Enhanced UV-B Radiation Research Articles

Effects of UV-B Radiation Exposure on Transgenerational Plasticity in Grain Morphology and Proanthocyanidin Content in Yuanyang Red Rice.

The effect of UV-B radiation exposure on transgenerational plasticity, the phenomenon whereby the parental environment influences both the parent's and the offspring's phenotype, is poorly understood. To investigate the impact of exposing successive generations of rice plants to UV-B radiation on seed morphology and proanthocyanidin content, the local traditional rice variety 'Baijiaolaojing' was planted on terraces in Yuanyang county and subjected to enhanced UV-B radiation treatments. The radiation intensity that caused the maximum phenotypic plasticity (7.5 kJ·m-2) was selected for further study, and the rice crops were cultivated for four successive generations. The results show that in the same generation, enhanced UV-B radiation resulted in significant decreases in grain length, grain width, spike weight, and thousand-grain weight, as well as significant increases in empty grain percentage and proanthocyanidin content, compared with crops grown under natural light conditions. Proanthocyanidin content increased as the number of generations of rice exposed to radiation increased, but in generation G3, it decreased, along with the empty grain ratio. At the same time, biomass, tiller number, and thousand-grain weight increased, and rice growth returned to control levels. When the offspring's radiation memory and growth environment did not match, rice growth was negatively affected, and seed proanthocyanidin content was increased to maintain seed activity. The correlation analysis results show that phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), dihydroflavonol 4-reductase (DFR), and 4-coumarate:CoA ligase (4CL) enzyme activity positively influenced proanthocyanidin content. Overall, UV-B radiation affected transgenerational plasticity in seed morphology and proanthocyanidin content, showing that rice was able to adapt to this stressor if previous generations had been continuously exposed to treatment.

Effects of Enhanced UV-B Radiation on Decomposition and Nutrient Release Rates of Litter from Cunninghamia lanceolata (Lamb.) Hook

In order to explore the effects of enhanced UV-B radiation on the decomposition and nutrient cycling characteristics of Cunninghamia lanceolata (Lamb.) Hook litter, we collected material from C. lanceolata in a middle-aged forest (16 years) and over-mature forest (49 years). Four different UV-B radiation enhancement gradient treatments of CK, CK + 30 uw/cm2 (T1), CK + 45 uw/cm2 (T2), and CK + 60 uw/cm2 (T3), with natural light (CK) as the baseline, were conducted to determine the impact of UV-B radiation indoor simulation enhancement on the litter decomposition and nutrient release of C. lanceolata at various developmental stages. The results indicate that UV-B radiation increases the dry weight decomposition rate and the nutrient decomposition rate of C. lanceolata litter, and the decomposition rate of C. lanceolata litter in an over-mature forest is always greater than that in a middle-aged forest litter, with observable influences on its chemical composition. Such changes significantly alter the nutrient release pattern of N, P, and K in litter in middle-aged forests and N in litter from over-mature forests, and promote the release of C, which may affect the nutrient cycle and carbon sink function of C. lanceolata plantations.

The antioxidant response mechanism of flavonoids in ‘Tainong 1’ mango pulp under enhanced UV-B radiation

The antioxidant response mechanism of flavonoids in ‘Tainong 1’ mango pulp under enhanced UV-B radiation

Response of two different Phoenix dactylifera cultivars to future climate conditions

Plants are naturally exposed to various environmental stresses that affect their growth and development. As a desert plant, Phoenix dactylifera (date palm) has developed strategies to protect itself from most abiotic stresses. However, projected climate changes and the interaction between the various abiotic stressors will have profound effects on date palm adaptation and production In the present study, the two date palm cultivars, Sultana and Zamli cultivars were exposed to elevated levels of CO2 and enhanced UVB radiation and non-enzymatic antioxidants (total phenols, α-tocopherol, reduced glutathione content) and antioxidant enzyme activities (polyphenol oxidase, peroxidase, superoxide dismutase, catalase, ascorbate peroxidase) activities were analysed. The results showed that the Sultana cultivar is tolerant to future climate conditions. However, more biotic stress and yield parameters are needed for the identification of biotic stress tolerant date palm cultivars.

