Phenolic compounds from Allium schoenoprasum, Tragopogon pratensis and Rumex acetosa and their antiproliferative effects.

Experimental studies have shown that phenolic compounds have antiproliferative and tumour arresting effects. The aim of this original study was to investigate the content of phenolic compounds (PhC) in flowers of Allium schoenoprasum (chive), Tragopogon pratensis (meadow salsify) and Rumex acetosa (common sorrel) and their effect on proliferation of HaCaT cells. Antiproliferative effects were evaluated in vitro using the following concentrations of phenolic compounds in cultivation medium: 100, 75, 50 and 25 µg/mL. Phenolic composition was also determined by HPLC. The results indicate that even low concentrations of these flowers' phenolic compounds inhibited cell proliferation significantly and the possible use of the studied herb's flowers as sources of active phenolic compounds for human nutrition.

Herbivore resistance of invasive Fallopia species and their hybrids.

Hybridization has been proposed as a mechanism by which exotic plants can increase their invasiveness. By generating novel recombinants, hybridization may result in phenotypes that are better adapted to the new environment than their parental species. We experimentally assessed the resistance of five exotic Fallopia taxa, F. japonica var. japonica, F. sachalinensis and F. baldschuanica, the two hybrids F. × bohemica and F. × conollyana, and the common European plants Rumex obtusifolius and Taraxacum officinale to four native European herbivores, the slug Arion lusitanicus, the moth Noctua pronuba, the grasshopper Metrioptera roeselii and the beetle Gastrophysa viridula. Leaf area consumed and relative growth rate of the herbivores differed significantly between the Fallopia taxa and the native species, as well as among the Fallopia taxa, and was partly influenced by interspecific variation in leaf morphology and physiology. Fallopia japonica, the most abundant Fallopia taxon in Europe, showed the highest level of resistance against all herbivores tested. The level of resistance of the hybrids compared to that of their parental species varied depending on hybrid taxon and herbivore species. Genotypes of the hybrid F. × bohemica varied significantly in herbivore resistance, but no evidence was found that hybridization has generated novel recombinants that are inherently better defended against resident herbivores than their parental species, thereby increasing the hybrid's invasion success. In general, exotic Fallopia taxa showed higher levels of herbivore resistance than the two native plant species, suggesting that both parental and hybrid Fallopia taxa largely escape from herbivory in Europe.

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.

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.

Trade-off between root porosity and mechanical strength in species with different types of aerenchyma.

The objective of this work was to study the existence of a trade-off between aerenchyma formation and root mechanical strength. To this end, relationships among root anatomical traits and mechanical properties were analysed in plant species with contrasting root structural types: Paspalidium geminatum (graminaceous type), Cyperus eragrostis (cyperaceous type), Rumex crispus (Rumex type) and Plantago lanceolata (Apium type). Variations in anatomical traits and mechanical strength were assessed as a function of root diameter by exposing plants to 0, 7, 15 and 30 d of control and flooded conditions. For each species, the proportion of root cortex was positively associated with the increment of root diameter, contributing to the increase in root porosity under both control and flooded conditions. Moreover, cell lysis produced an additional increase in root porosity in most species under flooded conditions (except R. crispus). Both structural types that presented a uniseriate layer (epidermis) to cope with compression (Rumex and Apium types) were progressively weakened as root porosity increased. This effect was significant even when the increment of root porosity was solely because of increased root diameter (R. crispus), as when both processes (root diameter and cell lysis) added porosity to the roots (P. lanceolata). Conversely, structural types that presented a multiseriate ring of cells in the outer cortex (graminaceous and cyperaceous types) maintained mechanical strength over the whole range of porosity, in spite of lysogenic processes registered in the inner cortex. In conclusion, our study demonstrates a strong trade-off between aerenchyma formation and mechanical strength in root structural types that lacked a multiseriate ring of tissue for mechanical protection in the outer cortex. The results suggest that this ring of tissue plays a significant role in maintaining the mechanical strength of roots when flooding induces the generation of additional aerenchyma tissue in the root cortex.

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.

Photosynthetic consequences of phenotypic plasticity in response to submergence: Rumex palustris as a case study.

