Showing papers in "Journal of Integrative Plant Biology in 2006"

Hairy Root and Its Application in Plant Genetic Engineering

Abstract: Agrobacterium rhizogenes Conn. causes hairy root disease in plants. Hairy root-infected A. rhizogenes is characterized by a high growth rate and genetic stability. Hairy root cultures have been proven to be an efficient means of producing secondary metabolites that are normally biosynthesized in roots of differentiated plants. Furthermore, a transgenic root system offers tremendous potential for introducing additional genes along with the Ri plasmid, especially with modified genes, into medicinal plant cells with A. rhizogenes vector systems. The cultures have turned out to be a valuable tool with which to study the biochemical properties and the gene expression profile of metabolic pathways. Moreover, the cultures can be used to elucidate the intermediates and key enzymes involved in the biosynthesis of secondary metabolites. The present article discusses various applications of hairy root cultures in plant genetic engineering and potential problems associated with them. (Managing editor: Wei Wang)

Does Seed Priming Induce Changes in the Levels of Some Endogenous Plant Hormones in Hexaploid Wheat Plants Under Salt Stress

Abstract: In order to assess whether salt tolerance could be improved in spring wheat (Triticum aestivum L.), the present study was performed by soaking the seeds of two cultivars, namely MH-97 (salt sensitive) and Inqlab-91 (salt tolerant), for 12 h in distilled water or 100 mol/m3 CaCl2, KCl, or NaCl. Primed seeds from each treatment group and non-primed seeds were sown in a field in which NaCl salinity of 15 dS/m was developed. Priming of seeds with CaCl2, followed by priming with KCl and NaCl, was found to be effective in alleviating the adverse effects of salt stress on both wheat cultivars in terms of shoot fresh and dry weights and grain yield. Priming with CaCl2 alleviated the adverse effects of salt stress on hormonal balance in plants of both cultivars. In MH-97 plants, CaCl2 pretreatment considerably reduced leaf abscisic acid (ABA) concentrations and increased leaf free salicylic acid (SA) concentrations under both saline and non-saline conditions. In contrast, in the Inqlab-91 plant, CaCl2 increased free indoleacetic acid (IAA) and indolebutyric acid (IBA) content. However, priming of seeds with CaCl2 did not alter free polyamine levels in either cultivar, although spermidine levels were considerably lower in plants raised from seeds treated with CaCl2 for both cultivars under saline conditions. Priming with KCl increased growth in Inqlab-91 plants, but not in MH-97 plants, under saline conditions. The salinity induced reduction in auxins (IAA and IBA) was alleviated by NaCl priming in both cultivars under saline conditions. However, NaCl increased leaf free ABA content and lowered leaf SA and putrescine levels in Inqlab-91 plants under saline conditions. In conclusion, although all three priming agents (i.e. CaCl2, KCl, and NaCl) were effective in alleviating the adverse effects of salt stress on wheat plants, their effects on altering the levels of different plant hormones were different in the two cultivars. (Managing editor: Ping He)

Effects of Overexpression of the Endogenous Farnesyl Diphosphate Synthase on the Artemisinin Content in Artemisia annua L.

Abstract: Artemisinin is a novel effective antimalarial drug extracted from the medicinal plant Artemisia annua L. Owing to the tight market and low yield of artemisinin, there is great interest in enhancing the production of artemisinin. In the present study, farnesyl diphosphate synthase (FPS) was overexpressed in high-yield A. annua to increase the artemisinin content. The FPS activity in transgenic A. annua was two- to threefold greater than that in non-transgenic A. annua. The highest artemisinin content in transgenic A. annua was approximately 0.9% (dry weight), which was 34.4% higher than that in non-transgenic A. annua. The results demonstrate the regulatory role of FPS in artemisinin biosynthesis. (Managing editor: Wei Wang)

Application of Non-invasive Microsensing System to Simultaneously Measure Both H+ and O2 Fluxes Around the Pollen Tube

Abstract: Various ionic and molecular activities in the extracellular environment are vital to plant cell physiological processes. A noninvasive microsensing system (NMS) based on either the scanning ion-selective electrode technique (SIET) or the scanning polarographic electrode technique (SPET) is able to obtain information regarding the transportation of various ions/molecules in intact samples under normal physiological conditions. The two-probe simultaneous test system (2STS) is an integrated system composed of SIET, SPET, and a Xu-Kunkel sampling protocol. In the present study, 2STS was able to simultaneously measure fluxes of H+ and O2 of the lily (Lilium longiflorum Thunb. cv. Ace) pollen tube while avoiding interference between the two probes. The results indicate that the proton fluxes were effluxes, whereas the oxygen fluxes were influxes, and they were closely correlated to each other surrounding the constitutive alkaline band region. Specifically, when the proton effluxes increased, the oxygen influxes also increased. Therefore, the hypothesis of condensed active mitochondria existing in the alkalized area of the pollen tube proposed by Hepler's group is supported. (Managing editor: Wei Wang)

Expression of the Grifola frondosa Trehalose Synthase Gene and Improvement of Drought-Tolerance in Sugarcane (Saccharum officinarum L.)

