Root Growth Rate Research Articles

Linking fine‐root architecture, vertical distribution and growth rate in temperate mountain shrubs

Fine‐root branching, vertical distribution and morphology together with root growth rate are key dimensions that determine root strategies for belowground resource acquisition. However, few studies have addressed these traits together with coordinated measures of root growth rates, limiting generalizations about how these root traits coordinate among species. We conducted a common garden experiment to examine interspecific variation and coordination among architectural and morphological traits together with vertical distribution and growth rate of fine‐roots (≤ 2 mm in diameter) across 11 temperate shrub species. Across all species, root morphological traits showed only moderate differences among the first three branching orders and changed more dramatically in higher orders. We found that thin‐rooted shrub species had greater branching intensity than thick‐rooted species. Live fine‐root density (length and mass) decreased as an exponential pattern with increasing soil depth while the density of dead fine‐roots remained relatively constant. Patterns of fine‐root growth rates were independent of morphological and architectural traits, but were negatively related to rooting depth. The different root traits and relationships observed suggest diverse strategies for soil resource acquisition among shrub species. A deep root system would be associated with a slow growth rate. In contrast, the rooting depth was largely independent of root architecture and morphology.

Scale-up production of Rehmannia glutinosa adventitious root biomass in bioreactors and improvement of its acteoside content by elicitation

Rehmannia glutinosa is an important medicinal crop that has been widely used globally to treat various ailments such as hematinic deficiencies, diabetes, and adrenal disorders. To provide a sustainable supply to meet large demands, alternative cultivation methods, apart from conventional ones, are indispensable. This study developed an optimized condition for R. glutinosa adventitious root culture and a scale-up production system using a bioreactor. A woody plant medium enriched with vitamins, 30 g/L sucrose, and 2.0 mg/L 1-naphthaleneacetic acid (NAA) supported the optimum growth rate of adventitious roots (growth index of 25.67). The application of methyl jasmonate (MeJa) at a concentration of 200 μM showed the best enhancement of acteoside biosynthesis, with an approximately 2.53-fold increase (14.37 mg/g dry weight [DW]) compared with the control (5.67 mg/g DW). However, all treatments with MeJa and salicylic acid reduced the biomass of R. glutinosa adventitious roots compared with control. To validate the optimized protocol, the culture system was scaled up by comparing shake flask cultures with 2- and 20-L balloon type (air lift) bubble bioreactors (BTBB) along with elicitation using 200 μM MeJa. The 20-L BTBB cultures produced good-quality R. glutinosa roots with higher biomass (15.94 g DW), acteoside content (22.13 mg/g DW), and antioxidant activity (84.22 %) than shake flask cultures. In addition, fourier transform near-IR (FT-NIR) analysis showed no significant difference in the chemical composition of the in vitro adventitious roots and those that were commercially available. Thus, these findings will provide a basis for the development of large-scale R. glutinosa adventitious root production to meet the demands of pharmaceutical and oriental medicine industries without affecting its availability in nature.

Apical-root apoplastic acidification affects cell wall extensibility in wheat under salinity stress.

Plant salt tolerance is associated with a high rate of root growth. Although root growth is governed by cell wall and apoplastic pH, the relationship between these factors in the root elongation zone under salinity stress remains unclear. Herein, we assess apoplastic pH, pH- and expansin-dependent cell wall extensibility, and expansin expression in the root elongation zone of salt-sensitive (Yongliang-15) and -tolerant (JS-7) cultivars under salinity stress. A six-day 80 mM NaCl treatment significantly reduced apical root apoplastic pH in both cultivars. Using a pH-dependent cell wall extensibility experiment, we found that, under 0 mM NaCl treatment, the optimal pH for cell wall loosening was 6.0 in the salinity-tolerant cultivar and 4.6 in the salinity-sensitive cultivar. Under 80 mM treatment, a pH of 5.0 mitigated the cell wall stiffness caused by salinity stress in the salinity-tolerant cultivar but promoted cell wall stiffening in the salinity-sensitive cultivar. Salinity stress altered expansin expression and differentially affecting cell wall extensibility under pH5.0 and 6.0. TaEXPA8 might be relative to cell wall loosening at pH5.0, whereas TaEXPA5 relative to cell wall loosening at pH6.0. These results elucidate the relationship between expansins and cell wall extensibility in the root elongation zone, with important implications for enhancing plant growth under salinity stress.

