Xunling Wang

Effects of Enhanced Ultraviolet-B Radiation on Algae and Cyanobacteria

Abstract This article provides an overview of existing literature on the ultraviolet-B (UV-B) radiation effects on algae and cyanobacteria. We report on the effects of UV-B radiation to the growth and development, biomass, sensitivity, photosynthetic pigments, UV-B absorbing compounds, photosynthesis, protein and DNA damage, enzyme activity, nitrogen fixation and assimilation of nitrogen, protective mechanisms of algae and cyanobacteria, the accommodation of algae and cyanobacteria to environmental stress, and the effects to ecology system. Many of the studies show the dramatic effects of UV-B radiation; but typically these studies were conducted under conditions with supplemental UV-B irradiance that was higher than would ever occur outside experimental conditions or natural condition. A few of the studies reviewed used experimental conditions and supplemental UV-B irradiance that approached realism. Enhanced UV-B generally decreased chlorophyll content, whereas it increased UV-B absorbing compounds in many algae. Decrease in photosynthesis, particularly at higher UV-B doses, was due to both direct (effect on photosystem) and indirect (decrease in pigments) effects. The decreases in chlorophyll pigments and photosynthesis resulted in lower biomass. However, algae and cyanobacteria have evolved various avoidance and repair mechanisms to protect themselves against the damaging effects of UV radiation to acclimate to enhanced UV-B radiation. The review points to areas where further studies on the relationships among nitrogenase, Rubisco, antioxidase activity, signal, antioxidants, and free radicals under enhanced UV-B are needed to quantify the effects of UV-B radiation on algae and cyanobacteria. These studies are needed in order to develop dose response functions that can facilitate development of dynamic simulation models for use in UV-B and other environmental impact assessments.

The effect of enhanced ultraviolet-B radiation on growth, photosynthesis and stable carbon isotope composition (δ13C) of two soybean cultivars (Glycine max) under field conditions

Abstract Two Chinese cultivars of Glycine max , namely Heidou and Jindou, were exposed to ambient and supplemental levels of ultraviolet-B (UV-B) radiation simulating a 24% depletion in stratospheric ozone over a 9-week growing period at an outdoor experimental site. Enhanced UV-B irradiation significantly reduced leaf, stem and root biomass, and plant height in the Heidou cultivar. These changes were associated with a diminished photosynthetic (net CO 2 ) rate, stomatal conductance, transpiration rate and water use efficiency, and accompanied by decreased foliar chlorophyll a and b, and total carotenoid concentrations and elevated foliar flavonoid levels. In contrast, the Jindou cultivar displayed only a significantly reduced stem mass and stomatal conductance, but no changes in pigment composition under elevated UV-B. The greater tolerance of elevated UV-B exposures by the Jindou cultivar was attributed partly to its higher foliar flavonoid content, smaller leaf size, thicker leaf cuticle and scabrous (hairy) lamina. Nevertheless both the Heidou cultivar and the less UV-B sensitive Jindou cultivar displayed an altered carbon isotope composition (δ 13 C) in their tissues following exposure to elevated UV-B. Such carbon isotope composition changes in plant tissues suggested a means of early detection of photosynthetic disruption in plants with anticipated increase in UV-B due to stratospheric ozone depletion.

The Cascade Mechanisms of Nitric Oxide as a Second Messenger of Ultraviolet B in Inhibiting Mesocotyl Elongations

In this report, a number of physiological aspects was examined during developmental growth of maize seedlings mesocotyl. It was found that ultraviolet B (UVB) radiation was able to significantly induce nitric oxide synthase (NOS) activities and speedup the release of apparent nitric oxide (NO) of mesocotyl and that exogenous NO donors rhizospheric treatments may mimic the responses of the mesocotyl to UVB radiation, such as the inhibition of mesocotyl elongation, the decrease in exo‐ and endoglucanase activities and the increase in protein content of cell wall of mesocotyl. When the seedlings were treated with N‐nitro‐l‐arginine, an inhibitor of NOS, the mesocotyl elongation was promoted, the exo‐ and endoglucanase activities were raised and the protein content was reduced. However, under UVB radiation, the effects of exogenous NO on several physiological aspects of mesocotyl were similar to those of exogenous reactive oxygen species (ROS) eliminator, N‐acetyl‐cysteine. All the physiological changes were associated with either the exogenous NO supply or the activities of NOS in plant. Accordingly, it is assumed that reduction in mesocotyl length caused by UVB radiation was possibly achieved through modification of the chemical properties of the cell wall polysaccharides, which was induced by NO and ROS synergically mediated changes in exo‐ and endo‐β‐d‐glucanases activities in cell walls, and NO was one of the main signaling molecule of UVB radiation in inhibiting mesocotyl elongations. So NO might function as both a second messenger and an antioxidant of UVB radiation during developmental growth of the mesocotyl.

