Effects of NaCl and Na2SO4 on red-osier dogwood (Cornus stolonifera Michx) seedlings

Sodium chloride and sodium sulfate are commonly present in extraction tailings waters produced as a result of surface mining and affect plants on reclaimed areas. Red-osier dogwood (Cornus stolonifera Michx) seedlings were demonstrated to be relatively resistant to these high salinity oil sands tailings waters. The objectives of this study were to compare the effects of Na₂SO₄ and NaCl, on growth, tissue ion content, water relations and gas exchange in red-osier dogwood (Cornus stolonifera Michx) seedlings. In the present study, red-osier dogwood seedlings were grown in aerated half-strength modified Hoagland's mineral solution containing 0, 25, 50 or 100 mM of NaCl or Na₂SO₄. After four weeks of treatment, plant dry weights decreased and the amount of Na⁺ in plant tissues increased with increasing salt concentration. Na⁺ tissue content was higher in plants treated with NaCl than Na₂SO₄ and it was greater in roots than shoots. However, Cl^– concentration in the NaCl treated plants was higher in shoots than in roots. The decrease in stomatal conductance and photosynthetic rates observed in presence of salts is likely to contribute to the growth reduction. Our results suggest that red-osier dogwood is able to control the transport of Na⁺ from roots to shoots when external concentrations are 50 mM or less.     

Shoot regeneration of dwarf dogwood (Cornus canadensis L.) and morphological characterization of the regenerated plants

Dwarf dogwoods (or the bunchberries) are the only suffrutex in Cornaceae. They are attractive ground cover ornamentals with clusters of small flowers surrounded by petaloid bracts. Little has been reported on plant regeneration of dogwoods. As a step toward unraveling the molecular basis of inflorescence evolution in Cornus, we report an efficient regeneration system for a dwarf dogwood species C. canadensis through organogenesis from rejuvenated leaves, and characterize the development of the plantlets. We used the nodal stem segments of vegetative branches as explants. Micropropogated shoots were quickly induced from axillary buds of nodes on an induction medium consisting of basal MS medium supplemented with 4.44 μM BAP and 0.54 μM NAA. The new leaves of adventitious shoots were used as explants to induce calli on the same induction medium. Nearly 65% of leaf explants produced calli, 80% of which formed adventitious buds. Gibberellic acid (1.45 μM) added to the same induction medium efficiently promoted quick elongation of most adventitious buds, and 0.49 μM IBA added to the basal MS medium promoted root formation from nearly 50% of the elongated shoots. The growth of plantlets in pot soil was characterized by the development of functional woody rhizomes, which continuously developed new aboveground vegetative branches, but not flowering branches, within the past 12 months. Potential reasons causing the delay of flowering of the regenerated plants are discussed. The establishment of this regeneration system facilitates developing a genetic transformation system to test candidate genes involved in the developmental divergence of inflorescences in Cornus. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Development and characterization of simple sequence repeats for flowering dogwood (Cornus florida L.)

Abundant, codominant simple sequence repeats (SSRs) markers can be used for constructing genetic linkage maps and in marker-assisted breeding programs. Enrichment methods for SSR motifs were optimized with the ultimate aim of developing numerous loci in flowering dogwood (C. florida L.) genome. Small insert libraries using four motifs (GT, CT, TGG, and AAC) were constructed with C. florida ‘Cherokee Brave’ deoxyribonucleic acid (DNA). Colony polymerase chain reaction (PCR) of 2,208 selected clones with three primers we reported previously indicated that 47% or 1,034 of the clones harbored one of the four targeted SSR motifs. Sequencing the putative positive clones confirmed that nearly 99% (1,021 of 1,034) of them contained the desired motifs. Of the 871 unique SSR loci, 617 were dinucleotide repeats (70.8%), and 254 were trinucleotide or longer repeats (29.2%). In total, 379 SSR loci had perfect structure, 237 had interrupted, and 255 had compound structure. Primer pairs were designed from 351 unique sequences. The ability of the 351 SSR primer pairs to amplify specific loci was evaluated with genomic DNA of ‘Appalachian Spring’ and ‘Cherokee Brave’. Of these primers, 311 successfully amplified product(s) with ‘Cherokee Brave’ DNA, 21 produced weak or faint products, and 19 did not amplify any products. Additionally, 218 of the 311 primers pairs revealed polymorphisms between the two cultivars, and 20 out of 218 primers detected an average of 13.7 alleles from 38 selected Cornus species and hybrids. These SSR loci constitute a valuable resource of ideal markers for both genetic linkage mapping and gene tagging of flowering dogwood. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mediation of deep supercooling of peach and dogwood by enzymatic modifications in cell-wall structure

