scholarly journals Autophagy contributes to quality control of leaf mitochondria

2020 ◽  
Author(s):  
Sakuya Nakamura ◽  
Shinya Hagihara ◽  
Kohei Otomo ◽  
Hiroyuki Ishida ◽  
Jun Hidema ◽  
...  
Keyword(s):  
Quality Control ◽  
Fluorescent Protein ◽  
Ultraviolet B ◽  
Uvb Radiation ◽  
Plant Tolerance ◽  
Leaf Chlorosis ◽  
Mitochondrial Distribution ◽  
Cytoplasmic Accumulation ◽  
Uvb Exposure ◽  
Mitochondria Functions

Abstract In autophagy, cytoplasmic components of eukaryotic cells are transported to lysosomes or the vacuole for degradation. Autophagy is involved in plant tolerance to the photooxidative stress caused by ultraviolet B (UVB) radiation, but its roles in plant adaptation to UVB damage have not been fully elucidated. Here, we characterized organellar behavior in UVB-damaged Arabidopsis (Arabidopsis thaliana) leaves and observed the occurrence of autophagic elimination of dysfunctional mitochondria, a process termed mitophagy. Notably, Arabidopsis plants blocked in autophagy displayed increased leaf chlorosis after a 1-h UVB exposure compared to wild-type plants. We visualized autophagosomes by labeling with a fluorescent protein-tagged autophagosome marker, AUTOPHAGY8 (ATG8), and found that a 1-h UV-B treatment led to increased formation of autophagosomes and the active transport of mitochondria into the central vacuole. In atg mutant plants, the mitochondrial population increased in UVB-damaged leaves due to cytoplasmic accumulation of fragmented, depolarized mitochondria. Furthermore, we observed that autophagy was involved in the removal of depolarized mitochondria when mitochondrial function was disrupted by mutation of the FRIENDLY gene, which is required for proper mitochondrial distribution. Therefore, autophagy of mitochondria functions in response to mitochondrion-specific dysfunction as well as UVB damage. Together, these results indicate that autophagy is centrally involved in mitochondrial quality control in Arabidopsis leaves.

scholarly journals Melatonin and Its Metabolites Ameliorate UVR-Induced Mitochondrial Oxidative Stress in Human MNT-1 Melanoma Cells

2018 ◽  
Vol 19 (12) ◽  
pp. 3786 ◽  
Author(s):  
Konrad Kleszczyński ◽  
Bernadetta Bilska ◽  
Agatha Stegemann ◽  
Damian Flis ◽  
Wieslaw Ziolkowski ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Oxidative Phosphorylation ◽  
Melanoma Cells ◽  
Ultraviolet B ◽  
Melatonin Receptors ◽  
Biologically Active ◽  
Uvb Radiation ◽  
Mitochondrial Oxidative Stress ◽  
Uncoupling Of Oxidative Phosphorylation ◽  
Uvb Exposure

Melatonin (Mel) is the major biologically active molecule secreted by the pineal gland. Mel and its metabolites, 6-hydroxymelatonin (6(OH)Mel) and 5-methoxytryptamine (5-MT), possess a variety of functions, including the scavenging of free radicals and the induction of protective or reparative mechanisms in the cell. Their amphiphilic character allows them to cross cellular membranes and reach subcellular organelles, including the mitochondria. Herein, the action of Mel, 6(OH)Mel, and 5-MT in human MNT-1 melanoma cells against ultraviolet B (UVB) radiation was investigated. The dose of 50 mJ/cm2 caused a significant reduction of cell viability up to 48%, while investigated compounds counteracted this deleterious effect. UVB exposure increased catalase activity and led to a simultaneous Ca++ influx (16%), while tested compounds prevented these disturbances. Additional analysis focused on mitochondrial respiration performed in isolated mitochondria from the liver of BALB/cJ mice where Mel, 6(OH)Mel, and 5-MT significantly enhanced the oxidative phosphorylation at the dose of 10−6 M with lower effects seen at 10−9 or 10−4 M. In conclusion, Mel, 6(OH)Mel and 5-MT protect MNT-1 cells, which express melatonin receptors (MT1 and MT2) against UVB-induced oxidative stress and mitochondrial dysfunction, including the uncoupling of oxidative phosphorylation.

scholarly journals Almond Consumption Increased UVB Resistance in Healthy Asian Women

