High-intensity Light Treatment Research Articles

Effects of Light Intensity and Photoperiod on the Fresh Locking and Quality of Hydroponic Arugula in the Harvesting Period

At present, the research on the light environment of arugula mostly stays in its emergence and growth stage and there is a lack of research on the fresh-keeping quality of hydroponic arugula under light treatment during the harvest period. This study takes hydroponic arugula as the research object and explores the influence of light intensity and photoperiod on the fresh-keeping quality of arugula during the harvest period. With light intensity and photoperiod as experimental factors; and fresh weight, water content, chlorophyll, soluble sugar, nitrate, and cellulose content of arugula during harvest as experimental indicators, combined with sensory evaluation methods, a two-factor completely random experiment was completed. The experimental results show that medium and high intensity light treatment effectively enhances the fresh-keeping ability of arugula during the harvest period, which is conducive to reducing the decline in leaf fresh weight and water content caused by aging of arugula and delaying the decline in quality of arugula; 3 h and 6 h photoperiods can significantly delay the decomposition of chlorophyll in hydroponic arugula during harvest, reduce the loss of soluble sugar, inhibit excessive accumulation of nitrate, and slow down the production of leaf cellulose; and LED red-blue composite light irradiation is conducive to maintaining the sensory quality of hydroponic arugula during harvest. Among them, the sensory quality of cabbage leaves under 200 μmol·m−2·s−1 light intensity and 6 h photoperiod treatment is the best. This study provides an important theoretical basis for improving the quality and yield of hydroponic arugula and provides a strong basis for setting intelligent environmental lighting in artificial light-type plant factories.

PIGMENT COMPOSITION OF THE GREEN ALGA HAEMATOCOCCUS PLUVIALIS DURING ACTION OF MULTIPLE ASTAXANTHIN ACCUMULATION INDUCTORS

The content of astaxanthin, including its mono- and diesters, and photosynthetic pigments, was studied in cells of H. pluvialis strain IBCE-H17 under combined prolonged action of several inducers of astaxanthin accumulation. The ineffectiveness of the simultaneous introduction of several inducers of astaxanthin accumulation in the culture medium during high-intensity light treatment was shown.

Exposure to High-Intensity Light Systemically Induces Micro-Transcriptomic Changes in Arabidopsis thaliana Roots.

In full sunlight, plants often experience a light intensity exceeding their photosynthetic capacity and causing the activation of a set of photoprotective mechanisms. Numerous reports have explained, on the molecular level, how plants cope with light stress locally in photosynthesizing leaves; however, the response of below-ground organs to above-ground perceived light stress is still largely unknown. Since small RNAs are potent integrators of multiple processes including stress responses, here, we focus on changes in the expression of root miRNAs upon high-intensity-light (HL) stress. To achieve this, we used Arabidopsis thaliana plants growing in hydroponic conditions. The expression of several genes that are known as markers of redox changes was examined over time, with the results showing that typical HL stress signals spread to the below-ground organs. Additionally, micro-transcriptomic analysis of systemically stressed roots revealed a relatively limited reaction, with only 17 up-regulated and five down-regulated miRNAs. The differential expression of candidates was confirmed by RT-qPCR. Interestingly, the detected differences in miRNA abundance disappeared when the roots were separated from the shoots before HL treatment. Thus, our results show that the light stress signal is induced in rosettes and travels through the plant to affect root miRNA levels. Although the mechanism of this regulation is unknown, the engagement of miRNA may create a regulatory platform orchestrating adaptive responses to various simultaneous stresses. Consequently, further research on systemically HL-regulated miRNAs and their respective targets has the potential to identify attractive sequences for engineering stress tolerance in plants.

Effect of high light intensity on photoinhibition, oxyradicals and artemisinin content in Artemisia annua L.

Artemisia annua L. produces a compound called artemisinin that is a potent anti-malarial compound. However concentration of artemisinin within the plant is typically low (less than 0.8% of dry mass) and currently supply of the drug by the plant does not meet world demand. This investigation was carried out to determine whether high intensity light treatment would increase production of artemisinin in leaves of A. annua. Photoinhibition (14%) was induced in leaves of A. annua when they were subjected to 6 h of high-intensity light [2,000 μmol(photon) m-2 s−1]. Maximum photochemical efficiency of PSII showed a recovery of up to 95% within 24 h of light induced inhibition. During the light treatment, photochemical efficiency of PSII in leaves of the high-intensity light-treated plants was 38% lower than for those from leaves of plants subjected to a low-intensity-light treatment of 100 μmol(photon) m-2 s−1. Nonphotochemical quenching of excess excitation energy was 2.7 times higher for leaves treated with high-intensity light than for those irradiated with low-intensity light. Elevation in oxidative stress in irradiated leaves increased presence of reactive oxygen species (ROS) including singlet oxygen, superoxide anions, and hydrogen peroxide. Importantly, the concentration of artemisinin in leaves was two-fold higher for leaves treated with high-intensity light, as compared to those treated with low-intensity light. These results indicate that A. annua responds to high irradiance through nonphotochemical dissipation of light energy yet is subject to photoinhibitory loss of photosynthetic capacity. It can be concluded that A. annua is capable of rapid recovery from photoinhibition caused by high light intensity. High light intensity also induced oxidative stress characterized by increased concentration of ROS which enhanced the content of artemisinin. Such a light treatment may be useful for the purpose of increasing artemisinin content in A. annua prior to harvest.

