Secondary Metabolites, Ferulic Acid and p-Hydroxybenzoic Acid Induced Toxic Effects on Photosynthetic Process in Rumex acetosa L

The elimination of broadleaf weeds from agricultural fields has become an urgent task in plant and environment protection. Allelopathic control is considered a potential approach because of its exclusive and ecological safety measures. Plant secondary metabolites also called allelochemicals are released from plant leaves, roots, stem, bark, flowers and play significant roles in soil rhizosphere signaling, chemical ecology, and plant defense. The present study was carried out to evaluate the impact of two allelochemicals; ferulic acid (FA) and p-hydroxybenzoic acid (pHBA) on photosynthetic characteristics; F_v/F_m: efficiency of photosystem II photochemistry in the dark-adapted state; ΦPSII: photosynthetic quantum yield; NPQ, non-photochemical quenching; qP, photochemical quenching, and photon energy dissipation (1−qP)/NPQ in Rumex acetosa following 6 days exposure. R. acetosa seedlings were grown in perlite culture, irrigated with Hoagland solution and treated with allelopathic compounds FA and pHBA and were evaluated against the photosynthetic attributes. Both compounds behaved as potent inhibitors of photosynthetic traits such as F_v/F_m, ΦPSII, qP, and NPQ in R. acetosa. Photon energy dissipation (1−qP)/NPQ increased significantly from days 3 to 6. Higher dissipation of absorbed energy indicates the inactivation state of reaction centers and their inability to effectively use the absorbed energy in photosynthesis. These results indicated the potential allelopathic application of FA and pHBA for control of broadleaf weed, Rumex acetosa.

Growth performance and emergence of invasive alien Rumex confertus in different soil types

Rumex confertus is known to be one of the most serious invasive weed species infesting meadows, pastures and ruderal lands throughout the Central Europe. Rumex confertus was grown in pot experiments using 8 soil types at 5 concentrations of nitrogen (N) and phosphorus (P). Based on harvest data, the variables, seedlings emergence, root: shoot (R: S) ratio, N and P concentration, chlorophyll content, Relative Colimitation Index (RCI) and dry matter allocation to plant components, were determined. N and P addition stimulated the growth of plants in different soils, as reflected by a significant increase in seedling growth parameters such as total plant biomass and shoot biomass. Across all soil types, emergence of seedlings was negatively affected by very high N, but positively affected by increased P availability. This study indicates that Dystric Arenosol, Entic Podzol, Brunic Arenosol and Calcaric Leptosol are unfavorable for R. confertus growth, excluding  R. confertus completely. Moreover, evidence suggests that plant growth is limited by both N and P, therefore R. confertus could be controlled by reducing available N and P content in the soil.

Optimization of plant hormonal balance by microorganisms prevents plant heavy metal accumulation

Heavy metal contamination is a threat to global food safety. Reducing heavy metal uptake in plants is a promising way to make plants safer, yet breeding the right set of traits can be tedious. We test whether microorganisms are able to impact the plant's hormonal balance hereby helping to manage plant heavy metal uptake. We focus on ethylene, a plant hormone regulating plant stress tolerance and nutrition. We grew three phylogenetically distinct plants, Rumex palustris, Alcea aucheri and Arabidopsis thaliana, on a cadmium-spiked soil. Plants roots were coated with the bacterium Pseudomonas putida UW4, which degrades the precursor of ethylene, or an isogenic ACC deaminase-deficient mutant lacking this ability. We followed ethylene concentrations, plant growth and cadmium uptake. Wildtype bacteria reduced shoot cadmium concentration by up to 35% compared to the control, while the mutant increased cadmium concentration. This effect was linked to ethylene, which was consistently positively correlated with cadmium concentration. We therefore propose that bacteria modulating plant hormonal balance may offer new possibilities to improve specific aspects of plant phenotype, in the present context reducing heavy metal. They may thus pave the way for new strategies to improve food safety in a context of the widespread soil contamination.

Testing the translocation hypothesis and Haldane's rule in Rumex hastatulus

The translocation hypothesis regarding the origin of the XX/XY1Y2 sex chromosome system was tested with reference to the F1 hybrids between two chromosomal races of Rumex hastatulus. The hybrids derived from reciprocal crossing between the Texas (T) race and the North Carolina (NC) race were investigated for the first time with respect to the meiotic chromosome configuration in the pollen mother cells, pollen viability, and sex ratio. A sex chromosome trivalent in the NC × T males and two sex chromosome bivalents in the T × NC males were detected. The observed conjugation patterns confirmed the autosomal origin of the extra chromosome segments occurring in the North Carolina neo-sex chromosomes. Decreased pollen viability was found in the T × NC hybrid in contrast to the NC × T hybrid and the parental forms. Moreover, only in the T × NC hybrid sex ratio was significantly female-biased (1:1.72). Thus, Haldane's rule for both male fertility and male rarity was shown in this hybrid. According to the authors' knowledge, R. hastatulus is just the second plant with sex chromosomes in which Haldane's rule was evidenced.

The improvement of bioactive secondary metabolites accumulation in Rumex gmelini Turcz through co-culture with endophytic fungi

Aspergillus sp., Fusarium sp., and Ramularia sp. were endophytic fungi isolated from Rumex gmelini Turcz (RGT), all of these three strains could produce some similar bioactive secondary metabolites of their host. However the ability to produce active components degraded significantly after cultured these fungi alone for a long time, and were difficult to recover. In order to obtain more bioactive secondary metabolites, the co-culture of tissue culture seedlings of RGT and its endophytic fungi were established respectively, and RGT seedling was selected as producer. Among these fungi, Aspergillus sp. showed the most significant enhancement on bioactive components accumulation in RGT seedlings. When inoculated Aspergillus sp. spores into media of RGT seedlings that had taken root for 20d, and made spore concentration in co-culture medium was 1×10⁴mL^-1, after co-cultured for 12d, the yield of chrysophaein, resveratrol, chrysophanol, emodin and physcion were 3.52-, 3.70-, 3.60-, 4.25-, 3.85-fold of the control group. The extreme value of musizin yield was 0.289mg, which was not detected in the control groups. The results indicated that co-culture with endophytic fungi could significantly enhance bioactive secondary metabolites production of RGT seedlings.

