Plant Xanthium Strumarium Research Articles

Phytochemical Profiling and Antibacterial Dynamics of Xanthium strumarium L Extract: Unlocking Potential Therapeutic Pathways

This investigation focuses on the analysis of the chemical constituents and possible therapeutic effects of extracts derived from botanical sources. The research entails a quantitative evaluation of phenolic compounds, alkaloids, carotenoids and tannins present in an ethanolic extract from the aerial components of the plant Xanthium strumarium L. Analytical results indicate a considerable presence of these phytochemicals within the extract, with phenolics, alkaloids and carotenoids as predominant constituents. Phenolic compounds represent 19% of the extract, notable for their role in antioxidative activities which are critical in scavenging free radicals and may contribute to lowering the incidence of chronic diseases. Alkaloids, accounting for 12% of the extract, have been recognized for their wide-ranging pharmacological actions. Carotenoids, which constitute 25% of the extract, suggest the extract's potential as a nutraceutical agent for health enhancement and disease prophylaxis. The study underscores the significant levels of these bioactive molecules, reflecting a phytochemical matrix with potential for antioxidative, anti-inflammatory and extensive pharmacological utilities. Additionally, the manuscript investigates the in vitro antibacterial efficacy of the Xanthium extract against various bacterial pathogens. By assessing the extract's minimum inhibitory concentration (MIC) and zone of inhibition (ZOI) and comparing these parameters to those of tetracycline, a standard antibiotic, the research delineates a concentration-dependent antibacterial activity of the extract. It is noteworthy that an increase in the extract's concentration resulted in a reduction in MIC and an augmentation in ZOI, particularly against E. coli and S. aureus, suggesting the extract's potential as an antibacterial agent.

Histochemical analysis of Xanthium strumarium raw materials, growing on the territory of Kazakhstan

Histochemical analysis of medicinal plants and raw materials is designed to study the localization of various chemical substances and metabolic products in their tissues. The article presents the results of a histochemical analysis of leaves, stems, roots and fruits of a promising medicinal plant Xanthium strumarium, the herb of which is used in folk medicine to treat iodine deficiency. Goal. Determination of the features of localization of individual groups of biologically active substances in the aerial and underground organs of Xanthium strumarium, growing on the territory of Kazakhstan. Materials and methods. Materials for the study: cross sections of the stem; cross and superficial sections of leaves; cross sections of the root and the surface preparation of Xanthium strumarium’s fruit. Samples of raw materials were fixed in Strauss-Fleming solution, cross sections were prepared manually, after which histochemical reactions were carried out to locate and identify the following biologically active substances: essential oil, starch, flavonoids, polysaccharides, sesquiterpene lactones and alkaloids. The study of microscopic features, as well as histochemical tests, was carried out according to the methods of the State Pharmacopoeia of the Republic of Kazakhstan using a “Biomed-4” light microscope. Results: By histochemical methods using light microscopy determined the localization of biologically active substances in plant raw materials. The presence of essential oil, flavonoids, alkaloids, polysaccharides and sesquiterpene lactones on cross sections of the leaf, stem, root and fruit was established. The accumulation of starch in all organs of the plant has not been established. Conclusion: For the first time, by histochemical tests, the localization of biologically active substances in the tissues of Xanthium strumarium were studied. The results of histochemical studies can be used to confirm the authenticity, identification and standardization of the aerial and underground parts of Xanthium strumarium.

Green Synthesis and Characterization of Xanthium strumarium-Mediated Titanium Dioxide Nanoparticles.