Photosystem II Function and Dynamics in Three Widely Used Arabidopsis thaliana Accessions

Columbia-0 (Col-0), Wassilewskija-4 (Ws-4), and Landsberg erecta-0 (Ler-0) are used as background lines for many public Arabidopsis mutant collections, and for investigation in laboratory conditions of plant processes, including photosynthesis and response to high-intensity light (HL). The photosystem II (PSII) complex is sensitive to HL and requires repair to sustain its function. PSII repair is a multistep process controlled by numerous factors, including protein phosphorylation and thylakoid membrane stacking. Here we have characterized the function and dynamics of PSII complex under growth-light and HL conditions. Ws-4 displayed 30% more thylakoid lipids per chlorophyll and 40% less chlorophyll per carotenoid than Col-0 and Ler-0. There were no large differences in thylakoid stacking, photoprotection and relative levels of photosynthetic complexes among the three accessions. An increased efficiency of PSII closure was found in Ws-4 following illumination with saturation flashes or continuous light. Phosphorylation of the PSII D1/D2 proteins was reduced by 50% in Ws-4 as compared to Col-0 and Ler-0. An increase in abundance of the responsible STN8 kinase in response to HL treatment was found in all three accessions, but Ws-4 displayed 50% lower levels than Col-0 and Ler-0. Despite this, the HL treatment caused in Ws-4 the lagest extent of PSII inactivation, disassembly, D1 protein degradation, and the largest decrease in the size of stacked thylakoids. The dilution of chlorophyll-protein complexes with additional lipids and carotenoids in Ws-4 may represent a mechanism to facilitate lateral protein traffic in the membrane, thus compensating for the lack of a full complement of STN8 kinase. Nevertheless, additional PSII damage occurs in Ws-4, which exceeds the D1 protein synthesis capacity, thus leading to enhanced photoinhibition. Our findings are valuable for selection of appropriate background line for PSII characterization in Arabidopsis mutants, and also provide the first insights into natural variation of PSII protein phosphorylation.

Investigation of the maximum quantum yield of PS II in Haematococcus pluvialis cell cultures during growth: Effects of chemical or high-intensity light treatment

In this study, we investigated the increase in photosynthetic quantum yield that occurs in advance of increased microalgal growth. Haematococcus pluvialis was cultivated under normal conditions; the number of cells, the maximum quantum yield of photosystem II ( F v/ F m), and optical density were measured. We observed an increase in F v/ F m approximately 72 h prior to the cell growth phase. To confirm the relationship between photosynthetic yield and growth, samples were treated with several chemicals under high-intensity light illumination and control conditions to inhibit photosystem II and induce a decrease in the quantum photosynthetic yield. The samples were exposed to high-intensity light at an irradiance of 400 μmol photons m −2 s −1 for varied amount of time and were treated with chemicals such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea, nigericin sodium salt and valinomycin. We observed that both the photooxidation of photosystem II reaction centers and the formation of transmembrane electrochemical gradients led to an initial decrease in fluorescence yield after the onset of high-intensity light illumination. We also observed that treatment of high-intensity light illuminated cells with antibiotics after adaptation to moderate light intensities caused a difference in photosynthetic activity. In conclusion, the maximum quantum yield of photosystem II is obtained prior to the cell growth phase and can therefore be used as a prediction parameter for cell growth.

Dose Response to Adjunctive Light Therapy in Citalopram-Treated Patients with Post-Stroke Depression

Background:Post-stroke depression affects the outcome of stroke rehabilitation and is observed in approximately 30% of all stroke patients. We investigated whether the addition of light treatment to medical antidepressants influences the course of depression as measured by the Hamilton Depression Scale. Methods: The effect of a combination of light therapy and citalopram in stroke victims receiving citalopram was examined by use of two different doses of light therapy under double-blind conditions. Altogether, 63 patients were included in the study. The mean age was 74.9 years. Results: After 4 weeks of therapy, the 6-item subscale of the Hamilton Depression Scale showed a statistically significantly larger improvement in patients receiving high-intensity light treatment compared to those treated with medium-intensity light (p < 0.05). Conclusion: This pilot study demonstrates a dose response effect of light used as an adjunct therapy to antidepressants in post-stroke patients with major depression.

Light Activated Copper Defects in P-Type Silicon Studied by PCD

We have studied copper defects in p-type silicon by measuring its precipitation kinetics by means of the microwave photoconductive decay (µPCD) technique. Copper atoms precipitated during high intensity light treatment at room temperature. We used the total reflection X-ray fluorescence (TXRF) and the transient ion drift (TID) techniques to determine the bulk concentration of copper. We estimated the density and the radius of the copper precipitates as well as the average capture cross-section for precipitated copper atoms from the measured copper precipitation time constant, bulk concentration of copper, and the change in the recombination rate. We also studied how the density of oxygen defect affects the copper precipitation. Our results show that copper precipitates at two different kinds of defects.