The influence of elevated CO2 concentrations and UVB radiation in antioxidant activity of selected Chenopodium quinoa varieties

Ecosystems have been affected by climate change. Both agriculture and environmental changes are correlated with various features since climate change is the main cause of abiotic and biotic stress, which affects crop plants. Climate change and its severe impact on plant productivity showed great intensity due to the effects of abiotic stress. In the present investigation, we selected two quinoa varieties to study the response to future climatic factors such as eCO2, enhanced UVB radiation, and UVB+eCO2 combined effects in open-top chambers in the hot climate of the UAE. The treatments were administered for 90 days in the hot UAE weather conditions and the experiment was carried out in a transparent OTC facility. The response of the studied quinoa varieties was measured by analyzing their non-enzymatic antioxidant and antioxidant enzyme activities. Our findings showed that quinoa varieties are suitable as industrial crops for their levels of antioxidants under stimulating climatic conditions because the quantity and quality of their yield have not been affected. Based on the results obtained in the present investigation, further study is warranted for screening more varieties with the addition of climate change factors such as temperature and humidity to find more tolerant varieties of quinoa suitable for future climatic conditions.

Ultraviolet-B radiation in relation to agriculture in the context of climate change: a review.

Over the past few decades, the amount of ultraviolet-B radiation (UV-B) reaching the earth's surface has been altered due to climate change and stratospheric ozone dynamics. This narrow but highly biologically active spectrum of light (280-320nm) can affect plant growth and development. Depletion of ozone and climate change are interlinked in a very complicated manner, i.e., significantly contributing to each other. The interaction of climate change, ozone depletion, and changes in UV-B radiation negatively affects the growth, development, and yield of plants. Furthermore, this interaction will become more complex in the coming years. The ozone layer reduction is paving a path for UV-B radiation to impact the surface of the earth and interfere with the plant's normal life by negatively affecting the plant's morphology and physiology. The nature and degree of the future response of the agricultural ecosystem to the decreasing or increasing UV-B radiation in the background of climate change and ozone dynamics are still unclear. In this regard, this review aims to elucidate the effects of enhanced UV-B radiation reaching the earth's surface due to the depletion of the ozone layer on plants' physiology and the performance of major cereals.

Effects of UV-B radiation on epiphytic bacterial communities on male and female Sargassum thunbergii

The effects of increased UV-B radiation on macroalgae have been widely studied, but knowledge concerning the response of communities of algal epiphytic bacteria to increased UV-B radiation and differences between male and female algae is still lacking. Via 16S rDNA high-throughput sequencing technology, changes in the epiphytic bacterial communities on male and female S. thunbergii under increased UV-B radiation were studied in the lab. Under different UV-B radiation intensities, although the α diversity and community composition of epiphytic bacteria changed little, the β diversity indicated that the community structure of bacteria on S. thunbergii was obviously clustered, and the relative abundance of dominant bacteria and indicator species changed considerably. There were unique bacteria in each experimental group, and the bacteria whose abundance obviously changed were members of groups related to environmental resistance or adaptability. The variation in the abundance of epiphytic bacteria was different in male and female S. thunbergii, and the bacteria whose abundance greatly changed were mainly related to algal growth and metabolism. The abundance of genes with predicted functions related to metabolism, genetic information processing, environmental adaptation and infectious diseases changed with increased UV-B radiation, and those variations differed between epiphytic bacteria on male and female S. thunbergii. This study found that the algal epiphytic bacteria were influenced by the increase in UV-B radiation and underwent certain adaptations through adjustments to community structure and function, and this response was also affected by the sex of the macroalgae. These results are expected to serve as experimental basis and provide reference for further understanding of the response of algae epiphytic bacteria to enhanced UV-B radiation caused by the thinning of the ozone layer and the resulting changes in the relationship between algae and bacteria, which may change the community of the marine ecosystem and affect important marine ecological process.