A preliminary evaluation of the environmental toxicology of road salts on plant root dynamics

Although critical for the deicing of roads and bridges throughout the winter season in North America, road salts continue to have yearlong negative impacts on both anthropogenic and biological systems. Our objective was to measure the impact of four commonly used road salt ingredients on the dynamics of plant growth and development. Using onions as a model system, we hypothesized that exposing plants to different concentrations of sodium chloride, calcium chloride, potassium chloride, and magnesium chloride treatments would allow us to calculate the environmental concentration at which root development is halted by each road salt. We found that root growth decreased with sodium chloride, calcium chloride, and potassium chloride treatments, but increased with magnesium chloride. We used a linear model of root growth rates and concentrations to calculate the level at which each road salt becomes toxic to plants in the surrounding environment. We also apply the ecological theory of the principle of allocation to discuss how the chemical induction of root growth by magnesium chloride road salts may result in a life history trade-off that reduces investment toward plant-defense. The predicted trade-off in plant defense suggests that crop species in urban environments would be more susceptible to herbivory and as such would rely more on agricultural pesticides to sustain food security. We propose further studies to evaluate applications of plant defense theory in an urban context.

A nutrient recommendation system for soil fertilization based on evolutionary computation

In agricultural production, soil characteristics play a vital role in maintaining fertility by allowing crops to develop better through root nutrition with minimal energy inputs. Nitrogen (N), Phosphorus (P), and Potassium (K) are all important nitrogen fertilizers extensively utilized in crops to supply a sufficient level of nutrients and keep their production level high. However, the application is generally limited to specific crops because of the global variability in these essential nutrients. Stability in fertilizer application, growth, and root growth rate increases crop fertility and crop production. To predict the suitable nutrients for different crops and provide nutrients recommendations by analyzing the crop fertility and yield production, this paper proposes nutrient recommendations through an improved genetic algorithm (IGA) that uses time-series sensor data and recommends various crop settings. A neighborhood-based strategy is then presented to handle exploration and exploitation for optimizing the parameters to obtain the maximum yield. The method can expand knowledge by using the population exploration strategy. The final recommendation is made by using the similarity between recommended patterns and real-time sensor data. With time, crop fertility decreases due to the low level of nutrients. This crop model will help to increase yield by analysis of the seasonal fertility performance of the soil. The proposed method is also a useful tool to improve soil fertility performance by providing the nutrient recommendation of optimal conditions for crop development. Experimental results show that the proposed model can recommend optimizing patterns and increasing the yearly yield efficiently. The method can help identify the region to assess crop suitability under certain nutrients levels and give insight into nutrient suitability assessments concerning specific crops in a climate-changing world.

In situ Root Phenotypes of Cotton Seedlings Under Phosphorus Stress Revealed Through RhizoPot.

Phosphorus (P) deficiency is a common challenge in crop production because of its poor mobility through the soil. The root system plays a significant role in P absorption from the soil and is the initial indicator of low P levels. However, the phenotypic dynamics and longevity of cotton roots under P stress remain unknown. In this study, RhizoPot, an improvised in situ root observation device, was used to monitor the dynamics of root phenotypes of cotton seedlings under P-deficient (PD) and P-replete (PR) conditions. Low P stress reduced P absorption and accumulation in the roots, leading to low dry weight accumulation. Cotton seedlings responded to low P stress by increasing the number of lateral roots, specific root length, branch density, root length density, and length of root hairs. Additionally, the life span of root hairs was prolonged. Low P stress also reduced the average diameter of roots, promoted root extension, expanded the root coverage area, and increased the range of P acquisition. Principal component analysis revealed that the net root growth rate, root length density, root dry weight, P absorption efficiency, average root hair length, and taproot daily growth significantly influenced the cotton root architecture. Collectively, these results show that low P stress reduces the net growth rate of cotton seedling roots and restricts plant growth. Plants respond to P deficiency by extending the life span of root hairs and increasing specific root length and lateral root branch density. This change in root system architecture improves the adaptability of plants to low P conditions. The findings of this study may guide the selection of cotton varieties with efficient P utilization.

