Comparative Analyses of the Self-Sealing Mechanisms in Leaves of Delosperma cooperi and Delosperma ecklonis (Aizoaceae).

Within the Aizoaceae, the genus Delosperma exhibits a vast diversification colonizing various ecological niches in South-Africa and showing evolutionary adaptations to dry habitats that might include rapid self-sealing. Leaves of Delosperma react to external damage by the bending or contraction of the entire leaf until wound edges are brought into contact. A study of leaf morphology and anatomy, biomechanics of entire leaves and individual tissues and self-sealing kinematics after a ring incision under low and high relative humidity (RH) was carried out comparing the closely related species Delosperma cooperi and Delosperma ecklonis, which are indigenous to semi-arid highlands and regions with an oceanic climate, respectively. For both species, the absolute contractions of the examined leaf segments ("apex", "incision", "base") were more pronounced at low RH levels. Independent of the given RH level, the absolute contractions within the incision region of D. cooperi were significantly higher than in all other segments of this species and of D. ecklonis. The more pronounced contraction of D. cooperi leaves was linked mainly to the elastic properties of the central vascular strand, which is approximately twice as flexible as that of D. ecklonis leaves.

Co-expression of SpSOS1 and SpAHA1 in transgenic Arabidopsis plants improves salinity tolerance.

BACKGROUND: Na+ extrusion from cells is important for plant growth in high saline environments. SOS1 (salt overly sensitive 1), an Na+/H+ antiporter located in the plasma membrane (PM), functions in toxic Na+ extrusion from cells using energy from an electrochemical proton gradient produced by a PM-localized H+-ATPase (AHA). Therefore, SOS1 and AHA are involved in plant adaption to salt stress. RESULTS: In this study, the genes encoding SOS1 and AHA from the halophyte Sesuvium portulacastrum (SpSOS1 and SpAHA1, respectively) were introduced together or singly into Arabidopsis plants. The results indicated that either SpSOS1 or SpAHA1 conferred salt tolerance to transgenic plants and, as expected, Arabidopsis plants expressing both SpSOS1 and SpAHA1 grew better under salt stress than plants expressing only SpSOS1 or SpAHA1. In response to NaCl treatment, Na+ and H+ in the roots of plants transformed with SpSOS1 or SpAHA1 effluxed faster than wild-type (WT) plant roots. Furthermore, roots co-expressing SpSOS1 and SpAHA1 had higher Na+ and H+ efflux rates than single SpSOS1/SpAHA1-expressing transgenic plants, resulting in the former amassing less Na+ than the latter. As seen from comparative analyses of plants exposed to salinity stress, the malondialdehyde (MDA) content was lowest in the co-transgenic SpSOS1 and SpAHA1 plants, but the K+ level was the highest. CONCLUSION: These results suggest SpSOS1 and SpAHA1 coordinate to alleviate salt toxicity by increasing the efficiency of Na+ extrusion to maintain K+ homeostasis and protect the PM from oxidative damage induced by salt stress.

C4-like photosynthesis and the effects of leaf senescence on C4-like physiology in Sesuvium sesuvioides (Aizoaceae).

Sesuvium sesuvioides (Sesuvioideae, Aizoaceae) is a perennial, salt-tolerant herb distributed in flats, depressions, or disturbed habitats of southern Africa and the Cape Verdes. Based on carbon isotope values, it is considered a C4 species, despite a relatively high ratio of mesophyll to bundle sheath cells (2.7:1) in the portulacelloid leaf anatomy. Using leaf anatomy, immunocytochemistry, gas exchange measurements, and enzyme activity assays, we sought to identify the biochemical subtype of C4 photosynthesis used by S. sesuvioides and to explore the anatomical, physiological, and biochemical traits of young, mature, and senescing leaves, with the aim to elucidate the plasticity and possible limitations of the photosynthetic efficiency in this species. Assays indicated that S. sesuvioides employs the NADP-malic enzyme as the major decarboxylating enzyme. The activity of C4 enzymes, however, declined as leaves aged, and the proportion of water storage tissue increased while air space decreased. These changes suggest a functional shift from photosynthesis to water storage in older leaves. Interestingly, S. sesuvioides demonstrated CO2 compensation points ranging between C4 and C3-C4 intermediate values, and immunocytochemistry revealed labeling of the Rubisco large subunit in mesophyll cells. We hypothesize that S. sesuvioides represents a young C4 lineage with C4-like photosynthesis in which C3 and C4 cycles are running simultaneously in the mesophyll.