Enhanced UV-B Radiation Induced the Proanthocyanidins Accumulation in Red Rice Grain of Traditional Rice Cultivars and Increased Antioxidant Capacity in Aging Mice

Proanthocyanidins are major UV-absorbing compounds. To clarify the effect of enhanced UV-B radiation on the proanthocyanidin synthesis and antioxidant capacity of traditional rice varieties in Yuanyang terraced fields, we studied the effects of enhanced UV-B radiation (0, 2.5, 5.0, 7.5 kJ·m-2·d-1) on the rice grain morphology, proanthocyanidins content, and synthesis. The effects of UV-B radiation on the antioxidant capacity of rice were evaluated by feeding aging model mice. The results showed that UV-B radiation significantly affected the grain morphology of red rice and increased the compactness of starch grains in the starch storage cells of central endosperm. The content of proanthocyanidin B2 and C1 in the grains was significantly increased by 2.5 and 5.0 kJ·m-2·d-1 UV-B radiation. The activity of leucoanthocyanidin reductase was higher in rice treated by 5.0 kJ·m-2·d-1 than other treatments. The number of neurons in the hippocampus CA1 of mice brain fed red rice increased. After 5.0 kJ·m-2·d-1 treatment, red rice has the best antioxidant effect on aging model mice. UV-B radiation induces the synthesis of rice proanthocyanidins B2 and C1, and the antioxidant capacity of rice is related to the content of proanthocyanidins.

The Role of Reactive Oxygen Species in Plant Response to Radiation.

Radiation is widespread in nature, including ultraviolet radiation from the sun, cosmic radiation and radiation emitted by natural radionuclides. Over the years, the increasing industrialization of human beings has brought about more radiation, such as enhanced UV-B radiation due to ground ozone decay, and the emission and contamination of nuclear waste due to the increasing nuclear power plants and radioactive material industry. With additional radiation reaching plants, both negative effects including damage to cell membranes, reduction of photosynthetic rate and premature aging and benefits such as growth promotion and stress resistance enhancement have been observed. ROS (Reactive oxygen species) are reactive oxidants in plant cells, including hydrogen peroxide (H2O2), superoxide anions (O2•-) and hydroxide anion radicals (·OH), which may stimulate the antioxidant system of plants and act as signaling molecules to regulate downstream reactions. A number of studies have observed the change of ROS in plant cells under radiation, and new technology such as RNA-seq has molecularly revealed the regulation of radiative biological effects by ROS. This review summarized recent progress on the role of ROS in plant response to radiations including UV, ion beam and plasma, and may help to reveal the mechanisms of plant responses to radiation.

The Effects of Enhanced Ultraviolet-B Radiation on Leaf Photosynthesis and Submicroscopic Structures in Mangifera indica L. cv. ‘Tainong No 1’