Treatment of stem sections of peach (Prunus persica (L.) Batsch) and flowering dogwood (Cornus florida L.) with macerase, an enzyme mixture rich in pectinase, for 24–48 h resulted in a complete flattening of the low-temperature exotherm (LTE) as determined by differential thermal analysis (DTA). Ultrastructural analysis of macerase-treated tissue demonstrated a nearly complete digestion of the pit membrane (black cap and primary cell-wall) of nearly 100% of the xylem-parenchyma cells examined after 48 h of exposure to the enzyme. Additionally, the underlying amorphous layer was partially degraded in up to 57% of the cells examined. The macerase treatment had no visible effect on secondary cell-walls of xylem tissue. In contrast, treatment of stem tissue with cellulysin (mostly cellulase) resulted in a shift of the LTE to warmer temperatures as determined by DTA, and a digestion of only the outermost layer of the pit membrane in nearly 100% of the cells examined, with little or no effect on the underlying layers. Treatment of tissue with 25 mM sodiumphosphate buffer also resulted in a shift of the LTE to warmer temperatures but the shift was not as great as in cellulysin-treated tissue. The shift was associated with a partial degradation of the outermost layer of the pit membrane in dogwood (33–45% of the cells examined) but not in peach (3–7% of the cells). Collectively, the data indicate that pectins may be an integral structural element of the pit membrane and that this portion of the cell-wall, along with the underlying amorphous layer, play a major role in forming a barrier to water movement and growth of ice crystals. This barrier allows xylem parenchyma of some species of woody plants to undergo deep supercooling.Abbreviations DTA Differential thermal analysis - HTE high-temperature exotherm - LTE low-temperature exotherm     

Architectural strategies of Cornus sericea, a native but invasive shrub of Southern Quebec, Canada, under an open or a closed canopy

Background and Aims

Qualitative and quantitative studies of the pattern of invasive plant development is considered a key aspect in understanding invasiveness. An architectural analysis was therefore performed in order to understand the relationship between shoot architecture and invasiveness in red-osier dogwood, Cornus sericea (Cornaceae).

Methods

The structural and ontogenic characteristics of individuals in invading and non-invading populations in the native range of the species were compared to test the implication of developmental plasticity on invasiveness.

Key Results and Conclusions

The results show that the shrub has a modular architecture governed by strong developmental rules. Cornus sericea is made up of two levels of organization, each with its own intrinsic sequence of differentiation. These intrinsic mechanisms were used as a framework for comparison and it was found that, in response to the light environment, developmental plasticity was elevated, resulting in two architectural strategies. This developmental plasticity concerns the growth direction and the size of the modules, the speed of their time-course changes, their branching and flowering. Under an open canopy, C. sericea rapidly develops large vertical structures and abundant flowering. This strategy leads the plant to be invasive by excluding competitors and disseminating in the landscape. In the understorey, C. sericea slowly develops long horizontal structures which creep across the soil surface, while assimilating structures are poorly developed. This strategy does not lead to invasiveness but may allow the plant to survive in the understorey and reach sunny patches.     

Changes in chemical components in the freshwater apple snail, Pomacea canaliculata (Gastropoda: Ampullariidae), in relation to the development of its cold hardiness

The apple snail, Pomacea canaliculata, is an invasive freshwater snail. It increases its cold hardiness before winter. However, the physiological mechanism of cold hardiness in molluscs is poorly understood, especially in freshwater molluscs. In this study, we examined the changes in low molecular weight compounds, glycogen and lipids, in the body of P. canaliculata in association with the development of cold hardiness. When snails without cold hardiness were experimentally cold-acclimated, the amount of glycerol, glutamine, and carnosine increased, while glycogen and phenylalanine decreased. Overwintering cold-tolerant snails collected from a drained paddy field in November also showed increased glycerol in their bodies with decreasing glycogen concentration, compared to summer snails collected from a submerged field. Water content also decreased during the cold acclimation, although the water loss was minimal. These results indicate that the freshwater snail, P. canaliculata enhances cold hardiness by accumulation of some kinds of low molecular weight compounds in its body as some insects do. However, the actual function of each low molecular compound is still unknown.     

