Allelopathic effects of Eucalyptus extract and wood vinegar on germination and sprouting of rapeseed (Brassica rapa L.).

Eucalyptus plantations are usually characterized by low biodiversity due to allelopathy effects. Wood vinegar is considered a complex growth regulator that can promote plant growth at low concentrations. However, there is information scarcity about the co-application of eucalypt leaf water extract and wood vinegar on plants. This study aimed at clarifying whether wood vinegar can protect seed germination against suppression by eucalypt-induced allelopathy. We examined germination behavior and seedling elongation characteristics in rapeseed (Brassica rapa L.) treated with different solutions of wood vinegar and eucalypt leaf water extract. The results showed that eucalypt leaf water extracts, wood vinegar solutions, and their mixture allelopathically suppressed seed germination rate. After rapeseed sprouting, eucalypt leaf water extracts promoted root elongation, stem elongation, and fresh weight elongation. Malondialdehyde content was also lower under the influence of eucalypt leaf water extract. Mixture of high concentration of eucalypt leaf water extract and lower concentration of wood vinegar significantly promoted root elongation. Therefore, both eucalypt leaf water extract and wood vinegar are complex plant growth regulators, which can be used to inhibit or stimulate plants at different ontogenic stages. During the seed germination period, both eucalypt leaf extracts and wood vinegar could be used as weed inhibitors. Conversely, during the period of sprouting (seedling establishment), low concentrations of eucalypt leaf extracts and wood vinegar can promote growth.

Elevated ozone effects on potato leaf physiology, growth, and yield: a meta-analysis.

Potato is an important crop worldwide and threatened by various environmental stresses, including elevated ozone (e[O3]). Here, we conducted a meta-analysis to quantify the effect of e[O3] on potato plants and how it varies depending upon different experimental conditions. Regarding plant growth and biomass, e[O3] significantly decreased shoot biomass by 18% and belowground biomass by 35%, while it increased the leaf area index by 19% and total number of injured leaves by 146%. As for yield, e[O3] significantly decreased the total tuber number by 21%. A relatively pronounced effect of e[O3] on the stomatal conductance was observed when exposure lasted 31-60 days, which was significantly greater than that after exposure lasted 96-311 days. The overall quantity of leaves was mainly decreased by higher (100-150 ppb) than lower (30-80 ppb) concentrations of e[O3] compared to ambient O3. The effect of e[O3] on the total tuber number was significant mainly when exposure lasted 31-90 days and was greater in plants grown in growth chambers than those planted in open-top chambers and glasshouses. The effect of e[O3] stress on physiology, growth, and yield varied among cultivars, with some cultivars showing marked tolerance relative to other cultivars. The findings can guide strategies to manage the negative impacts of e[O3] stress on potato production.

Polyamines and hormesis: Making sense of a dose response dichotomy.

The diverse biological effects of polyamines (putrescine, spermidine and spermine) were reviewed in the context of hormesis in an integrative manner for the first time. The findings illustrate that each of these polyamines commonly induces hormetic dose responses in a wide range of biological models and types of cells for multiple endpoints in numerous plant species and animal models. Plant research emphasized preconditioning experimental studies in which the respective polyamines conferred some protection against the damaging effects of a broad range of environmental stressors such as drought, salinity, cold/heat, heavy metals and UV-damage in an hormetic manner. Polyamine-based animal hormesis studies emphasized biomedical endpoints such as longevity and neuroprotection. These findings have important biological and biomedical implications and should guide experimental designs of low dose investigations.

Moringa induces its beneficial effect via hormesis.

Moringa oleifera, a traditional Indian herb, is widely known for its capacity to induce antioxidant, anti-inflammatory and other chemoprotective effects in a broad range of biomedical models. These perspectives have led to an extensive number of studies using various moringa extracts to evaluate its capacity to protect biological systems from oxidative stress and to explore whether it could be used to slow the onset of numerous age-related conditions and diseases. Moringa extracts have also been applied to prevent damage to plants from oxidative and saline stresses, following hormetic dose­response patterns. The present paper provides the first integrated and mechanistically based assessment showing that moringa extracts commonly induce hormetic dose responses and that many, perhaps most, of the beneficial effects of moringa are due to its capacity to act as an hormetic agent.

