Manxiao Zhang

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.

Role of Poly-Galacturonase Inhibiting Protein in Plant Defense

Polygalacturonase-inhibiting proteins (PGIPs) are plant proteins believed to play an important role in the defense against plant pathogen fungals. PGIPs are glycoproteins located in plant cell wall which reduce the hydrolytic activity of polygalacturonases (PGs), limit the growth of plant pathogens, and also elicit defense responses in plant. Furthermore, PGIPs belong to the super family of leucine reach repeat (LRR) proteins which also include the products of several plant resistance genes. Many of the studies show the PGIP properties, molecular characteristics, and PGIP gene expression induced by some elicitors. Some of the studies review individual PGIP gene expression in different signal transduction pathways. This article summarizes the properties, different signal transduction mechanisms, detecting methods, transgenic plants, and function of PGIP. It also presents PGIP gene expression in different stages of maturity, tissues, and varieties. The review especially reports the particular PGIP gene expression induced by different biotic and abiotic stresses, offers some questions, and prospects the future study, which are needed in order to develop efficient strategies for disease-resistant plants. They may be useful for genetic engineering to obtain transgenic plants with increased tolerance to fungal infection, which decrease the use of insecticide.

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.

Bacterial diversity and distribution in the southeast edge of the Tengger Desert and their correlation with soil enzyme activities

The nature of microbial communities and their relation to enzyme activities in desert soils is a neglected area of investigation. To address this, the bacterial diversity and distribution and soil physico-chemical factors were investigated in the soil crust, the soil beneath the crust and rhizosphere soil at the southeast edge of the Tengger Desert, using the denaturing gradient gel electrophoresis of 16S rRNA genes amplified by the polymerase chain reaction. Phylogenetic analysis of the sequenced DGGE bands revealed a great diversity of bacteria. The Proteobacteria, consisting of the alpha, beta, and gamma subdivisions, were clearly the dominant group at all depths and in rhizosphere soil. Analysis of the enzyme activities indicated that the rhizosphere soil of Caragana korshinskii exhibited the highest protease and polyphenol oxidase activities, and in the soil crust there were increased activities of catalase, urease, dehydrogenase and sucrase. The bacterial community abundance closely correlated with soil enzyme activities in different soils. The presence of Cyanobacteria correlated with significant increases in protease, catalase and sucrase in the soil crust, and increased urease in the rhizosphere soil of Artemisia ordosica. The occurrence of Acidobacteria was associated with significant increases in urease, dehydrogenase, and sucrase in the rhizosphere soil of C. korshinski. The presence of gamma-Proteobacteria correlated with a significant increase in polyphenol oxidase in the rhizosphere soil of A. ordosica. The study indicated a close relationship between the soil bacterial community and soil enzymes, suggesting the necessity of further investigations into bacterial function in this desert ecosystem.

Regulation of the plasma membrane during exposure to low temperatures in suspension-cultured cells from a cryophyte (Chorispora bungeana)

Summary.As the outermost boundary of the cell, the plasma membrane plays an important role in determining the stress resistance of organisms. To test this concept in a cryophyte, we analyzed alterations of several components in plasma membranes isolated from suspension-cultured cells of Chorispora bungeana Fisch. & C.A. Mey in response to treatment at 0 and −4 °C for 192 h. When compared with the controls growing at 25 °C, both the membrane permeability and fluidity showed recovery after the initial impairment. Linolenic acid and membrane lipid unsaturation increased by about 0.8-fold following cold treatments, although the kinetics of the increase varied with the temperatures examined. During the treatments, the plasma membrane H+-ATPase (EC 3.6.1.3) activity increased by 78.06% at 0 °C and 100.47% at −4 °C. However, the plasma membrane NADH oxidase (EC 1.6.99.3) activity only decreased when exposed to a lower temperature (−4 °C), and remained at 63.93% after being treated for 192 h. After the treatments, the physical properties of the plasma membranes of suspension-cultured cells, especially the −4 °C treated cells, were similar to those in the wild plants. These findings indicate that the specific mechanism of cold resistance of C. bungeana is tightly linked with the rapid and flexible regulation of membrane lipids and membrane-associated enzymes, which ensure the structural and functional integrity of the plasma membrane that is essential for withstanding low temperature.