Changes in wheat leaf phenolome in response to cold acclimation

A study of wheat (Triticum aestivum L.) leaves phenolome was carried out during cold acclimation of the winter (Claire) and spring (Bounty) varieties using a combination of HPLC–ESI–MS techniques. A total of 40 phenolic and flavonoid compounds were identified, and consisted mainly of two coumarin derivatives, eight simple phenolic derivatives, 10 hydroxycinnamoyl amides and 20 flavonoid derivatives. Identification and quantification of individual compounds were performed using an HPLC system coupled with a photodiode array detector and two different ESI–MS systems, in combination with a multiple reaction monitoring (MRM) technique. The analyses indicated that, although there were no qualitative differences in their profiles, the winter variety exhibited a higher phenolic content compared to the spring variety when both were grown under non-acclimated (control) conditions. Cold acclimation, on the other hand, resulted in a significant differential accumulation of phenolic compounds in both varieties: mostly as luteolin C-glycosides and their O-methyl derivatives in the winter variety (Claire) and a derivative of hydroxycinnamoyl amide in the spring variety (Bounty). These compounds accumulated in relatively large amounts in the apoplastic compartment. The accumulation of the O-methylated derivatives was associated with a marked increase in O-methyltransferase (OMT) activity. In addition, the trimethylated flavone, 3′,4′,5′-trimethyltricetin was identified for the first time in the native extracts of both control and cold-acclimated wheat leaves. The accumulation of a mixture of beneficial flavonoids, such as iso-orientin, vitexin and tricin in cold acclimated wheat leaves, attests for its potential as an inexpensive source of a health-promoting supplement to the human diet.     

Evolutionary patterns in the antR-Cor gene in the dwarf dogwood complex (Cornus, Cornaceae)

The evolutionary pattern of the myc-like anthocyanin regulatory gene antR-Cor was examined in the dwarf dogwood species complex (Cornus Subgenus Arctocrania) that contains two diploid species (C. canadensis and C. suecica), their putative hybrids with intermediate phenotypes, and a tetraploid derivative (C. unalaschkensis). Full-length sequences of this gene (∼4 kb) were sequenced and characterized for 47 dwarf dogwood samples representing all taxa categories from 43 sites in the Pacific Northwest. Analysis of nucleotide diversity indicated departures from neutral evolution, due most likely to local population structure. Neighbor-joining and haplotype network analyses show that sequences from the tetraploid and diploid intermediates are much more strongly diverged from C. suecica than from C. canadensis, and that the intermediate phenotypes may represent an ancestral group to C. canadensis rather than interspecific hybrids. Seven amino acid mutations that are potentially linked to myc-like anthocyanin regulatory gene function correlate with petal colors differences that characterize the divergence between two diploid species and the tetraploid species in this complex. The evidence provides a working hypothesis for testing the role of the gene in speciation and its link to the petal coloration. Sequencing and analysis of additional nuclear genes will be necessary to resolve questions about the evolution of the dwarf dogwood complex.     

Gibberellic-acid causes flowering in the short-day plants Panicum miliaceum L., P. miliare lamk., and Setaria italica (L.) P. Beauv.

Treatment with gibberellic acid (GA₃) causes formation of flowers in Panicum ciliaceum and Panicum miliare, two short-day plants, under long days (continuous light), and hastens the emergence of ears in Setaria italica, a quantitative short-day plant, under both inductive and non-inductive photoperiods. The GA₃-induced inflorescences, however, remain short and bear only few spikelets; in the two Panicum species, the spikelets also remain sterile.     