Abstract: Trehalose is a nonreducing disaccharide of glucose that functions as a protectant in the stabilization of biological structures and enhances stress tolerance to abiotic stresses in organisms. We report here the expression of a Grifola frondosa trehalose synthase (TSase) gene for improving drought tolerance in sugarcane (Saccharum officinarum L.). The expression of the transgene was under the control of two tandem copies of the CaMV35S promoter and transferred into sugarcane by Agrobacterium tumefaciens EHA105. The transgenic plants accumulated high levels of trehalose, up to 8.805–12.863 mg/g fresh weight, whereas it was present at undetectable level in nontransgenic plants. It has been reported that transgenic plants transformed with Escherichia coli TPS (trehalose-6-phosphatesynthase) and/or TPP (trehalose-6-phosphate phosphatase) are severely stunted and have root morphologic alterations. Interestingly, our transgenic sugarcane plants had no obvious morphological changes and no growth inhibition in the field. Trehalose accumulation in 35S–35S:TSase plants resulted in increased drought tolerance, as shown by the drought and the drought physiological indexes, such as the rate of bound water/free water, plasma membrane permeability, malondialdehyde content, chlorophyll a and b contents, and activity of SOD and POD of the excised leaves. These results suggest that transgenic plants transformed with the TSase gene can accumulate high levels of trehalose and have enhanced tolerance to drought. (Managing editor: Li-Hui Zhao)

Involvement of Hydrogen Peroxide Generated by Polyamine Oxidative Degradation in the Development of Lateral Roots in Soybean

Abstract: In order to determine whether hydrogen peroxide (H2O2) generated by polyamine oxidative degradation is involved in the development of lateral roots in soybean, the length and the number of lateral roots, the activities of polyamine oxidases and diamine oxidases, and the endogenous free polyamine and H2O2 content were analyzed in soybean (Glycine max (Linn.) Merr.) main roots of 2-d-old seedlings after treatments for 2 d with exogenous β-hydroxyethylhydrazine (an inhibitor of polyamine oxidases), H2O2, putrescine, cyclohexylamine (an inhibitor of spermidine synthase) or N, N′-dimethylthiourea (a scavenger of hydrogen peroxide). β-hydroxyethylhydrazine treatment strongly inhibited the development of lateral roots in soybean seedlings, reduced the activities of polyamine oxidases and diamine oxidases, decreased H2O2 levels, and led to the accumulation of endogenous polyamines in the main roots. The inhibitory effect of β-hydroxyethylhydrazine on root development could be alleviated by exogenously applied 10 μmol/L H2O2 (a major product of polyamine oxidation). Treatment with cyclohexylamine and putrescine promoted root growth slightly, but treatment with cyclohexylamine plus N, N′-dimethylthiourea or putrescine plus N, N′-dimethylthiourea prevented the development of soybean lateral roots. The effects of these treatments on the development of soybean lateral roots were consistent with the changes in endogenous H2O2 levels. These results suggest that the development of soybean lateral roots is associated with the oxidative degradation of polyamines, and that their products, especially H2O2, are likely to play an important role in the growth of soybean lateral roots. (Managing editor: Ping He)

Dependence of Soil Respiration on Soil Temperature and Soil Moisture in Successional Forests in Southern China

Abstract: The spatial and temporal variations in soil respiration and its relationship with biophysical factors in forests near the Tropic of Cancer remain highly uncertain. To contribute towards an improvement of actual estimates, soil respiration rates, soil temperature, and soil moisture were measured in three successional subtropical forests at the Dinghushan Nature Reserve (DNR) in southern China from March 2003 to February 2005. The overall objective of the present study was to analyze the temporal variations of soil respiration and its biophysical dependence in these forests. The relationships between biophysical factors and soil respiration rates were compared in successional forests to test the hypothesis that these forests responded similarly to biophysical factors. The seasonality of soil respiration coincided with the seasonal climate pattern, with high respiration rates in the hot humid season (April-September) and with low rates in the cool dry season (October-March). Soil respiration measured at these forests showed a clear increasing trend with the progressive succession. Annual mean (±SD) soil respiration rate in the DNR forests was (9.0 ± 4.6) Mg CO2-C/hm2per year, ranging from (6.1 ± 3.2) Mg CO2-C/hm2per year in early successional forests to (10.7 ± 4.9) Mg CO2-C/hm2 per year in advanced successional forests. Soil respiration was correlated with both soil temperature and moisture. The T/M model, where the two biophysical variables are driving factors, accounted for 74%-82% of soil respiration variation in DNR forests. Temperature sensitivity decreased along progressive succession stages, suggesting that advanced-successional forests have a good ability to adjust to temperature. In contrast, moisture increased with progressive succession processes. This increase is caused, in part, by abundant respirators in advanced-successional forest, where more soil moisture is needed to maintain their activities. (Managing editor: Ya-Qin Han)