Overexpression of a flower-specific aerolysin-like protein from the dioecious plant Rumex acetosa alters flower development and induces male sterility in transgenic tobacco

Sex determination in Rumex acetosa, a dioecious plant with a complex XY1 Y2 sex chromosome system (females are XX and males are XY1 Y2 ), is not controlled by an active Y chromosome but depends on the ratio between the number of X chromosomes and autosomes. To gain insight into the molecular mechanisms of sex determination, we generated a subtracted cDNA library enriched in genes specifically or predominantly expressed in female floral buds in early stages of development, when sex determination mechanisms come into play. In the present paper, we report the molecular and functional characterization of FEM32, a gene encoding a protein that shares a common architecture with proteins in different plants, animals, bacteria and fungi of the aerolysin superfamily; many of these function as β pore-forming toxins. The expression analysis, assessed by northern blot, RT-PCR and in situ hybridization, demonstrates that this gene is specifically expressed in flowers in both early and late stages of development, although its transcripts accumulate much more in female flowers than in male flowers. The ectopic expression of FEM32 under both the constitutive promoter 35S and the flower-specific promoter AP3 in transgenic tobacco showed no obvious alteration in vegetative development but was able to alter floral organ growth and pollen fertility. The 35S::FEM32 and AP3::FEM32 transgenic lines showed a reduction in stamen development and pollen viability, as well as a diminution in fruit set, fruit development and seed production. Compared with other floral organs, pistil development was, however, enhanced in plants overexpressing FEM32. According to these effects, it is likely that FEM32 functions in Rumex by arresting stamen and pollen development during female flower development. The aerolysin-like pore-forming proteins of eukaryotes are mainly involved in defence mechanisms against bacteria, fungi and insects and are also involved in apoptosis and programmed cell death (PCD), a mechanism that could explain the role of FEM32 in Rumex sex determination.

Antifungal and Herbicidal Effects of Fruit Essential Oils of Four Myrtus communis Genotypes

The chemical composition of the essential oils isolated by hydrodistillation from the fruits of four selected Myrtus communis L. genotypes from Turkey was characterized by GC-FID and GC/MS analyses. 1,8-Cineole (29.20-31.40%), linalool (15.67-19.13%), α-terpineol (8.40-18.43%), α-pinene (6.04-20.71%), and geranyl acetate (3.98-7.54%) were found to be the major constituents of the fruit essential oils of all M. communis genotypes investigated. The oils were characterized by high amounts of oxygenated monoterpenes, representing 73.02-83.83% of the total oil compositions. The results of the fungal growth inhibition assays showed that the oils inhibited the growth of 19 phytopathogenic fungi. However, their antifungal activity was generally lower than that of the commercial pesticide benomyl. The herbicidal effects of the oils on the seed germination and seedling growth of Amaranthus retroflexus L., Chenopodium album L., Cirsium arvense (L.) Scop., Lactuca serriola L., and Rumex crispus L. were also determined. The oils completely or partly inhibited the seed germinations and seedling growths of the plants. The findings of the present study suggest that the M. communis essential oils might have potential to be used as natural herbicides as well as fungicides.

Content of Zinc and Copper in Selected Plants Growing Along a Motorway

In 2011 a study was carried out analyzing the effects of road traffic on bioaccumulation of zinc and copper in selected species of dicotyledonous plants growing on adjacent grasslands. To do the research the plants were sampled from the 9-km-long Siedlce bypass, a part of the international route E-30. They were collected during the flowering stage, at following distances from the road: 1, 5, 10, 15 m. The content of zinc and copper was determined with the AAS method, with dry mineralisation done before. The highest concentration of the elements, regardless of the distance from the road, was found in Taraxacum spec. Among the tested plants, the lowest zinc content was in Vicia cracca, and the lowest copper content in Rumex acetosa. The limit for copper content was exceeded in Taraxacum spec. and, slightly, in Achillea millefolium growing at the roadside, closest to the roadway.

Effect of Environmental Factors on Germination and Emergence of Invasive Rumex confertus in Central Europe

Rumex confertus is a biennial species native to Eastern Europe and Asia, where it thrives on meadow-steppes and glades in forest-steppe. This species has increased its range rapidly within central Europe, yet its biology is not well understood, which has led to poorly timed management. Effects of temperature, light, sodium chloride (NaCl), hydrogen ion concentration (pH), potassium nitrate (KNO3), and polyethylene glycol 6000 on seed germination were examined. Seedling emergence was examined for seeds sown at different depths in sand-filled pots. Seeds of R. confertus were nondormant at maturity. The germination percentage and rate of germination were significantly higher in light than in darkness. Secondary dormancy was induced in these seeds by 12 weeks of dark incubation at 4°C. The seeds of R. confertus undergo a seasonal dormancy cycle with deep dormancy in winter and early spring and a low level of dormancy in early autumn. Germination decreased as soil salinity increased. NO3(-) increased the percentage and rate of germination in the studied species. Decrease in seedling emergence from the seeds buried at >0.5 cm may be due to deficiency of light. From our experiments, we conclude that the weed R. confertus normally becomes established in vegetation gaps or due to disturbance of the uppermost soil layer during the growing season through the germination of seeds originating from a long-lived seed bank.

Comparative study of root growth and sucrose-cleaving enzymes in metallicolous and non-metallicolous populations of Rumex dentatus under copper stress

Sucrose metabolism in roots of metallophytes is very important for root growth and maintenance of heavy metal tolerance. However, rare researches have been carried out on this topic so far. We tested here a hypothesis that roots of copper-tolerant plants should manifest higher activities of sucrose-cleaving enzymes than non-tolerant plants for maintaining root growth under Cu stress. Plants of two contrasting populations of metallophyte Rumex dentatus, one from an ancient Cu mine (MP) and the other from a non-mine site (NMP), were treated with Cu in controlled experiments. Cu treatment resulted in a higher root biomass and root/shoot biomass ratio in MP compared to NMP. More complicated root system architecture was showed in MP under Cu stress. Activities and transcript levels of acid invertase as well as contents of sucrose and reducing sugar in MP were elevated under Cu treatment, while activities of neutral/alkaline invertase and sucrose synthase showed no significant differences between two populations. The results indicate important roles of acid invertase in governing root growth under Cu stress.

