Ethylene Levels Research Articles

Integrating microRNAs and mRNAs reveals the hormones synthesis and signal transduction of maize under different N rates

The effect of nitrogen (N) fertilizer on the development of maize kernels has yet to be fully explored. MicroRNA-mRNA analyses could help advance our understanding of how kernels respond to N. This study analyzed the morphological, physiological, and transcriptomic changes in maize kernels under different N rates (0, 100, 200, and 300 kg ha–1). The result showed that increasing N application significantly increased maize grains’ fresh and dry weight until N reached 200 kg ha–1. Higher levels of indole-3-acetic acid, cytokinin, gibberellin, and a lower level of ethylene were associated with increased N applications. We obtained 31 differentially expressed genes (DEGs) in hormone synthesis and transduction, and 9 DEGs were regulated by 14 differentially expressed microRNAs (DEMIs) in 26 pairs. The candidate DEGs and DEMIs provide valuable insight for manipulating grain filling under different N rates.

Fabrication and properties of natural rubber/rice starch/activated carbon biocomposite-based packing foam sheets and their application to shelf life extension of ‘Hom Thong’ banana

Natural rubber (NR) and rice starch (RS) biocomposite-based packing foam sheets were successfully prepared by the Dunlop method, with activated carbon (AC) as a filler to enhance mechanical properties (and to absorb ethylene gas released by packaged bananas). The primary objective of this study was to examine the influences of activated carbon contents from 0 to 20 phr on physical, morphological, mechanical, and thermal properties of the biocomposite foams. With increasing AC content, the foam cell size, density, hardness, compression force deflection (CFD), compression set, tensile strength, elongation at break, tear strength and glass transition temperature (Tg) increased, while the number density of foam cells and rebound resilience decreased. However, the content of activated carbon did not affect the thermal stability. Furthermore, the developed biocomposite foam with 15 phr AC, which had the highest ethylene removal, was used to evaluate the ethylene absorption capacity and the quality of 'Hom Thong' bananas during 12 days of storage in terms of weight loss, pulp firmness, total soluble solids (TSS), physical appearance, and peel color, with comparison to a commercial foam and control. The biocomposite foam with 15 phr AC lowered the ambient ethylene levels considerably, hence delaying fruit ripening and decreasing chlorophyll degradation, TSS, and pulp firmness at 6 days of ambient storage. The proposed biocomposite foam shows potential for enhancing the postharvest storage stability of bananas and has great potential as packaging for other fresh fruit products.

Effect of Postharvest Treatments on the Biosynthesis of Fruit Volatile Compounds: A Literature Review

Abstract: Fruits have different aromatic profiles according to their stage of ripeness, therefore, volatile compounds profile is an important quality attribute, which also determines flavor and aroma characteristics, making this profile a perfect option to guide the optimization of postharvest treatment of fruits. In this context, the objective was to discuss the effects of postharvest treatments, associating them with the biosynthesis of volatile compounds in fruits. There are three major groups of fruit flavor precursors: carbohydrates, amino acids, and fatty acids. The biosynthesis of volatile compounds is directly related to metabolic changes that occur according to the fruit ripening stage. This process occurs under the regulation of hormones, which have ethylene as one of the main agents. Several hormones are also part of this complex mechanism and interact by regulating ethylene levels positively or negatively to form a fine adjustment. Therefore, hormonal treatments have an impact on the biosynthesis of volatile compounds in different ways. Other postharvest treatments such as cold storage, controlled atmosphere, and UV radiation can also impact the volatile compounds biosynthesis, but are generally used synergistically, which circumvents the negative effects on the aromatic profile of the fruits.

Integrating BSA-Seq with RNA-Seq Reveals a Novel Fasciated Ear5 Mutant in Maize

Increasing grain yield is required to meet the rapidly expanding demands for food, feed, and fuel. Inflorescence meristems are central to plant growth and development. However, the question concerning whether inflorescence development can be regulated to improve grain yield remains unclear. Here, we describe a naturally occurring single recessive mutation called fea5 that can increase grain yield in maize. Using bulk segregant analysis sequencing (BSA-seq), the candidate region was initially mapped to a large region on chromosome 4 (4.68 Mb-11.26 Mb). Transcriptome sequencing (RNA-seq) revealed a total of 1246 differentially expressed genes (DEGs), of which 835 were up-regulated and 411 were down-regulated. Further analysis revealed the enrichment of DEGs in phytohormone signal transduction. Consistently, phytohormone profiling indicated that auxin (IAA), jasmonic acid (JA), ethylene (ETH), and cytokinin (CK) levels increased significantly, whereas the gibberellin (GA) level decreased significantly in fea5. By integrating BSA-seq with RNA-seq, we identified Zm00001d048841 as the most likely candidate gene. Our results provide valuable insight into this new germplasm resource and the molecular mechanism underlying fasciated ears that produce a higher kernel row number in maize.