Nutritional Composition and Assessment of Gracilaria lemaneiformis Bory

Abstract: The chemical composition, mineral elements, vitamins, free fatty acids and amino acid content of the edible red alga Gracilaria lemaneiformis Bory, grown in the sea near Nan'ao island, Guangdong Province, were analyzed in the present study. Gracilaria lemaneiformis Bory showed a total sugar content of 14.65%. The protein content was 21%, of which approximately 41% was determined to be essential amino acids (EAA). The major amino acid components were glutamic acid, leucine, arginine, and alanine. Of the EAA assayed, methionine and cysteine appeared to be the most limiting amino acids compared with the EAA pattern provided by Food and Agricultural Organization of the United Nations. The total lipids content was 0.87% and comprised a high composition of unsaturated fatty acids (61%), mainly as linoleic acid and oleic acid, and a little amount of polyunsaturated fatty acid; palmitic acid was the main component (39%) of saturated acids. Relatively high levels of vitamin C, iodine, phosphorus, and zinc were also present in G. lemaneiformis. The nutritional composition between G. lemaneiformis and Nostoc flagelliforme, a rare alga that is widely eaten in Chinese society, was compared. The results suggest that N. flagelliforme can be substituted for by G. lemaneiformis, not only because of their similar shape, but also because of their approximate nutritional composition. Gracilaria lemaneiformis may possibly serve as a potential healthy food in human diets in the future. (Managing editor: Ping He)

Screening for High-Temperature Tolerant Cotton Cultivars by Testing In Vitro Pollen Germination, Pollen Tube Growth and Boll Retention

Abstract: With radical global climate change and global warming, high temperature stress has become one of major factors exerting a major influence on crop production. In the cotton (Gossypium hirsutum L.)-growing areas of China, especially in the Yangtze River valley, unexpected periodic episodes of extreme heat stress usually occur in July and August, the peak time of cotton flowering and boll loading, resulting in lower boll set and lint yield. Breeding programs for screening high temperature-tolerant cotton germplasm and cultivars are urgent in order to stabilize yield in the current and future warmer weather conditions. In the present study, 14 cotton cultivars were quantified for in vitro pollen germination and pollen tube growth in response to temperatures ranging from 10 to 50 °C at 5 °C intervals. Different cotton genotypes varied in their in vitro pollen germination and pollen tube length responses to the different temperatures. Maximum pollen germination and pollen tube length ranged from 25.2% to 56.2% and from 414 to 682 μm, respectively. The average cardinal temperatures (Tmin, Topt, and Tmax) also varied among the 14 cultivars and were 11.8, 27.3, and 42.7 °C for pollen germination and 11.8, 27.8, and 44.1 °C for maximum pollen tube length. Variations in boll retention and boll numbers per plant in field experiments were found for the 14 cotton cultivars and the boll retention and boll retained per plant on 20 August varied considerably in different years according to weather conditions. Boll retention on 20 August was highly correlated with maximum pollen germination (R2= 0.84) and pollen tube length (R2=0.64). A screening method based on principle component analysis of the combination of pollen characteristics in an in vitro experiment and boll retention testing in the field environment was used in the present study and, as a result, the 14 cotton cultivars could be classified as tolerant, moderately tolerant, moderately susceptible and susceptible to high temperature. (Managing editor: Li-Hui Zhao)

Carbon Monoxide Alleviates Salt-Induced Oxidative Damage in Wheat Seedling Leaves

Abstract: Carbon monoxide (CO), a by-product released during the degradation of heme by heme oxygenases (EC 1.14.99.3) in animals, is regarded as an important physiological messenger or bioactive molecule involved in many biological events that has been recently reported as playing a major role in mediating the cytoprotection against oxidant-induced lung injury. In the present study, we first determined the protective effect of exogenous CO against salt-induced oxidative damage in wheat seedling leaves. Wheat seedlings treated with 0.01 μmol/L hematin as the CO donor demonstrated significant reversal of chlorophyll decay, dry weight, and water loss induced by 300 mmol/L NaCl stress. Interestingly, the increase in lipid peroxidation observed in salt-treated leaves was reversed by 0.01 nmol/L hematin treatment. Time-course analyses showed that application of 0.01 μmol/L hematin enhanced guaiacol peroxidase, superoxide dismutase, ascorbate peroxidase and catalase activities in wheat seedling leaves subjected to salt stress. These effects are specific for CO because the CO scavenger hemoglobin (1.2 mg/L) blocked the actions of the CO donor hematin. However, higher concentration of the CO donor (1.0 μmol/L) did not alleviate dry weight and water loss of salt-stressed wheat seedlings. These results suggest that exogenous application of low levels of a CO donor may be advantageous against salinity toxicity. (Managing editor: Ping He)

Effects of salt stress on carbohydrate metabolism in desert soil alga Microcoleus vaginatus Gom.

Abstract: The effects of salt stress on carbohydrate metabolism in Microcoleus vaginatus Gom., a cyanobacterium isolated from desert algal crusts, were investigated in the present study. Extracellular total carbohydrates and exopolysaccharides (EPS) in the culture medium produced by M. vaginatus increased significantly during the growth phase and reached a maximum during the stationary phase. The production of extracellular carbohydrates also significantly increased under higher salt concentrations, which was attributed to an increase in low molecular weight carbohydrates. In the presence of NaCl, the production of cellular total carbohydrates decreased and photosynthetic activity was impaired, whereas cellular reducing sugars, water-soluble sugars and sucrose content and sucrose phosphate synthase activity increased, reaching a maximum in the presence of 200 mmol/L NaCl. These parameters were restored to original levels when the algae were transferred to a non-saline medium. Sodium and K+ concentrations of stressed cells decreased significantly and H+-ATPase activity increased after the addition of exogenous sucrose or EPS. The results suggest that EPS and sucrose are synthesized to maintain the cellular osmotic equilibrium between the intra- and extracellular environment, thus protecting algal cells from osmotic damage, which was attributed to the selective exclusion of cellular Na+ and K+ by H+-ATPase.