Objective: In the future, the stress of enhanced UV-B radiation on the Earth will first affect the photosynthesis of plants, including mangoes. Therefore, it is necessary to study the effects of enhanced UV-B radiation on the photosynthesis of mangoes. Methods: ‘Tainong No 1’ mango trees in the field were selected as the experimental material and divided into 2 groups: one group was shined under 96 kJ·m−2·d−1 UV-B lamps for artificially simulated treatment of enhanced UV-B radiation, and the other group was shined under sunshine directly as the control (CK). The main photosynthetic physiological indicators were measured with conventional methods, and the expression levels of the genes encoding large and small subunits of the Rubisco enzyme were measured with fluorescent qPCR. The changes in stomatal morphology and chloroplast structure were observed with scanning electron microscopy and transmission electron microscopy. Results: The content of malondialdehyde (MDA) and the relative conductivity in the leaves of the treatment tended to be significantly higher than those of the CK. The net photosynthetic rate (Pn) of the treatment tended to decrease and be lower than that of CK. The dynamics of intercellular CO2 concentration (Ci) of the treatment and CK changed differently from each other but generally tended to decrease, and that of the treatment tended to be significantly higher than that of CK. The stomatal conductance (Gs) of the treatment and CK both generally decreased, and that of the treatment was always significantly lower than that of CK. The contents of chlorophyll a, chlorophyll b and total chlorophyll and the ratio of chlorophyll a/b of the treatment were lower than those of CK, while the carotenoid content showed the opposite trend. The stomata and the surface of leaves of the treatment were sunken and damaged, respectively. The palisade tissue, spongy tissue and upper epidermis thickened more, and the total thickness significantly increased. Meanwhile, the ratio of palisade tissue to spongy tissue decreased. During treatment, the chloroplasts were swollen and shortened, the number of chloroplasts was reduced, the starch grains were degraded, and the grana lamella were distorted, loosely arranged and blurred. The expression of the genes encoding the Rubisco large subunit (rbcL) in the treatment was significantly inhibited, while that encoding the Rubisco small subunit (rbcS) decreased first and increased later. In conclusion, 96 kJ·m−2·d−1 enhanced UV-B radiation treatment caused damage to the leaf cell membrane system. This led to stomatal limitation of photosynthesis by destroying the stomatal structure and nonstomatal limitation of photosynthesis by damaging the submicrostructure of the chloroplasts and downregulating the expression of rbcL. The leaves may resist the photosynthetic damage caused by enhanced UV-B radiation by upregulating rbcS expression as much as possible.

UV-B Radiation Effects on the Alpine Plant Kobresia humilis in a Qinghai-Tibet Alpine Meadow.

Enhanced UV-B radiation resulting from stratospheric ozone depletion has been documented both globally and on the Qinghai-Tibet Plateau in China. The response of Kobresia humilis, an important alpine meadow plant species, to enhanced UV-B radiation was experimentally investigated at the Haibei Alpine Meadow Ecosystem Research Station (37°29'-37°45' N, 101°12'-101°23' E; alt. 3200 m). K. humilis was exposed to UV-B radiation including ambient UV-B and enhanced UV-B (simulating a 14% reduction in the ozone layer) in a randomized design with three replications of each treatment. Enhanced UV-B radiation resulted in a significant increase of both leaf area and fresh weight chlorophyll and carotenoid but had no effect on UV-B absorbing pigments. Similarly, enhanced UV-B radiation did not significantly change the photosynthetic O2 elevation rate while leaf thickness, width, and length significantly increased (p < 0.01). The enhanced UV-B radiation was associated with 2-3 days earlier flowering and a larger number of flowers per spikelet. The enhanced UV-B generally resulted in larger leaves and more flowers but earlier phenology. In summary, these findings suggest that alpine species of K. humilis have adapted to the strong solar UV-B radiation intensity presented on the Qinghai-Tibet Plateau, but the interspecies differences and their influence on trophic level should be more concerning.

Ultraviolet-B radiation stress triggers reactive oxygen species and regulates the antioxidant defense and photosynthesis systems of intertidal red algae Neoporphyra haitanensis

The enhancement of harmful ultraviolet-B (UV-B, 280–320 nm wavelength) radiation is a serious problem generally faced by photosynthetic organisms. Previous studies have reported that the currently increasing level of UV-B radiation received on earth can promote the formation of reactive oxygen species (ROS) by altering the antioxidant defense system or by hampering of photosynthesis system of plants. However, the relationship between the UV-B-induced ROS production, antioxidant capacity, and photosynthetic performance in macroalgae remains unclear. In this study, the regulation of the antioxidant system and photosynthetic activity by ROS triggered by UV-B radiation were investigated in an intertidal seaweed, Neoporphyra haitanensis. The contents of hydrogen peroxide and malondialdehyde increased with enhanced UV-B radiation, indicating N. haitanensis experienced oxidative stress. Increased activities of antioxidant enzymes showed a positive response of enzymatic antioxidants to maintain the balance of ROS under low UV-B conditions. Likewise, an accumulation of non-enzymatic antioxidants occurred and glutathione redox status was maintained at a high level, suggesting that the ascorbate–glutathione cycle played an indispensable role in detoxifying ROS. Nevertheless, high UV-B radiation markedly inhibited the efficiency of the enzymatic and non-enzymatic antioxidants, causing oxidative damage and a depression of photosynthesis. The addition of ROS scavengers alleviated the increased oxidation level caused by UV-B radiation, implying that oxidative damage under UV-B condition was ascribed to accumulated ROS. The activation of the antioxidant defense system was also modulated by ROS. Additionally, the decreased photosynthetic activities induced by enhanced UV-B radiation were reversed by ROS scavengers, indicating that ROS-mediated oxidative damage caused by UV-B radiation is one of the important causes of photo-inhibitory damage in N. haitanensis. Overall, these results shed some light on the close relationship between UV-B-induced ROS production, the antioxidant defense system, and photosynthetic performance in macroalgae, which helps to reveal their survival strategies for adapting to highly variable marine intertidal environments.