Survival and growth of terrestrial plants is negatively affected by complete submergence. This is mainly the result of hampered gas exchange between plants and their environment, since gas diffusion is severely reduced in water compared with air, resulting in O2 deficits which limit aerobic respiration. The continuation of photosynthesis could probably alleviate submergence-stress in terrestrial plants, but its potential under water will be limited as the availability of CO2 is hampered. Several submerged terrestrial plant species, however, express plastic responses of the shoot which may reduce gas diffusion resistance and enhance benefits from underwater photosynthesis. In particular, the plasticity of the flooding-tolerant terrestrial species Rumex palustris turned out to be remarkable, making it a model species suitable for the study of these responses. During submergence, the morphology and anatomy of newly developed leaves changed: 'aquatic' leaves were thinner and had thinner cuticles. As a consequence, internal O2 concentrations and underwater CO2 assimilation rates were higher at the prevailing low CO2 concentrations in water. Compared with heterophyllous amphibious plant species, underwater photosynthesis rates of terrestrial plants may be very limited, but the effects of underwater photosynthesis on underwater survival are impressive. A combination of recently published data allowed quantification of the magnitude of the acclimation response in this species. Gas diffusion resistance in terrestrial leaves underwater was about 15,000 times higher than in air. Strikingly, acclimation to submergence reduced this factor to 400, indicating that acclimated leaves of R. palustris had an approximately 40 times lower gas diffusion resistance than non-acclimated ones.

Submergence-induced morphological, anatomical, and biochemical responses in a terrestrial species affect gas diffusion resistance and photosynthetic performance.

Gas exchange between the plant and the environment is severely hampered when plants are submerged, leading to oxygen and energy deficits. A straightforward way to reduce these shortages of oxygen and carbohydrates would be continued photosynthesis under water, but this possibility has received only little attention. Here, we combine several techniques to investigate the consequences of anatomical and biochemical responses of the terrestrial species Rumex palustris to submergence for different aspects of photosynthesis under water. The orientation of the chloroplasts in submergence-acclimated leaves was toward the epidermis instead of the intercellular spaces, indicating that underwater CO(2) diffuses through the cuticle and epidermis. Interestingly, both the cuticle thickness and the epidermal cell wall thickness were significantly reduced upon submergence, suggesting a considerable decrease in diffusion resistance. This decrease in diffusion resistance greatly facilitated underwater photosynthesis, as indicated by higher underwater photosynthesis rates in submergence-acclimated leaves at all CO(2) concentrations investigated. The increased availability of internal CO(2) in these "aquatic" leaves reduced photorespiration, and furthermore reduced excitation pressure of the electron transport system and, thus, the risk of photodamage. Acclimation to submergence also altered photosynthesis biochemistry as reduced Rubisco contents were observed in aquatic leaves, indicating a lower carboxylation capacity. Electron transport capacity was also reduced in these leaves but not as strongly as the reduction in Rubisco, indicating a substantial increase of the ratio between electron transport and carboxylation capacity upon submergence. This novel finding suggests that this ratio may be less conservative than previously thought.

Intersex inflorescences of Rumex acetosa demonstrate that sex determination is unique to each flower.

* A triploid intersex individual of the normally dioecious species Rumex acetosa showed extreme variability in gynoecium development. Analysis of the development and distribution of these flowers on inflorescences enabled insight to be gained into the mechanism of sex determination. * Floral phenotypes on intersex inflorescences were classified according to gynoecium development. Flower morphology was investigated by scanning electron and light microscopy. Organ identity gene expression in intersex floral primordia was assessed using in situ hybridization. * The distribution of the different floral phenotypes shows that each individual flower is determined separately, and that the phenotype of each flower is not influenced by its position on the inflorescence, or by the phenotype of neighbouring flowers. C-function gene expression persisted in gynoecia that had ceased development. * Gynoecium development in mutant flowers resembled the phenotype of the Arabidopsis mutant ettin and suggests that a hormone gradient may be involved. C-function expression does not appear to control the extent of female development, and indicates that genes which are downstream of the organ-identity genes must control organ suppression.