Overexpression of the Wounding‐Responsive Gene AtMYB15 Activates the Shikimate Pathway in Arabidopsis

Abstract: The MYB transcription factor genes play important roles in many developmental processes and various defense responses of plants. The shikimate pathway is a major biosynthetic pathway for the production of three aromatic amino acids and other aromatic compounds that are involved in multiple responses of plants, including protection against UV and defense. Herein, we describe the characterization of the R2R3-MYB gene AtMYB15 as an activator of the shikimate pathway in Arabidopsis. The AtMYB15 protein is nuclear localized and a transcriptional activation domain is found in its C-terminal portion. Northern blots showed that AtMYB15 is an early wounding-inducible gene. Resutls of microarray analysis, confirmed using quantitative real-time polymerase chain reaction, showed that overexpression of AtMYB15 in transgenic plants resulted in elevated expression of almost all the genes involved in the shikimate pathway. Bioinformatics analysis showed that one or more AtMYB15-binding AC elements were detected in the promoters of these upregulated genes. Furthermore, these genes in the shikimate pathway were also found to be induced by wounding. These data suggest an important role of AtMYB15 as a possible direct regulator of the Arabidopsis shikimate pathway in response to wounding. (Managing editor: Ya-Qin Han)

Disruption of Cortical Microtubules by Overexpression of Green Fluorescent Protein‐Tagged α‐Tubulin 6 Causes a Marked Reduction in Cell Wall Synthesis

Abstract: It has been known that the transverse orientation of cortical microtubules (MTs) along the elongation axis is essential for normal cell morphogenesis, but whether cortical MTs are essential for normal cell wall synthesis is still not clear. In the present study, we have investigated whether cortical MTs affect cell wall synthesis by direct alteration of the cortical MT organization in Arabidopsis thaliana. Disruption of the cortical MT organization by expression of an excess amount of green fluorescent protein-tagged α-tubulin 6 (GFP-TUA6) in transgenic Arabidopsis plants was found to cause a marked reduction in cell wall thickness and a decrease in the cell wall sugars glucose and xylose. Concomitantly, the stem strength of the GFP-TUA6 overexpressors was markedly reduced compared with the wild type. In addition, expression of excess GFP-TUA6 results in an alteration in cell morphogenesis and a severe effect on plant growth and development. Together, these results suggest that the proper organization of cortical MTs is essential for the normal synthesis of plant cell walls. (Managing editor: Wei Wang)

Quantitative Trait Loci Mapping of Maize Yield and Its Components Under Different Water Treatments at Flowering Time

Abstract: Drought or water stress is a serious agronomic problem resulting in maize (Zea mays L.) yield loss throughout the world. Breeding hybrids with drought tolerance is one important approach for solving this problem. However, lower efficiency and a longer period of breeding hybrids are disadvantages of traditional breeding programs. It is generally recognized that applying molecular marker techniques to traditional breeding programs could improve the efficiency of the breeding of drought-tolerant maize. To provide useful information for use in studies of maize drought tolerance, the mapping and tagging of quantitative trait loci (QTL) for yield and its components were performed in the present study on the basis of the principle of a mixed linear model. Two hundred and twenty-one recombinant inbred lines (RIL) of Yuyu 22 were grown under both well-watered and water-stressed conditions. In the former treatment group, plants were well irrigated, whereas those in the latter treatment group were stressed at flowering time. Ten plants of each genotype were grown in a row that was 3.00 m × 0.67 m (length × width). The results show that a few of the QTL were the same (one additive QTL for ear length, two additive QTL and one pair of epistatic QTL for kernel number per row, one additive QTL for kernel weight per plant), whereas most of other QTL were different between the two different water treatment groups. It may be that genetic expression differs under the two different water conditions. Furthermore, differences in the additive and epistatic QTL among the traits under water-stressed conditions indicate that genetic expression also differs from trait to trait. Major and minor QTL were detected for the traits, except for kernel number per row, under water-stressed conditions. Thus, the genetic mechanism of drought tolerance in maize is complex because the additive and epistatic QTL exist at the same time and the major and minor QTL all contribute to phenotype under water-stressed conditions. In particular, epidemic QTL under water-stressed conditions suggest that it is important to investigate the drought tolerance of maize from a genetic viewpoint.