Revealing mechanisms of salinity tissue tolerance in succulent halophytes: A case study for Carpobrotus rossi.

Efforts to breed salt tolerant crops could benefit from investigating previously unexplored traits. One of them is a tissue succulency. In this work, we have undertaken an electrophysiological and biochemical comparison of properties of mesophyll and storage parenchyma leaf tissues of a succulent halophyte species Carpobrotus rosii ("pigface"). We show that storage parenchyma cells of C. rossii act as Na+ sink and possessed both higher Na+ sequestration (298 vs. 215 mM NaCl in mesophyll) and better K+ retention ability. The latter traits was determined by the higher rate of H+ -ATPase operation and higher nonenzymatic antioxidant activity in this tissue. Na+ uptake in both tissues was insensitive to either Gd3+ or elevated Ca2+ ruling out involvement of nonselective cation channels as a major path for Na+ entry. Patch-clamp experiments have revealed that Caprobrotus plants were capable to downregulate activity of fast vacuolar channels when exposed to saline environment; this ability was higher in the storage parenchyma cells compared with mesophyll. Also, storage parenchyma cells have constitutively lower number of open slow vacuolar channels, whereas in mesophyll, this suppression was inducible by salt. Taken together, these results provide a mechanistic basis for efficient Na+ sequestration in the succulent leaf tissues.

Sodium chloride decreases cadmium accumulation and changes the response of metabolites to cadmium stress in the halophyte Carpobrotus rossii.

Background and Aims: Salinity affects the bioavailability of cadmium (Cd) in soils and Cd accumulation in plants, but the associated mechanisms remain unclear. This study aimed to assess the metabolic response to NaCl and Cd and the relationship between metabolites and Cd accumulation in the halophyte Carpobrotus rossii, which has potential for Cd phytoextraction. Methods: Plants were grown in nutrient solution with 0-400 mm NaCl in the presence of 5 or 15 µm Cd, with varied or constant solution Cd2+ activity. Plant growth and Cd uptake were measured, and the accumulation of peptides, and organic and amino acids in plant tissues were assessed. Key Results: The addition of NaCl to Cd-containing solutions improved plant growth along with 70-87 % less shoot Cd accumulation, resulting from decreases in Cd root uptake and root-to-shoot translocation irrespective of Cd2+ activity in solutions. Moreover, Cd exposure increased the concentration of phytochelatins, which correlated positively with Cd concentrations in plants regardless of NaCl addition. In comparison, Cd inhibited the synthesis of organic acids in shoots and roots in the absence of NaCl, but increased it in shoots in the presence of NaCl. While Cd increased the concentrations of amino acids in plant shoots, the effect of NaCl on the synthesis of amino acids was inconsistent. Conclusions: Our data provide the first evidence that NaCl decreased Cd shoot accumulation in C. rossii by decreasing Cd root uptake and root-to-shoot translocation even under constant Cd2+ activity. The present study also supports the important role of peptides and organic acids, particular of phytochelatins, in Cd tolerance and accumulation although the changes of those metabolites was not the main reason for the decreased Cd accumulation.

Reproductive heat tolerance in a Mojave Desert annual plant, Trianthema portulacastrum.