Azo dye containing wastewater treatment in earthen membrane based unplanted two chambered constructed wetlands-microbial fuel cells: A new design for enhanced performance

This investigation is the first of its kind to enhance detoxification of azo dye and other pollutants containing wastewater using an innovative earthen membrane-based two-chambered constructed wetland cum microbial fuel cell (CW-MFC). The present innovative design simulates the core of a shallow unplanted CW-MFC, which runs the sequential anaerobic and aerobic regimes without mixing of the cathodic and anodic wastewater. The obtained results revealed 94.04 ± 2.87% chemical oxygen demand (COD) and 94.22 ± 1.33% azo dye removal from the synthetic wastewater containing 550 mg/L initial COD and 50 mg/L Methyl orange (MO) azo dye, along with the current density and power density production of 544.6 mA/m3 and 148.29 mW/m3, respectively. The UV-visible spectrum demonstrated azo bond degradation in the anodic region, which was confirmed by the presence of sulphanilic acid as an intermediate of the azo dye degradation in the anodic effluent. The gas chromatography-mass spectrometry (GC-MS) analysis of anodic effluent proved the presence of an another intermediate, N.N-dimethyl-p-phenylenediamine (DMPD) and further confirms mineralization in the cathodic effluent with the elution of several mineralized polar compounds. Phytotoxicity study with Vigna radiata, Triticum aestivum, and Cicer arietinum indicated higher root growth rates (in comparison to control) of 30.72%, 13.53%, and 11.62% in the anodic effluent, whereas 69.70%, 60.28%, and 34.27% in the cathodic effluent, respectively, indicating decreased toxicity. The microbial analysis revealed a shift in microbial community of CW-MFC; the inoculum was abundant with Methanomicrobia class (18.55%), which shifted to class Bacteroidetes (13.99%) in the anodic region which was attributed to azo dye degrading bacteria. Whereas, cathodic microbial community consists of Alpha and Gamma Proteobacteria (59.50%), which are considered as the aromatic ring-degrading microbes.

Pengaruh Medan Listrik sebagai Stimulan Pertumbuhan Bawang Putih Lokal Timor

The decline in Timorese local garlic yields will have an impact on farmers' income and the existence of the garlic. One of the decline factors is production. The purpose of this study is the implementation of an electric field as a stimulant for garlic growth. The electric field used is an AC electric field with an output frequency of 1.0 kHz. The variation of the electric field used is 1.28 kV/m, 1.55 kV/m. 1.80 kV/m, 2.12 kV/m and 2.48 kV/m. The results showed that exposure to an electric field in garlic resulted in a better germination rate, average germination time, and shoot and root growth rate compared to the control. The treatment of exposure to an electric field of 1.55 kV/m resulted the most optimum in the germination rate, average germination time and growth rate of shoots and roots with the respective values (11.4 ± 0.6) %/etmal, (1.4 ± 0, 1) day, (2.83 ± 0.09) mm/day, and (2.04 ± 0.09) mm/day. Increasing germination, shortening the average germination time and growth rate are expected to increase local Timor garlic production.

Screening endophyte with capability to improve phytoremediation efficiency from hyperaccumulators: A novel and efficient microfluidic method

Screening endophyte is the most important but also difficult to achieve a successful application in endophyte assisted phytoremediation process. Traditional screening procedure faced certain limitations including long time, difficulty in ascertaining the optimum strain and insignificant promotion efficiency of the selected strain in application. In this study, a novel endophyte screening method was established using microfluidic technology, realizing the real time observation of plant root phenotyping and allowing simultaneous incubation of different endophyte-plant systems. Using this method within two weeks, showed that endophyte Bacillus paramycoides (PE1), which possessed the best capability to improve phytoremediation efficiency from hyperaccumulator P. acinosa was successfully screened by evaluating root growth rate and effluent heavy metal (HM) concentration. PE1 increased root growth rate by 54.31 % and reduced the Cd concentration of chip effluent by 46.33 %. The results were verified by pot experiment, which showed that with PE1 inoculation, the biomass of P. acinosa promoted 42.50 % and Cd removal efficiency increased 55.49 %. Besides, significant and positive correlations were observed among the phytoremediation indicators obtained from microfluidic and traditional method, indicating the feasibility of microfluidic method. Our research provided a new and efficient method for endophyte screening, which could give a better understanding of endophyte assisted phytoremediation technology of HM contaminated soil.