Diversity of Nitrogenase Systems in Diazotrophs

Abstract: Nitrogenase is a metalloprotein complex that catalyses the reaction of biological nitrogen fixation. At least three genetically distinct nitrogenase systems have been confirmed in diazotrophs, namely Nif, Vnf, and Anf, in which the active-site central metals are Mo, V, and Fe, respectively. The present review summarizes progress on the genetic, structural, and functional investigations into the three nitrogenases and discusses the possibility of the existence of other novel nitrogenases. (Managing editor: Ping He)

Transcriptional Responses to Gibberellin and Abscisic Acid in Barley Aleurone

Abstract: Cereal aleurone has been established as a model system to investigate giberrellin (GA) and abscisic acid (ABA) responses. Using Barley 1 GeneChip, we examined the mRNA accumulation of over 22 000 genes in de-embryonated barley aleurone treated with GA and ABA. We observed that 1 328 genes had more than a threefold change in response to GA treatment, whereas 206 genes had a more than threefold change in response to ABA treatment. Interestingly, approximately 2.5-fold more genes were up-regulated than downregulated by ABA. Eighty-three genes were differentially regulated by both GA and ABA. Most of the genes were subject to antagonistic regulation by ABA and GA, particularly for genes related to seed maturation and germination, such as genes encoding late embryogenesis abundant proteins and storage mobilization enzymes. This supports the antagonistic roles of GA and ABA in seed maturation and seed germination. Interestingly, we observed that a significant percentage of the genes were coordinately regulated by both GA and ABA. Some GA-responsive genes encoded proteins involved in ethylene, jasmonate, brassinosteroid and auxin metabolic and signaling transduction pathways, suggesting their potential interaction with the GA response. We also identified a group of transcription factor genes, such as MYB and Homeobox genes, that were differentially regulated by GA. In addition, a number of GA- and/or ABA-responsive genes encoded components potentially involved in GA and ABA signal transduction pathway. Overall, the present study provides a comprehensive and global view of transcript expression accompanying the GA and ABA response in barley aleurone and identifies a group of genes with potential regulatory functions in GA- and ABA-signaling pathways for future functional validation.

Antisense-Mediated Depletion of Tomato Chloroplast Omega-3 Fatty Acid Desaturase Enhances Thermal Tolerance

Abstract: A chloroplast-localized tomato (Lycopersicon esculentum Mill.) ω-3 fatty acid desaturase gene (LeFAD7) was isolated and characterized with regard to its sequence, response to various temperatures, and function in antisense transgenic tomato plants. The deduced amino acid sequence had four histidine-rich regions, of which three regions were highly conserved throughout the whole ω-3 fatty acid desaturase gene family. Southern blotting analysis showed that LeFAD7 was encoded by a single copy gene and had two homologous genes in the tomato genome. Northern blot showed that LeFAD7 was expressed in all organs and was especially abundant in leaf tissue. Meanwhile, expression of LeFAD7 was induced by chilling stress (4 °C), but was inhibited by high temperature (45 °C), in leaves. Transgenic tomato plants were produced by integration of the antisense LeFAD7 DNA under the control of a CaMV35S promoter into the genome. Antisense transgenic plants with lower 18:3 content could maintain a higher maximal photochemical efficiency (Fv/Fm) and O2 evolution rate than wild-type plants. These results suggested that silence of the LeFAD7 gene alleviated high-temperature stress. There was also a correlation between the low content of 18:3 resulting from silence of the LeFAD7 gene and tolerance to high-temperature stress. (Managing editor: Li-Hui Zhao)

Effects of Exogenous Spermidine on Photosystem II of Wheat Seedlings Under Water Stress

Abstract: The effects of exogenous spermidine (Spd) on lipid peroxidation, relative plasma membrane permeability, photosystem II (PSII) gene expression and PSII photochemical activity in water-stressed wheat seedlings were investigated. The decrease in relative water content (RWC), Chl content, and 2,6-dichlorophenol indophenol (DCIP) photoreduction of PSII, and increases in electrolyte leakage of plasma membranes and malonyldialdehyde (MDA) in water-stressed leaves was alleviated by Spd pretreatment. Furthermore, Western and Northern blot analysis showed that decreases in the PSII major proteins D1, D2 and LHCII and the transcripts of corresponding genes psbA, psbD and cab were also alleviated by Spd pretreatment under water stress. These results suggest that the application of exogenous Spd protects PSII against water stress at both the transcriptional level and the translational level, and allows PSII to retain a higher activity level during water stress. The protective role of Spd in the photosynthetic apparatus also is discussed. (Managing editor: Ping He)

Antioxidant Activities of Aqueous Extract from Cultivated Fruit-bodies of Cordyceps militaris (L.) Link In Vitro

Abstract: Biological antioxidants extracted from plants and fungi have potential abilities to scavenge free radicals and inhibit lipid peroxidation, playing important roles in preventing diseases, for example, cancer, and aging induced by reactive oxygen species, which may cause oxidative damage to DNA, proteins and other macromolecules. The antioxidant potency of cultivated fruit-bodies of Cordyceps militaris (L.) Link was investigated in this study. Five established in vitro systems were employed, including the 1,1-diphenyl-2-picryldrazyl (DPPH) free radical scavenging, hydroxyl radical eliminating, iron chelating, inhibition of linoleic acid lipid peroxidation and reducing power. The aqueous extract from cultivated fruit-bodies was subjected to the test of amino acid, polysaccharide and mannitol. Ascorbic acid (Vc), butylated hydroxytoluene (BHT) and ethylenediaminetetraacetic acid (EDTA) were used as positive controls for comparisons. Among the assays, the aqueous extract of C. militaris fruit-bodies shows a significant scavenging effect on DPPH, eliminating the capability on hydroxyl radicals and the chelating effect on ferrous iron. The extract also shows positive results of inhibiting linoleic acid lipid peroxidation and reducing power. (Managing editor: Wei Wang)