2021 ◽  
Vol 5 (Supplement_2) ◽  
pp. 319-319
Author(s):  
Susanne Henning ◽  
Jason Li ◽  
Gail Thames ◽  
Omar Bari ◽  
Patrick Tran ◽  
...  
Keyword(s):  
Skin Aging ◽  
Ultraviolet B ◽  
In Vivo Studies ◽  
Asian Women ◽  
Skin Extract ◽  
Uvb Radiation ◽  
Facial Skin ◽  
Uvb Exposure

Abstract Objectives Almonds are a rich source of phenolic and polyphenolic compounds, which have antioxidant activity. In vitro and in vivo studies have demonstrated that topical application of almond oil and almond skin extract reduces UVB-induced photoaging. Ultraviolet-B (UVB) protection by oral almond consumption has not been previously studied in humans. It was the objective to investigate whether oral almond consumption can increase resistance to UVB radiation and reduce skin aging in healthy Asian women. Methods Thirty-nine female participants (18–45 years) with Fitzpatrick skin type II-IV were randomly assigned to consume either 1.5 oz of almonds or 1.8 oz of pretzels daily for 12 weeks. Minimal erythema dose (MED) was determined using a standardized protocol, which determined the minimal radiation inducing erythema on the inner arm 24 hours following UVB exposure. Facial skin texture was evaluated by two dermatologists using the Clinician's Erythema Assessment scale and Allergan Roughness scale. Facial melanin index, hydration, sebum, and erythema were determined using a cutometer. Results Women who consumed almonds, experienced a significant increase in MED from 415 ± 64 to 487 ± 59 (18.7 ± 19.2%, P = 0.006) from baseline to week 12 compared to women in the pretzel group from 415 ± 67 to 421 ± 67 (1.8 ± 11.1%). The exposure time to reach minimal erythema was also increased significantly in the almond group from 160 ± 23 to 187 ± 25 (17.5 ± 22.2%) compared to the pretzel group from 165 ± 27 to 166 ± 25 (1.7 ± 14%) (p=0.026). There were no differences noted between the groups consuming almonds versus pretzels in Allergan roughness, melanin, hydration, or sebum on facial skin. Conclusions Our findings suggest that daily oral almond consumption may lead to enhanced protection from UVB photodamage by increasing the MED. Protection from other UV radiation was not tested and therefore almond consumption will not replace other methods of sun protection such as application of sunscreen or wearing protective closing. Funding Sources Almond Board of California.

scholarly journals MORIN PREVENTS ULTRAVIOLET-B RADIATION-INDUCED PHOTOCARCINOGENESIS THROUGH ACTIVATING THROMBOSPONDIN-1 IN THE MOUSE SKIN

2018 ◽  
Vol 11 (3) ◽  
pp. 171
Author(s):  
Anjugam C ◽  
Sridevi M ◽  
Rajendra Prasad N ◽  
Agilan Balupillai
Keyword(s):  
Growth Factor ◽  
Transforming Growth Factor Beta ◽  
Transforming Growth Factor ◽  
Mouse Skin ◽  
Ultraviolet B ◽  
Uvb Radiation ◽  
Thrombospondin 1 ◽  
Radiation Induced ◽  
Cox 2 ◽  
Uvb Exposure

 Objective: In this study, we investigated whether morin, a natural flavonoid, could able to inhibit ultraviolet B (UVB)-induced carcinogenesis in the skin of Swiss albino mice.Methods: The mice were exposed to UVB radiation (180 mJ/cm2) on weekly thrice for 30 weeks, and morin was administered intraperitoneal and topical application 1 h before UVB exposure. UVB radiation induces the overexpression of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), vascular endothelial growth factor (VEGF), transforming growth factor-beta (TGF-β), and Bcl-2 genes.Results: Morin significantly prevented UVB-induced activation of COX-2, iNOS, VEGF, TGF-β, and Bcl-2 expression in mouse skin. Thrombospondin-1 (TSP), a novel endogenous factor, inhibits angiogenesis and inflammation.Conclusion: The present study illustrates that the protective effect of morin against UVB-induced carcinogenesis may be modulated through activation of TSP-1 in UVB-exposed Swiss albino mice.

scholarly journals Does Lockdown Decrease the Protective Role of Ultraviolet-B (UVB) Radiation in Reducing COVID-19 Deaths?