Evaluation of Salt Tolerance in Italian Ryegrass at Different Developmental Stages

Soil salinity is one of the major abiotic stresses that continues to threaten plant growth and agricultural productivity. Screening germplasm with salinity tolerance is therefore necessary. This study was designed to evaluate salt tolerance based on the integrated tolerance index. Fifteen Italian ryegrass cultivars were used to evaluate the degree of genotypic variation in salt tolerance at the germination and vegetative growth stages of plant development. Evident variations in salt tolerance were observed at the germination stage under 255 mM NaCl treatment. Root growth rate, chlorophyll content, and germination rates played a vital role in determining salt tolerance. Based on combined attributes at the germination and vegetative growth stages, Gongniu, Chuangnong, Splendor, and Abundant were identified as the most tolerant cultivars. Furthermore, the constant crude protein, lower neutral detergent fiber, and acid detergent fiber contents were measured under salinity. Compared to the control, the cultivars Tetragold, Abundant, Splendor, Muyao, Harukaze, Tegao, Dongmu 70, and Doraian were identified to have high forage quality under salt stress. Finally, we selected Splendor and Abundant as the cultivars that expressed the highest degree of salt tolerance based on combined attributes related to germination, salt tolerance, and overall forage quality. In addition, gene expression analysis between salinity tolerant and sensitive cultivars revealed that the gene response to photosystem and carbohydrate synthesis may have played a mediating role in providing tolerance to salt stress.

Two centuries of breeding has altered root system architecture of winter wheat

Crop selection and breeding has influenced plant phenotypes and genotypes. The necessary selection and breeding steps which resulted in today's cultivated plants have greatly reduced plant genetic diversity. Genetic bottlenecks in plant populations are thought to be a direct result of modern breeding programs. This study used a custom root phenotyping platform to characterize root system architecture (RSA) parameters in a diverse panel of winter wheat released between 1803 and 2002. Cultivars were grown in P-deficient phytagel and images captured through 360° using light tomography. RSA parameters were measured using GiA Roots software. Network length, width, surface area, and volume differed between old cultivars and both intermediate and modern cultivars. RSA did not vary between intermediate and modern cultivars. Growth rates of old cultivars were two times greater than both intermediate and modern cultivars regardless of dwarfing status. These results support the idea that plant breeding has had unintended effects on winter wheat root systems. The reduction of root system size and growth rates with increased year of release may have important implications for further breeding work related to nutrient use, drought tolerance, and C-sequestration. The faster root growth of older cultivars may also provide a breeding target for developing plants that establish and respond to stress faster, potentially improving crop resilience.

Simulating rhizodeposition patterns around growing and exuding root systems

Abstract In this study, we developed a novel model approach to compute the spatio-temporal distribution patterns of rhizodeposits around growing root systems in three dimensions. This model approach allows us to study the evolution of rhizodeposition patterns around complex three-dimensional root systems. Root systems were generated using the root architecture model CPlantBox. The concentration of rhizodeposits at a given location in the soil domain was computed analytically. To simulate the spread of rhizodeposits in the soil, we considered rhizodeposit release from the roots, rhizodeposit diffusion into the soil, rhizodeposit sorption to soil particles and rhizodeposit degradation by microorganisms. To demonstrate the capabilities of our new model approach, we performed simulations for the two example rhizodeposits mucilage and citrate and the example root system Vicia faba. The rhizodeposition model was parameterized using values from the literature. Our simulations showed that the rhizosphere soil volume with rhizodeposit concentrations above a defined threshold value (i.e. the rhizodeposit hotspot volume) exhibited a maximum at intermediate root growth rates. Root branching allowed the rhizospheres of individual roots to overlap, resulting in a greater volume of rhizodeposit hotspots. This was particularly important in the case of citrate, where overlap of rhizodeposition zones accounted for more than half of the total rhizodeposit hotspot volumes. Coupling a root architecture model with a rhizodeposition model allowed us to get a better understanding of the influence of root architecture as well as rhizodeposit properties on the evolution of the spatio-temporal distribution patterns of rhizodeposits around growing root systems.