PREMISE OF THE STUDY: Reproduction in many crop species is impaired above 30° to 35°C; however, the sensitivity of reproduction in the natural flora remains uncertain. Studies focusing on the effect of high temperature on plant reproduction in wild species are necessary to improve our understanding of how rising global temperatures will impact global plant reproductive success and may ultimately inform models of plant distribution in the future. Additionally, these studies may highlight candidates for thermotolerance that could be further explored for crop improvement. METHODS: We studied reproductive heat tolerance in Trianthema portulacastrum, a weedy species found in hot microsites throughout the tropics and subtropics. Plants were grown at seven day/night temperature combinations: 30°/24°C, 33°/24°C, 36°/24°C, 40°/24°C, 44°/24°C, 24°/40°C, and 40°/40°C to study the effect of both high-day and high-night temperatures. The reproductive parameters measured include anther dehiscence, pollen viability, germination, ovule number, and seed set. KEY RESULTS: Pollen viability and germination declined with increasing daytime temperature up to 44°C, but this did not affect fruit production or seed set. Seed set was reduced under high night temperature. Continuous high temperature over the day and night (40°C day/40°C night) decreased pollen viability by half and reduced seed set by two-thirds. CONCLUSIONS: Our results demonstrate Trianthema portulacastrum has much higher reproductive thermotolerance than commonly identified in crop species, and though inhibited, can retain fecundity at 40°C. Through a combination of night escape and increased thermal tolerance, it maintains fertility in the hot microsites of its natural environment.

Contrasting phenotypic plasticity in the photoprotective strategies of the invasive species Carpobrotus edulis and the coexisting native species Crithmum maritimum.

Photoprotective strategies vary greatly within the plant kingdom and reflect a plant's physiological status and capacity to cope with environment variations. The plasticity and intensity of these responses may determine plant success. Invasive species are reported to show increased vigor to displace native species. Describing the mechanisms that confer such vigor is essential to understanding the success of invasive species. We performed an experiment whereby two species were monitored: Carpobrotus edulis, an aggressive invasive species in the Mediterranean basin, and Crithmum maritimum, a coexisting native species in the Cap de Creus Natural Park (NE Spain). We analyzed their photoprotective responses to seasonal environmental dynamics by comparing the capacity of the invader to respond to the local environmental stresses throughout the year. Our study analyses ecophysiological markers and photoprotective strategies to gain an insight into the success of invaders. We found that both species showed completely different but effective photoprotective strategies: in summer, C. edulis took special advantage of the xanthophyll cycle, whereas the success of C. maritimum in summer stemmed from morphological changes and alterations on ß-carotene content. Winter also presented differences between the species, as the native showed reduced Fv /Fm ratios. Our experimental design allowed us to introduce a new approach to compare phenotypic plasticity: the integrated phenotypic plasticity index (PPint ), defined as the maximum Euclidian distance between phenotypes, using a combination of different variables to describe them. This index revealed significantly greater phenotypic plasticity in the invasive species compared to the native species.

Adaptive plasticity to heterogeneous environments increases capacity for division of labor in the clonal invader Carpobrotus edulis (Aizoaceae).

UNLABELLED: • PREMISE OF THE STUDY: Clonality has been proposed as an important mechanism favoring plant invasions, but few studies have been conducted to determine the role of clonal traits on successful invaders. An interesting trait associated with clonality is the capacity for division of labor. Division of labor requires a negative spatial correlation between the availabilities of two essential resources and ramet specialization for locally abundant resources to increase the overall performance of the clone. We hypothesized that the capacity for division of labor in the clonal invader Carpobrotus edulis will be selected in those clones from patchy environments where this trait could be an advantage.• METHODS: Morphological and physiological division of labor was compared between clones from coastal sand dunes (where nutrients and light show a negative spatial covariance) and from rocky coasts (where nutrients and light are homogenously distributed).• KEY RESULTS: Clones from coastal sand dunes showed a greater capacity than clones from rocky coasts for division of labor. Specialization for abundance was found at the morphological (biomass allocated to roots) and the physiological (photochemical efficiency) level.• CONCLUSIONS: The greater ability for division of labor in the patchy environment where the presence of this trait would be more beneficial demonstrates the existence of local adaptation and suggests that rapid evolution in clonal traits could be contributing to the success of the invader C. edulis. This study is one of the few showing that division of labor is under selection and is the first reporting adaptive division of labor of an aggressive invader.

Nitrate modulates the physiological tolerance responses of the halophytic species Sarcocornia fruticosa to copper excess.