Background Green synthesis of nanoparticles is a growing trend. The annual plant Xanthium strumarium L. (X. strumarium) belongs to the Asteraceae family. The herb has traditionally been used to treat a variety of ailments, including leucoderma, dangerous insect bites, epilepsy, salivation, allergic rhinitis, sinusitis, etc.Inorganic, biocompatible, and non-toxic titanium is a substance employed in the pharmaceutical and biomedical industries as well as in fields like bone tissue engineering. The aim of the study is to characterize titanium dioxidenanoparticles (TiO₂NPs), which were synthesized from X.strumarium. Also, this study aims to assess the cytotoxic properties of the synthesized leaf extract and the TiO₂NPs. Materials and methods In this study, the biosynthesis of TiO₂NPs was made from X. strumarium leaf extract. The characterization of the green-synthesized TiO₂NPswas done using the spectral analysis of an ultraviolet (UV)-visible spectrophotometer, scanning electron microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR). The advantage of usingTiO₂NPs is that they possess antimicrobial,antibacterial, chemical stability, and catalytic properties.The leaf extract and the biosynthesized nanoparticles were tested against human fibroblast cell lines for biocompatibility using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Results SEM investigation showed that TiO₂NPs were crystalline in nature. FTIR confirms the presence of alkyne and amine functional groups, and the pointed vertices in the X-ray diffraction(XRD) pattern show the crystalline nature of TiO2NPs. The study found that the cell viability of TiO₂NPs was 110%. Conclusion TiO₂NPs were synthesized from X. strumarium leaf extract and characterized usingSEM, FTIR, and XRD. The TiO₂NPs were found to be crystalline in nature with various functional groups. MTT assay shows that the synthesized nanoparticles are promising biocompatibleagents that can be used in future research in the medical field.

Transgenerational plasticity in morphological characteristics and biomass of the invasive plant Xanthium strumarium.

Transgenerational plasticity (TGP) allows a plant to acclimate to external variable environments and is a potential mechanism that explains the range expansion and invasion success of some exotic plants. Most studies explored the traits of TGP associated with the success of exotic plant invasions by comparison studies among exotic, native, invasive, and noninvasive species. However, studies on the TGP of invasive plants in different resource environments are scarce, and the biological mechanisms involved are not well understood. This study aimed to determine the role of TGP in the invasiveness of Xanthium strumarium in northeast China. We measured the plant morphology of aboveground parts and the growth of three generations of the invader under different environmental conditions. The results showed that the intergenerational plasticity of X. strumarium was stronger under stress conditions. We found that the X. strumarium parent generation (F0) grown under water and/or nutrient deficiency conditions transferred the environmental information to their offspring (F1 and F2). The F1 generation grown under high-resource conditions has greater height with larger crown sizes, thicker basal diameters, and higher biomass. Both water and nutrients can affect the intergenerational transmission of plant plasticity, nutrients play a more important role compared with water. The high morphological intergenerational plasticity of X. strumarium under a pressure environment can help it quickly adapt to the new environment and accelerate the rapid expansion of the population in the short term. The root:shoot ratio and reproductive and nutrient distribution of the X. strumarium F0 and F1 generations showed high stability when the growth environment of the F0 generation differed from that of the F1 generation. The stable resource allocation strategy can ensure that the obtained resources are evenly distributed to each organ to maintain the long-term existence of the community. Therefore, the study of intergenerational transmission plasticity is of great significance for understanding the invasion process, mechanism, and prevention of invasive plants.

Molecular bases for the stronger plastic response to high nitrate in the invasive plant Xanthium strumarium compared with its native congener.

High expressions of nitrate use and photosynthesis-related transcripts contribute to the stronger plasticity to high nitrate for the invader relative to its native congener, which may be driven by hormones. Strong phenotypic plasticity is often considered as one of the main mechanisms underlying exotic plant invasions. However, few studies have been conducted to investigate the related molecular mechanisms. Here, we determined the differences in the plastic responses to high nitrate between the invasive plant X. strumarium and its native congener, and the molecular bases by transcriptome analysis and quantitative real-time PCR validation. Our results showed that the invader had higher plasticity of growth, nitrogen accumulation and photosynthesis in responses to high nitrate than its native congener. Compared with its congener, more N utilization-related transcripts, including nitrate transporter 1/peptide transporter family 6.2 and nitrate reductase 1, were induced by high nitrate in the root of X. strumarium, improving its N utilization ability. More transcripts coding for photosynthetic antenna proteins were also induced by high nitrate in the shoot of X. strumarium, enhancing its photosynthesis. Hormones may be involved in the regulation of the plastic responses to high nitrate in the two species. Our study contributes to understanding the molecular mechanisms underlying the stronger plasticity of the invader in responses to high nitrate, and the potential function of plant hormones in these processes, providing bases for precise control of invasive plants using modern molecular techniques.