Two Rumex species from contrasting hydrological niches regulate flooding tolerance through distinct mechanisms

Global climate change has increased flooding events, which affect both natural vegetation dynamics and crop productivity. The flooded environment is lethal for most plant species because it restricts gas exchange and induces an energy and carbon crisis. Flooding survival strategies have been studied in Oryza sativa, a cultivated monocot. However, our understanding of plant adaptation to natural flood-prone environments remains scant, even though wild plants represent a valuable resource of tolerance mechanisms that could be used to generate stress-tolerant crops. Here we identify mechanisms that mediate the distinct flooding survival strategies of two related wild dicot species: Rumex palustris and Rumex acetosa. Whole transcriptome sequencing and metabolite profiling reveal flooding-induced metabolic reprogramming specific to R. acetosa. By contrast, R. palustris uses the early flooding signal ethylene to increase survival by regulating shade avoidance and photomorphogenesis genes to outgrow submergence and by priming submerged plants for future low oxygen stress. These results provide molecular resolution of flooding survival strategies of two species occupying distinct hydrological niches. Learning how these contrasting flood adaptive strategies evolved in nature will be instrumental for the development of stress-tolerant crop varieties that deliver enhanced yields in a changing climate.

Influences on the establishment and dominance of vegetation in stormwater infiltration basins

Infiltration basins are widely used in urban environments as a technique for managing and reducing the volume of stormwater. These basins can be spontaneously colonized by wild plants, which can be used as bioindicators of edaphic characteristics. As the basins are anthropogenic environments, the description of plant biodiversity allows the determination of which species colonize such environments and identification of the relationships between plants, basin type and operation. Nineteen infiltration basins were selected according to their catchment types (industrial, urban, agricultural). The dominant species were identified and sampled. Rumex sp., Taraxacum sp. and Artemisia sp. are the three types most represented (88, 61 and 55% respectively of the basins studied). Their families and their respective orders are those most commonly found (Caryophyllales, Asterales and Polygonaceae, Asteraceae). Poaceae is the family grouping with the largest number of different species (11). Although each species occupies only 1 or 2 basins, plants of this family occupy 61% of the basins. Although the catchment characteristics of the 19 basins do not play a direct role in the diversity of plant families, they can influence the presence or absence of certain species. Thus, these plants can be used as bio-indicators of basin soil and operating characteristics, such as sediment depths, inundation frequency and duration.

Uptake and translocation of Ti from nanoparticles in crops and wetland plants

Bioavailability of engineered metal nanoparticles affects uptake in plants, impacts on ecosystems, and phytoremediation. We studied uptake and translocation of Ti in plants when the main source of this metal was TiO2 nanoparticles. Two crops (Phaseolus vulgaris (bean) and Triticum aestivum (wheat)), a wetland species (Rumex crispus, curly dock), and the floating aquatic plant (Elodea canadensis, Canadian waterweed), were grown in nutrient solutions with TiO2 nanoparticles (0, 6, 18 mmol Ti L(-1) for P. vulgaris, T. aestivum, and R. crispus; and 0 and 12 mmol Ti L(-1) for E. canadensis). Also examined in E. canadensis was the influence of TiO2 nanoparticles upon the uptake of Fe, Mn, and Mg, and the influence of P on Ti uptake. For the rooted plants, exposure to TiO2 nanoparticles did not affect biomass production, but significantly increased root Ti sorption and uptake. R. crispus showed translocation of Ti into the shoots. E. canadensis also showed significant uptake of Ti, P in the nutrient solution significantly decreased Ti uptake, and the uptake patterns of Mn and Mg were altered. Ti from nano-Ti was bioavailable to plants, thus showing the potential for cycling in ecosystems and for phytoremediation, particularly where water is the main carrier.

Plasticity as a plastic response: how submergence-induced leaf elongation in Rumex palustris depends on light and nutrient availability in its early life stage

Plants may experience different environmental cues throughout their development which interact in determining their phenotype. This paper tests the hypothesis that environmental conditions experienced early during ontogeny affect the phenotypic response to subsequent environmental cues. This hypothesis was tested by exposing different accessions of Rumex palustris to different light and nutrient conditions, followed by subsequent complete submergence. Final leaf length and submergence-induced plasticity were affected by the environmental conditions experienced at early developmental stages. In developmentally older leaves, submergence-induced elongation was lower in plants previously subjected to high-light conditions. Submergence-induced elongation of developmentally younger leaves, however, was larger when pregrown in high light. High-light and low-nutrient conditions led to an increase of nonstructural carbohydrates in the plants. There was a positive correlation between submergence-induced leaf elongation and carbohydrate concentration and content in roots and shoots, but not with root and shoot biomass before submergence. These results show that conditions experienced by young plants modulate the responses to subsequent environmental conditions, in both magnitude and direction. Internal resource status interacts with cues perceived at different developmental stages in determining plastic responses to the environment.

Seed longevity and fire: germination responses of an exotic perennial herb in NW Patagonian grasslands (Argentina)

Fire affects grassland composition by selectively influencing recruitment. Some exotic species can increase their abundance as a consequence of fire-stimulated seed germination, but response may depend on seed age. Rumex acetosella L. (Polygonaceae, sheep's sorrel) is a cosmopolitan herb that has invaded NW Patagonia's grasslands. This species forms persistent soil seed banks and increases after disturbances, particularly fire. We studied how fire and seed longevity influence R. acetosella germination. In 2008, we conducted laboratory experiments where we exposed different-aged seeds (up to 19 years old) to heat, smoke, charcoal, ash and control treatments. Total percentage germination and mean germination time depended on both seed age and fire treatment. Germination of younger seeds decreased with increasing temperature. There was no general pattern in germination responses of different-aged seeds to smoke, charcoal and ash. While smoke improved the germination of fresh seeds, charcoal decreased germination. Germination of untreated seeds was negatively correlated with seed age, and mean germination time increased with seed age. In most treatments, fresh seeds had lower germination than 1-5-year-old seeds, indicating an after-ripening requirement. Smoke stimulates R. acetosella germination, causing successful recruitment during post-fire conditions. Fresh seeds are particularly responsive to fire factors, possibly because they have not experienced physical degradation and are more receptive to environmental stimuli. Knowing the colonisation potential from the soil seed bank of this species during post-fire conditions will allow us to predict their impact on native communities.