Growth, Gas Exchange, Abscisic Acid, and Calmodulin Response to Salt Stress in Three Poplars

Abstract: In the present study, we investigated the effects of increasing salinity on growth, gas exchange, abscisic acid (ABA), calmodulin (CaM), and the relevance to salt tolerance in seedlings of Populus euphratica Oliv. and cuttings of P. “pupularis 35–44” (P. popularis) and P. x euramericana cv. I-214 (P. cv. Italica). The relative growth rates of shoot height (RGRH) for P. cv. Italica and P. popularis were severely reduced by increasing salt stress, whereas the growth reduction was relatively less in P. euphratica. Similarly, P. euphratica maintained higher net photosynthetic rates (Pn) and unit transpiration rates (TRN) than P. cv. Italica and P. popularis under conditions of higher salinity. Salinity caused a significant increase in leaf ABA and CaM in the three genotypes after the onset of stress, but NaCl-induced ABA and CaM accumulation was more pronounced in P. euphratica, suggesting that P. euphratica plants are more sensitive in sensing soil salinity than the other two poplars. Furthermore, P. euphratica maintained relatively higher ABA and CaM concentrations under conditions of high salinity. The higher capacity to synthesize stress signals, namely ABA and CaM, in P. euphratica and the contribution of this to the salt resistance of P. euphratica are discussed. (Managing editor: Ping He)

Genetic Diversity of Landraces in Gossypium arboreum L. Race sinense Assessed with Simple Sequence Repeat Markers

Abstract: Asiatic cotton (Gossypium arboreum L.) is an “Old World” cultivated cotton species, the sinense race of which is planted extensively in China. This species is still used in the current tetraploid cotton breeding program as an elite germplasm line, and is also used as a model for genomic research in Gossypium. In the present study, 60 cotton microsatellite markers, averaging 4.6 markers for each A-genome chromosome, were chosen to assess the genetic diversity of 109 accessions. These included 106 G. arboreum landraces, collected from 18 provinces throughout four Asiatic cotton-growing regions in China. A total of 128 alleles were detected, with an average of 2.13 alleles per locus. The largest number of alleles, as well as the maximum number of polymorphic loci, was detected in the A03 linkage group. No polymorphic alleles were detected on chromosome 10. The polymorphism information content for the 22 polymorphic microsatellite loci varied from 0.52 to 0.98, with an average of 0.89. Genetic diversity analysis revealed that the landraces in the Southern region had more genetic variability than those from the other two regions, and no significant difference was detected between landraces in the Yangtze and the Yellow River Valley regions. These findings are consistent with the history of sinense introduction, with the Southern region being the presumed center of origin for Chinese Asiatic cotton, and with subsequent northeastward extension to the Yangtze and Yellow River Valleys. Cluster analysis, based on simple sequence repeat data for 60 microsatellite loci, clearly differentiated Vietnamese and G. herbaceum landraces from the sinense landrace. No relationship between inter-variety similarity and geographical ecological region was observed. The present findings indicate that the Southern region landraces may have been directly introduced into the provinces in the middle and lower Yangtze River Valley, where Asiatic cotton was most extensively grown, and further race sinense crops were subsequently produced. (Managing editor: Ya-Qin Han)

Secretory Cavity Development and Its Relationship with the Accumulation of Essential Oil in Fruits of Citrus medica L. var. sarcodactylis (Noot.) Swingle

Abstract: The developmental types of secretory cavities in Citrus remain controversial. The relationship between secretory cavity development and the accumulation of essential oil in fruits of Citrus species is also unknown. In order to develop better insights into these problems, histological, histochemical, and cytochemical methods were used to investigate secretory cavity development and the accumulation of essential oil at different developmental stages of fruits of Citrus medica L. var. sarcodactylis (Noot.) Swingle. The results indicate that the secretory cavity of the variety seemed to originate from an epidermal cell and a subepidermal cell. These two cells underwent successive divisions, resulting in the formation of two parts: (i) a conical cap; and (ii) a globular gland. The formation of the lumen was schizolysigenous. Regular changes in the size of vacuoles and the accumulation of essential oil were revealed during the process of secretory cavity development. In addition, when fruits were a light yellow or golden color, the structure of secretory cavities was well developed and the content of essential oil in a single fruit reached a maximum. It would be most appropriate to collect the fruit as a medicinal material at this time. (Managing editor: Wei Wang)

Climate Signals from Tree Ring Chronologies of the Upper and Lower Treelines in the Dulan Region of the Northeastern Qinghai‐Tibetan Plateau

Abstract: The radial growth of trees in mountainous areas is subject to environmental conditions associated with changes in elevation. To assess the sensitivity of tree-ring growth to climate variation over a wide range of elevations, we compared the chronological characteristics of Sabina przewalskii Kom. and their relationships with climatic variables at the upper and lower treelines in the Dulan region of the northeastern Qinghai-Tibetan Plateau. It was found that the radial growth in this region was controlled primarily by precipitation in late spring and early summer (from May to June). In addition, a higher temperature from April to June could intensify drought stress and lead to narrow tree rings. The significant similarity in climate-tree growth relationships at both the upper and lower treelines indicated that tree rings of S. przewalskii in this region are able to provide common regional climate information. However, the chronologies at the lower forest limits showed a higher standard deviation and more significant correlations with climatic factors, suggesting that the radial growth there was more significantly influenced by climate variation. The first principal component of the four chronologies showed a common growth response to local climate. The second principal component showed a contrasting growth response between different sampling sites. The third principal component revealed different growth patterns in response to altitudinal variation. Further analysis indicated that the precipitation in late spring and early summer controlled the growth of S. przewalskii on a regional scale and that other factors, such as microenvironment at the sampling sites, also affected the strength of the climatic response of tree growth.