Coexistence impact of pollutants of different nature on halophytes tolerance to metal excess has not been thoroughly examined, and plant functional responses described so far do not follow a clear pattern. Using the Cu-tolerant halophyte Sarcocornia fruticosa as a model species, we conducted a greenhouse experiment to evaluate the impact of two concentration of copper (0 and 12 mM CuSO4) in combination with three nitrate levels (2, 14 and 50 mM KNO3) on plant growth, photosynthetic apparatus performance and ROS-scavenging enzymes system. The results revealed that S. fruticosa was able to grow adequately even when exposed to high concentrations of copper and nitrate. This response was linked to the plant capacity to uptake and retain a large amount of copper in its roots (up to 1500 mg kg-1 Cu), preventing its transport to aerial parts. This control of translocation was further magnified with nitrate concentration increment. Likewise, although Cu excess impaired S. fruticosa carbon assimilation capacity, the plant was able to downregulate its light-harvesting complexes function, as indicated its lowers ETR values, especially at 12 mM Cu + 50 mM NO3. This downregulation would contribute to avoid excess energy absorption and transformation. In addition, this strategy of avoiding excess energy was accompanied by the upregulation of all ROS-scavenging enzymes, a response that was further enhanced by the increase in nitrate concentration. Therefore, we conclude that the coexistence of nitrate would favor S. fruticosa tolerance to copper excess, and this effect is mediated by the combined activation of several tolerance mechanisms.

How succulent leaves of Aizoaceae avoid mesophyll conductance limitations of photosynthesis and survive drought.

In several taxa, increasing leaf succulence has been associated with decreasing mesophyll conductance (g M) and an increasing dependence on Crassulacean acid metabolism (CAM). However, in succulent Aizoaceae, the photosynthetic tissues are adjacent to the leaf surfaces with an internal achlorophyllous hydrenchyma. It was hypothesized that this arrangement increases g M, obviating a strong dependence on CAM, while the hydrenchyma stores water and nutrients, both of which would only be sporadically available in highly episodic environments. These predictions were tested with species from the Aizoaceae with a 5-fold variation in leaf succulence. It was shown that g M values, derived from the response of photosynthesis to intercellular CO2 concentration (A:C i), were independent of succulence, and that foliar photosynthate δ(13)C values were typical of C3, but not CAM photosynthesis. Under water stress, the degree of leaf succulence was positively correlated with an increasing ability to buffer photosynthetic capacity over several hours and to maintain light reaction integrity over several days. This was associated with decreased rates of water loss, rather than tolerance of lower leaf water contents. Additionally, the hydrenchyma contained ~26% of the leaf nitrogen content, possibly providing a nutrient reservoir. Thus the intermittent use of C3 photosynthesis interspersed with periods of no positive carbon assimilation is an alternative strategy to CAM for succulent taxa (Crassulaceae and Aizoaceae) which occur sympatrically in the Cape Floristic Region of South Africa.

Carbon and nitrogen stable isotope compositions provide new insights into the phenotypic plasticity of the invasive species Carpobrotus sp. pl. in different coastal habitats.

The genus Carpobrotus N.E.Br. comprises several aggressive invasive species that threaten biodiversity in coastal areas worldwide. We studied the phenotypic plasticity of Carpobrotus sp. pl. invading four coastal habitats in the north-western Iberian Peninsula (coastal cliffs, disturbed areas, dunes and coastal forests). We measured morphological traits and carbon (δ13C) and nitrogen (δ15N) stable isotope compositions of Carpobrotus sp. pl. individuals collected in each habitat. Our results indicated that leaf carbon content (% C) and dry shoot weight were higher on cliffs and lower in mixed forests. In contrast, leaf hydration was higher in mixed forests and lower on cliffs. Leaf nitrogen content (% N) was higher in forests, which might be due to the presence of Acacia longifolia, an alien tree that accumulates N in the soil through symbiotic associations with N fixing bacteria. Differences in δ15N showed the use of different N sources in each habitat. Values were higher in disturbed areas with greater human activity and lower on cliffs and forests. δ13C was higher in cliffs and dunes, suggesting CAM activity where drought and salinity are more intense. Water use efficiency (iWUE) and δ13C were higher on cliffs and dunes, suggesting an adaptation and high tolerance of Carpobrotus sp. pl. to unfavourable conditions such as drought or salinity in the invaded areas.

Variation in decomposition rates in the fynbos biome, South Africa: the role of plant species and plant stoichiometry.