Phytoextraction and uptake patterns of weathered polychlorinated biphenyl-contaminated soils using three perennial weed species

Three promising phytoextracting perennial weed species [ L. (ox-eye daisy), L. (curly dock), and L. (Canada goldenrod)] were planted in monoculture plots at two polychlorinated biphenyl (PCB)-contaminated sites in southern Ontario and followed over 2 yr to investigate the effects of plant age, contaminant characteristics, and species-specific properties on PCB uptake and accumulation patterns in plant tissues. Results from this study indicate that, for each of these weed species, shoot contaminant concentrations and total biomass are dependent on plant age and life cycle (vegetative and reproductive stages), which affects the total amount of PCBs phytoextracted on a per-plant basis. Even at suboptimal planting densities of 3 to 5 plants m, all three weed species extracted a greater quantity of PCBs per unit area (4800-10,000 μg m) than the known PCB-accumulator L. ssp (cv Howden pumpkins) (1500-2100 μg m) at one of the two sites. Calculated PCB extractions based on theoretical optimal planting densities were significantly higher at both sites and illustrate the potential of these weeds for site remediation. This study also demonstrates that plants may accumulate PCBs along the stem length in a similar manner as plants.

Effects of copper on phenology and reproduction in Rumex dentatus from metalliferous and non-metalliferous sites

The responses of phenology and reproductive traits to copper stress in two populations of Rumex dentatus were comparatively studied with pot culture experiments. Seeds used for the experiments were, respectively, collected from metalliferous and normal soils. It was found that the responses of phenology and reproductive traits to Cu treatment between the two populations were significantly different. Compared to the non-metallicolous population, the metallicolous population of R. dentatus had a short life cycle, large reproductive effort, and high fertility under Cu stress. In addition, the reproductive effort in metallicolous population of R. dentatus was maintained at the expense of a curtailment of vegetative development. The results suggested that change in phenological traits and more resources allocation to reproduction might play an important role in the adaptation of metallicolous population of R. dentatus to the Cu-enriched mine soils.

Fitness consequences of natural variation in flooding-induced shoot elongation in Rumex palustris

• Plants can respond to their environment by morphological plasticity. Generally, the potential benefits of adaptive plastic responses are beyond doubt under predictable environmental changes. However, the net benefits may be less straightforward when plants encounter temporal stresses, such as flooding in river flood plains. • Here, we tested whether the balance of costs and benefits associated with flooding-induced shoot elongation depends on the flooding regime, by subjecting Rumex palustris plants with different elongation capacity to submergence of different frequency and duration. • Our results showed that reaching the surface by shoot elongation is associated with fitness benefits, as under less frequent, but longer, flooding episodes plants emerging above the floodwater had greater biomass production than plants that were kept below the surface. As we predicted, slow-elongating plants had clear advantages over fast-elongating ones if submergence was frequent but of short duration, indicating that elongation also incurs costs. • Our data suggest that high costs select for weak plasticity under frequent environmental change. In contrast to our predictions, however, fast-elongating plants did not have an overall advantage over slow-elongating plants when floods lasted longer. This indicates that the delicate balance between benefits and costs of flooding-induced elongation depends on the specific characteristics of the flooding regime.

[Combined effects of copper and simulated acid rain on copper accumulation, growth, and antioxidant enzyme activities of Rumex acetosa]

A pot experiment was conducted to study the combined effects of Cu (0-1500 mg x kg(-1)) and simulated acid rain (pH 2.5-5.6) on the copper accumulation, growth, and antioxidant enzyme activities of Rumex acetosa. With the increasing concentration of soil Cu, the Cu accumulation in R. acetosa increased, being higher in root than in stem and leaf. The exposure to low pH acid rain promoted the Cu uptake by R. acetosa. With the increase of soil Cu concentration and/or of acid rain acidity, the biomass of R. acetosa decreased, leaf and root MDA contents increased and had good correlation with soil Cu concentration, and the SOD and POD activities in leaf and root displayed a decreasing trend after an initial increase. This study showed that R. acetosa had a strong adaptive ability to Cu and acid rain stress, exhibiting a high application potential in the remediation of Cu-contaminated soil in acid rain areas.

Growth-mediated stress escape: convergence of signal transduction pathways activated upon exposure to two different environmental stresses

• Plants can escape from specific environmental stresses through active growth strategies. Here, we compared two such stress-escape syndromes to investigate whether plants use conserved signal transduction pathways to escape from different stresses. • Full submergence is a threat to terrestrial plants as it cuts off their access to oxygen and CO(2). Proximate neighbors, in contrast, take away resources such as light. Both submergence and shade can be escaped through rapid shoot elongation. We analysed the precise kinetics and physiological control of petiole elongation responses to shade and submergence in the flood-tolerant species Rumex palustris. • We found that petiole elongation induced by submergence and that induced by shade occurred with similar kinetics, both involving cell expansion. These responses were induced by two different signals, elevated ethylene and a reduced red : far-red light ratio (R : FR), respectively. A downstream target for ethylene was abscisic acid, but low R : FR appeared to act independently of this hormone. Gibberellin, however, appeared to be essential to both ethylene- and low R : FR-induced petiole elongation. • We propose that gibberellin and expansins, a family of cell wall-loosening proteins, represent elements of a conserved growth machinery that is activated by stress-specific signaling events to regulate escape from stress.

Endogenous abscisic acid as a key switch for natural variation in flooding-induced shoot elongation

Elongation of leaves and stem is a key trait for survival of terrestrial plants during shallow but prolonged floods that completely submerge the shoot. However, natural floods at different locations vary strongly in duration and depth, and, therefore, populations from these locations are subjected to different selection pressure, leading to intraspecific variation. Here, we identified the signal transduction component that causes response variation in shoot elongation among two accessions of the wetland plant Rumex palustris. These accessions differed 2-fold in petiole elongation rates upon submergence, with fast elongation found in a population from a river floodplain and slow elongation in plants from a lake bank. Fast petiole elongation under water consumes carbohydrates and depends on the (inter)action of the plant hormones ethylene, abscisic acid, and gibberellic acid. We found that carbohydrate levels and dynamics in shoots did not differ between the fast and slow elongating plants, but that the level of ethylene-regulated abscisic acid in petioles, and hence gibberellic acid responsiveness of these petioles explained the difference in shoot elongation upon submergence. Since this is the exact signal transduction level that also explains the variation in flooding-induced shoot elongation among plant species (namely, R. palustris and Rumex acetosa), we suggest that natural selection results in similar modification of regulatory pathways within and between species.