Abscisic acid signaling activates distinct VND transcription factors to promote xylem differentiation in Arabidopsis

Plants display remarkable abilities to adjust growth and development to environmental conditions, such as the amount of available water. This developmental plasticity is apparent not only in root and shoot growth rates, but also in tissue patterning and cell morphology.1,2 We have previously shown that in response to limited water availability, Arabidopsis thaliana root displays changes in xylem morphology, mediated by the non-cell-autonomous action of abscisic acid, ABA.2 Here, we show, through analyses of ABA response reporters and tissue-specific suppression of ABA signaling, that xylem cells themselves act as primary signaling centers governing both xylem cell fate and xylem differentiation rate, revealing the cell-autonomous control of multiple aspects of xylem development by ABA. ABA rapidly activates the expression of genes encoding VASCULAR-RELATED NAC DOMAIN (VND) transcription factors. Molecular and genetic analyses revealed that the two ABA-mediated xylem developmental changes are regulated by distinct members of this transcription factor family, with VND2 and VND3 promoting differentiation rate of metaxylem cells, while VND7 promotes the conversion of metaxylem toward protoxylem morphology. This phenomenon shows how different aspects of developmental plasticity can be interlinked, yet genetically separable. Moreover, similarities in phenotypic and molecular responses to ABA in diverse species indicate evolutionary conservation of the ABA-xylem development regulatory network among eudicots. Hence, this study gives molecular insights into how environmental stress modifies plant vascular anatomy and has potential relevance for water use optimization and adaptation to drought conditions.

Interactive Impacts of Temperature and Elevated CO2 on Basil (Ocimum basilicum L.) Root and Shoot Morphology and Growth

Recent evidence suggests that the effects of temperature significantly affect the growth and development of basil plants with detrimental impacts on yield. The current research investigated the interactive effects of varying temperature and CO2 levels on the shoot and root morphology and growth of early and late-season basil plants. Basil plants were subjected to control (30/22 °C), low (20/12 °C), and high (38/30 °C) temperature under ambient (420 μL L−1) and elevated (720 μL L−1) CO2 concentrations. Decreasing the temperature to 20/12 °C caused more adverse effects on the morphological traits of the early-season basil. Relative to the control treatments, low- and high-temperature stresses decreased 71 and 14% in marketable fresh mass, respectively. Basil exhibited an increase in plant height, node and branch numbers, specific leaf area, anthocyanin and nitrogen balance index, root tips, and root crossings when subjected to high-temperature stress. Furthermore, elevated CO2 affected many morphological features compared to ambient CO2 concentrations. The findings of this study suggest that varying the growth temperature of basil plants would more significantly impact the shoot and root morphologies and growth rates of basil than increasing the CO2 concentrations, which ameliorated the adverse impacts of temperature stress.

Artificial almond flavoring additive: A potential toxic compound for the environment

In this work, the chemical composition of the artificial almond flavoring was investigated, as well as the toxicity of this additive against bioassays commonly used to assess the environmental risk offered by chemical compounds and/or substances. The chemical identification detected ethanol (solvent), saccharin, benzaldehyde and benzoic acid. In L. sativa and A. cepa, concentrations of 100 and 10 µL/L flavoring caused a reduction in the germination rate and inhibition of root growth. In A. cepa, at 24 and 48 hours of exposure, concentrations 100 and 10µL/L significantly reduced the division of root meristems, and concentrations 1 and 0.10 µL/L induced cellular changes and were aneugenic to plant meristems. The flavoring was highly toxic to A. salina with LC50 = 0.082 ppm. Also, by partitioning into saturated solutions of octane and water, the commercial solution of the almond presented a log Kow of 1.37. Based on the results obtained, under the established analysis conditions, the flavoring was significantly phytotoxic, cytogenotoxic and toxic, and based on Kow it is estimated to have good stability in water and soil. These results indicate that almond flavoring is a potential environmentally toxic compound.

