasma named Octaplas ® with an identical, but universally applicable, development product (Uniplas, working title) and single-donor fresh-frozen plasma (FFP) units subjected to a medical device treatment using a combination of methylene-blue dye and subsequent white-light exposure (MB plasma). Our study showed that there are differences in the biochemical characteristics between Octaplas ® and MB plasma, while Uniplas revealed the same quality as Octaplas ®. The variability of selected plasma proteins in the 20 individual MB plasma units tested was high compared to Octaplas ®/Uniplas. Beyond the reported decreased levels of protein S and plasmin inhibitor found in Octaplas ®/Uniplas, and the significant loss of fully functional fibrinogen in MB plasma and its impact on selected global coagulation parameters, the latter product additionally revealed several coagulation factor activities outside the ranges given for normal single-donor FFP. It is important for plasma prescribers to be aware of the major inherent differences between Octaplas ® and MB plasma.

The effect of light spectral quality on leaf senescence and oxidative stress in wheat

We have investigated the effects of deprivation of specific wavelengths on the induction of leaf senescence and oxidative metabolism in wheat. Excised leaves of 18–20-day-old plants were incubated in plastic boxes on distilled water and exposed to light filters with different ratios of red (R = 660 nm) to far-red (FR = 730 nm) radiation (treatments red (R), R/FR = 0.84; green (G), R/FR = 0.12; or blue (B), R/FR = 0.13). Boxes with no added filters (white light treatment) or covered with black cardboard served as controls. Incubation in darkness induced a fast protein and chlorophyll degradation and oxidative stress development as compared to the white light (W) illuminated leaves. A decrement of the R/FR ratio failed to induce senescence symptoms in leaves exposed to the B light treatment, which behaved in a similar way as the white light control. Senescence symptoms developed to a similar extent under both the R and G light treatments. Our results indicate that light spectral quality affects the oxidative metabolism of wheat leaves, and that blue light can specifically delay the onset of senescence in shaded leaves. The effects of incubation on benzylaminopurine (BAP), LaCl 3 (a Ca 2+ channel blocker), or salicylhydroxamic acid (SHAM) suggest that blue light prevents senescence by maintaining high levels of catalase activity.

Adaptive color vision in Pullosquilla litoralis (Stomatopoda, Lysiosquilloidea) associated with spectral and intensity changes in light environment.

Some stomatopod crustacean species that inhabit a range of habitat depths have color vision systems that adapt to changes in ambient light conditions. To date, this change in retinal function has been demonstrated in species within the superfamily Gonodactyloidea in response to varying the spectral range of light. Intrarhabdomal filters in certain ommatidia within the specialized midband of the eye change spectrally, modifying the sensitivity of underlying photoreceptors to match the spectrum of available light. In the present study, we utilized Pullosquilla litoralis, a member of the superfamily Lysiosquilloidea that also has a wide depth range. Individuals were placed within one of three light treatments: (1) full-spectrum, high-intensity 'white' light, (2) narrow-spectrum 'blue' light and (3) full-spectrum, reduced-intensity 'gray' light. After 3 months, the intrarhabdomal filters in Row 3 ommatidia of the midband in blue- and gray-light-treated animals were short-wavelength shifted by 10-20 nm compared with homologous filters in animals in white-light treatments. These spectral changes increase the relative sensitivity of associated photoreceptors in animals that inhabit environments where light spectral range or intensity is reduced. The adaptable color vision system of stomatopods may allow animals to make the best use of the ambient light occurring at their habitat regardless of depth. The major controlling element of the plasticity in lysiosquilloid stomatopod color vision appears to be light intensity rather than spectral distribution.

Changes in the structure of chlorophyll–protein complexes and excitation energy transfer during photoinhibitory treatment of isolated photosystem I submembrane particles

The activity of light-induced oxygen consumption, absorption spectra, low temperature (77 K) chlorophyll fluorescence emission and excitation spectra were studied in suspensions of photosystem (PS) I submembrane particles illuminated by 2000 μE m −2 s −1 strong white light (WL) at 4 °C. A significant stimulation of oxygen uptake was observed during the first 1–4 h of photoinhibitory treatment, which rapidly decreased during further light exposure. Chlorophyll (Chl) content gradually declined during the exposure of isolated PSI particles to strong light. In addition to the Chl photobleaching, pronounced changes were found in Chl absorption and fluorescence spectra. The position of the major peak in the red part of the absorption spectrum shifted from 680 nm towards shorter wavelengths in the course of strong light exposure. A 6-nm blue shift of that peak was observed after 5-h illumination. Even more pronounced changes were found in the characteristics of Chl fluorescence. The magnitude of the dominating long-wavelength emission band at 736 nm located in untreated particles was five times reduced after 2-h exposure, whereas the loss in absolute Chl contents did not exceed 10% of its initial value. The major peak in low-temperature Chl fluorescence emission spectra shifted from 736 to 721 nm after 6-h WL treatment. Individual Chl–protein complexes differed in the response of their absorption spectra to strong WL. Unlike light-harvesting complexes (LHC), LHCI-680 and LHC-730, which did not exhibit changes in the major peak position, its maximum was shifted from 678 to 671 nm in CPIa complex after PSI submembrane particles were irradiated with strong light for 6 h. The results demonstrated that excitation energy transfer represents the stage of photosynthetic utilization of absorbed quanta which is most sensitive to strong light in isolated PSI particles.

Limited acclimation of photosynthesis to blue light in the seaweed Gracilaria tenuistipitata.

Changes in photosynthetic capacity of the seaweed Gracilaria tenuistipitata Zhang et Xia acclimated to monochromatic blue light were studied. For this purpose, affinity for external inorganic carbon, light use efficiency, carbonic anhydrase (CA; EC 4.2.1.1) activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were determined in thalli acclimated to 45 &mgr;mol m-2 s-1 of blue light. Thalli cultured in white light of the same photon fluence rate were used as a control. Lower maximal photosynthetic rates (i.e. at light and carbon saturation) were obtained in the thalli cultured in blue light. Apparently, this lower photosynthetic capacity was not due to differences in affinity and/or capacity for use of external dissolved inorganic carbon (DIC) since (1) CA activity did not change significantly and (2) similar values of photosynthetic conductance for DIC at alkaline pH were obtained (0.95 x 10-6 m s-1). In addition, the pool size of Rubisco was not modified by the blue light treatment since there were no significant differences in Rubisco content between white (12.14% of soluble proteins) and blue light (12.13% of soluble proteins) treatments. In contrast, Fv/Fm was increased by 11% and photosynthetic efficiency for oxygen production was reduced by 50% in blue light. This absence of correlation between quantum yields for maximum stable charge separation of photosystem II and oxygen evolution suggests that blue light promote changes in rates of photosynthetic electron flow.