Exploring the Identity and Properties of Two Bacilli Strains and their Potential to Alleviate Drought and Heavy Metal Stress

Naturally available plant growth-promoting rhizobacteria (PGPR) have 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzymes, and are capable of processing the plant-borne ACC by converting it into α-ketobutyrate and ammonia. Thus, the PGPRs help in the depletion of ethylene levels, and enhance abiotic stress tolerance in plants. In the present study, two rhizobacterial strains, i.e., Bacillus cereus and B. haynesii, isolated from Vigna mungo and Phaseolus vulgaris, were used. These strains were taxonomically identified by 16S rDNA sequencing as B. cereus and B. haynesii, with NCBI accession numbers LC514122 and LC 514123, respectively. The phylogeny of these strains has also been worked out based on homology, with data available on NCBI GenBank. The strains were screened for their plant growth-promoting traits, and quantified in the same way. The enzymatic activity and molecular weight of the ACC deaminase obtained from both bacterial strains have also been determined. An in vitro drought tolerance study was done by using PEG 6000. These bacterial strains exhibited higher ACC deaminase activity (~5 to 6 µmol/mL), exopolysaccharide yield (15 to 18 mg/10 mL protein), and indole acetic acid (27–32 µg/mL). These characteristics indicate that the bacterial strains under present study may be helpful in enhancing the drought tolerance of the crops with enhanced yield. Bacillus cereus has been found to be a tolerant strain to As, Ba, and Ni, based on the plate assay method, and so it has the potential to be used as biofertilizer in fields affected by these metals.

Theoretical screening of M3(btc)2 metal–organic frameworks for ethylene and 1-methylcyclopropene storage

Metal-organic frameworks (MOFs) can find numerous potential applications due to their ability of (selective) gas sorption, separation, storage, and release. One such application is active food packaging, in which controlled levels of ethylene and 1-methylcyclopropene (1-MCP) gasses can speed up or slow down fruit ripening. Following our recent experimental study of Cu3(btc)2 (HKUST-1) MOF, this work is aimed to theoretical screening isostructural M3(btc)2 (M = Cr, Mn, Fe, Co, Ni, Cu, Zn) materials for potential ethylene and 1-MCP storage and release. The optimal geometries and bonding energies were calculated for ethylene, 1-MCP and water molecules adsorbed in different configurations on open metal sites of M3(btc)2 at B3LYP-D3 level of theory. The results are discussed in frame of potential practical application and correlated with the available experimental data.

Microcontroller-Based Gas Detection in Transformer Oil

The transformer is one of the essential parts of an electric power system. The distribution transformer is a part of the electric power system which plays a vital role in providing electrical energy services to customers. The increasing population and the development of the times make the need for continuous electrical energy. One of the causes of insulation failure in transformers is overheating in the central part. The transformer requires a cooling system to control the heat energy generated. Transformer oil is an insulating and cooling medium for the central part of the transformer. At the time of operation, some disturbances cause the emergence of gases such as carbon dioxide, ethane, and ethylene. The purpose of this study was to design a device for detecting levels of carbon dioxide (CO2), ethane (C2H6), and ethylene (C2H4) dissolved in transformer oil by displaying the ppm (parts per million) value for each gas. Atmega328 microcontroller is used for system control and as a data processor. The data is in the form of a voltage that the ADC microcontroller feature will change. This information is used to calculate the ppm value for each gas. The concentration of this gas will be displayed on the LCD control panel. From the results of this study, the DS18B20 sensor used has an error of 0.00315%, the MG-811 sensor has an error of 10,022, the MQ-6 sensor has an error of 7,918, and the MQ-2 sensor has an error of 9,356. This is indicated by the LCD output, which receives data automatically.

Ethylene: A Master Regulator of Plant-Microbe Interactions under Abiotic Stresses.

The plant phytohormone ethylene regulates numerous physiological processes and contributes to plant-microbe interactions. Plants induce ethylene production to ward off pathogens after recognition of conserved microbe-associated molecular patterns (MAMPs). However, plant immune responses against pathogens are essentially not different from those triggered by neutral and beneficial microbes. Recent studies indicate that ethylene is an important factor for beneficial plant-microbial association under abiotic stress such as salt and heat stress. The association of beneficial microbes with plants under abiotic stresses modulates ethylene levels which control the expression of ethylene-responsive genes (ERF), and ERFs further regulate the plant transcriptome, epi-transcriptome, Na+/K+ homeostasis and antioxidant defense mechanisms against reactive oxygen species (ROS). Understanding ethylene-dependent plant-microbe interactions is crucial for the development of new strategies aimed at enhancing plant tolerance to harsh environmental conditions. In this review, we underline the importance of ethylene in beneficial plant-microbe interaction under abiotic stresses.