A kinetic analysis of hyponastic growth and petiole elongation upon ethylene exposure in Rumex palustris

BACKGROUND AND AIMS

Complete submergence is an important stress factor for many terrestrial plants, and a limited number of species have evolved mechanisms to deal with these conditions. Rumex palustris is one such species and manages to outgrow the water, and thus restore contact with the atmosphere, through upward leaf growth (hyponasty) followed by strongly enhanced petiole elongation. These responses are initiated by the gaseous plant hormone ethylene, which accumulates inside plants due to physical entrapment. This study aimed to investigate the kinetics of ethylene-induced leaf hyponasty and petiole elongation.

METHODS

Leaf hyponasty and petiole elongation was studied using a computerized digital camera set-up followed by image analyses. Linear variable displacement transducers were used for fine resolution monitoring and measurement of petiole growth rates.

KEY RESULTS

We show that submergence-induced hyponastic growth and petiole elongation in R. palustris can be mimicked by exposing plants to ethylene. The petiole elongation response to ethylene is shown to depend on the initial angle of the petiole. When petiole angles were artificially kept at 0 degrees, rather than the natural angle of 35 degrees, ethylene could not induce enhanced petiole elongation. This is very similar to submergence studies and confirms the idea that there are endogenous, angle-dependent signals that influence the petiole elongation response to ethylene.

CONCLUSIONS

Our data suggest that submergence and ethylene-induced hyponastic growth and enhanced petiole elongation responses in R. palustris are largely similar. However, there are some differences that may relate to the complexity of the submergence treatment as compared with an ethylene treatment.

Intraspecific variation in the magnitude and pattern of flooding-induced shoot elongation in Rumex palustris

BACKGROUND AND AIMS

Intraspecific variation in flooding tolerance is the basic pre-condition for adaptive flooding tolerance to evolve, and flooding-induced shoot elongation is an important trait that enables plants to survive shallow, prolonged flooding. Here an investigation was conducted to determine to what extent variation in flooding-induced leaf elongation exists among and within populations of the wetland species Rumex palustris, and whether the magnitude of elongation can be linked to habitat characteristics.

METHODS

Offspring of eight genotypes collected in each of 12 populations from different sites (ranging from river mudflats with dynamic flooding regimes to areas with stagnant water) were submerged, and petioles, laminas and roots were harvested separately to measure traits related to elongation and plant growth.

KEY RESULTS

We found strong elongation of petioles upon submergence, and both among- and within-population variation in this trait, not only in final length, but also in the timing of the elongation response. However, the variation in elongation responses could not be linked to habitat type.

CONCLUSIONS

Spatio-temporal variation in the duration and depth of flooding in combination with a presumably weak selection against flooding-induced elongation may have contributed to the maintenance of large genetic variation in flooding-related traits among and within populations.

Is elongation-induced leaf emergence beneficial for submerged Rumex species?

BACKGROUND AND AIMS

Plant species from various taxa 'escape' from low oxygen conditions associated with submergence by a suite of traits collectively called the low oxygen escape syndrome (LOES). The expression of these traits is associated with costs and benefits. Thus far, remarkably few studies have dealt with the expected benefits of the LOES.

METHODS

Young plants were fully submerged at initial depths of 450 mm (deep) or 150-240 mm (shallow). Rumex palustris leaf tips emerged from the shallow flooding within a few days, whereas a slight lowering of shallow flooding was required to expose R. acetosa leaf tips to the atmosphere. Shoot biomass and petiole porosity were measured for all species, and treatments and data from the deep and shallow submergence treatments were compared with non-flooded controls.

KEY RESULTS

R. palustris is characterized by submergence-induced enhanced petiole elongation. R. acetosa lacked this growth response. Upon leaf tip emergence, R. palustris increased its biomass, whereas R. acetosa did not. Furthermore, petiole porosity in R. palustris was twice as high as in R. acetosa.

CONCLUSIONS

Leaf emergence restores gas exchange between roots and the atmosphere in R. palustris. This occurs to a much lesser extent in R. acetosa and is attributable to its lower petiole porosity and therefore limited internal gas transport. Leaf emergence resulting from fast petiole elongation appears to benefit biomass accumulation if these plants contain sufficient aerenchyma in petioles and roots to facilitate internal gas exchange.

Effect of Cu stress on the invertase activity and root growth in two populations of Rumex dentatus L. with different Cu tolerance

There has been no study on key enzymes in sucrose cleavage in metallophyte plants so far, which may be crucial for the plants' root growth and heavy metal tolerance maintenance. Acid invertases are rate-limiting enzymes in sucrose metabolism. Here, we tested the hypothesis that the roots of copper-tolerant plants should manifest a higher activity of acid invertases than nontolerant plants both for supporting growth and for their maintaining tolerance under Cu stress. Two populations of Rumex dentatus L., one from an ancient waste heap at a Cu mine (Cu-tolerant population), and the other from a noncontaminated site (Cu nontolerant population), were used in the experiments. The seedlings of Rumex dentatus L. were exposed to 0, 10, and 40 microM CuCl(2) for 14 days. Cu exposure had a stronger inhibition on root growth and thus resulted in a lower root/shoot ratio in the plants of nontolerant population compared with the Cu-tolerant population. Cu exposure showed a stronger inhibition of acid invertase activity of Cu nontolerant plants than Cu tolerant plants, whereas neutral/alkaline invertase was insensitive to Cu. A positive correlation between the activity of acid invertases and the root growth and root/shoot ratio was observed. The results suggested that the higher activities in acid invertases of Cu-tolerant population might at least partly associate with the plants' Cu tolerance, and their higher activities in acid invertases in turn played an role in maintenance of the Cu tolerance by supplying carbon and energy for tolerance mechanisms.

