Responses to nonaeration and/or salinity stress in hydroponically cultured <Emphasis Type="Italic">Populus nigra</Emphasis> and <Emphasis Type="Italic">Populus alba</Emphasis> cuttings

Growth, photosynthesis, and Na⁺, K⁺, Ca²⁺, and Mg²⁺ distributions were examined in two-year-old hydroponically cultured Populus nigra and Populus alba cuttings exposed to salt stress (0, 50, or 100 mM NaCl) for four or six weeks and to nonaeration stress for one or three weeks, followed by a three-week aeration period in 2/5 Hoagland solution. Salt stress with 100 mM NaCl totally inhibited height increase in P. nigra cuttings. Combined salinity and nonaeration inhibited height increase to a greater degree than either stress alone in both species. Simple salt stress did not affect diameter increase in P. alba, whereas combined high salinity (100 mM NaCl) and nonaeration inhibited diameter increase. Growth and biomass accumulation were more sensitive to salt stress in P. nigra cuttings than in P. alba, although P. alba showed a more rapid decrease in photosynthesis in response to nonaeration stress. Ion distributions in the leaves and roots differed between species. P. alba was superior to P. nigra in terms of Na⁺ exclusion capacity, such that most of the absorbed Na⁺ was confined to the root system, with little reaching the leaves. The distributions of K⁺, Ca²⁺, and Mg²⁺ in the leaves and roots of each species under the two stressors were also analyzed. The lower Na⁺/K⁺ ratio in leaves indicated that P. alba was more tolerant to salt stress than P. nigra.     

Adaptive responses of <Emphasis Type="Italic">Populus przewalskii</Emphasis> to drought stress and SNP application

In this study we used the cuttings of Populus przewalskii Maximowicz as experimental material and sodium nitroprusside (SNP) as nitric oxide (NO) donor to determine the physiological and biochemical responses to drought stress and the effect of NO on drought tolerance in woody plants. The results indicated that drought stress not only significantly decreased biomass production, but also significantly increased hydrogen peroxide content and caused oxidative stress to lipids and proteins assessed by the increase in malondialdehyde and total carbonyl contents, respectively. The cuttings of P. przewalskii accumulated many amino acids for osmotic adjustment to lower water potential, and activated the antioxidant enzymes such as superoxide dismutase, guaiacol peroxidase and ascorbate peroxidase to maintain the balance of generation and quenching of reactive oxygen species. Moreover, exogenous SNP application significantly heightened the growth performance of P. przewalskii cuttings under drought treatment by promotion of proline accumulation and activation of antioxidant enzyme activities, while under well-watered treatment the effect of SNP application was very little.     

Association of Misexpression with Sterility in Hybrids of <Emphasis Type="Italic">Drosophila simulans</Emphasis>and <Emphasis Type="Italic">D. mauritiana</Emphasis>

Recent studies have identified genes associated with hybrid sterility and other hybrid dysfunctions, but the consequences of introgressions of these speciation genes are often poorly understood. Previously, we identified a panel of genes that are underexpressed in sterile male hybrids of Drosophila simulans and D. mauritiana relative to pure species. Here, we build on this reverse-genetics approach to demonstrate that the underexpression of at least five of these genes in hybrids is associated with hybrid sterility and that these five genes are coordinately regulated. We map one upstream regulator of these genes to a region previously shown to harbor one or more factors causing hybrid sterility. Finally, we show that the genes underexpressed in hybrids are often highly conserved, as might be predicted for downstream targets of the genetic changes that cause hybrid sterility. This approach integrates forward genetics with reverse genetics to show a proximate consequence of the introgression of particular hybrid sterility-conferring regions between species: underexpression of genes necessary for normal spermatogenesis.[Reviewing Editor: Martin Kreitman]     

Cloning and expression of <Emphasis Type="Italic">Tenebrio molitor</Emphasis> antifreeze protein in <Emphasis Type="Italic">Escherichia coli</Emphasis>

A novel antifreeze protein cDNA was cloned by RT-PCR from the larva of the yellow mealworm Tenebrio molitor. The coding fragment of 339 bp encodes a protein of 112 amino acid residues and was fused to the expression vectors pET32a and pTWIN1. The resulted expression plasmids were transformed into Escherischia coli strains BL21 (DE3), ER2566, and Origami B (DE3), respectively. Several strategies were used for expression of the highly disulfide-bonded β-helix-contained protein with the activity of antifreeze in different expression systems. A protocol for production of refolded and active T. molitor antifreeze protein in bacteria was obtained.     