ISSR Analysis of the Genetic Diversity of the Endangered Species Sinopodophyllum hexandrum (Royle) Ying from Western Sichuan Province, China

Abstract: Sinopodophyllum hexandrum (Royle) Ying is an important medicinal and endangered species. Inter-simple sequence repeats (ISSR) analysis was conducted on seven natural populations from western Sichuan Province to investigate the genetic diversity of S. hexandrum. Leaf samples of 140 individuals were collected. Of the 139 discernible fragments generated by 12 selected primers (among 100 primers), 54 appeared to be polymorphic. The percentage of polymorphic bands (PPB) was 38.85% at the species level, and PPB within a population ranged from 7.91% to 23.74%. Low levels of genetic variation (He= 0.092, Ho= 0.142) and high levels of genetic differentiation among the populations (Gst= 62.25%) was detected on the basis of results from POPGENE and analysis of molecular variance (AMOVA), respectively. Furthermore, the limited gene flow (Nm= 0.361) may result from biological characteristics, such as self-pollination and short distance seed dispersal. Based on the genetic and ecological information available for S. hexandrum, we propose some appropriate strategies for the conservation of the endangered medicinal species in this region, namely rescuing and conserving the core populations for in situ conservation and sampling and preserving more populations with fewer individuals from each population for ex situ conservation. (Managing editor: Li-Hui Zhao)

Achene Wall Anatomy and Surface Sculpturing of Lactuca L. and Related Genera (Compositae: Lactuceae) with Notes on Their Systematic Significance

Abstract: The achene wall anatomy and surface sculpturing of 14 species representing Lactuca L. and related genera were investigated to evaluate inter- and intrageneric relationships. The achene wall anatomy of the studied species can be divided into two types: winged and ribbed. The winged type is present in Lactuca L., Pterocypsela Shih, Cicerbita Wallr., Chaetoseris Shih and Stenoseris Shih, and is characterized by protruding wings and costae in transverse section. Winged type achene mesocarps are composed of parenchymatous cells and fiber cells, and the distinct fibrous strands are confined to the costae or wings of the achenes. The ribbed type is present in Notoseris Shih and Paraprenanthes Chang ex Shih, and is characterized by only having costae in transverse section. Fiber cells are continuous in the costae and intercostae. In surface sculpturing, the ornamentation and the shape of epidermal cells are different among these genera. The results indicate that L. altaica and L. serriola should be conspecific, and that L. dolichophylla is probably an intermediate taxon between Lactuca and Chaetoseris. The results also support the separation of Pterocypsela, Paraprenanthes, Notoseris, Chaetoseris and Stenoseris from Lactuca and Cicerbita as independent entities. Close affinities between Pterocypsela and Lactuca, Paraprenanthes and Notoseris, and Chaetoseris and Stenoseris are also proposed. (Managing editor: Wei Wang)

Effects of Different Levels of Water Stress on Leaf Water Potential, Stomatal Resistance, Protein and Chlorophyll Content and Certain Anti-oxidative Enzymes in Tomato Plants

Abstract: A greenhouse experiment was performed in order to investigate the effects of different levels of water stress on leaf water potential (Ψw), stomatal resistance (rs), protein content and chlorophyll (Chl) content of tomato plants (Lycopersicon esculentum Mill. cv. Nikita). Water stress was induced by adding polyethylene glycol (PEG 6 000) to the nutrient solution to reduce the osmotic potential (Ψs). We investigated the behavior of anti-oxidant enzymes, such as catalase (CAT) and superoxide dismutase (SOD), during the development of water stress. Moderate and severe water stress (i.e. Ψs= -0.51 and -1.22 MPa, respectively) caused a decrease in Ψw for all treated (water-stressed) plants compared with control plants, with the reduction being more pronounced for severely stressed plants. In addition, rs was significantly affected by the induced water stress and a decrease in leaf soluble proteins and Chl content was observed. Whereas CAT activity remained constant, SOD activity was increased in water-stressed plants compared with unstressed plants. These results indicate the possible role of SOD as an anti-oxidant protector system for plants under water stress conditions. Moreover, it suggests the possibility of using this enzyme as an additional screening criterion for detecting water stress in plants. (Managing editor: Ping He)

Two Divergent Members of 4‐Coumarate: Coenzyme A Ligase from Salvia miltiorrhiza Bunge: cDNA Cloning and Functional Study