Previous studies in the fynbos biome of the Western Cape, South Africa, have suggested that biological decomposition rates in the fynbos vegetation type, on poor soils, may be so low that fire is the main factor contributing to litter breakdown and nutrient release. However, the fynbos biome also comprises vegetation types on more fertile soils, such as the renosterveld. The latter is defined by the shrub Elytropappus rhinocerotis, while the shrub Galenia africana may become dominant in overgrazed areas. We examined decomposition of litter of these two species and the geophyte Watsonia borbonica in patches of renosterveld in an agricultural landscape. In particular, we sought to understand how plant species identity affects litter decomposition rates, especially through variation in litter stoichiometry. Decomposition (organic matter mass loss) varied greatly among the species, and was related to litter N and P content. G. africana, with highest nutrient content, lost 65% of its original mass after 180 days, while E. rhinocerotis had lost ca. 30%, and the very nutrient poor W. borbonica <10%. Litter placed under G. africana decomposed slightly faster than when placed under E. rhinocerotis. Over the course of the experiment, G. africana and E. rhinocerotis lost N and P, while W. borbonica showed strong accumulation of these elements. Decomposition rates of G. africana and E. rhinocerotis were substantially higher than those previously reported from fynbos vegetation, and variation among the species investigated was considerable. Our results suggest that fire may not always be the main factor contributing to litter breakdown and nutrient release in the fynbos biome. Thus, biological decomposition has likely been underestimated and, along with small-scale variation in ecosystem processes, would repay further study.

Demographic analysis of an Israeli Carpobrotus population.

Carpobrotus species are harmful invaders to coastal areas throughout the world, particularly in Mediterranean habitats. Demographic models are ideally suited to identify and understand population processes and stages in the life cycle of the species that could be most effectively targeted with management. However, parameterizing these models has been limited by the difficulty in accessing the cliff-side locations where its populations are typically found, as well as accurately measuring the growth and spread of individuals, which form large, dense mats. This study uses small unmanned aerial vehicles (drones) to collect demographic data and parameterize an Integral Projection Model of an Israeli Carpobrotus population. We validated our data set with ground targets of known size. Through the analysis of asymptotic growth rates and population sensitivities and elasticities, we demonstrate that the population at the study site is demographically stable, and that reducing the survival and growth of the largest individuals would have the greatest effect on reducing overall population growth rate. Our results provide a first evaluation of the demography of Carpobrotus, a species of conservation and economic concern, and provide the first structured population model of a representative of the Aizoaceae family, thus contributing to our global knowledge on plant population dynamics. In addition, we demonstrate the advantages of using drones for collecting demographic data in understudied habitats such as coastal ecosystems.

Unmatched tempo of evolution in Southern African semi-desert ice plants.

The Succulent Karoo is an arid region, situated along the west coast of southern Africa. Floristically this region is part of the Greater Cape Flora and is considered one of the Earth's 25 biodiversity hotspots. Of about 5,000 species occurring in this region, more than 40% are endemic. Aizoaceae (ice plants) dominate the Succulent Karoo both in terms of species numbers (1,750 species in 127 genera) and density of coverage. Here we show that a well-supported clade within the Aizoaceae, representing 1,563 species almost exclusively endemic to southern Africa, has diversified very recently and very rapidly. The estimated age for this radiation lies between 3.8 and 8.7 million years (Myr) ago, yielding a per-lineage diversification rate of 0.77-1.75 per million years. Both the number of species involved and the tempo of evolution far surpass those of any previously postulated continental or island plant radiation. Diversification of the group is closely associated with the origin of several morphological features and one anatomical feature. Because species-poor clades lacking these features occur over a very similar distribution area, we propose that these characteristics are key innovations that facilitated this radiation.

Reproductive load modulates drought stress response but does not compromise recovery in an invasive plant during the Mediterranean summer.