Transcripts related with ammonium use and effects of gibberellin on expressions of the transcripts responding to ammonium in two invasive and native Xanthium species.

Soil nitrogen forms are important for exotic plant invasions. However, little effort has been made to study the molecular mechanisms underlying the utilization of different N forms in co-occurring invasive and native plants. The invasive plant Xanthium strumarium prefers nitrate relative to ammonium, and mainly invades nitrate-dominated environments, while it co-occurring native congener X. sibiricum prefers ammonium. Here, we addressed the genetic bases for the interspecific difference in ammonium use and the effects of gibberellin (GA). Twenty-six transcripts related with GA biosynthesis and ammonium utilization were induced by ammonium in X. sibiricum, while only ten in X. strumarium and none for ammonium uptake. XsiAMT1.1a, XsiGLN1.1 and XsiGLT1b may be crucial for the strong ability to absorb and assimilate ammonium in X. sibiricum. All tested transcripts were significantly up-regulated by GA1 and GA4 in X. sibiricum. XsiGA3OX1a, which was also induced by ammonium, may be involved in this regulation. Consistently, glutamine synthetase activity increased significantly with increasing ammonium-N/nitrate-N ratio for X. sibiricum, while decreased for X. strumarium. Our study is the first to determine the molecular mechanisms with which invasive and native plants use ammonium differently, contributing to understanding the invasion mechanisms of X. strumarium and its invasion habitat selection.

Differences and related physiological mechanisms in effects of ammonium on the invasive plant Xanthium strumarium and its native congener X. sibiricum.

Few studies explore the effects of nitrogen forms on exotic plant invasions, and all of them are conducted from the perspective of nitrogen form utilization without considering the effects of ammonium toxicity. The invasive plant Xanthium strumarium prefers to use nitrate, while its native congener X. sibiricum prefers to use ammonium, and the invader is more sensitive to high ammonium based on our preliminary observations. To further reveal the effects of nitrogen forms on invasiveness of X. strumarium, we studied the difference and related physiological mechanisms in sensitivity to ammonium between these species. With increasing ammonium, total biomass, root to shoot ratio and leaf chlorophyll content of X. strumarium decreased, showing ammonium toxicity. For X. sibiricum, however, ammonium toxicity did not occurr. With increasing ammonium, ammonium concentration increased in leaves and roots of X. strumarium, which is associated with the decreased activities of glutamine synthetase and glutamate synthase and the increased ammonium uptake; and consequently the contents of hydrogen peroxide and malondialdehyde also increased, which is associated with the decreased contents of reduced glutathione and ascorbic acid. By contrast, the abilities of ammonium assimilation and antioxidation of X. sibiricum were less affected by the increase of ammonium, and the contents of ammonium nitrogen, hydrogen peroxide and malondialdehyde in leaves and roots were significantly lower than those in X. strumarium. Our results indicate that ammonium accumulation and oxidative damage may be the physiological mechanisms for the ammonium toxicity of X. strumarium, providing a possible explanation that it generally invades nitrate-dominated and disturbed habitats and a theoretical basis for future studies on the control of invasive plants by regulating soil nitrogen.

Stronger ability to absorb nitrate and associated transporters in the invasive plant Xanthium strumarium compared with its native congener