Abstract: 4-Coumarate: coenzyme A ligase (4CL) is one of the key enzymes in phenylpropanoid metabolism leading to series of phenolics, including water-soluble phenolic acids, which are important compounds determining the medicinal quality of Danshen (Salvia miltiorrhiza Bunge), a traditional Chinese medicinal herb. To investigate the function of 4CL in the biosynthesis of water-soluble phenolic acid in Danshen, we have cloned two cDNAs (Sm4CL1 and Sm4CL2) encoding divergent 4CL members by applying nested reverse transcription-polymerase chain reaction (RT-PCR) with degenerate primers followed by 5′/3′ rapid amplification of cDNA ends (RACE) (Note, these sequence data have been submitted to the GenBank database under accession numbers AY237163 and AY237164). Either of the coding regions was inserted into a pRSET vector and a kinetic assay was performed with purified recombinant proteins. The substrate utilization profile of Sm4CL1 was distinct from that of Sm4CL2. The Km values of Sm4CL1 and Sm4CL2 to 4-coumaric acid were (72.20±4.10) and (6.50±1.45) μmol/L, respectively. These results, in conjunction with Northern blotting and other information, imply that Sm4CL2 may play an important role in the biosynthesis of water-soluble phenolic compounds, whereas Sm4CL1 may play a minor role in the pathway. Southern blotting analysis suggested that both Sm4CL1 and Sm4CL2 genes are present as a single copy and are located at different sites in the genome. (Managing editor: Wei Wang)

Analysis of Global Expression Profiles of Arabidopsis Genes Under Abscisic Acid and H2O2 Applications

Abstract: To gain insight into the coordination of gene expression profiles under abscisic acid (ABA) and H2O2 applications, global changes in gene expression in response to ABA and H2O2 in Arabidopsis seedlings were investigated using GeneChip (Santa Clara, CA, USA) arrays. Among over 24 000 genes present in the arrays, 459 transcripts were found to be significantly increased, whereas another 221 decreased following H2O2 treatment compared with control. Similar to treatment with H2O2, ABA treatment elevated the transcription of 391 genes and repressed that of 322 genes. One hundred and forty-three upregulated genes and 75 downregulated genes were shared between the two treatments and these genes were mainly involved in metabolism, signal transduction, transcription, defense, and resistance. Only two genes, which encode an APETALA2/dehydration-responsive element binding protein (AP2/DREBP) family transcriptional factor and a late embryogenesis-abundant protein, were downregulated by H2O2, but upregulated by ABA. These results suggest that, similar to ABA, H2O2 plays a global role in gene transcription of Arabidopsis seedlings. The transcriptional responses induced by the application of exogenous ABA and H2O2 overlapped substantially. These two treatments regulated most of the downstream genes in a coordinated manner. (Managing editor: Li-Hui Zhao)

Soil Carbon Changes Following Afforestation with Olga Bay Larch (Larix olgensis Henry) in Northeastern China

Abstract: After converting cropland to forest, carbon is sequestered in the aggrading biomass of the new forests, but the question remains, to what extent will the former arable soil contribute as a sink for CO2? Quantifying changes in soil carbon is an important consideration in the large-scale conversion of cropland to forest. Extensive field studies were undertaken to identify a number of suitable sites for comparison of soil properties under pasture and forest. The present paper describes results from a study of the effects of first rotation larch on soil carbon in seven stands in an afforestation chronosequence compared with adjacent Korean pine, pasture, and cropland. An adjacent 250-year-old natural forest was included to give information on the possible long-term changes in soil carbon in northeast China in 2004. Soil carbon initially decreased during the first 12 yr before a gradual recovery and accumulation of soil carbon occurred. The initial (0–12 yr) decrease in soil carbon was an average 1.2% per year among case studies, whereas the increase in soil carbon (12–33 yr) was 1.90% per year. Together with the carbon sequestration of forest floors, this led to total soil carbon stores of approximately 101.83 Mg/hm2 over the 33-year chronosequence. Within the relatively short time span, carbon sequestration occurred mainly in tree biomass, whereas soil carbon stores were clearly higher in the 250-year-old plantation (184 Mg/hm2). The ongoing redistribution of mineral soil carbon in the young stands and the higher soil carbon contents in the 250-year-old afforested stand suggest that nutrient-rich afforestation soils may become greater sinks for carbon (C) in the long term. (Managing editor: Ya-Qin Han)

Density Effects on Plant Height Growth and Inequality in Sunflower Populations

Abstract: Comparisons between competing and non-competing sunflower (Helianthus annuus L.) populations demonstrate pronounced effects of density on plant height growth, height-to-crown width ratio, and a population's height inequality. In the present study, non-destructive measurements of height and the projected crown area of sunflower plants were taken at seven times from emergence to fruit maturation in even-aged monospecific stands with initial densities of 1, 4, 16, and 64 plants/m2. The mean height of populations increased and then decreased with increasing population density; the height inequalities of uncrowded populations decreased during stand growth, whereas the height inequalities of crowded populations decreased first and then increased during stand development. The interindividual relationships between the relative height growth rate and height within uncrowded populations became significantly negative during population growth, whereas these relationships were negative first and then became positive during the development of crowded populations. In the uncrowded populations, the static interindividual relationship between height-to-crown width ratio and volume was positive, whereas for the crowded population these relationships became negative with increasing competition for light. The data suggest that the plastic responses of plant height and height-to-crown width ratio to light competition will become more intense with increasing competition intensity. The results of the present study argue strongly for the importance of size-dependent individual-level plastic responses due to size-asymmetric light competition in generating the variations in population height inequality. (Managing editor: Ya-Qin Han)