Effect of enhanced ultraviolet-B radiation on pollen germination and tube growth of 19 taxa in vitro

Abstract In order to determine the response of pollen to UV-B irradiation and cumulative effects of UV-B exposure time on pollen germination and tube growth, 19 taxa of higher plants were investigated in vitro concerning the exposure of pollen grains to two levels of enhanced ultraviolet-B (UV-BBE) (280–320 nm, 350 and 500 mW/m 2 biologically effective UV-B radiation) simulating 8 and 21% stratospheric ozone depletion in Lanzhou, China (36.04°N, 1550 m) and to no UV-B (control group). Compared with the control, enhanced UV-B radiation significantly inhibited pollen germination and tube growth in most species. Higher UV-B flux rate caused a greater inhibitory effect than lower UV-B radiation level. Several taxa exhibited insensitivity of pollen germination and tube growth to UV-B and were even stimulated by UV-B. Reduction in pollen germination rates and tube growth increased with longer exposure time and this indicated a cumulative effect of UV-B radiation. It is concluded that changes in pollen susceptibility to UV-B would lead to severe ecological consequences under natural conditions.

The Damage Repair Role of He–Ne Laser on Plants Exposed to Different Intensities of Ultraviolet-B Radiation¶

Light‐grown broad bean (Vicia faba L.) seedlings were subjected to different intensities of UV‐B radiation (0, 0.05, 0.15, 0.45, 0.90, 1.45 and 1.98 W m−2) for 7 h under photosynthetically active radiation (70 μmol m−2 s−1) and then exposed to He–Ne laser (632.8 nm, 5.43 mW mm−2) radiation for 5 min or red light radiation for 4 h without ambient light radiation. When He–Ne laser radiated leaves were treated using lower intensity UV‐B, the activities of superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and catalase (EC 1.11.1.6) improved significantly. Moreover, the UV‐B–injured plants treated with laser light recovered faster from UV‐B treatment because the concentration of malondialdehyde and the rate of electrolyte leakage from leaf disks reached control levels (no UV‐B or laser treatment) early compared with those exposed only to ambient light or in dark conditions. Laser treatment, however, had no repair effect on seedling damage induced by higher UV‐B radiation (1.45 and 1.98 W m−2), even with higher laser flux rates and longer laser treatment. In addition, the red light treatment had no repair effect on UV‐B–induced damage. Meanwhile, the long‐term physiological effect of He–Ne laser treatment on UV‐B damaged plants was presented and evaluated. The results showed that the laser had a long‐term positive physiological effect on the growth of UV‐B–damaged plants. With the exception of the severe damage caused by higher UV‐B radiation, a laser with the proper flux rate and treatment time can repair UV‐B–induced damage and shorten the recovery time.

Nitric oxide alleviates oxidative damage in the green alga Chlorella pyrenoidosa caused by UV-B radiation.

The effect of ultraviolet-B radiation (UV-B; 280–320 nm) on induction of nitric oxide was estimated in the suspensions of green algaChlorella pyrenoidosa with or without the NO scavengerN-acetyl-l-cysteine, and reductants such as 1,4-dithiothreitol, glutathione (reduced form), and ascorbic acid. Exogenously added sodium nitroprusside (NO donor), glutathione, 1,4-dithiothreitol, and ascorbic acid were able to prevent chlorophyll loss mediated by UV-B. Addition of NO to algal suspensions irradiated by UV-B increased the activity of catalase and superoxide dismutase but lowered the activity of phenylalanine ammonia-lyase. UV-B thus appears to be a strong inducer of NO production, exogenously added NO and reductants protecting the green alga against UV-B-induced oxidative damage.