Variations in soil culturable bacteria communities and biochemical characteristics in the Dongkemadi glacier forefield along a chronosequence

The variations in the soil culturable bacterial communities and biochemical parameters of early successional soils from a receding glacier in the Tanggula Mountain were investigated. We examined low organic carbon (C) and nitrogen (N) contents and enzymatic activity, correlated with fewer bacterial groups and numbers in the glacier forefield soils. The soil pH values decreased, but the soil water content, organic C and total N significantly increased, along the chronosequence. The soil C/N ratio decreased in the early development soils and increased in the late development soils and it did not correlate with the soil age since deglaciation. The activities of soil urease, sucrase, protease, polyphenol oxidase, catalase, and dehydrogenase increased along the chronosequence. The numbers of culturable bacteria in the soils increased as cultured at 25°C while decreased at 4°C from younger soils to older soils. Total numbers of culturable bacteria in the soils cultured at 25°C were significantly positively correlated to the soil total N, organic C, and soil water content, as well as the activities of soil urease, sucrase, dehydrogenase, catalase, and polyphenol oxidase. We have obtained 224 isolates from the glacier forefield soils. The isolates were clustered into 28 groups by amplified ribosomal DNA restriction analysis (ARDRA). Among them, 27 groups and 25 groups were obtained from the soils at 25°C and at 4°C incubation temperatures, respectively. These groups are affiliated with 18 genera that belong to six taxa, viz, Actinobacteria, Gammaproteobacteria, Bacteroidetes, Firmicutes, Alphaproteobacteria, and Betaproteobacteria. The dominant taxa were Actinobacteria, Gammaproteobacteria, and Bacteroidetes in all the samples. The abundance and the diversity of the genera isolated at 25°C incubation temperature were greater than that at 4°C.

Evolution of Threonine Aldolases, a Diverse Family Involved in the Second Pathway of Glycine Biosynthesis

Threonine aldolases (TAs) catalyze the interconversion of threonine and glycine plus acetaldehyde in a pyridoxal phosphate-dependent manner. This class of enzymes complements the primary glycine biosynthetic pathway catalyzed by serine hydroxymethyltransferase (SHMT), and was shown to be necessary for yeast glycine auxotrophy. Because the reverse reaction of TA involves carbon–carbon bond formation, resulting in a β-hydroxyl-α-amino acid with two adjacent chiral centers, TAs are of high interests in synthetic chemistry and bioengineering studies. Here, we report systematic phylogenetic analysis of TAs. Our results demonstrated that l-TAs and d-TAs that are specific for l- and d-threonine, respectively, are two phylogenetically unique families, and both enzymes are different from their closely related enzymes SHMTs and bacterial alanine racemases (ARs). Interestingly, l-TAs can be further grouped into two evolutionarily distinct families, which share low sequence similarity with each other but likely possess the same structural fold, suggesting a convergent evolution of these enzymes. The first l-TA family contains enzymes of both prokaryotic and eukaryotic origins, and is related to fungal ARs, whereas the second contains only prokaryotic l-TAs. Furthermore, we show that horizontal gene transfer may occur frequently during the evolution of both l-TA families. Our results indicate the complex, dynamic, and convergent evolution process of TAs and suggest an updated classification scheme for l-TAs.

Antisense and RNAi expression for a chloroplastic superoxide dismutase gene in transgenic plants

Abstract. The cDNA of tomato chloroplastic Cu/Zn-superoxide dismutase was used to construct transgenic tobacco (Nicotiana plumbaginifolia). It was found that the gene expression of Cu/Zn-superoxide dismutase can constitutively be reduced in the transgenic tobacco plants because of double-stranded (dsRNA) expressed in the form of intron-spliced hairpin structures and antisense suppression. Furthermore, the endogenous chloroplastic Cu/Zn-superoxide dismutase gene in tobacco was established as a target for silencing due to the operation of hpRNA and antisense RNA constructs. However, under salt and PEG-induced stress, the cytosolic Cu/Zn-superoxide dismutase activity in transformed plants obviously increased. At the same time, the PEG pretreatment was able to promote tolerance of the transgenic plants to the salt stress. These results indicated that the use of hpRNA and anti-sense was able to successfully knockout the transcript encoding a chloroplast superoxidase dismutase. The null transformed plants grown under stress produced or retained other superoxide dismutase to compensate for the loss of the chloroplast. Consequently, hpRNA constructs would be helpful in discovering and validating the endogenous chloroplastic Cu/Zn-superoxide disinutase gene, and to prove the cytosolic alternative pathway of plant antioxidation associated with the function of Cu/Zn-superoxide dismutase gene under an unfavorable environment. Meanwhile, the experiment will provide an important technique for the antisensing strategies operating in tobacco.

Genome Sequence of Streptomyces violaceusniger Strain SPC6, a Halotolerant Streptomycete That Exhibits Rapid Growth and Development

ABSTRACT Streptomyces violaceusniger strain SPC6 is a halotolerant streptomycete isolated from the Linze desert in China. The strain has a very high growth rate and a short life cycle for a streptomycete. For surface-grown cultures, the period from spore germination to formation of colonies with mature spore chains is only 2 days at 37°C. Additionally, the strain is remarkably resistant to osmotic, heat, and UV stress compared with other streptomycetes. Analysis of the draft genome sequence indicates that the strain has the smallest reported genome (6.4 Mb) of any streptomycete. The availability of this genome sequence allows us to investigate the genetic basis of adaptation for growth in an extremely arid environment.