Effects of different NO3 −: NH4 + ratios on the ultrastructure and ion flux rate of lettuce roots

Nitrogen is a vital nutrient element for plants. The two main forms of nitrogen (N) are nitrate N (NO3 −) and ammonium N (NH4 +). The effects of the different NO3 −:NH4 + ratios (0:100, 25:75, 50:50, 75:25, and 100:0) in the nutrient solution on the growth, root morphology, ultrastructure and ion flux rate of lettuce roots were studied. The results showed that the biomass and leaf area were greatest when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25. The shoot NO3 − content was highest when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25. The shoot NH4 +-N content was highest when the ratio of NO3ˉ:NH4 + was 50:50. The NO3 − flux was greatest when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25. Superoxide dismutase (SOD) activity was lowest when the ratio of NO3ˉ:NH4 + was 0:100, and peroxidase (POD) activity was highest when the ratio of NO3ˉ:NH4 + was 100:0. The malonic dialdehyde (MDA) content was lowest when the ratio of NO3ˉ:NH4 + was 50:50, and the MDA content was higher when the ratio of NO3ˉ:NH4 + was 0:100 or 25:75. It was smooth and complete when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25.

Racial and ethnic differences in response to treatment for Marfan syndrome.

To determine whether racial/ethnic differences exist for the treatment of Marfan syndrome aortopathy. The 2014 Pediatric Heart Network randomised trial of losartan versus atenolol in Marfan syndrome paediatric and young adult patients showed no treatment differences in the rate of aortic root growth over 3 years; however, they did not examine racial/ethnic differences, and recent data suggest that angiotensin receptor blockers may have different pharmacologic effects in different racial/ethnic populations. We performed a secondary analysis of public-use data from the Pediatric Heart Network randomised trial comparing the differences by race/ethnicity (non-Hispanic White, non-Hispanic Black, and Hispanic patients) amongst the treatment groups for the primary outcome of rate of aortic root enlargement by z score and secondary outcome of rate of change of absolute diameter of aortic root, z score and absolute diameter of ascending aorta, and blood pressure changes. For aortic root enlargement by z score amongst non-Hispanic White patients, patients on losartan exhibited an annual z score change of -0.090 ± 0.016, compared to -0.146 ± 0.015 for those on atenolol (p = 0.01), favouring atenolol. For Hispanic and non-Hispanic Black patients, there was no difference in primary or secondary outcomes between treatment groups. Non-Hispanic White patients had a small, but statistically significantly greater decrease in aortic root z score favouring atenolol over losartan. There were no significant differences amongst Hispanic or non-Hispanic Black patients, which may be due to relatively small size numbers. These findings may have important implications for medication selection by race/ethnicity in Marfan syndrome patients, which has not previously been evaluated in studies.

ComBase Models Are Valid for Predicting Fate of Listeria monocytogenes on 10 Whole Intact Raw Fruits and Vegetables

Listeria monocytogenes was associated with more than 60 produce recalls, including tomato, cherry, broccoli, lemon, and lime, between 2017 and 2020. This study describes the effects of temperature, time, and food substrate as factors influencing L. monocytogenes behavior on whole intact raw fruits and vegetables. Ten intact whole fruit and vegetable commodities were chosen based on data gaps identified in a systematic literature review. Produce investigated belong to major commodity families: Ericaceae (blackberry, raspberry, and blueberry), Rutaceae (lemon and mandarin orange), Roseaceae (sweet cherry), Solanaceae (tomato), Brassaceae (cauliflower and broccoli), and Apiaceae (carrot). A cocktail of five L. monocytogenes strains that included clinical, food, or environmental isolates linked to foodborne outbreaks was used to inoculate intact whole fruits and vegetables. Samples were incubated at 2, 12, 22, 30, and 35°C with relative humidities matched to typical real-world conditions. Foods were sampled (n = 6) for up to 28 days, depending on temperature. Growth and decline rates were estimated using DMFit, an Excel add-in. Growth rates were compared with ComBase modeling predictions for L. monocytogenes. Almost every experiment showed initial growth, followed by subsequent decline. L. monocytogenes was able to grow on the whole intact surface of all produce tested, except for carrot. The 10 produce commodities supported growth of L. monocytogenes at 22 and 35°C. Growth and survival at 2 and 12°C varied by produce commodity. The standard deviation of the square root growth and decline rates showed significantly larger variability in both growth and decline rates within replicates as temperature increased. When L. monocytogenes growth occurred, it was conservatively modeled by ComBase Predictor, and growth was generally followed by decreases in concentration. This research will assist in understanding the risks of foodborne disease outbreaks and recalls associated with L. monocytogenes on fresh whole produce.