Nitrogen (N) is the limiting factor for plant growth in natural ecosystems, and increasing soil N availability often promotes exotic plant invasions. However, few studies have considered the effects of N forms. In this study, we tested the hypothesis that Xanthium strumarium, a noxious invader in disturbed habitats (generally with nitrate as dominant soil N form), may have higher N uptake rates and therefore higher biomass production under nitrate treatments than its co-occurring native congener X. sibiricum. We also determined the nitrate transporters associated with the stronger nitrate uptake ability of the invader. We first compared N uptake rates and biomass production between and within these species under different N forms and levels, and then conducted the PacBio and HiSeq sequencings. Consistent with our hypothesis, the invader had significantly stronger nitrate uptake ability than its native congener and its own ammonium uptake ability. Similar patterns were also found for total biomass. Six of the seven highly expressed common NPF transcripts, especially XstNPF6.2a, XstNPF6.1b and XstNPF3.1a, and three highly expressed common NRT2 transcripts (XstNRT2.9c, XstNRT2.8c and XstNRT2.9d) may all contribute to the stronger nitrate uptake ability of the invader. The highly expressed unique transporters such as XstNPF6.2b, XstNPF6.1a, XstNPF6.2c, XstNPF6.2d, XstNPF5.2, XstNPF7.2, XstNRT2.5a, XstNRT2.4 and others may also contribute to the stronger nitrate uptake ability of the invader. Our results explain the mechanisms of interspecific differences in phenotypic plasticity and hence exotic plant invasions at a molecular level, and indicate that invasiveness of X. strumarium may be aggravated in the future under the background of global change.

Phytoremediation potential of hybrids of the exotic plant Xanthium strumarium and its native congener Xanthium sibiricum for cadmium-contaminated soils

Exotic plants could play an essential role in the restoration of heavy metal-contaminated soil. This study evaluated the tolerance of and extraction of cadmium (Cd) by ZCR (CR♀ × LT♂), hybrids of Xanthium strumarium (LT, exotic species) and X. sibiricum (CR, indigenous congener), and their parental species under different Cd treatments (0, 10, 40, and 80 mg·kg−1). The results showed that the hybrids had significantly improved tolerance to Cd. Under Cd stress, the biomass of ZCR increased by more than 50% on average compared with that of CR. Moreover, the hybrids showed a more remarkable ability to transport Cd from the root to the shoot. The Cd content of the shoots of ZCR increased by 128.33, 147.22, and 252.63% when treated with 10, 40, and 80 mg·kg−1 Cd, respectively. ZCR stored more than 70% of Cd in litter leaves, thereby reducing the toxic effects of Cd on photosynthesis and growth. The results showed that ZCR showed excellent Cd tolerance and enrichment in the presence of Cd. The hybrids of Xanthium strumarium and its native congener X. sibiricum may remediate soil Cd pollution. Novelty statement With the changing world economy and increasing human activities, exotic plants have become a global issue of common concern to the international community. This study describes new findings on using hybrids of the exotic plant of Xanthium strumarium and its native congener Xanthium sibiricum for the restoration of cadmium-contaminated soils. Under Cd stress, the hybrids' biomass, tolerance, and ability to accumulate Cd were significantly higher than that of X. sibiricum, indicating that hybrids gained useful heavy metal extraction traits from X. strumarium.

Ecological impacts of the invasive plant Xanthium strumarium and the impacts of three aboveground herbivores on the invader

Exotic plant invasions are generally assumed to negatively impact biodiversity of recipient communities. However, experimental evidence for this assumption is little, especially in developing countries. In addition, there is hardly applicable method to control invasive plants. Enemy release is often hypothesized to facilitate exotic plant invasions, thus re-association with natural enemies of invasive ranges may inhibit invasions of exotic plants, and these enemies may have the potential to be used as biological control agents for these invaders. To address above problems, we determined abundance of the invasive plant Xanthium strumarium, its impacts on co-occurring native plants, and abundances of three herbivores and their impacts on the invader at five sites in the rice tract of Punjab, Pakistan. Relative abundance of the invader varied greatly among the study sites, ranging from 3.5% to 50.4%. The invader significantly reduced abundance of co-occurring native plants at all study sites, and their richness and evenness at some sites with high abundances of the invader. The polyphagous insects Phenacoccus solenopsis, Podisus maculiventris and Spodoptera frugiperda were all found on the invader (not on crops) at all study sites, which significantly reduced growth of the invader. The abundance of P. solenopsis on the invader was much higher than those of P. maculiventris and S. frugiperda. The abundances of the herbivores were significantly higher at sites with high relative to low relative abundances of the invader. Our study indicates that natural enemies may accumulate on invasive plants with the increase of their abundance and/or invasion time, inhibiting further invasions, and provides evidence for enemy release hypothesis. More studies are needed to determine whether these herbivores, especially P. solenopsis, could be used as biological control agents for the invader.