Laser pretreatment protects cells of broad bean from UV-B radiation damage.

In order to determine the role of lasers in the stress resistance of broad bean (Vicia faba L.) to ultraviolet-B (UV-B) radiation, the embryos in seeds were exposed to He-Ne laser or CO2 laser radiation. Afterwards they were cultivated in Petri dishes in a constant temperature incubator until the lengths of epicotyls were nearly 3 cm. The epicotyls were then exposed to 1.02, 3.03 or 4.52 kJ m(-2) UV-B radiation, respectively, under 70 micromol m(-2) s(-1) photosynthetically active radiation (PAR) in a growth cabinet. Changes in the concentration of malondialdehyde (MDA), ascorbic acid (AsA) and UV-B absorbing compounds (absorbance at 300 nm) were measured to test the effects of laser pretreatment. The results showed that laser pretreatment of embryos enhanced UV-B stress resistance in the epicotyls of the broad bean by decreasing the MDA concentration and increasing the content of AsA and UV-B absorbing compounds. We suggest that those changes in MDA, AsA and UV-B absorbing compounds were responsible for the increase in stress resistance observed in the broad bean. This is the first investigation reporting the use of laser pretreatment to protect the cells of the broad bean from UV-B-induced damage.

Effect of enhanced UV-B radiation on polyamine content and membrane permeability in cucumber leaves (SCI)

Cucumber plants (Cucumis sativus L., cv. Jingchun 3) were grown in a greenhouse under PAR illumination of 400–600 μmol/(m2 s) at 30/15°C (day/night) temperature. Two enhanced biologically effective UV-B radiation levels per day were applied: 8.82 kJ/m2 (T1) and 12.6 kJ/m2 (T2). Cucumber seedlings were irradiated 7 h per day for 25 days under T1 and T2. A comparative study of growth, membrane permeability, and polyamine content in cucumber leaves under T1 and T2 treatments was conducted. UV-B radiation resulted in the dose-dependent decrease in leaf area, dry weight of foliage, and plant height. The T1 and T2 treatments caused an increase in the contents of putrescine, spermine, and spermidine. However, the total polyamine content declined slightly when electrolyte leakage increased dramatically on the 18th day of treatment, especially after T2 treatment. It can be concluded that polyamine accumulation in the cucumber leaves is an adaptive mechanism to the stress caused by UV-B radiation.

Testing the hypothesis of an ancient Roman soldier origin of the Liqian people in northwest China: a Y-chromosome perspective.

AbstractThe Liqian people in north China are well known because of the controversial hypothesis of an ancient Roman mercenary origin. To test this hypothesis, 227 male individuals representing four Chinese populations were analyzed at 12 short tandem repeat (STR) loci and 12 single nucleotide polymorphisms (SNP). At the haplogroup levels, 77% Liqian Y chromosomes were restricted to East Asia. Principal component (PC) and multidimensional scaling (MDS) analysis suggests that the Liqians are closely related to Chinese populations, especially Han Chinese populations, whereas they greatly deviate from Central Asian and Western Eurasian populations. Further phylogenetic and admixture analysis confirmed that the Han Chinese contributed greatly to the Liqian gene pool. The Liqian and the Yugur people, regarded as kindred populations with common origins, present an underlying genetic difference in a median-joining network. Overall, a Roman mercenary origin could not be accepted as true according to paternal genetic variation, and the current Liqian population is more likely to be a subgroup of the Chinese majority Han.

Changes in polyamine contents and arginine decarboxylase activity in wheat leaves exposed to ozone and hydrogen fluoride

Summary The effects of O 3 , HF or both on wheat leaves were shown by chlorophyll loss and changes in membrane permeability. The changes of the ADC activity and polyamine contents were also examined in wheat leaves exposed to pollutants. The ADC activity and polyamine contents increased significantly in pollutant-treated leaves when visible injury was hardly apparent. The increase in ADC activity may be a mechanism to increase the polyamine levels in pollutant-treated leaves so as to minimize the damaging effects of the pollutants. ADC activity and polyamine contents decreased, although Spd and Spm remained higher when visible injury was considerable. The above results may reflect an adaptive mechanism to stresses. The role of polyamines in conferring pollutant-resistance in plants is also discussed.