Effects and Mechanism of Enhanced UV-B Radiation on the Flag Leaf Angle of Rice.

Leaf angle is an influential agricultural trait that influences rice (Oryza sativa L.) plant type and yield, which results from the leaf bending from the vertical axis to the abaxial axis. UV-B radiation affects plant morphology, but the effects of varying UV-B intensities on rice flag leaves and the underlying molecular, cellular, and physiological mechanisms remain unknown. This experiment aims to examine the effect of natural light and field-enhanced UV-B radiation (2.5, 5.0, 7.5 kJ·m-2) on the leaf angle of the traditional rice variety Baijiaolaojing on Yuanyang terraces. In comparison with natural light, the content of brassinolide and gibberellin in rice flag leaves increased by 29.94% and 60.1%, respectively. The auxin content decreased by 17.3%. Compared with the natural light treatment, the cellulose content in the pulvini was reduced by 13.8% and hemicellulose content by 25.7% under 7.5 kJ·m-2 radiation intensity. The thick-walled cell area and vascular bundle area of the leaf pulvini decreased with increasing radiation intensity, and the growth of mechanical tissue in the rice leaf pulvini was inhibited. The flag leaf angle of rice was greatest at 7.5 kJ·m-2 radiation intensity, with an increase of 50.2%. There are two pathways by which the angle of rice flag leaves is controlled under high-intensity UV-B radiation. The leaf angle regulation genes OsBUL1, OsGSR1, and OsARF19 control hormone levels, whereas the ILA1 gene controls fiber levels. Therefore, as cellulose, hemicellulose, sclerenchyma, and vascular bundles weaken the mechanical support of the pulvini, the angle of the flag leaf increases.

Tissue-specific metabolic response of Acanthopanax senticosus (Rupr.et. Maxim.) Harms leaves to enhanced UV-B radiation

Tissue-specific metabolic response of Acanthopanax senticosus (Rupr.et. Maxim.) Harms leaves to enhanced UV-B radiation

Effect of Enhanced Ultraviolet-B Radiation on Fruit Maturity and Quality and Leaf Photosynthesis in ‘Guifei’ Mango

To investigate the characteristics of photosynthetic physiological changes in leaves of Mangifera indica L. cv. Guifei under enhanced ultraviolet (UV)-B radiation, natural light-exposed trees were used as controls and 96 kJ·m−2·d−1 enhanced UV-B radiation was artificially simulated in the field. The changes in fruit maturity and quality, the leaf net photosynthetic rate (Pn), photosynthetic pigment contents, photochemical reactions, the activities of photosynthetic enzymes and related gene expression levels were determined. Compared with the control, the percentage of mature fruits under the treatment significantly increased, and fruit quality improved. The net photosynthetic rate (Pn), photosynthetic pigment content, Hill reaction activity, and photochemical quenching coefficient (qP) of the treated leaves showed significantly higher values than those of the control leaves. The activities of Rubisco and Rubisco activating enzyme (RCA) and the expression levels of the Rubisco large subunit and Rubisco small subunit were significantly increased. Treatment with 96 kJ·m−2·d−1 enhanced ultraviolet-B radiation improved Rubisco activity by increasing the expression of the Rubisco large and small subunit genes, thereby enhancing the CO2-fixing capacity and dark reaction capacity of leaves. Thus, the net photosynthetic rate of leaves increased, which promoted the early maturity of ‘Guifei’ mango by the rapid accumulation of photosynthetic products.