Involvement of ethylene receptors in the salt tolerance response of Cucurbita pepo

Abiotic stresses have a negative effect on crop production, affecting both vegetative and reproductive development. Ethylene plays a relevant role in plant response to environmental stresses, but the specific contribution of ethylene biosynthesis and signalling components in the salt stress response differs between Arabidopsis and rice, the two most studied model plants. In this paper, we study the effect of three gain-of-function mutations affecting the ethylene receptors CpETR1B, CpETR1A, and CpETR2B of Cucurbita pepo on salt stress response during germination, seedling establishment, and subsequent vegetative growth of plants. The mutations all reduced ethylene sensitivity, but enhanced salt tolerance, during both germination and vegetative growth, demonstrating that the three ethylene receptors play a positive role in salt tolerance. Under salt stress, etr1b, etr1a, and etr2b germinate earlier than WT, and the root and shoot growth rates of both seedlings and plants were less affected in mutant than in WT. The enhanced salt tolerance response of the etr2b plants was associated with a reduced accumulation of Na+ in shoots and leaves, as well as with a higher accumulation of compatible solutes, including proline and total carbohydrates, and antioxidant compounds, such as anthocyanin. Many membrane monovalent cation transporters, including Na+/H+ and K+/H+ exchangers (NHXs), K+ efflux antiporters (KEAs), high-affinity K+ transporters (HKTs), and K+ uptake transporters (KUPs) were also highly upregulated by salt in etr2b in comparison with WT. In aggregate, these data indicate that the enhanced salt tolerance of the mutant is led by the induction of genes that exclude Na+ in photosynthetic organs, while maintaining K+/Na+ homoeostasis and osmotic adjustment. If the salt response of etr mutants occurs via the ethylene signalling pathway, our data show that ethylene is a negative regulator of salt tolerance during germination and vegetative growth. Nevertheless, the higher upregulation of genes involved in Ca2+ signalling (CpCRCK2A and CpCRCK2B) and ABA biosynthesis (CpNCED3A and CpNCED3B) in etr2b leaves under salt stress likely indicates that the function of ethylene receptors in salt stress response in C. pepo can be mediated by Ca2+ and ABA signalling pathways.

Effects of Different Fumigants on the Replanted Soil Environment and Growth of Malus hupehensis Rehd. Seedlings

Apple replant disease (ARD) has been reported in all major fruit-growing regions of the world and is often caused by biotic factors (pathogen fungi) and abiotic factors (phenolic compounds). Soil chemical fumigation can kill soil pathogenic fungi; however, the traditionally used fumigant methyl bromide has been banned because of its ozone-depleting effects. There is thus a need to identify greener fumigant candidates. We characterized the effects of different fumigants on the replanted soil environment and the growth characteristics of Malus hupehensis Rehd. seedlings. All five experimental treatments [treatment 1 (T1), metham-sodium; treatment 2 (T2), dazomet; treatment 3 (T3), calcium cyanamide; treatment 4 (T4), 1,3-dichloropropene; and treatment 5 (T5), methyl bromide] promoted significantly the biomass, root growth, and root respiration rate of M. hupehensis seedlings and the ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3–-N) contents of replanted soil. Metham sodium (T1) and dazomet (T2) had stronger effects compared with 1,3-dichloropropene (T4) and calcium cyanamide (T3). At 172 days after T1, the height, root length, and root respiration rate of Malus hupehensis Rehd. seedlings, and the NH4+-N and NO3–-N contents of replanted soil increased by 91.64%, 97.67%, 69.78%, 81.98%, and 27.44%, respectively, compared with the control. Thus, dazomet and metham sodium were determined to be the optimal fumigants for use in practical applications.