AMF colonization and community of a temperate invader and co-occurring natives grown under different CO2 concentrations for 3 years

AbstractGlobal changes such as atmospheric CO2 enrichment often facilitate exotic plant invasions and alter soil arbuscular mycorrhizal fungi (AMF) community. However, it is still unclear whether the effects of CO2 enrichment on exotic plant invasions are associated with its effects on root-AMF symbiosis of invasive and native plants. To address this issue, the annual invasive plant Xanthium strumarium and two phylogenetically related annual natives were compared under ambient and elevated CO2 concentrations for three consecutive years. Atmospheric CO2 enrichment increased AMF colonization rates for the species only in few cases, and the invader did not benefit more from CO2 enrichment in terms of AMF colonization. Under ambient CO2 concentration, however, the invader had a higher AMF colonization rate than the natives in the first year of the study, which disappeared in the second and third year of the study due to the increase of AMF colonization rates in the natives but not in the invader. The influences of species, CO2 concentrations and planting year on AMF colonization were associated with their effects on both soil nutrient and AMF community, and the former may be more important as it also influenced the latter. Our results indicate that the invader could more quickly form symbiosis with soil AMF, contributing to adaptation and occupation of new habitats, and that it is necessary to consider the roles of AMF and the effects of time when determining the effects of global changes such as atmospheric CO2 enrichment on exotic plant invasions.

Determination of the chemical composition of the ground part of Xanthium Strumarium plants and isolation of pectin substances

This article defines the chemical composition and content of biologically active substances, macromicro elements of plants Xanthium strumarium. In addition, pectin substances were isolated from the ground part (stem and leaves) of the Xanthium strumarium plant; the composition and structure of pectin substances were determined by elemental analysis, IR, UV, NMR spectral methods.

Effects of the invasive plant Xanthium strumarium on diversity of native plant species: A competitive analysis approach in North and Northeast China.

Xanthium strumarium is native to North America and now has become one of the invasive alien species (IAS) in China. In order to detect the effects of the invader on biodiversity and evaluate its suitable habitats and ecological distribution, we investigated the abundance, relative abundance, diversity indices, and the number of the invasive and native plants in paired invaded and non-invaded quadrats in four locations in North and Northeast China. We also analyzed the effects of monthly mean maximum and minimum temperatures, relative humidity (%), and precipitations (mm). Strong positive significant (P < 0.01) correlation and maximum interspecific competition (41%) were found in Huailai between invaded and non-invaded quadrats. Shannon’s Diversity Index showed that non-invaded plots had significantly (P < 0.05) more diversified species than invaded ones. The significant (P < 0.05) Margalef’s Richness Index was found in Huailai and Zhangjiakou in non-invaded recorded heterogeneous nature of plant communities. Similarly, significant (P < 0.05) species richness found in Huailai and Zhangjiakou in non-invaded quadrats compared to invaded ones. Maximum evenness of Setaria feberi (0.47, 0.37), Seteria viridis (0.43) found in Fushun and Zhangjiakou recorded more stable in a community compared to other localities. Evenness showed positive relationship of Shannon Entropy within different plant species. The higher dissimilarity in plant communities found in Huailai (87.06%) followed by Yangyuan (44.43%), Zhangjiakou (40.13%) and Fushun (29.02%). The significant (P < 0.01) value of global statistics R (0.943/94.3%) showed high species diversity recorded in Huailai followed by Zhangjiakou recorded by non-metric multidimensional scaling and analysis of similarity between invaded and non-invaded plots. At the end it was concluded that the diversity indices reduced significantly (P < 0.05) in invaded quadrats indicated that native plant species become less diverse due to X. strumarium invasion. The degrees of X. strumarium invasion affected on species richness resulted to reduce diversity indices significantly in invaded quadrats.