Despite summer drought may challenge plant survival in Mediterranean-type ecosystems, the role of reproductive load on drought stress and recovery has been poorly studied in invasive plants, most particularly under natural field conditions. In this study, a highly plastic clonal invasive species, Carpobrotus edulis was used to explore a putative differential response to drought between reproductive (senescent) ramets and non-reproductive ramets. Furthermore, fruit removal was used to assess how alterations on the source-sink dynamics influence plant performance during drought stress and recovery. We examined the variations in chloroplast pigments, antioxidants, lipid peroxidation and cytokinins in leaves of non-reproductive and reproductive ramets (either with intact or fruit-removed ramets) in response to summer drought stress and recovery after rains under Mediterranean field conditions. Results showed that although both ramet types within a C. edulis patch recovered at the end of the summer, increased photoprotective investment was found in leaves from reproductive ramets, thus indicating an increased photoprotective demand associated with reproduction at the ramet level. This response was associated with differentiated cytokinin contents in leaves of reproductive ramets compared to those of non-reproductive ramets. Although leaf senescence was not reversed by the fruit removal, leaves recovered their chlorophyll content after rainfall during late summer in parallel with the accumulation of cytokinins. In conclusion, C. edulis shows a huge plasticity in drought stress responses with a marked compartmentation at the ramet level, which helps at least in part to an efficient recovery from unpredictable water shortage periods in the current frame of climate change.

Comparative physiological and proteomic analyses of the chloroplasts in halophyte Sesuvium portulacastrum under differential salt conditions.

Sesuvium portulacastrum, an important mangrove-associated true halophyte belongs to the family Aizoaceae, has excellent salt tolerance. Chloroplasts are the most sensitive organelles involved in the response to salinity. However, the regulation mechanism of chloroplasts of S. portulacastrum under salinity stress has not been reported. In this study, morphological and physiological analyses of leaves and comparative proteomics of chloroplasts isolated from the leaves of S. portulacastrum under different NaCl treatments were performed. Our results showed that the thickness of the palisade tissue, the leaf area, the maximum photochemical efficiency of photosystem II, and the electron transport rate increased remarkably after the plants were subjected to differential saline environments, indicating that salinity can increase photosynthetic efficiency and improve the growth of S. portulacastrum. Subsequently, 55 differentially expressed protein species (DEPs) from the chloroplasts of S. portulacastrum under differential salt conditions were positively identified by mass spectrometry. These DEPs were involved in multiple metabolic pathways, such as photosynthesis, carbon metabolism, ATP synthesis and the cell structure. Among these DEPs, the abundance of most proteins was induced by salt stress. Based on a combination of the morphological and physiological data, as well as the chloroplast proteome results, we speculated that S. portulacastrum can maintain photosynthetic efficiency and growth by maintaining the stability of the photosystem II complex, promoting the photochemical reaction rate, enhancing carbon fixation, developing plastoglobules, and preserving the biomembrane system of chloroplasts under salt stress.

Metabolomic insights into the mechanisms underlying tolerance to salinity in different halophytes.

Salinity is among the most detrimental and diffuse environmental stresses. Halophytes are plants that developed the ability to complete their life cycle under high salinity. In this work, a mass spectrometric metabolomic approach was applied to comparatively investigate the secondary metabolism processes involved in tolerance to salinity in three halophytes, namely S. brachiata, S. maritima and S. portulacastrum. Regarding osmolytes, the level of proline was increased with NaCl concentration in S. portulacastrum and roots of S. maritima, whereas glycine betaine and polyols were accumulated in S. maritima and S. brachiata. Important differences between species were also found regarding oxidative stress balance. In S. brachiata, the amount of flavonoids and other phenolic compounds increased in presence of NaCl, whereas these metabolites were down regulated in S. portulacastrum, who accumulated carotenoids. Furthermore, distinct impairment of membrane lipids, hormones, alkaloids and terpenes was observed in our species under salinity. Finally, several other nitrogen containing compounds were involved in response to salinity, including amino acids, serotonin and polyamine conjugates. In conclusion, metabolomics highlighted that the specific mechanism each species adopted to achieve acclimation to salinity differed in the three halophytes considered, although response osmotic stress and oxidative imbalance have been confirmed as the key processes underlying NaCl tolerance.

The functional identification of glycine-rich TtASR from Tetragonia tetragonoides (Pall.) Kuntze involving in plant abiotic stress tolerance.