Protective effects of alpha lipoic acid (ALA) are mediated by hormetic mechanisms.

The endogenous and dietary agent, alpha lipoic acid (ALA), is evaluated for its capacity to induce a broad spectrum of adaptive responses via hormetic dose responses and their underlying mechanisms. ALA was shown to induce hormetic effects in a wide range of experimental models within in vitro and in vivo experimental settings which included direct exposure and pre- and post-conditioning experimental protocols. The hormetic effects occur in a broad range of organ systems, including the brain, heart, kidney and other tissues, with possible public health and clinical/therapeutic applications linked to reducing the onset and progression of neurogenerative diseases and also in the preservation of sperm health and functionality during cryopreservation. This paper provides the first integrated assessment of ALA-induced hormetic dose responses. Underlying mechanisms that mediated the occurrence of ALA-induced hormetic effects involved the induction of low levels of ROS that activate key cell signaling antioxidant (e.g. Nrf2) pathways.

Rhodiola rosea and salidroside commonly induce hormesis, with particular focus on longevity and neuroprotection.

The biological effects of Rhodiola rosea extracts and one of its major constituents, salidroside, were evaluated for their capacity to induce hormesis/hormetic effects. The findings indicate that the Rhodiola rosea extracts and salidroside commonly induce hormetic dose responses within a broad range of biological models, cell types and across a broad range of endpoints, with particular emphasis on longevity and neuroprotective endpoints. This paper represents the first integrative documentation and assessment of Rhodiola rosea extracts and salidroside induction of hormetic effects. These findings have important biomedical applications and should have an important impact with respect to critical study design, dose selection and other experimental features.

Hormesis: wound healing and fibroblasts.

Hormetic dose responses are reported here to occur commonly in the dermal wound healing process, with the particular focus on cell viability, proliferation, migration and collagen deposition of human and murine fibroblasts with in vitro studies. Hormetic responses were induced by a wide range of substances, including endogenous agents, pharmaceutical preparations, plant-derived extracts including many well-known dietary supplements, as well as physical stressor agents such as low-level laser treatments. Detailed mechanistic studies have identified common signaling pathways and their cross-pathway communications that mediate the hormetic dose responses. These findings complement and extend a similar comprehensive assessment concerning the occurrence of hormetic dose responses in keratinocytes. These findings demonstrate the generality of the hormetic dose response for key wound healing endpoints, suggesting that the hormesis concept has a fundamental role in wound healing, with respect to guiding strategies for experimental evaluation as well as therapeutic applications.

Effects of elevated ozone on bacterial communities inhabiting the phyllo- and endo-spheres of rice plants.

To explore the effects of elevated ozone (O3) on microbial communities inhabiting phyllo- and endo-spheres of Japonica rice leaves, cultivars Nangeng 5055 (NG5055) and Wuyujing 27 (WYJ27) were grown in either charcoal-filtered air (CF) or elevated O3 (ambient O3 + 40 ppb, E-O3) in field open-top chambers (OTCs) during a growing season. E-O3 increased the values of the Shannon (43-80%) and Simpson (34-51%) indexes of the phyllo-and endo-spheric bacterial communities in NG5055. E-O3 also increased the values of the phyllosphere Simpson index by 58% and the endosphere Shannon index by 54% in WYJ27. Both diversity indexes positively correlated with the contents of nitrogen, phosphorus, magnesium, and soluble sugar, and negatively correlated with the contents of starch and condensed tannins. The leaf-associated bacterial community composition significantly changed in both rice cultivars under E-O3. Moreover, the leaf-associated bacterial communities in NG5055 were more sensitive to E-O3 than those in WYJ27. The chemical properties explained 70% and 98% of variations in the phyllosphere and endosphere bacterial communities, respectively, suggesting a predominant role of chemical status for the endospheric bacterial community. Most variation (57.3%) in the endosphere bacterial community assembly was explained by phosphorus. Gammaproteobacteria and Pantoea were found to be the most abundant class (63-76%) and genus (38-48%) in the phyllosphere and endosphere, respectively. E-O3 significantly increased the relative abundance of Bacteroidetes in the phyllosphere bacterial community and decreased the relative abundance of Gammaproteobacteria in the endophytic community. In conclusion, elevated O3 increased the diversity of bacterial communities of leaf phyllosphere and endosphere, and leaf chemical properties had a more pronounced effect on the endosphere bacterial community.