AKR-deficiency disturbs the balance of some signal transduction pathways in Arabidopsis thaliana

High-intensity light induces anthocyanin production in wild-type Arabidopsis leaves, but this induction is largely abolished in the chlorotic leaf tissues of AKR (ankyrin repeat-containing protein)-deficient plants. The steady-state mRNA levels of three anthocyanin biosynthetic genes, CHI, CHS and DFR, did not increase in response to high-intensity light treatment in chlorotic leaf tissues, whereas they increased several fold in green leaf tissues. There is a good correlation between anthocyanin production and transcript levels of anthocyanin biosynthetic genes, especially DFR, in green leaf tissues. In contrast, the transcripts of TCH2 and TCH3 that encode for calmodulin-related proteins and GPA that encodes for the α subunit of the trimeric G protein were much higher in chlorotic leaf tissues than those in green leaf tissues. These data suggest that the AKR-deficiency could increase gene expression in one signal transduction pathway and at the same time repress gene expression in another signal transduction pathway, which alludes to a possible mechanism for AKR involvement in chloroplast development.

The circadian rhythm of temperature during light treatment for winter depression

Circadian rhythm abnormalities have been implicated in winter seasonal affective disorder. We examined the circadian temperature rhythm of 22 patients with winter depression and 10 normal controls who had participated in various high-intensity light treatment experiments. We did not find abnormalities in the baseline phase or amplitude of the temperature rhythm in patients compared to controls. Nor did we find abnormalities in the phase-shifting response to morning light. There was some evidence that the “phase-delayed” half of the patients responded poorly to phase advances produced by morning light, whereas the “phase-advanced” half of the patients responded poorly when their rhythms delayed. However, the antidepressant responses during the best week (week of lowest depression score) were unrelated to temperature rhythm phase shifts. In general, there was not strong support for a relationship between circadian rhythms changes and antidepressant response.

Treatment of seasonal affective disorder with high-intensity light: A phototherapy study with an icelandic group of patients

The standard phototherapy procedure for seasonal affective disorder (SAD) has been to expose patients to 2500 lux light intensity for 2 h. This study investigated whether high-intensity light treatment with a brief exposure time would relieve symptoms of SAD. Ten SAD patients were randomly assigned to 40-min exposure to 10,000 lux white light or to 400 lux red light which served as placebo. Each patient received treatment for 8 days, and after a wash-out period was crossed over to the other treatment condition. Depression was assessed by the 21-item HDRS and SIGH-SAD by a blind rater and the patients completed the BDI for self-assessment. Significantly greater improvement was found with 10,000 lux treatment than with the placebo ( P = 0.011, P = 0.017 and P = 0.028 for SIGH-SAD, HDRS and BDI respectively). The 10,000 lux therapy improved the SIGH-SAD score by an average of 16.1 while the average improvement on placebo treatment was 5.0. The patients were rated again the following summer; most of them were then symptomless. Those patients who improved most on phototherapy also tended to improve most during the summer.

Transcriptional regulation of the Arabidopsis thaliana chalcone synthase gene.

We have cloned an Arabidopsis thaliana chalcone synthase (CHS) gene on the basis of cross-hybridization with a Petroselinum hortense CHS cDNA clone. The protein sequence deduced from the A. thaliana CHS DNA sequence is at least 85% homologous to the CHS sequences from P. hortense, Antirrhinum majus, and Petunia hybrida. Southern blot analysis indicated that CHS is a single-copy gene in A. thaliana. High-intensity light treatment of A. thaliana plants for 24 h caused a 50-fold increase in CHS enzyme activity and an accumulation of visibly detectable levels of anthocyanin pigments in the vegetative structures of these plants. A corresponding increase in the steady-state level of CHS mRNA was detected after high-intensity light treatment for the same period of time. The accumulation of CHS mRNA in response to high-intensity light was due, at least in part, to an increased rate of transcription of the CHS gene as demonstrated by nuclear runoff experiments.

Transcriptional regulation of the Arabidopsis thaliana chalcone synthase gene.

We have cloned an Arabidopsis thaliana chalcone synthase (CHS) gene on the basis of cross-hybridization with a Petroselinum hortense CHS cDNA clone. The protein sequence deduced from the A. thaliana CHS DNA sequence is at least 85% homologous to the CHS sequences from P. hortense, Antirrhinum majus, and Petunia hybrida. Southern blot analysis indicated that CHS is a single-copy gene in A. thaliana. High-intensity light treatment of A. thaliana plants for 24 h caused a 50-fold increase in CHS enzyme activity and an accumulation of visibly detectable levels of anthocyanin pigments in the vegetative structures of these plants. A corresponding increase in the steady-state level of CHS mRNA was detected after high-intensity light treatment for the same period of time. The accumulation of CHS mRNA in response to high-intensity light was due, at least in part, to an increased rate of transcription of the CHS gene as demonstrated by nuclear runoff experiments.