Changes in leaf ultrastructure and carbohydrates inArabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation

Summary We studied cell ultrastructure and carbohydrate levels in the leaf tissue ofArabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation. Freezing tolerance of the leaves from 26 day old plants was determined after 48 h and 10 days at 4°C. Acclimation treatment of 48 h decreased the lethal freezing temperature from –5.7°C to –9.4°C. Freezing tolerance was not altered further by acclimation at 4 °C for 10 days. Ultrastructural changes in the parenchyma cells were evident after 6 to 24 h of cold acclimation. The plasma membrane showed signs of extensive turnover. Evidence of membrane invaginations and sequestering of membrane material was observed. In addition, numerous microvesicles, paramural bodies, and fragments of endoplasmic reticulum were noticed in the vicinity of plasma membrane. Modifications in the structure of cell membranes were evident after 5 days of exposure to low temperature. Small, darkly stained globules were seen on the plasma membrane, tonoplast, chloroplast envelope membrane, mitochondrion outer membrane, dictyosome cisternae membrane, and microvesicle membrane. As far as we are aware, this type of membrane modification has not been described previously in plant cells exposed to low temperature. We propose to call these structures membraglobuli. Acclimation treatment also increased the concentrations of soluble sugars and starch. These observations suggest that cold acclimation inA. thaliana induces changes in both plasma membrane properties and carbohydrate composition.     

Protective systems against active oxygen species in spinach: response to cold acclimation in excess light

Spinach (Spinacia oleracea L.) plants were acclimated to 1° C or maintained at 18° C under the same light regime (260–300 mol photons·m^–2·s^–1). The cold acclimation led to several metabolic and biochemical changes that apparently include improved protection of the photosynthetic apparatus against active oxygen species. In particular, cold-acclimated leaves exhibited a considerably higher ascorbate content and significantly increased activities of superoxide dismutase, ascorbate peroxidase, and monodehydroascorbate reductase in the chloroplasts. The level of dehydroascorbate reductase did not alter. Catalase activity decreased. The photosynthetic pigment composition of cold-acclimated spinach was characterized by increased levels of the xanthophylls lutein + zeaxanthin and violaxanthin. The observed changes are discussed in terms of their possible relevance for plant resistance to photoinhibition at chilling temperatures.Abbreviations DHA dehydroascorbate - GSH reduced glutathione - MDA monodehydroascorbate - SOD superoxide dismutase The authors thank the Deutsche Forschungsgemeinschaft for financial support of this study.     

Expression of SK3-type dehydrin in transporting organs is associated with cold acclimation in Solanum species

The expression of a gene, encoding a dehydrin protein designated as DHN24 was analyzed at the protein level in two groups of Solanum species differing in cold acclimation ability. The DHN24 protein displays consensus amino acid sequences of dehydrins, termed K- and S-segments. The S-segment precedes three K-segments, classifying the protein into SK₃-type dehydrins. A group of Solanum species able to cold acclimation constituted by S. sogarandinum and S. tuberosum, cv. Aster, and a second one composed of a S. sogarandinum line, that lost ability to cold acclimation, and of S. tuberosum, cv. Irga, displaying low ability to cold acclimation were studied. Under control conditions, noticeable levels of the DHN24 protein was observed in stems, tubers, and roots of Solanum species. No protein was detected in leaves. During low temperature treatment the DHN24 protein level substantially increased in tubers, in transporting organs and in apical parts, and only a small increase was observed in leaves. The increase in protein abundance was only observed in the plants able to cold acclimate and was found to parallel the acclimation capacity. Upon drought stress, the DHN24 level decreased in stems and in leaves, but increased in apical parts. These results suggest that Dhn24 expression is regulated by organ specific factors in the absence of stress and by factors related to cold acclimation processes during low temperature treatment in collaboration with organ-specific factors. A putative function of the SK₃-type dehydrin proteins during plant growth and in the tolerance to low temperature is discussed.     