Biochar application improves karstic lime soil physicochemical properties and enzymes activity and enhances sweet tea seedlings physiological performance.

Karst lime soil, commonly found in rocky desert ecosystems of Southwest China, exhibits high pH, poor water retention, and intense erosion. To prevent further soil erosion and soil losses from these ecosystems, stabilization measures based on improved green infrastructure are needed. The present study aimed at elucidating the performance of sweet tea (Lithocarpus polystachyus) seedlings grown on this soil type upon biochar application. Biochar was classified into different particle sizes, viz. 0.25-0.5 mm (medium), 0.5-1 mm (coarse), 1-2 mm (gravel), and their mixture, and added at the concentrations of 1, 2, or 5% soil mass. The pH, moisture, and porosity of soil increased upon biochar application compared to control; however, soil bulk density significantly decreased. The activity of soil phosphatase was increased by biochar particle size. Biochar particle size and concentration significantly enhanced the soil organic carbon content, but they differently affected total and plant-available nutrients in the soil. Light-saturated photosynthesis was positively affected, while stomatal conductance, leaf transpiration, and the intercellular CO2 concentrations of sweet tea leaves were negatively affected by biochar particle size and/or concentration compared to control. Leaf chlorophyll and soluble protein contents were increased by biochar application. From these results, we conclude that biochar can improve soil properties and the performance of sweet tea seedlings grown on Karst lime soil. We suggest its application at a concentration of 2% soil mass for keeping a high physiological performance of sweet tea seedlings in this environment. The selection of the ideal particle size is context-specific and depends on the target outcome.

Human dental pulp stem cells and hormesis.

This paper represents the first assessment of hormetic dose responses by human dental pulp stem cells (hDPSCs) with particular emphasis on cell renewal (proliferation) and differentiation. Hormetic dose responses were commonly reported in this model, encompassing a broad range of chemicals, including principally pharmaceuticals (e.g., metformin and artemisinin), dietary supplements/extracts from medicinal plants (e.g., berberine, N-acetyl-L-cysteine, and ginsenoside Rg1) and endogenous agents (e.g., ATP, TNF-α). The paper assesses mechanistic foundations of the hDPSCs hormetic dose responses for both cell proliferation and cell differentiation, study design considerations, and therapeutic implications.

Exogenous application of melatonin to plants, algae, and harvested products to sustain agricultural productivity and enhance nutritional and nutraceutical value: A meta-analysis.

Melatonin is produced by plants, algae, and animals. Worldwide studies show diverse positive effects of exogenous melatonin on plants, edible plant products, and algae, but the potential of melatonin to enhance food and feed systems through these positive effects remains largely unexplored. Through a meta-analysis of about 25,000 observations, we show for the first time that exogenous application of melatonin significantly increases crop productivity and yields, and enhances the nutritional and nutraceutical value of edible plant products and algae by regulating diverse biological functions. We demonstrate that melatonin can improve plants, edible plant products, and algae under various current climate change scenarios, environmental pollution factors, and other stresses by about 7% to nearly 30%, on average, depending on the stressor. We also analyze various technical/methodological factors influencing the desired outcomes and identify conditions that offer optimal enhancement. We show that the positive effect of melatonin on plants and edible plant products varies among species, genera, and families, and strongly depends on the concentration of melatonin and treatment duration. The effect of melatonin is slightly lower on the monocot clade Commelinids than on the eudicot clades Asterids and Rosids. We also show that its stimulatory effect on plants depends on cultivation system, with a larger effect obtained in hydroponic systems. However, it does not depend on application stage (seed or vegetative), application route (foliage, roots, or seed), and whether the cultivation system is ex vivo or in vivo. This is the first meta-analysis examining the effects of melatonin on plants, edible plant products, and algae, and offers a scientific and technical roadmap facilitating sustainable food and feed production through the application of exogenous melatonin.