2020 ◽  
Author(s):  
Rahul Kalippurayil Moozhipurath ◽  
Lennart Kraft
Keyword(s):  
Time Constant ◽  
Growth Rates ◽  
Protective Role ◽  
Ultraviolet B ◽  
Time Varying ◽  
Uvb Radiation ◽  
Percentage Points ◽  
Uvb Exposure ◽  
Country Specific

AbstractBackgroundNations are imposing unprecedented measures at large-scale to contain the spread of COVID-19 pandemic. Recent studies indicate that measures such as lockdowns may have slowed down the growth of COVID-19. However, in addition to substantial economic and social costs, these measures also limit the exposure to Ultraviolet-B radiation (UVB). Emerging observational evidence indicate the protective role of UVB and vitamin D in reducing the severity and mortality of COVID-19 deaths. In this observational study, we empirically outline the independent protective roles of lockdown and UVB exposure as measured by ultraviolet index (UVI), whilst also examining whether the severity of lockdown is associated with a reduction in the protective role.MethodsWe apply a log-linear fixed-effects model to a panel dataset of 162 countries over a period of 108 days (n=6049). We use the cumulative number of COVID-19 deaths as the dependent variable and isolate the mitigating influence of lockdown severity on the association between UVI and growth-rates of COVID-19 deaths from time-constant country-specific and time-varying country-specific potentially confounding factors.FindingsAfter controlling for time-constant and time-varying factors, we find that a unit increase in UVI and lockdown severity are independently associated with 17% [-1.8 percentage points] and 77% [-7.9 percentage points] decline in COVID-19 deaths growth rate, indicating their respective protective roles. However, the widely utilized and least severe lockdown (recommendation to not leave the house) already fully mitigates the protective role of UVI by 95% [1.8 percentage points] indicating its downside.InterpretationWe find that lockdown severity and UVI are independently associated with a slowdown in the daily growth rates of cumulative COVID-19 deaths. However, we find consistent evidence that increase in lockdown severity is associated with a significant reduction in the protective role of UVI in reducing COVID-19 deaths. Our results suggest that lockdowns in conjunction with adequate exposure to UVB radiation might have provided even more substantial health benefits, than lockdowns alone. For example, we estimate that there would be 21% fewer deaths on average with sufficient UVB exposure while people were recommended not to leave their house. Therefore, our study outlines the importance of considering UVB exposure, especially while implementing lockdowns and may support policy decision making in countries imposing such measures.

scholarly journals Association of lockdowns with the protective role of ultraviolet-B (UVB) radiation in reducing COVID-19 deaths

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rahul Kalippurayil Moozhipurath ◽  
Lennart Kraft
Keyword(s):  
Time Constant ◽  
Growth Rates ◽  
Protective Role ◽  
Ultraviolet B ◽  
Cumulative Number ◽  
Time Varying ◽  
Uvb Radiation ◽  
Uvb Exposure ◽  
Country Specific

AbstractNations are imposing unprecedented measures at a large scale to contain the spread of the COVID-19 pandemic. While recent studies show that non-pharmaceutical intervention measures such as lockdowns may have mitigated the spread of COVID-19, those measures also lead to substantial economic and social costs, and might limit exposure to ultraviolet-B radiation (UVB). Emerging observational evidence indicates the protective role of UVB and vitamin D in reducing the severity and mortality of COVID-19 deaths. This observational study empirically outlines the protective roles of lockdown and UVB exposure as measured by the ultraviolet index (UVI). Specifically, we examine whether the severity of lockdown is associated with a reduction in the protective role of UVB exposure. We use a log-linear fixed-effects model on a panel dataset of secondary data of 155 countries from 22 January 2020 until 7 October 2020 (n = 29,327). We use the cumulative number of COVID-19 deaths as the dependent variable and isolate the mitigating influence of lockdown severity on the association between UVI and growth rates of COVID-19 deaths from time-constant country-specific and time-varying country-specific potentially confounding factors. After controlling for time-constant and time-varying factors, we find that a unit increase in UVI and lockdown severity are independently associated with − 0.85 percentage points (p.p) and − 4.7 p.p decline in COVID-19 deaths growth rate, indicating their respective protective roles. The change of UVI over time is typically large (e.g., on average, UVI in New York City increases up to 6 units between January until June), indicating that the protective role of UVI might be substantial. However, the widely utilized and least severe lockdown (governmental recommendation to not leave the house) is associated with the mitigation of the protective role of UVI by 81% (0.76 p.p), which indicates a downside risk associated with its widespread use. We find that lockdown severity and UVI are independently associated with a slowdown in the daily growth rates of cumulative COVID-19 deaths. However, we find evidence that an increase in lockdown severity is associated with significant mitigation in the protective role of UVI in reducing COVID-19 deaths. Our results suggest that lockdowns in conjunction with adequate exposure to UVB radiation might have even reduced the number of COVID-19 deaths more strongly than lockdowns alone. For example, we estimate that there would be 11% fewer deaths on average with sufficient UVB exposure during the period people were recommended not to leave their house. Therefore, our study outlines the importance of considering UVB exposure, especially while implementing lockdowns, and could inspire further clinical studies that may support policy decision-making in countries imposing such measures.