In this study, we reported on an ASR gene (TtASR) related to salt/drought tolerance from the edible halophyte Tetragonia tetragonoides (Pall.) Kuntze (Aizoaceae). A phylogenetic analysis revealed that TtASR was evolutionarily close to other two halophytic glycine-rich ASR members, SbASR-1 (from Salicornia brachiate) and SlASR (from Suaeda liaotungensis), with a typical abscisic acid (ABA)/water-deficit stress (WDS) domain at C-terminal. Quantitative RT-PCR analyses showed that TtASR was expressed in all tested different organs of the T. tetragonoides plant and that expression levels were apparently induced after salt, osmotic stress, and ABA treatments in T. tetragonoides seedlings. An induction of TtASR improved the growth performance of yeast and bacteria more than the control under high salinity, osmotic stress, and oxidative stress. TtASR was not a nuclear-specific protein in plant, and the transcriptional activation assay also demonstrated that TtASR could not activate reporter gene's expression in yeast. TtASR overexpressed Arabidopsis plants exhibited higher tolerance for salt/drought and oxidative stresses and lower ROS accumulation than wild type (WT) plants, accompanied by increased CAT, SOD activities, higher proline content, and lower MDA content in vivo. The results indicated that the TtASR was involved in plant responses to salt and drought, probably by mediating water homeostasis or by acting as ROS scavengers, and that it decreased the membrane damage and improved cellular osmotic adjustment that respond to abiotic stresses in microorganisms and plants.

High invasive pollen transfer, yet low deposition on native stigmas in a Carpobrotus-invaded community.

BACKGROUND AND AIMS: Invasive plants are potential agents of disruption in plant-pollinator interactions. They may affect pollinator visitation rates to native plants and modify the plant-pollinator interaction network. However, there is little information about the extent to which invasive pollen is incorporated into the pollination network and about the rates of invasive pollen deposition on the stigmas of native plants. METHODS: The degree of pollinator sharing between the invasive plant Carpobrotus affine acinaciformis and the main co-flowering native plants was tested in a Mediterranean coastal shrubland. Pollen loads were identified from the bodies of the ten most common pollinator species and stigmatic pollen deposition in the five most common native plant species. KEY RESULTS: It was found that pollinators visited Carpobrotus extensively. Seventy-three per cent of pollinator specimens collected on native plants carried Carpobrotus pollen. On average 23 % of the pollen on the bodies of pollinators visiting native plants was Carpobrotus. However, most of the pollen found on the body of pollinators belonged to the species on which they were collected. Similarly, most pollen on native plant stigmas was conspecific. Invasive pollen was present on native plant stigmas, but in low quantity. CONCLUSIONS: Carpobrotus is highly integrated in the pollen transport network. However, the plant-pollination network in the invaded community seems to be sufficiently robust to withstand the impacts of the presence of alien pollen on native plant pollination, as shown by the low levels of heterospecific pollen deposition on native stigmas. Several mechanisms are discussed for the low invasive pollen deposition on native stigmas.

Combined effects of long-term salinity and soil drying on growth, water relations, nutrient status and proline accumulation of Sesuvium portulacastrum.

The interaction between soil drying and salinity was studied in the perennial halophyte, Sesuvium portulacastrum. Rooted cuttings were individually cultivated for three months in silty-sandy soil under two irrigation modes: 100 and 25% of field capacity (FC). The amount of the evapotranspirated water was replaced by a nutrient solution containing either 0 or 100 mM NaCl. Whole-plant growth, leaf water content, leaf water potential (Psi(w)), and Na+, K+, and proline concentrations in the tissues were measured. When individually applied, both drought and salinity significantly restricted whole-plant growth, with a more marked effect of the former stress. However, the effects of the two stresses were not additive on whole-plant biomass or on leaf expansion. Root growth was more sensitive to salt than to soil drying, the latter being even magnified by the adverse impact of salinity. Leaf water content was significantly reduced following exposure to water-deficit stress, but was less affected in salt-treated plants. When simultaneously submitted to water-deficit stress and salinity, plants displayed higher values of water and potassium use efficiencies, leaf proline and Na+ concentrations, associated with lower leaf water potential (-1.87 MPa), suggesting the ability of S. portulacastrum to use Na+ and proline for osmotic adjustment.