[Study on correlation of soil nutrients and content of active constituents in root of Rumex gmelini]

OBJECTIVE

To provide scientific basis for the selection of agrotype and property fertilization for Rumex gmelini cultivated in compliance with good agricultural practice (GAP).

METHOD

HPLC method was applied to determinate the content of seven active constituents (resveratrol, polydatin, chrysophanol 1-glucoside, nepodin, emodin, chrysophanol and physcion) of annual R. gmelini. And the correlation between soil nutrients and content of active constituents in the root of R. gmelini were analyzed by stepwise regression analysis.

RESULT

Seven regression equation were established. The statistic significance was found in three of them.

CONCLUSION

The soil with high total K level is not suitable for R. gmelini cultivation. But the higher available N, available P, available K level of soil is suitable.

Phytotoxicity of volatile oil from Eucalyptus citriodora against some weedy species

A study was undertaken to explore the phytotoxicity of volatile essential oil from Eucalyptus citriodora Hook. against some weeds viz. Bidens pilosa, Amaranthus viridis, Rumex nepalensis, and Leucaena leucocephala in order to assess its herbicidal activity. Dose-response studies conducted under laboratory conditions revealed that eucalypt oils (in concentration ranging from 0.0012 to 0.06%) greatly suppress the germination and seedling height of test weeds. At 0.06% eucalypt oil concentration, none of the seed of test weeds germinated. Among the weed species tested, A. viridis was found to be the most sensitive and its germination was completed inhibited even at 0.03%. Not only the germination and seedling growth, even the chlorophyll content and respiratory activity in leaves of emerged seedlings were severely affected. In A. viridis chlorophyll content and respiratory activity were reduced by over 51% and 71%, respectively, even at a very low concentration of 0.06%. These results indicated an adverse effect of eucalypt oils on the photosynthetic and energy metabolism of the test weeds. A strong negative correlation was observed between the observed effect and the concentration of eucalypt oil. Based on the study, it can be concluded that oil from E. citriodora possess strong inhibitory potential against weeds that could be exploited for weed management.

Long-term submergence-induced elongation in Rumex palustris requires abscisic acid-dependent biosynthesis of gibberellin1

Rumex palustris (polygonceae) responds to complete submergence with enhanced elongation of its youngest petioles. This process requires the presence of gibberellin (GA) and is associated with an increase in the concentration of GA1 in elongating petioles. We have examined how GA biosynthesis was regulated in submerged plants. Therefore, cDNAs encoding GA-biosynthetic enzymes GA 20-oxidase and GA 3-oxidase, and the GA-deactivating enzyme GA 2-oxidase were cloned from R. palustris and the kinetics of transcription of the corresponding genes was determined during a 24 h submergence period. The submergence-induced elongation response could be separated into several phases: (1) during the first phase of 4 h, petiole elongation was insensitive to GA; (2) from 4 to 6 h onward growth was limited by GA; and (3) from 15 h onward underwater elongation was dependent, but not limited by GA. Submergence induced an increase of GA1 concentration, as well as enhanced transcript levels of RpGA3ox1. Exogenous abscisic acid repressed the transcript levels of RpGA20ox1 and RpGA3ox1 and thus inhibited the submergence-induced increase in GA1. Abscisic acid had no effect on the tissue responsiveness to GA.

The stimulating effects of ethylene and auxin on petiole elongation and on hyponastic curvature are independent processes in submerged Rumex palustris

The flooding-tolerant plant species Rumex palustris (Sm.) responds to complete submergence with stimulation of petiole elongation mediated by the gaseous hormone ethylene. We examined the involvement of auxin in petiole elongation. The manipulation of petiolar auxin levels by removing the leaf blade, or by addition of synthetic auxins or auxin transport inhibitors, led to the finding that auxin plays an important role in submergence-induced petiole elongation in R. palustris. A detailed kinetic analysis revealed a transient effect of removing the auxin source (leaf blade), explaining why earlier studies in which less frequent measurements were taken failed to identify any role for auxin in petiole elongation. We previously showed that the onset of stimulated petiole elongation depends on a more upright petiole angle being reached by means of hyponastic (upward) curvature, a differential growth process that is also regulated by ethylene and auxin. This raised the possibility that both ethylene and auxin stimulate elongation only indirectly by influencing hyponastic growth. We show here that the action of ethylene and auxin in promoting petiole elongation in submerged R. palustris is independent of the promoting effect that these hormones also exert on the hyponastic curvature of the same petiole.

Limited costs of wrong root placement in Rumex palustris in heterogeneous soils

Nutrient hot spots in the soil have a limited life span, but the costs and benefits for root foraging are still underexposed. We assessed short-term costs that may arise when a nutrient-rich patch induces root proliferation, but then rapidly disappears. Rumex palustris plants were grown with a homogeneous or a heterogeneous nutrient application. After root proliferation in a nutrient-rich patch, nutrient supply was switched from homogeneous to heterogeneous, and vice versa, or the patch location was changed. R. palustris proliferated its roots in the rich patch. After switching, the relative growth rates of the roots were adjusted to the novel pattern of nutrient availability. However, the changes in local root biomass lagged behind the rapid shift in nutrient supply, because the root mass realized in specific sectors could not be rapidly relocated. Despite this, R. palustris did not exhibit costs of switching in terms of biomass or nitrogen uptake. Our data suggest that rapid shifts in uptake rate and redistribution of nitrogen within the plant may have lowered the costs of incorrect root placement.

How plants cope with complete submergence

Flooding is a widespread phenomenon that drastically reduces the growth and survival of terrestrial plants. The dramatic decrease of gas diffusion in water compared with in air is a major problem for terrestrial plants and limits the entry of CO(2) for photosynthesis and of O(2) for respiration. Responses to avoid the adverse effects of submergence are the central theme in this review. These include underwater photosynthesis, aerenchyma formation and enhanced shoot elongation. Aerenchyma facilitates gas diffusion inside plants so that shoot-derived O(2) can diffuse to O(2)-deprived plant parts, such as the roots. The underwater gas-exchange capacity of leaves can be greatly enhanced by a thinner cuticle, reorientation of the chloroplasts towards the epidermis and increased specific leaf area (i.e. thinner leaves). At the same time, plants can outgrow the water through increased shoot elongation, which in some species is preceded by an adjustment of leaf angle to a more vertical position. The molecular regulatory networks involved in these responses, including the putative signals to sense submergence, are discussed and suggestions made on how to unravel the mechanistic basis of the induced expression of various adaptations that alleviate O(2) shortage underwater.