A new <Emphasis Type="Italic">Dactylella</Emphasis> species from <Emphasis Type="Italic">Orbilia alba</Emphasis>

A new Dactylella species, Dactylella alba was isolated from the ascospores of Orbilia alba collected in Wenshan County, Yunnan Province, China. Conidiophores were either not branched or occasionally branched, bearing divergent sterigmata on the tip with single conidium on each. Conidia were elongated ellipsoids, 1–2 septate, mostly 1 septate. By combining the ITS sequence with morphological characteristics, a new anamorphic species is described and illustrated together with its teleomorph.     

Expression of PHA polymerase genes of <Emphasis Type="Italic">Pseudomonas putida</Emphasis> in <Emphasis Type="Italic">Escherichia coli</Emphasis> and its effect on PHA formation

Poly-3-hydroxyalkanoates (PHAs) are synthesized by many bacteria as intracellular storage material. The final step in PHA biosynthesis is catalyzed by two PHA polymerases (phaC) in Pseudomonas putida. The expression of these two phaC genes (phaC1 and phaC2)was studied in Escherichia coli, either under control of the native promoter or under control of an external promoter. It was found that the two phaC genes are not expressed in E. coli without an external promoter. During heterologous expression of phaC from Plac on a high copy number plasmid, a rapid reduction of the number of colony forming units was observed, especially for phaC2. It appears that the plasmid instability was partially caused by high-level production of PHA polymerase. Subsequently, tightly regulated phaC2 expression systems on a low copy number vector were applied in E. coli. This resulted in PHA yields of over 20 of total cell dry weight, which was 2 fold higher than that obtained from the system where phaC2 is present on a high copy number vector. In addition, the PHA monomer composition differed when different gene expression systems or different phaC genes were applied.     

Genetic linkage maps of <Emphasis Type="Italic">Populus alba</Emphasis> L. and comparative mapping analysis of sex determination across <Emphasis Type="Italic">Populus</Emphasis> species

White poplar (Populus alba L.) is native to Eurasia and is unexploited for its growth potential and stress-adaptive mechanisms. A better knowledge of its genome will allow for more effective protection and use of critical genetic resources. The main objective of this study was the construction of highly informative P. alba genetic maps. Two genotypes were selected from contrasting natural Italian populations and crossed to generate an F₁ mapping pedigree. Amplified fragment length polymorphism and simple sequence repeat markers were used to genotype 141 F₁ individuals. The pseudo-testcross strategy was applied for linkage analysis. The generated maps showed good overall colinearity to each other and allowed for a complete alignment with the 19 haploid chromosomes of the Populus genome sequence. The locus that determines sex as a morphological trait was positioned on a non-terminal position of LG XIX of the female parent map. Comparison among Populus species revealed differences in the location of the sex locus on LG XIX as well as inconsistencies in the heterogametic sex. The genetic analysis of the sex locus in P. alba provides insights into sex determination in the genus and is useful for the identification of sex-linked markers and the early assessment of plant gender. Furthermore, these genetic maps will greatly facilitate the study of the genomics of Populus and how it can be exploited in applied breeding programs.     

Evaluation of orange-fleshed sweet potato (<Emphasis Type="Italic">Ipomoea batatas</Emphasis> L.) genotypes for salt tolerance through shoot apex culture under in vitro NaCl mediated salinity stress conditions

