Neighbour-induced changes in root exudation patterns of buckwheat results in altered root architecture of redroot pigweed.

Roots are crucial in plant adaptation through the exudation of various compounds which are influenced and modified by environmental factors. Buckwheat root exudate and root system response to neighbouring plants (buckwheat or redroot pigweed) and how these exudates affect redroot pigweed was investigated. Characterising root exudates in plant-plant interactions presents challenges, therefore a split-root system which enabled the application of differential treatments to parts of a single root system and non-destructive sampling was developed. Non-targeted metabolome profiling revealed that neighbour presence and identity induces systemic changes. Buckwheat and redroot pigweed neighbour presence upregulated 64 and 46 metabolites, respectively, with an overlap of only 7 metabolites. Root morphology analysis showed that, while the presence of redroot pigweed decreased the number of root tips in buckwheat, buckwheat decreased total root length and volume, surface area, number of root tips, and forks of redroot pigweed. Treatment with exudates (from the roots of buckwheat and redroot pigweed closely interacting) on redroot pigweed decreased the total root length and number of forks of redroot pigweed seedlings when compared to controls. These findings provide understanding of how plants modify their root exudate composition in the presence of neighbours and how this impacts each other's root systems.

Polyethylene microplastic modulates lettuce root exudates and induces oxidative damage under prolonged hydroponic exposure.

Root exudates are pivotal in plant stress responses, however, the impact of microplastics (MPs) on their release and characteristics remains poorly understood. This study delves into the effects of 0.05 % and 0.1 % (w/w) additions of polyethylene (PE) MPs on the growth and physiological properties of lettuce (Lactuca sativa L.) following 28 days of exposure. The release characteristics of root exudates were assessed using UV-vis and 3D-EEM. The results indicated that PE increased leaf number but did not significantly affect other agronomic traits or pigment contents. Notably, 0.05 % PE increased the total root length and surface area compared to the 0.1 % addition, while a non-significant trend towards decreased root activity was observed with PE MPs. PE MPs with 0.1 % addition notably reduced the DOC concentration in root exudates by 37.5 %, while 0.05 % PE had no impact on DOC and DON concentrations. PE addition increased the SUVA254, SUVA260, and SUVA280 values of root exudates, with the most pronounced effect seen in the 0.05 % PE treatment. This suggests an increase of aromaticity and hydrophobic components induced by PE addition. Fluorescence Regional Integration (FRI) analysis of 3D-EEM revealed that aromatic proteins (region I and II) were dominant in root exudates, with a slight increase in fulvic acid-like substances (region III) under 0.1 % PE addition. Moreover, prolonged PE exposure induced ROS damage in lettuce leaves, evidenced by a significant increase in content and production rate of O2·-. The decrease in CAT and POD activities may account for the lettuce's response to environmental stress, potentially surpassing its tolerance threshold or undergoing adaptive regulation. These findings underscore the potential risk of prolonged exposure to PE MPs on lettuce growth.

Plant Extracellular Vesicles: Current Landscape and Future Directions.

Plant cells secrete membrane-enclosed micrometer- and nanometer-sized vesicles that, similarly to the extracellular vesicles (EVs) released by mammalian or bacterial cells, carry a complex molecular cargo of proteins, nucleic acids, lipids, and primary and secondary metabolites. While it is technically complicated to isolate EVs from whole plants or their tissues, in vitro plant cell cultures provide excellent model systems for their study. Plant EVs have been isolated from the conditioned culture media of plant cell, pollen, hairy root, and protoplast cultures, and recent studies have gathered important structural and biological data that provide a framework to decipher their physiological roles and unveil previously unacknowledged links to their diverse biological functions. The primary function of plant EVs seems to be in the secretion that underlies cell growth and morphogenesis, cell wall composition, and cell-cell communication processes. Besides their physiological functions, plant EVs may participate in defence mechanisms against different plant pathogens, including fungi, viruses, and bacteria. Whereas edible and medicinal-plant-derived nanovesicles isolated from homogenised plant materials ex vivo are widely studied and exploited, today, plant EV research is still in its infancy. This review, for the first time, highlights the different in vitro sources that have been used to isolate plant EVs, together with the structural and biological studies that investigate the molecular cargo, and pinpoints the possible role of plant EVs as mediators in plant-pathogen interactions, which may contribute to opening up new scenarios for agricultural applications, biotechnology, and innovative strategies for plant disease management.