Complexity of the cold acclimation response in Drosophila melanogaster

Insects can increase their resistance to cold stress when they are exposed to non-lethal conditions prior to the stress; these plastic responses are normally described only in terms of immediate effects on mortality. Here we examine in Drosophila melanogaster the short- and longer-term effects of different conditions on several measures of cold resistance, but particularly chill coma recovery. Short-term exposure to sublethal temperature (cold hardening) did not decrease chill coma recovery times even though it decreased mortality. Exposure to 12 degrees C for 2 days (acclimation) decreased chill coma recovery times for a range of stressful temperatures when flies were cultured at 25 degrees C, but did not usually affect recovery times when flies were cultured at 19 degrees C. In contrast, 2-day exposure to 12 degrees C decreased mortality regardless of rearing temperature. Rearing at 19 degrees C decreased mortality and chill coma recovery time relative to rearing at 25 degrees C. Acclimation increased the eclosion rate of eggs from stressed females, but did not affect development time or size of the offspring. These results indicate that plastic responses to cold in D. melanogaster are complex when resistance is scored in different ways, and that effects can extend across generations.     

Influence of calcium, potassium, and magnesium on Cornus florida L. density and resistance to dogwood anthracnose

Dogwood anthracnose, a major disease of Cornus florida L., has caused heavy mortality of C. florida in eastern United States forests. Disease severity and rate of infection have been shown to vary with several environmental factors, but the link between soil cation availability and anthracnose has not been examined. We hypothesized that soil cation availability, particularly calcium (Ca), potassium (K), and magnesium (Mg), would influence dogwood survival from anthracnose. In forested stands, positive correlations between soil Ca, K, and Mg saturation and C. florida stem density and basal area were found. The effect of these cations at four levels (0, 50, 100, and 200%) of a standard nursery fertilization rate on C. florida seedling survival and resistance to dogwood anthracnose was tested. Although most of the seedlings died after one season of exposure to dogwood anthracnose, seedlings that had lower inputs of Ca and K cations showed higher levels of disease severity sooner than seedlings in other treatments, suggesting that these nutrients play a role in C. florida survival from anthracnose. Magnesium treatment levels did not appear to have an effect on C. florida disease severity or mortality.     

Inheritance of freezing resistance in interspecific F1 hybrids of Eucalyptus

Summary The inheritance of freezing resistance in interspecific F₁ hybrid families of Eucalyptus encompassing 27 different species combinations and a range of levels of hardiness was examined. Freezing resistance was assessed by determining the temperatures required to cause either 30% (T30), 40% (T40), or 50% (T50) leakage of electrolytes from excised leaf discs subjected to artificial freezing. Highly significant variation in freezing resistance occurred between species; the maximum difference between parents in any specific combination was over 9°C (E. gunnii x E. globulus). Freezing resistance was inherited in a predominantly additive manner in interspecific hybrids, although there was a tendency towards partial dominance toward the more sensitive species in some combinations (e.g., E. nitens x E. Globulus, E. nitens x E. camaldulensis, E. gunnii x E. globulus). The full expression of this genetic variation appeared to increase with hardiness and in some cases appeared to vary with ontogeny. Estimates of individual narrow-sense heritability of freezing resistance for pure E. nitens families were h ² = 0.66±0.44 and 0.46±0.44. Across all species combinations examined, the heritability of F₁ family means estimated from midparent regression was h ² = 0.76±0.06 and h ² = 0.89±0.06 for T40 and T50 values, respectively. The advantage of using selected parents for interspecific hybridization is demonstrated and the implications of these results for breeding for freezing resistance in Eucalyptus are discussed.     

Cold acclimation was partially impaired in boron deficient Norway spruce seedlings

Susceptibility of trees to freezing injury has been suggested to increase in boron (B) deficiency but there is no experimental evidence to support this proposition. In this study, Norway spruce (Picea abies L. Karst.) seedlings were cultivated for two growing seasons in deficient, intermediate and ‘optimal’ B levels. Cold hardening of the seedlings was measured after the second growing season. Freezing tolerance in tips of shoots, needles, stems and roots was determined by controlled freezing tests and electrolyte leakage method, and that of buds, in addition, by differential thermal analysis (DTA). Electrical impedance was used to monitor changes in the apoplastic space during cold acclimation. Root dry weight and shoot height growth were lower in B deficiency. Cold acclimation of buds and stems was reduced by B deficiency. When hardened seedlings were subjected to subzero temperatures for 3 weeks, extracellular electrical resistance of stems became the highest at the lowest B supply which was probably due to decreased desiccation tolerance. As a conclusion, susceptibility to freezing damage may be increased by B deficiency in Norway spruce trees.