Effects of enhanced UV-B radiation on nitrogen transformation and functional biological properties in the rice rhizosphere

ABSTRACT To clarify the effect of enhanced UV-B radiation on soil nitrogen transformation and its biological processes in paddy fields, the effects of enhanced ultraviolet-B radiation (0, 2.5, 5.0 and 7.5 kJ m−2) on soil nitrogen transformation and N2O emission, functional microbial quantity, enzyme activity, and gene expression during the growth period (tillering, jointing, booting and maturity stage) of rice were investigated in situ in a rice paddy field in the Yuanyang terraces, Yunnan Province, southwest China. The results show that UV-B radiation decreased the NH4 +-N content, increased the NO3 –N content in the rhizosphere, decreased N2O emissions from paddy fields, and significantly affected the properties of soil nitrogen transforming microorganisms. The 5.0 kJ m−2 UV-B radiation increased the quantity of ammonifying bacteria and ammonia oxidizing bacteria by 18–160% and 34–151%, respectively, decreased the urease activity in the rice rhizosphere by 11.9–27%; and significantly increased the expression of AOB-amoA and nosZ genes. Thus, the enhanced UV-B radiation increased the ammonia-oxidizing bacteria and AOB-amoA and nosZ gene expression, promoted the transformation of NH4 +-N to NO3 –N in the rice rhizosphere, and reduced N2O emissions in the paddy field.

Cell damage repair mechanism in a desert green algae Chlorella sp. against UV-B radiation

The protective ozone layer is continually depleting owing to an increase in the levels of solar UV-B radiation, which has harmful effects on organisms. Algae in desert soil can resist UV-B radiation, but most research on the radiation resistance of desert algae has focused on cyanobacteria. In this study, we found that desert green algae, Chlorella sp., could maintain high photosynthetic activity under UV-B stress. To examine the tolerance mechanism of the desert green algae photosystem, we observed the physiological and transcriptome-level responses of Chlorella sp. to high doses of UV-B radiation. The results showed that the reactive oxygen species (ROS) content first increased and then decreased, while the malondialdehyde (MDA) content revealed no notable lipid peroxidation during the UV-B exposure period. These results suggested that Chlorella sp. may have strong system characteristics for scavenging ROS. The antioxidant enzyme system showed efficient alternate coordination, which exhibited a protective effect against enhanced UV-B radiation. DNA damage and the chlorophyll and soluble protein contents had no significant changes in the early irradiation stage; UV-B radiation did not induce extracellular polysaccharides (EPS) synthesis. Transcriptomic data revealed that a strong photosynthetic system, efficient DNA repair, and changes in the expression of genes encoding ribosomal protein (which aid in protein synthesis and improve resistance) are responsible for the high UV-B tolerance characteristics of Chlorella sp. In contrast, EPS synthesis was not the main pathway for UV-B resistance. Our results revealed the potential cell damage repair mechanisms within Chlorella sp. that were associated with high intensity UV-B stress, thereby providing insights into the underlying regulatory adaptations of desert green algae.

Effect of enhanced UV-B radiation on growth and photosynthetic physiology of Iris tectorum maxim.