Chemotaxis and Motility of Spongospora subterranea Zoospores in Response to Potato Root Exudate Constituents and pH.

Spongospora subterranea f. sp. subterranea is an important pathogen of potato responsible for major losses in most potato growing regions of the world. Infection is initiated by biflagellated motile zoospores released from long-lived resting spores. Zoospore chemotaxis to the host plant root is widely believed to be stimulated by host root exudate compounds, although direct evidence is lacking. This study refined the traditional chemotaxis capillary assay, with which we provided the first empirical evidence of S. subterranea zoospore chemotaxis. Individual potato root exudate metabolites were either taxis neutral, inhibitory, or attractant to the zoospores. L-Glutamine was the strongest chemoattractant, while spermine was the most inhibitory. Zoospore motility and chemotaxis were constrained by strongly acidic or alkaline solutions of pH < 5.3 and >8.5, respectively. Beyond pH, ionic constituents of the test solution affected zoospore motility as Sorensen's phosphate buffer stalled zoospore motility, but HEPES buffer at the same concentration and pH had little or no negative motility effect. Zoospore motility, as characterized by several parameters, influenced chemotaxis. Among the parameters measured, total distance traveled was the best predictor of zoospore chemotaxis. The characterization of environmental and ecological effects on zoospore motility and chemotaxis highlights useful targets for S. subterranea disease control through manipulation of zoospore taxis or selection of host resistance traits.

[Effects of root exudates C:N on soil physical and chemical characteristics and soil respiration in Robinia pseudoacacia plantation]. / æ ¹ç³»åˆ†æ³Œç‰©C∶N对刺槐林地土壤理化特征和土壤呼吸的影响.

We explored the effects of C:N ratio in root exudates of Robinia pseudoacacia plantations on soil nutrient cycling and microbial activity on the Loess Plateau. We collected in-situ soil from the R. pseudoacacia plantations with essentially identical habitat conditions and growing time of 15, 25, 35, and 45 years. By adding root exudates with different C:N ratios (N only, C:N=10, C:N=50, C:N=100, C only) to the soil and using deionized water as a control, we analyzed the effects of C:N ratio of root exudates on the physicochemical properties of elements such as carbon, nitrogen and phosphorus, soil pH, and soil respiration. The results showed that: 1) Organic carbon content was positively correlated with the C:N ratio of root exudates. Soil organic carbon (SOC) decomposition was faster when root exudates C:N=10. Higher C:N ratio of root exudates (C:N=100) could inhibit SOC decomposition, but only C addition had no significant effect on SOC. 2) Different root exudate C:N produced no significant influence on the total nitrogen. The addition of carbon promoted microbial uptake of ammonium nitrogen, while the addition of nitrogen promoted the nitrification of ammonium nitrogen. As the C:N ratio of root exudates increased, soil ammonium nitrogen content decreased. 3) The addition of nitrogen would reduce soil pH and increase soil total phosphorus content. 4) Soil respiration of R. pseudoacacia plantations was positively correlated with the C:N ratio of root exudates. With the increases of C:N ratio, the promoting effect of root exudates on soil respiration at 25 and 35 years R. pseudoacacia plantations was stronger. In conclusion, higher C:N ratio of root exudates will significantly promote the effect on soil respiration of R. pseudoacacia plantations. Our results improved the understan-ding of the root-soil-microbial interactions in forests.

Linking Short-Chain N-Acyl Homoserine Lactone-Mediated Quorum Sensing and Replant Disease: A Case Study of Rehmannia glutinosa.