Early Identification of Herbicide Modes of Action by the Use of Chlorophyll Fluorescence Measurements.

The effect of seven herbicides (U-46 Combi Fluid, Cruz, MR, Basagran Bromicide, Lumax, and Gramoxone) on Xanthium strumarium plants was studied. Chlorophyll content and fluorescence, leaf temperature, and stomatal conductance were evaluated at 12 h, 36 h, 60 h, and 84 h after herbicides application. U46 Combi Fluid, Cruz, and MR did not have a significant effect on chlorophyll fluorescence induction curves as compared to the control treatment. However, Basagran, Bromicide, Lumax, and Gramoxone showed significant changes in the shape of polyphasic fluorescence transients (OJIP transients). Variations in chlorophyll content index, leaf temperature, and stomatal conductance parameters were dependent on the type of applied herbicide. Our study revealed that the specific impact of the applied herbicides on the photosynthetic efficiency of plants is related to their chemical groups and their mechanism of action.

Differential microRNA Analysis of Glandular Trichomes and Young Leaves in Xanthium strumarium L. Reveals Their Putative Roles in Regulating Terpenoid Biosynthesis.

The medicinal plant Xanthium strumarium L. (X. strumarium) is covered with glandular trichomes, which are the sites for synthesizing pharmacologically active terpenoids such as xanthatin. MicroRNAs (miRNAs) are a class of 21–24 nucleotide (nt) non-coding RNAs, most of which are identified as regulators of plant growth development. Identification of miRNAs involved in the biosynthesis of plant secondary metabolites remains limited. In this study, high-throughput Illumina sequencing, combined with target gene prediction, was performed to discover novel and conserved miRNAs with potential roles in regulating terpenoid biosynthesis in X. strumarium glandular trichomes. Two small RNA libraries from leaves and glandular trichomes of X. strumarium were established. In total, 1,185 conserved miRNAs and 37 novel miRNAs were identified, with 494 conserved miRNAs and 18 novel miRNAs being differentially expressed between the two tissue sources. Based on the X. strumarium transcriptome data that we recently constructed, 3,307 annotated mRNA transcripts were identified as putative targets of the differentially expressed miRNAs. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis suggested that some of the differentially expressed miRNAs, including miR6435, miR5021 and miR1134, might be involved in terpenoid biosynthesis in the X. strumarium glandular trichomes. This study provides the first comprehensive analysis of miRNAs in X. strumarium, which forms the basis for further understanding of miRNA-based regulation on terpenoid biosynthesis.

Investigation of the antimicrobial activity of extracts from indigenous Xanthium strumarium plants against Phytophthora infestans

Investigation of the antimicrobial activity of extracts from indigenous Xanthium strumarium plants against Phytophthora infestans

Antiplasmodial activity of Xanthium strumarium against Plasmodium berghei-infected BALB/c mice

The present work was undertaken to evaluate the antiplasmodial activity of ethanolic leaves extract of traditional medicinal plant Xanthium strumarium in Plasmodium berghei-infected BALB/c mice along with phytochemical screening and acute toxicity test to support its traditional medicinal use as a malaria remedy. The ethanolic leaves extract of X. strumarium (ELEXS) 150, 250, 350 and 500mg/kg/day demonstrated dose-dependent chemosuppression during early and established infection long with significant (p < 0.001) repository activity. The oral administration of 500mg/kg/day concentration showed a maximum of 88.6% chemosuppression during early infection, which was more than that of the standard drug chloroquine (5mg/kg/day) with 88.3% chemosuppression. However, 60% mortality has been found in this group. The LD(50) of ELEXS was found to be 1.5g/kg/mouse. The administration of 350mg/kg/day concentration of extract have been found to exert 90.40% chemosuppression during repository infection, which was well comparable to standard drug pyrimethamine (1.2mg/kg/day) exerting 92.91% chemosuppression. The extract has been found to enhance mean survival time of mice from 21 to 26days with 250 and 350mg/kg/day concentrations, while 150mg/kg/day concentration has been found to sustain all the mice up to 29days which was similar to the employed standard drug chloroquine (5mg/kg/day). All these findings support the ethanopharmacological use of X. strumarium as malarial remedy and indicate the potential of plant for active antiplasmodial components.