Pollen biology and hormesis: Pollen germination and pollen tube elongation.

This paper evaluated the occurrence of hormetic dose responses in pollen reported over the past eight decades. Hormetic doses responses were induced by a wide range of chemical and physical agents in 34 plant species for pollen germination and pollen tube growth/elongation. Agents inducing such hormetic dose/concentration responses in pollen included nutrients, growth-promoting agents, plant and animal hormones, toxic substances, including heavy metals such as cadmium, gaseous pollutants such as ozone, as well as ionizing and non-ionizing radiation. This paper provides further evidence for the broad generality of the hormesis dose response, supporting substantial prior findings that the hormetic response is independent of biological model, inducing agent, and endpoints measured. Given the widespread potential of inducing hormetic dose responses in pollen, these findings indicate the need to explore their emerging biological, ecological, agricultural, economic and public health implications.

Re-analysis of herbal extracts data reveals that inflammatory processes are mediated by hormetic mechanisms.

Using data from Schink et al. (2018), a large number of herbal extracts were assessed for their capacity to induce pro- and anti-inflammatory effects based on TLR4 expression normalized for cell viability in two immune cell models (i.e., HeLa-TLR4 transfected reporter cell line, and THP-1 monocytes) applying seven concentrations (0.01-3.0%). The analysis revealed that 70-80% of the extracts satisfying the a priori entry criteria also satisfied a priori evaluative criteria for hormetic concentration responses. These findings demonstrate that a large proportion of herbal extracts display hormetic dose responses in immune cells, indicating that hormetic mechanisms mediate pro- and anti-inflammatory processes and may provide a means to guide optimal dosing strategies. The identification of doses eliciting only anti-inflammatory therapeutic activity as well as the use of dose-variable herbal extracts in the treatment of inflammatory diseases will be challenging.

Ozone-induced impairment of night-time stomatal closure in O3-sensitive poplar clone is affected by nitrogen but not by phosphorus enrichment.

Nocturnal transpiration may be a key factor influencing water use in plants. Tropospheric ozone (O3) and availability of nutrients such as nitrogen (N) and phosphorus (P) in the soil can affect daytime water use through stomata, but the combined effects of O3, N and P on night-time stomatal conductance (gs) are not known. We investigated the effects of O3 and soil availability of N and P on nocturnal gs and the dynamics of stomatal response after leaf severing in an O3-sensitive poplar clone (Oxford) subjected to combined treatments over a growing season in an O3 free air controlled exposure (FACE) facility. The treatments were two soil N levels (0 and 80 kg N ha-1; N0 and N80), three soil P levels (0, 40 and 80 kg P ha-1; P0, P40 and P80) and three O3 levels (ambient concentration, AA [35.0 ppb as hourly mean]; 1.5 × AA; 2.0 × AA). The analysis of stomatal dynamics after leaf severing suggested that O3 impaired stomatal closure execution. As a result, nocturnal gs was increased by 2.0 × AA O3 in August (+39%) and September (+108%). Night-time gs was correlated with POD0 (phytotoxic O3 dose) and increased exponentially after 40 mmol m-2 POD0. Such increase of nocturnal gs was attributed to the emission of ethylene due to 2.0 × AA O3 exposure, while foliar abscisic acid (ABA) or indole-3-acetic acid (IAA) did not affect gs at night. Interestingly, the O3-induced stomatal opening at night was limited by N treatments in August, but not limited in September. Phosphorus decreased nocturnal gs, although P did not modify the O3-induced stomatal dysfunction. The results suggest that the increased nocturnal gs may be associated with a need to improve N acquisition to cope with O3 stress.