Rehmannia glutinosa, a perennial medicinal plant, suffers from severe replant disease under consecutive monoculture. The rhizosphere microbiome is vital for soil suppressiveness to diseases and for plant health. Moreover, N-acyl homoserine lactone (AHL)-mediated quorum sensing (QS) regulates diverse behavior in rhizosphere-inhabiting and plant pathogenic bacteria. The dynamics of short-chain AHL-mediated QS bacteria driven by consecutive monoculture and its relationships with R. glutinosa replant disease were explored in this study. The screening of QS bacteria showed that 65 out of 200 strains (32.5%) randomly selected from newly planted soil of R. glutinosa were detected as QS bacteria, mainly consisting of Pseudomonas spp. (55.4%). By contrast, 34 out of 200 (17%) strains from the diseased replant soil were detected as QS bacteria, mainly consisting of Enterobacteriaceae (73.5%). Functional analysis showed most of the QS bacteria belonging to the Pseudomonas genus showed strong antagonistic activities against Fusarium oxysporum or Aspergillus flavus, two main causal agents of R. glutinosa root rot disease. However, the QS strains dominant in the replant soil caused severe wilt disease in the tissue culture seedlings of R. glutinosa. Microbial growth assays demonstrated a concentration-dependent inhibitory effect on the growth of beneficial QS bacteria (i.e., Pseudomonas brassicacearum) by a phenolic acid mixture identified in the root exudates of R. glutinosa, but the opposite was true for harmful QS bacteria (i.e., Enterobacter spp.). Furthermore, it was found that the population of quorum quenching (QQ) bacteria that could disrupt the beneficial P. brassicacearum SZ50 QS system was significantly higher in the replant soil than in the newly planted soil. Most of these QQ bacteria in the replant soil were detected as Acinetobacter spp. The growth of specific QQ bacteria could be promoted by a phenolic acid mixture at a ratio similar to that found in the R. glutinosa rhizosphere. Moreover, these quorum-quenching bacteria showed strong pathogenicity toward the tissue culture seedlings of R. glutinosa. In conclusion, consecutive monoculture of R. glutinosa contributed to the imbalance between beneficial and harmful short-chain AHL-mediated QS bacteria in the rhizosphere, which was mediated not only by specific root exudates but also by the QQ bacterial community.

Autotoxicity of root exudates varies with species identity and soil phosphorus.

Root exudate autotoxicity (i.e. root exudates from a given plant have toxic effects on itself) has been recognized to be widespread. Here we examined how plant species identity and soil phosphorus (P) availability influenced this autotoxicity and the possible stoichiometric mechanisms. We conducted an experiment with three species (Luctuca sativa, Sesbania cannabina, and Solidago canadensis), which were subject to four treatments consisting of activated carbon (AC) and soil P. AC addition increased the whole-plant biomass of each species under high P conditions and this AC effect varied strongly with species identity. For Solidago, the relative increase in whole-plant biomass due to AC addition was larger in the low P than in the high P. Root exudate autotoxicity differed between roots and shoots. AC addition decreased root N:P ratios but failed to influence shoot N:P ratios in three species. These findings suggest that soil P enrichment might mediate root exudate autotoxicity and that this P-mediated autotoxicity might be related to root N and P stoichiometry. These patterns and their implications need to be addressed in the context of plant communities.

Desorption of atrazine in biochar-amended soils: Effects of root exudates and the aging interactions between biochar and soil.

The effects of wheat root exudates and the aging interactions between biochar and soil on atrazine desorption from biochar-amended soil were carefully examined. Compared with CaCl2 solution, wheat root exudates significantly increase the desorption of atrazine from biochar, mainly by promoting the desorption of atrazine adsorbed on biochar with specific forces. Wheat root exudates were effectively separated into three components with different electrical properties, namely, anionic, neutral, and cationic components. Mainly due to the carboxyl-containing compounds, the anionic component was the main active component in the wheat root exudates that enhances the desorption of atrazine from the biochar. Additionally, wheat root exudates can increase the desorption of atrazine from biochar-amended soil. The promotion of atrazine desorption by root exudates was more obvious in soils with low organic matter contents, where atrazine was mainly adsorbed by biochar. The aging interaction between the biochar and soil increased the total desorption rate and rapid desorbing fraction of the atrazine in the soil, most likely due to the reduction of the biochar sorption capacity in the aged biochar-amended soil.

[Antifungal effects of three medicinal crops on Phytophthora nicotianae].