scholarly journals The growth and tissue mineral concentrations of date palm (Phoenix dactylifera L.) cultivars in response to the ultraviolet-B radiation

2020 ◽  
pp. 354-361
Author(s):  
Saeedallah A. Niazwali ◽  
Annadurai Senthilkumar ◽  
Kandhan Karthishwaran ◽  
Mohammed A. Salem
Keyword(s):  
Date Palm ◽  
Growth Parameters ◽  
Principal Component ◽  
Dry Weight ◽  
Genotypic Diversity ◽  
Phoenix Dactylifera ◽  
Ultraviolet B ◽  
Uvb Radiation ◽  
Uvb Exposure ◽  
Mineral Concentrations

The ultraviolet-B (UVB) radiation is an integral part of the sun light and adversely affects the growth and development of date palm (Phoenix dactylifera). Although, date palm is an economically important fruit tree and the majority the world’s production is centered in the Arabian Peninsula, the studies evaluating date palm genotypic diversity and response to the UVB radiation are limited. To investigate this, five commercially grown date palm cultivars were exposed to the control and two elevated levels (four and eight hours per day for one year) of UVB radiations. The results showed that UVB radiation decreased plant height and leaf number by 8-14%, shoot root fresh weight by 66-87% and dry weight by 20-23%, total chlorophyll and carotenoids concentrations by 22-28%, while increased the proline and UVB absorbing compounds (phenolics) by 142% and 17.5%, respectively, across cultivars. These changes were more pronounced under the eight-hour UVB exposure. In general, roots tended to have greater concentrations of S and N by ≈1.4 folds, Co, Na, and P by 3.3-7 folds than shoots, compared to average across cultivars and treatments. However, under UVB, several mineral concentrations were either increased (e.g, Ca, Co, Fe, Mn, P) or decreased (e.g, K, Mo, S, N) consistently in shoots and roots. One exception to this rule was the Na concentration that increased in the shoot (9-45%) but decreased in the roots (8-10%) under UVB. Thus, the response of the date palm cultivars to the UVB was dependent on the measured traits, exhibiting decline in the growth parameters despite the increase in the UVB absorbing compounds and the tissue concentrations of several minerals. The principal component analysis (PCA) showed that the cultivars differed similarly in response to a given level of UVB treatments. Based on the PCA, the cultivars were grouped into two groups as BARHI and FRDWT in one group, while KHD, NBSTF, and RFDRD in other group.

scholarly journals Acute ultraviolet radiation exposure attenuates nitric oxide-mediated vasodilation in the cutaneous microvasculature of healthy humans

2018 ◽  
Vol 125 (4) ◽  
pp. 1232-1237 ◽  
Author(s):  
S. Tony Wolf ◽  
Anna E. Stanhewicz ◽  
Nina G. Jablonski ◽  
W. Larry Kenney
Keyword(s):  
Nitric Oxide ◽  
Radiation Exposure ◽  
Local Heating ◽  
Skin Pigmentation ◽  
Ultraviolet B ◽  
Uvb Radiation ◽  
Doppler Flowmetry ◽  
Healthy Humans ◽  
Cutaneous Vasodilation ◽  
Uvb Exposure