Modeling the growth of individuals in plant populations: local density variation in a strand population of Xanthium strumarium (Asteraceae)

We studied the growth of individual Xanthium strumarium plants growing at four naturally occurring local densities on a beach in Maine: (1) isolated plants, (2) pairs of plants ≤1 cm apart, (3) four plants within 4 cm of each other, and (4) discrete dense clumps of 10-39 plants. A combination of nondestructive measurements every 2 wk and parallel calibration harvests provided very good estimates of the growth in aboveground biomass of over 400 individual plants over 8 wk and afforded the opportunity to fit explicit growth models to 293 of them. There was large individual variation in growth and resultant size within the population and within all densities. Local crowding played a role in determining plant size within the population: there were significant differences in final size between all densities except pairs and quadruples, which were almost identical. Overall, plants growing at higher densities were more variable in growth and final size than plants growing at lower densities, but this was due to increased variation among groups (greater variation in local density and/or greater environmental heterogeneity), not to increased variation within groups. Thus, there was no evidence of size asymmetric competition in this population. The growth of most plants was close to exponential over the study period, but half the plants were slightly better fit by a sigmoidal (logistic) model. The proportion of plants better fit by the logistic model increased with density and with initial plant size. The use of explicit growth models over several growth intervals to describe stand development can provide more biological content and more statistical power than "growth-size" methods that analyze growth intervals separately.

Changes in photon flux can induce stomatal patchiness

ABSTRACTImages of chlorophyll fluorescence were used to detect the occurrence of stomatal patchiness in leaves from eight species under variable photon flux conditions. Pronounced stomatal patchiness was induced within 5–10 min after PFD was changed from intermediate (∼450 μmol quanta m−2 s−1) to low (∼150 μmol quanta m−2 s−1) levels. This effect was completely reversible by returning PFD to intermediate levels. The pattern of heterogeneous fluorescence for each leaf was usually similar during repeated applications of medium and low PFD. In three species, stomatal patchiness could only be induced in slightly water‐stressed plants. Leaves of more severely water‐stressed Xanthium strumarium plants in low air humidity exhibited oscillations in fluorescence that corresponded with oscillatory changes in leaf diffusion conductance for water vapour. Stomatal patchiness was also induced by illuminating dark‐adapted leaves with low PFD (below 200–300 μmol quanta m−2 s−1). Infiltration of leaves with distilled water showed that heterogeneous chlorophyll fluorescence was caused by changes in stomatal apertures.

Shoot-root interactions during floral transition: A possible role for cytokinins

This review discusses the role of roots in the control of floral transition. Classical physiological understanding indicates that flowering and root initiation and/or elongation are usually antagonistic processes. In several species, root removal promotes flowering. High or low temperatures applied to the root system also influence flower initiation in some plants. These observations clearly implicate the root system as possessing at least partial control of flowering. In various species, the inhibitory effect of the root can be mimicked by cytokinins which are known to be produced by roots. A few studies revealed, however, that the effect of exogenous cytokinins is strongly dependent on other factors such as the applied concentration, the environmental conditions, and the time and site of application, and that promotion or inhibition can be observed. These findings indicate that there is a permissive range of cytokinin concentrations and that the endogenous status of the plant affects cytokinin action, which is not comparable in all plant organs. Studies with the long-day plant Sinapis alba and the short-day plant Xanthium strumarium suggested the existence of a shoot-to-root signal, which is under photoperiodic control and affects cytokinin synthesis in and/or release from the roots. As a results, cytokinin levels are altered in the plant; these changes, triggered by the inductive treatment, may be transient and are not necessarily similar in different plant organs. Remarkably, in all species investigated, increases in cytokinin levels, most usually in buds or phloem sap, have been detected during the floral transition, suggesting that cytokinins could be required. A role as a mitotic stimulus is possible, as indicated by the work with Sinapis.