Fifteen genotypes of sweet potato were evaluated for salinity stress tolerance under in vitro NaCl mediated salinity stress conditions (MS, MS + 0.5% and MS + 1.0% NaCl). The growth parameters such as number of leaves, number of shoots, number of roots, length of plantlets and length of roots decreased significantly among the genotypes with increase in level of salinity. Of the 15 genotypes tested, six genotypes (108X1, 90/606, 90/696, CIP 8, S-30X15 and SP-61) were unable to sprout even at 0.5% NaCl and were characterized as susceptible to salt stress, three genotypes (CIP 6, 90/774 and CIP 3) which could tolerate 0.5% NaCl as moderately tolerant and six genotypes (CIP 12, CIP 13, JO 14, JP 13, SB-198/115 and Gouri) as tolerant to salinity at 1.0% NaCl. Amongst the six genotypes showing tolerance to 1.0% NaCl, the exotic genotypes––JP 13, CIP 12 and indigenous one SB-198/115 continued to exhibit significant higher values for growth parameters over the susceptible one. Based on the performance under NaCl mediated salinity stress (1.0%), the pattern of salinity tolerance in the genotypes through shoot apex culture was JP 13 > SB-198/115 > JO 14 > Gouri > CIP 12 > CIP 13. The effect of salt stress on the activity of antioxidative enzymes was studied in leaves of 8-week-old plantlets of those six genotypes, which responded at higher NaCl stress along with a susceptible genotype 90/606. In leaves of salt stressed plants, superoxide dismutase (SOD), guaiacol peroxidase (GPX) and catalase (CAT) activities increased when compared with the stress free control. The increase was more pronounced in the tolerant genotypes than that in the susceptible one. These results indicate that oxidative stress may play an important role in salt stressed sweet potato plants and that the greater protection of tolerant plants from salt induced oxidative damage results, at least in part, through the increase in the activity of antioxidant enzymes.     

Photosystem II photochemistry and physiological parameters of three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis> under salt stress

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Salt stress caused a marked decrease in osmotic potential and a significant accumulation of Na⁺ and Cl⁻ in leaves of both species. Moderate salinity had a stimulating effect on growth rate, net CO₂ assimilation, transpiration and stomatal conductance for the xero-halophytic species. At higher salinities, these physiological parameters decreased significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea they decreased linearly with salinity. Nitraria retusa PSII photochemistry and carotenoid content were unaffected by salinity, but a reduction in chlorophyll content was observed at 800 mM NaCl. Similar results were found in A. halimus, but with a decrease in the efficiency of PSII (F′v/F′m) occurred at 800 mM. Conversely, in M. arborea plants we observed a significant reduction in pigment concentrations and chlorophyll fluorescence parameters. The marked toxic effect of Na⁺ and/or Cl⁻ observed in M. arborea indicates that salt damage effect could be attributed to ions’ toxicity, and that the reduction in photosynthesis is most probably due to damages in the photosynthetic apparatus rather than factors affecting stomatal closure. For the two halophyte species, it appears that there is occurrence of co-limitation of photosynthesis by stomatal and non-stomatal factors. Our results suggest that both N. retusa and A. halimus show high tolerance to both high salinity and photoinhibition while M. arborea was considered as a slightly salt tolerant species.     

Nutritional regulation of <Emphasis Type="Italic">ANR1</Emphasis> and other root-expressed MADS-box genes in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

The ANR1 MADS-box gene in Arabidopsis thaliana (L.) Heynh. has previously been identified as a key regulator of lateral root growth in response to signals from external nitrate (NO₃⁻). We have used quantitative real-time PCR to investigate the responsiveness of ANR1 and 11 other root-expressed MADS-box genes to fluctuations in the supply of N, P and S. ANR1 expression in roots of hydroponically grown Arabidopsis plants was specifically regulated by changes in the N supply, being induced by N deprivation and rapidly repressed by N re-supply. This pattern of N responsiveness differs from the NO₃⁻ -inducibility of ANR1 previously observed in Arabidopsis root cultures [H.M. Zhang and B.G. Forde (1998) Science 279:407–409]. Seven of the other MADS-box genes responded to N in a manner similar to ANR1, but less strongly, while four (AGL12, AGL17, AGL18 and AGL79) were unaffected. Six of the N-regulated genes (ANR1, AGL14, AGL16, AGL19, SOC1 and AGL21) belong to just two clades within the type II MADS-box lineage, while the other two (AGL26 and AGL56) belong to the poorly characterized type I lineage. Only SOC1 was additionally found to respond to changes in the P and S supply, suggesting a possible role in a general response to nutrient stress. Studies with an ANR1 transposon-insertion mutant provided no evidence for regulatory interactions between ANR1 and the other root-expressed MADS-box genes. The implications of the current data for our understanding of the role of ANR1 and other MADS box genes in the nutritional regulation of lateral root growth are discussed.