Ethylene regulates fast apoplastic acidification and expansin A transcription during submergence-induced petiole elongation in Rumex palustris

The semi-aquatic dicot Rumex palustris responds to complete submergence by enhanced elongation of young petioles. This elongation of petiole cells brings leaf blades above the water surface, thus reinstating gas exchange with the atmosphere and increasing survival in flood-prone environments. We already know that an enhanced internal level of the gaseous hormone ethylene is the primary signal for underwater escape in R. palustris. Further downstream, concentration changes in abscisic acid (ABA), gibberellin (GA) and auxin are required to gain fast cell elongation under water. A prerequisite for cell elongation in general is cell wall loosening mediated by proteins such as expansins. Expansin genes might, therefore, be important target genes in submergence-induced and plant hormone-mediated petiole elongation. To test this hypothesis we have studied the identity, kinetics and regulation of expansin A mRNA abundance and protein activity, as well as examined pH changes in cell walls associated with this adaptive growth. We found a novel role of ethylene in triggering two processes affecting cell wall loosening during submergence-induced petiole elongation. First, ethylene was shown to promote fast net H(+) extrusion, leading to apoplastic acidification. Secondly, ethylene upregulates one expansin A gene (RpEXPA1), as measured with real-time RT-PCR, out of a group of 13 R. palustris expansin A genes tested. Furthermore, a significant accumulation of expansin proteins belonging to the same size class as RpEXPA1, as well as a strong increase in expansin activity, were apparent within 4-6 h of submergence. Regulation of RpEXPA1 transcript levels depends on ethylene action and not on GA and ABA, demonstrating that ethylene evokes at least three, parallel operating pathways that, when integrated at the whole petiole level, lead to coordinated underwater elongation. The first pathway involves ethylene-modulated changes in ABA and GA, these acting on as yet unknown downstream components, whereas the second and third routes encompass ethylene-induced apoplastic acidification and ethylene-induced RpEXPA1 upregulation.

[Study on the optimal harvesting time of Rumex gmelini by analyzing the contents of principal components]

OBJECTIVE

To establish a method used for optimization of harvesting time and determine the best time for harvesting Rumex gmelini.

METHOD

An HPLC method was applied to determinate the contents of seven active constituents(resveratrol, polydatin, chrysophanol 1-glucoside, nepodin, emodin, chrysophanol and physcion)of R. gmelini at different development stage. The result was analyzed by principal component analysis.

RESULT

The accumulation of active constituents showed a regular pattern.

CONCLUSION

The best harvesting time of R. gmelini is early July.

Mechanisms governing sex-ratio variation in dioecious Rumex nivalis

Sex ratios of flowering individuals in dioecious plant populations are often close to unity, or are male biased owing to gender-specific differences in flowering or mortality. Female-biased sex ratios, although infrequent, are often reported in species with heteromorphic sex chromosomes. Two main hypotheses have been proposed to account for female bias: (1) selective fertilization resulting from differential pollen-tube growth of female- versus male-determining microgametophytes (certation); (2) differences in the performance and viability of the sexes after parental investment. Here we investigate these hypotheses in Rumex nivalis (Polygonaceae), a European alpine herb with female-biased sex ratios in which females possess XX, and males XY1Y2, sex chromosomes. Using field surveys and a glasshouse experiment we investigated the relation between sex ratios and life-history stage in 18 populations from contrasting elevations and snowbed microsites and used a male-specific SCAR-marker to determine the sex of nonflowering individuals. Female bias among flowering individuals was one of the highest reported for populations of a dioecious species (mean female frequency = 0.87), but males increased in frequency at higher elevations and in the center of snowbeds. Female bias was also evident in nonflowering individuals (mean 0.78) and in seeds from open-pollinated flowers (mean 0.59). The female bias in seeds was weakly associated with the frequency of male flowering individuals in populations in the direction predicted when certation occurs. Under glasshouse conditions, females outperformed males at several life-history stages, although male seeds were heavier than female seeds. Poor performance of Y1Y2 gametophytes and male sporophytes in R. nivalis may be a consequence of the accumulation of deleterious mutations on Y-sex chromosomes.

The roles of ethylene, auxin, abscisic acid, and gibberellin in the hyponastic growth of submerged Rumex palustris petioles

Rumex palustris responds to complete submergence with upward movement of the younger petioles. This so-called hyponastic response, in combination with stimulated petiole elongation, brings the leaf blade above the water surface and restores contact with the atmosphere. We made a detailed study of this differential growth process, encompassing the complete range of the known signal transduction pathway: from the cellular localization of differential growth, to the hormonal regulation, and the possible involvement of a cell wall loosening protein (expansin) as a downstream target. We show that hyponastic growth is caused by differential cell elongation across the petiole base, with cells on the abaxial (lower) surface elongating faster than cells on the adaxial (upper) surface. Pharmacological studies and endogenous hormone measurements revealed that ethylene, auxin, abscisic acid (ABA), and gibberellin regulate different and sometimes overlapping stages of hyponastic growth. Initiation of hyponastic growth and (maintenance of) the maximum petiole angle are regulated by ethylene, ABA, and auxin, whereas the speed of the response is influenced by ethylene, ABA, and gibberellin. We found that a submergence-induced differential redistribution of endogenous indole-3-acetic acid in the petiole base could play a role in maintenance of the response, but not in the onset of hyponastic growth. Since submergence does not induce a differential expression of expansins across the petiole base, it is unlikely that this cell wall loosening protein is the downstream target for the hormones that regulate the differential cell elongation leading to submergence-induced hyponastic growth in R. palustris.