Iris tectorum Maxim. is an important plant that plays a very crucial role in the ecological welfare of wetlands. In this study, the effects of different intensities of UV-B radiation on the growth, photosynthetic pigment content, chlorophyll fluorescence characteristics, chloroplast ultrastructure, and gas exchange parameters of Iris tectorum Maxim. were studied. The results showed that enhanced UV-B radiation had a significant influence on the above-mentioned parameters of iris. Compared with the control, enhanced UV-B radiation caused certain damage to the leaf appearance. With the increasing intensity of radiation, the apparent damage degree became more serious. Enhanced UV-B radiation significantly decreased leaf chlorophyll contents, and the effect accumulated with the exposure time. Enhanced UV-B radiation increased Fo, significantly increased the non-photochemical quenching coefficient NPQ, reduced PSII and Qp, and significantly decreased the Fm, Fv/Fm, and Fv/Fo in leaves. The effect of UV-B radiation on PSII destruction of Iris tectorum Maxim. increased as the radiation intensity increased and the exposure time prolonged. The chloroplast structure was damaged under the enhanced UV-B radiation. More specifically, thylakoid lamellae were distorted, swelling and even blurred, and a large number of starch granules appeared. The effect of the high intensity of radiation on chloroplast ultrastructure was greater than that of lower intensity. Enhanced UV-B radiation reduced significantly the net photosynthetic rate, stomatal conductance, and transpiration rate, and the degree of degradation increased with the increasing irradiation intensity. However, the intercellular CO2 content increased, which suggests that the main reason for the decrease of photosynthetic rate was the non-stomatal factors.

Effects of enhanced UV-B radiation on photosynthetic performance and non-photochemical quenching process of intertidal red macroalgae Neoporphyra haitanensis

The effects of enhanced ultraviolet-B (UV-B, 280–320 nm) radiation reaching the Earth’s surface has become an important issue in terrestrial and marine ecosystems. Living in the land–marine boundary, intertidal macroalgae have various adaptive strategies to resist drastic environmental changes. In this study, we investigated the effects of enhanced UV-B radiation on the photosynthetic performance and photoprotective mechanisms of the red macroalgae Neoporphyra haitanensis . Our results showed that increasing UV-B radiation inhibited growth, damaged chloroplast structures and photosynthetic pigments, and reduced PSII activity and recovery ability in N. haitanensis . UV-B radiation significantly increased non-photochemical quenching (NPQ), indicating that NPQ is an effective photoprotection strategy in N. haitanensis . The transthylakoid proton gradient (ΔpH) uncoupler ammonium chloride (NH 4 Cl) significantly inhibited NPQ induction, showing that the induction of NPQ in N. haitanensis was dependent on ΔpH. Furthermore, violaxanthin and antheraxanthin, essential components of the xanthophyll cycle for modulating NPQ, were not detected in N. haitanensis , indicating the absence of the xanthophyll cycle in N. haitanensis . However, the increased NPQ under UV-B radiation was still associated with the accumulation of zeaxanthin. These findings will be useful for revealing adaptive strategies of intertidal macroalgae to cope with increasing UV-B radiation in the future. • Enhanced UV-B radiation significantly reduces photosynthetic performance of N. haitanensis. • NPQ can be used as effective strategy for photoprotection of N. haitanensis to resist UV-B radiation. • Although xanthophyll cycle is absent in N. haitanensis , NPQ is still regulated by the accumulation of zeaxanthin.

Silicon Mitigates Negative Impacts of Drought and UV-B Radiation in Plants.

Due to climate change, plants are being more adversely affected by heatwaves, floods, droughts, and increased temperatures and UV radiation. This review focuses on enhanced UV-B radiation and drought, and mitigation of their adverse effects through silicon addition. Studies on UV-B stress and addition of silicon or silicon nanoparticles have been reported for crop plants including rice, wheat, and soybean. These have shown that addition of silicon to plants under UV-B radiation stress increases the contents of chlorophyll, soluble sugars, anthocyanins, flavonoids, and UV-absorbing and antioxidant compounds. Silicon also affects photosynthesis rate, proline content, metal toxicity, and lipid peroxidation. Drought is a stress factor that affects normal plant growth and development. It has been frequently reported that silicon can reduce stress caused by different abiotic factors, including drought. For example, under drought stress, silicon increases ascorbate peroxidase activity, total soluble sugars content, relative water content, and photosynthetic rate. Silicon also decreases peroxidase, catalase, and superoxide dismutase activities, and malondialdehyde content. The effects of silicon on drought and concurrently UV-B stressed plants has not yet been studied in detail, but initial studies show some stress mitigation by silicon.