5-Methyltetrahydrofolate (5-MTHF) is important for nitric oxide (NO)-mediated cutaneous microvascular vasodilation. Ultraviolet B (UVB) radiation may deplete 5-MTHF, either directly or via production of reactive oxygen species (ROS), decreasing NO-mediated vasodilation. We hypothesized that 1) acute UVB exposure would attenuate NO-dependent cutaneous vasodilation, 2) local perfusion of 5-MTHF or ascorbate (ASC) (antioxidant) would augment NO-dependent vasodilation after UVB, and 3) darker skin pigmentation would be UVB-protective. Intradermal microdialysis fibers ( n = 3) placed in each forearm of 22 healthy young adults (23 ± 1 yr; 8M/14F) locally delivered lactated Ringer’s (control), 5 mM 5-MTHF, or 10 mM ASC. One arm was UVB-exposed (300 mJ/cm2), and the other served as a nonexposed control (CON). Following UVB exposure, a standardized local heating (42°C) protocol induced cutaneous vasodilation. After attaining a plateau blood flow, 15 mM NG-nitro-l-arginine methyl ester (nitric oxide synthase inhibiter) was infused at all sites to quantify the NO contribution. Red cell flux was measured at each site by laser-Doppler flowmetry (LDF), and cutaneous vascular conductance (CVC = LDF/mean arterial pressure) was expressed as a percentage of maximum (28 mM sodium nitroprusside + 43°C). UVB attenuated NO-mediated vasodilation compared with CON (23.1 ± 3.6 vs. 33.9 ± 3.4%; P = 0.001). Delivery of 5-MTHF or ASC improved NO-mediated vasodilation versus lactated Ringer’s in the UVB-exposed arm (MTHF: 30.1 ± 4.8% vs. 23.1 ± 3.8%; P = 0.03; ASC: 30.9 ± 4.3% vs. 23.1 ± 3.8%; P = 0.02). Neither treatment affected the response in the nonexposed arm ( P ≥ 0.09). Skin pigmentation (melanin index) was not predictive of the UVB response ( P ≥ 0.34). These data suggest that acute UVB exposure attenuates NO-mediated vasodilation via direct and/or ROS-induced reductions in 5-MTHF, independent of skin pigmentation. NEW & NOTEWORTHY Endothelial-derived nitric oxide (NO) contributes to normal healthy function of the human cutaneous microvasculature. Bioavailability of 5-methyltetrahydrofolate (5-MTHF) is important for the production of NO. Ultraviolet (UV) radiation exposure, specifically UVB, may deplete cutaneous 5-MTHF, thereby reducing NO-mediated microvascular function. Our findings suggest that acute UVB exposure attenuates NO-mediated vasodilation of the cutaneous microvasculature via degradation of 5-MTHF. These findings advance our understanding of the potential negative health impacts of acute UV exposure.

scholarly journals Protective Effect of Spirulina-Derived C-Phycocyanin against Ultraviolet B-Induced Damage in HaCaT Cells

Medicina ◽  
2021 ◽  
Vol 57 (3) ◽  
pp. 273
Author(s):  
Young Ah Jang ◽  
Bo Ae Kim
Keyword(s):  
Antioxidant Defense System ◽  
Skin Aging ◽  
Ultraviolet B ◽  
Control Group ◽  
Hacat Cells ◽  
Uvb Radiation ◽  
Skin Damage ◽  
Blue Green Algae ◽  
Radiation Group ◽  
Skin Wrinkles

Background and objectives: Reactive oxygen species (ROS) overwhelm the antioxidant defense system, induce oxidative stress, and increase matrix metalloproteinase (MMP) expression, resulting in skin aging. Thus, preventing ultraviolet B (UVB)-induced skin damage can attenuate skin aging. Spirulina (a biomass of cyanobacteria, also called blue-green algae) is comprised of prokaryotes, whereas microalgae are eukaryotes and are rich in phycocyanin, a powerful antioxidant. Materials and Methods: Here, we investigated the photoprotective effects of spirulina-derived C-phycocyanin (C-PC) against UVB radiation using keratinocytes (HaCaT cells). Results: UVB radiation increased MMP-1 and MMP-9 expression but decreased involucrin, filaggrin, and loricrin expression. C-PC showed no toxicity at concentrations of 5–80 μg/mL in terms of HaCaT cell viability. UVB-irradiated HaCaT cells had a 50.8% survival rate, which increased to 80.3% with C-PC treatment. MMP expression increased with UVB treatment, whereas MMP-1 and MMP-9 concentrations decreased with C-PC treatment. UVB reduced involucrin, filaggrin, and loricrin expression in HaCaT cells, but 80 μg/mL C-PC increased their expression by >25%. In the UVB radiation group, dichlorofluorescin diacetate fluorescence intensity in HaCaT cells increased by 81.6% compared with that in the control group, whereas ROS production was reduced by 51.2% and 55.1% upon treatment with 40 and 80 μg/mL C-PC, respectively. Conclusions: C-PC might reduce or prevent skin aging by reducing UVB irradiation-induced skin wrinkles and free radicals.

scholarly journals Could age increase the strength of inverse association between ultraviolet B exposure and colorectal cancer?