Expression of alpha-expansin genes during root acclimations to O2 deficiency in Rumex palustris

Thirteen alpha-expansin genes were isolated from Rumex palustris , adding to the six already documented for this species. Five alpha-expansin genes were selected for expression studies in various organs/tissues of R. palustris , with a focus on roots exposed to aerated or O2)-deficient conditions, using real-time RT-PCR. Several cases of differential expression of alpha-expansin genes in the various root types of R. palustris were documented, and the identity of the dominant transcript differed between root types (i.e., tap root vs. lateral roots vs. adventitious roots). Several genes were expressed differentially in response to low O2. In situ hybridizations showed expansin mRNA expression in the oldest region of the tap root was localized to cells near the vascular cambium; this being the first report of expansin expression associated with secondary growth in roots. In situ hybridization also showed abundant expression of expansin mRNA in the most apical 1 mm of adventitious roots. Such early expression of expansin mRNA in cells soon after being produced by the root apex presumably enables cell wall loosening in the elongation zone of roots. In addition, expression of some expansin mRNAs increased in 'mature zones' of roots; these expansins might be involved in root hair formation or in formation of lateral root primordia. The present findings support the notion that large gene families of alpha-expansins enable flexibility in expression for various organs and tissues as a normal part of plant development, as well as in response to abiotic stress.

Plant movement. Submergence-induced petiole elongation in Rumex palustris depends on hyponastic growth

The submergence-tolerant species Rumex palustris (Sm.) responds to complete submergence by an increase in petiole angle with the horizontal. This hyponastic growth, in combination with stimulated elongation of the petiole, can bring the leaf tips above the water surface, thus restoring gas exchange and enabling survival. Using a computerized digital camera set-up the kinetics of this hyponastic petiole movement and stimulated petiole elongation were studied. The hyponastic growth is a relatively rapid process that starts after a lag phase of 1.5 to 3 h and is completed after 6 to 7 h. The kinetics of hyponastic growth depend on the initial angle of the petiole at the time of submergence, a factor showing considerable seasonal variation. For example, lower petiole angles at the time of submergence result in a shorter lag phase for hyponastic growth. This dependency of the hyponastic growth kinetics can be mimicked by experimentally manipulating the petiole angle at the time of submergence. Stimulated petiole elongation in response to complete submergence also shows kinetics that are dependent on the petiole angle at the time of submergence, with lower initial petiole angles resulting in a longer lag phase for petiole elongation. Angle manipulation experiments show that stimulated petiole elongation can only start when the petiole has reached an angle of 40 degrees to 50 degrees. The petiole can reach this "critical angle" for stimulated petiole elongation by the process of hyponastic growth. This research shows a functional dependency of one response to submergence in R. palustris (stimulated petiole elongation) on another response (hyponastic petiole growth), because petiole elongation can only contribute to the leaf reaching the water surface when the petiole has a more or less upright position.

Soil contamination and plant uptake of heavy metals at polluted sites in China

We investigated heavy metal contamination in soils and plants at polluted sites in China including some with heavy industries, metal mining, smelting and untreated wastewater irrigation areas. We report our main findings in this paper. The concentrations of heavy metals, including Cd and Zn, in the soils at the investigated sites were above the background levels, and generally exceeded the Government guidelines for metals in soil. The concentrations of metals in plants served to indicate the metal contamination status of the site, and also revealed the abilities of various plant species to take up and accumulate the metals from the soil. Substantial differences in the accumulation of heavy metals were observed among the plant species investigated. Polygonum hydropiper growing on contaminated soils in a sewage pond had accumulated 1061 mg kg(-1) of Zn in its shoots. Rumex acetosa L. growing near a smelter had accumulated more than 900 mg kg(-1) of Zn both in its shoots and roots. Therefore these species have potential for phytoremediation of metal-contaminated sites. Our results indicate the need to elucidate the dynamics of soil metal contamination of plants and the onward movement of metal contaminants into the food chain. Also our results indicate that the consumption of rice grown in paddy soils contaminated with Cd, Cr or Zn may pose a serious risk to human health, because from 24 to 22% of the total metal content in the rice biomass was concentrated in the rice grain. Platanus acerifolia growing on heavily contaminated soil accumulated only very low levels of heavy metals, and this mechanism for excluding metal uptake may have value in crop improvement. Sources of metal entering the environmental matrices studied included untreated wastewater, tailings or slurries and dust depositions from metal ore mining, and sewage sludge. Pb, Zn or Cd concentrations declined with the distance from metal smelter in accordance with a good exponential correlation (R2>0.9), and this shows that metal dust deposition is an important contributor to metal contamination of soils.

3 beta,13-dihydroxylated C20 gibberellins from inflorescences of Rumex acetosa L

Using full scan GC-MS a wide range of gibberellins (GAs) was identified in the young inflorescences of the dioecious species Rumex acetosa L., consistent with the ubiquitous early 13-hydroxylation pathway in both male and female plants. In addition, R. acetosa is the first species in which all three 3beta,13-dihydroxylated C(20)-GAs-GA(18), GA(38) and GA(23)-have been identified in the same organism, suggesting an early 3beta,13-dihydroxylation biosynthesis pathway in this species. Authentic GA(18), GA(38) and GA(23) were synthesized and their effects and that of GA(1), a GA common to both pathways, on the time to inflorescence emergence was investigated. GA(1) accelerated the emergence of inflorescences in both male and female plants. In addition some evidence for biological activity per se of the C(20)-GA(38) was obtained.

De-submergence-induced ethylene production in Rumex palustris: regulation and ecophysiological significance

Rumex palustris responds to total submergence by increasing the elongation rate of young petioles. This favours survival by shortening the duration of submergence. Underwater elongation is stimulated by ethylene entrapped within the plant by surrounding water. However, abnormally fast extension rates were found to be maintained even when leaf tips emerged above the floodwater. This fast post-submergence growth was linked to a promotion of ethylene production that is presumed to compensate for losses brought about by ventilation. Three sources of ACC contributed to post-submergence ethylene production in R. palustris: (i) ACC that had accumulated in the roots during submergence and was transported in xylem sap to the shoot when stomata re-opened and transpiration resumed, (ii) ACC that had accumulated in the shoot during the preceding period of submergence and (iii) ACC produced de novo in the shoot following de-submergence. This new production of ethylene was associated with increased expression of an ACC synthase gene (RP-ACS1) and an ACC oxidase gene (RP-ACO1), increased ACC synthase activity and a doubling of ACC oxidase activity, measured in vitro. Out of seven species of Rumex examined, a de-submergence upsurge in ethylene production was seen only in shoots of those that had the ability to elongate fast when submerged.