Tobacco black shank is one of the most harmful soil-borne diseases infected by Phytophthora parasitica. In order to probe the control method to this disease, in this study, the mycelial growth rate method was employed to investigate the antifungal effects of extracts from stem-leaf and root, root exudates, and their combination of Scrophularia ningpoensis, Chuanmingshen violaceum and Pinellia ternata The results showed that: ①Stem-leaf and root extracts of S. ningpoensis, C. violaceum and P. ternata exhibited different antifungal activities, and the inhibition increased with the increase of extract concentration. The antifungal effect of S. ningpoensis extracts at 0.5 g•mL⁻¹ was the strongest than other medicinal plants, the inhibition rate of steam-leaf and root extracts reached 74.88%, 69.27%, respectively. The inhibitory effect of C. violaceum and P. ternata was relatively lower, however, there is a significant gain effect after combination of steam-leaf and root extracts of C. violaceum. ②The root exudates of S. ningpoensis, C. violaceum and P. ternata showed fungistasis to Phytophthora nicotianae, and fungistasis was enhanced with the increase of root exudate concentration. The antifungal effect in the order of C. violaceum > S. ningpoensis > P. ternata. ③The antifungal activity of combination of extract and root exudate from S. ningpoensis was similar with the effect of C. violaceum, they were both stronger than P. ternata, and the antifungal activity for three combination were located between the antifungal activity of their extracts and root exudates. S. ningpoensis and C. violaceum can be potentially applied to prevent and control the tobacco black shank.

Antifungal effects of three medicinal crops on Phytophthora nicotianae / 中国中药杂志

Tobacco black shank is one of the most harmful soil-borne diseases infected by Phytophthora parasitica. In order to probe the control method to this disease, in this study, the mycelial growth rate method was employed to investigate the antifungal effects of extracts from stem-leaf and root, root exudates, and their combination of Scrophularia ningpoensis, Chuanmingshen violaceum and Pinellia ternata The results showed that: ①Stem-leaf and root extracts of S. ningpoensis, C. violaceum and P. ternata exhibited different antifungal activities, and the inhibition increased with the increase of extract concentration. The antifungal effect of S. ningpoensis extracts at 0.5 g•mL⁻¹ was the strongest than other medicinal plants, the inhibition rate of steam-leaf and root extracts reached 74.88%, 69.27%, respectively. The inhibitory effect of C. violaceum and P. ternata was relatively lower, however, there is a significant gain effect after combination of steam-leaf and root extracts of C. violaceum. ②The root exudates of S. ningpoensis, C. violaceum and P. ternata showed fungistasis to Phytophthora nicotianae, and fungistasis was enhanced with the increase of root exudate concentration. The antifungal effect in the order of C. violaceum > S. ningpoensis > P. ternata. ③The antifungal activity of combination of extract and root exudate from S. ningpoensis was similar with the effect of C. violaceum, they were both stronger than P. ternata, and the antifungal activity for three combination were located between the antifungal activity of their extracts and root exudates. S. ningpoensis and C. violaceum can be potentially applied to prevent and control the tobacco black shank.

Influences of artificial root exudate components on the behaviors of BDE-28 and BDE-47 in soils: desorption, availability, and biodegradation.

Behaviors of BDE-28 and BDE-47 in two distinct soils (Phaeozem and Acrisol) as affected by the separate addition of root exudate components (i.e., oxalic acid, glycine, and fructose) were investigated by a soil microcosm incubation experiment. The results showed that root exudate components promoted the desorption of BDE-28 (57.6-235.0 %) and BDE-47 (56.9-223.7 %) from the soils due to the enhancement of their water solubilities. The addition of root exudate components increased the n-butanol extractability of BDE-28 and BDE-47 by 20.3-72.5 and 48.6-169.2 %, respectively, which had a positive correlation with the concentrations of dissolved organic carbon (DOC) in the soils (p < 0.01), suggesting that the increase of DOC in the soils by root exudate components was the major factor to enhance the extractability. Fructose and oxalic acid promoted the desorption and increased the availability of BDE-28 and BDE-47 in the soils more efficiently than glycine. The addition of different root exudate components resulted in distinct shifts in soil microbial community structure (p < 0.05). Oxalic acid caused the greatest impacts on the soil bacterial communities and increased the degradation rates of BDE-28 and BDE-47 most obviously. The findings of this study clarified the roles of root exudate components in affecting the behaviors of polybrominated diphenyl ethers (PBDEs) in soils.