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Vidya Lakshmi Purushothaman ◽  
Raphael E. Cuomo ◽  
Cedric F. Garland ◽  
Timothy K. Mackey
Keyword(s):  
Colorectal Cancer ◽  
Vitamin D ◽  
Vitamin D Deficiency ◽  
Age Groups ◽  
Incidence Rates ◽  
Ultraviolet B ◽  
Inverse Association ◽  
Crude Incidence ◽  
Age Dependent ◽  
Uvb Exposure

Abstract Background Vitamin D has been identified as a potential protective factor in the development of colorectal cancer (CRC). We expect to see a stronger association of ultraviolet B (UVB) exposure and CRC crude rates with increasing age since chronic vitamin D deficiency leads to sustained molecular changes that increase cancer risk. The DINOMIT (disjunction, initiation, natural selection, overgrowth, metastasis, involution, and transition) model postulates various stages of cancer development due to vitamin D deficiency and the associated latency period. The purpose of this study is to examine this age-dependent inverse relationship globally. Methods In this ecological study, a series of linear and polynomial regression tests were performed between country-specific UVB estimates adjusted for cloud cover and crude incidence rates of CRC for different age groups. Multiple linear regression was used to investigate the association between crude incidence rates of colorectal cancer and UVB estimate adjusting for urbanization, skin pigmentation, smoking, animal consumption, per capita GDP, and life expectancy. Statistical analysis was followed by geospatial visualization by producing choropleth maps. Results The inverse relationship between UVB exposure and CRC crude rates was stronger in older age groups at the country level. Quadratic curve fitting was preferred, and these models were statistically significant for all age groups. The inverse association between crude incidence rates of CRC and UVB exposure was statistically significant for age groups above 45 years, after controlling for covariates. Conclusion The age-dependent inverse association between UVB exposure and incidence of colorectal cancer exhibits a greater effect size among older age groups in global analyses. Studying the effect of chronic vitamin D deficiency on colorectal cancer etiology will help in understanding the necessity for population-wide screening programs for vitamin D deficiency, especially in regions with inadequate UVB exposure. Further studies are required to assess the need for adequate public health programs such as selective supplementation and food fortification.

Flavonoids and UV Photoprotection in Arabidopsis Mutants

2001 ◽  
Vol 56 (9-10) ◽  
pp. 745-754 ◽  
Author(s):  
Ken G Ryan ◽  
Ewald E Swinny ◽  
Chris Winefield ◽  
Kenneth R Markham
Keyword(s):  
Crucial Role ◽  
Hydroxycinnamic Acid ◽  
Ultraviolet B ◽  
Uvb Radiation ◽  
Wild Type ◽  
Hydroxycinnamic Acid Derivatives ◽  
Quercetin Glycosides ◽  
Kaempferol Glycosides ◽  
Low Levels ◽  
High Level

AbstractWild-type Arabidopsis L. leaves exposed to low ultraviolet-B (U V B ) conditions contained predominantly kaempferol glycosides, with low levels of quercetin glycosides. The flavonoid level doubled on treatment with UVB and an increase in the ratio of quercetin: kaempferol was observed. These results suggest that flavonols protect Arabidopsis plants from UVB damage, and indicate that the flavonoid 3’-hydroxylase (F3’H) enzyme, which converts dihydrokaempferol to dihydroquercetin, may play a crucial role. The tt7 mutant lacks this gene and, after treatment with sub-ambient UVB, contained kaempferol glycosides exclusively, to a level of total flavonols similar to that in wild-type Arabidopsis. Total flavonols after enhanced UVB treatment were higher in tt7 than in similarly treated wild-type plants, and only kaempferol glycosides were detected. Despite this high level, tt7 plants were less tolerant of UVB radiation than wild-type plants. These observations suggests that kaempferol is a less effective photoprotectant than quercetin. The chalcone isomerase (CHI) mutant (tt5) surprisingly did not accumulate naringenin chalcone, and this suggests that the mutation may not be restricted to the CHI gene alone. The concentration of hydroxycinnamic acid derivatives did not change with UVB treatment in most varieties indicating that their role in UV photoprotection may be subordinate to that of the flavonoids.

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