Use of halotolerant Bacillus amyloliquefaciens RHF6 as a bio-based strategy for alleviating salinity stress in Lotus japonicus cv Gifu

Halotolerant (HT) bacteria are a group of microorganisms able to thrive in environments with relatively high salt concentrations. HT-microorganisms with plant growth-promoting (PGP) characteristics have been proposed to increase plant tolerance in salty soil. Here, we evaluated the PGP properties at increasing NaCl concentrations of HT-Bacillus strains, previously shown to have beneficial effects under physiological conditions. Most of the isolated showed indole acetic acid and ammonia production and were able to solubilize phosphate and suppress the proliferation of the phytopathogenic fungus Macrophomina phaseolina 2013–1 at high salt concentrations. One of the selected strains, Bacillus amyloliquefaciens RHF6, which retained its beneficial properties up to 400 mM NaCl in vitro, was tested on the legume model plant Lotus japonicus cv Gifu under salt stress. The inoculation with RHF6 significantly improved the survival of plants under high salinity conditions, as reflected in seedling root and shoot growth and total fresh weight (increased by 40%) when compared with non-inoculated plants. The ability of RHF6 to induce a plant antioxidant response, secrete the osmoprotectant proline and reduce ethylene level via the enzymatic ACC deaminase activity indicated this strain as a potentially helpful PGPB for the treatment of degraded soils.

ACC Deaminase Produced by PGPR Mitigates the Adverse Effect of Osmotic and Salinity Stresses in Pisum sativum through Modulating the Antioxidants Activities.

Salinity-induced ethylene production and reactive oxygen species (ROS) inhibit agricultural productivity. The plant synthesizes ethylene directly from aminocyclopropane-1-carboxylic acid (ACC). By using ACC as a nitrogen source, bacteria with ACC deaminase (ACCD) inhibit the overproduction of ethylene, thereby maintaining the ROS. The present study investigated the ACCD activity of previously identified rhizobacterial strains in Dworkin and Foster (DF) minimal salt media supplemented with 5 mM ACC (as N-source). Bacterial isolates GKP KS2_7 (Pseudomonas aeruginosa) and MBD 133 (Bacillus subtilis) could degrade ACC into α-ketobutyrate, exhibiting ACCD activity producing more than ~257 nmol of α-ketobutyrate mg protein−1 h−1, and were evaluated for other plant growth-promoting (PGP) traits including indole acetic acid production (>63 µg/mL), phosphate solubilization (>86 µg mL−1), siderophore (>20%) ammonia and exopolysaccharide production. Furthermore, Fourier Transform Infrared analysis also demonstrated α-ketobutyrate liberation from ACC deamination in DF minimal salt media, thereby confirming the ACCD activity. These isolates also showed enhanced tolerance to salinity stress of 3% w/v NaCl in vitro, in addition to facilitating multifarious PGP activities. Seed bacterization by these ACCD-producing bacterial isolates (GKP KS2_7 and MBD 133) revealed a significant decline in stress-stimulated ethylene levels and its associated growth inhibition during seedling germination. They also mitigated the negative effects of salt stress and increased the root-shoot length, fresh and dry weight of root and shoot, root-shoot biomass, total sugar, protein, reducing sugar, chlorophyll content, and antioxidants enzymes in Pisum sativum. As a result, these strains (GKP KS2_7 and MBD 133) might be applied as biofertilizers to counteract the negative effects of soil salinity.

Insight of PBZ mediated drought amelioration in crop plants.

Water scarcity is a significant environmental limitation to plant productivity as drought-induced crop output losses are likely to outnumber losses from all other factors. In this context, triazole compounds have recently been discovered to act as plant growth regulators and multi-stress protectants such as heat, chilling, drought, waterlogging, heavy metals, etc. Paclobutrazol (PBZ) [(2RS, 3RS)-1-(4-chlorophenyl)- 4, 4-dimethyl-2-(1H-1, 2, 4-trizol-1-yl)-pentan-3-ol)] disrupts the isoprenoid pathway by blocking ent-kaurene synthesis, affecting gibberellic acid (GA) and abscisic acid (ABA) hormone levels. PBZ affects the level of ethylene and cytokinin by interfering with their biosynthesis pathways. Through a variety of physiological responses, PBZ improves plant survival under drought. Some of the documented responses include a decrease in transpiration rate (due to reduced leaf area), higher diffusive resistance, relieving reduction in water potential, greater relative water content, less water use, and increased antioxidant activity. We examined and discussed current findings as well as the prospective application of PBZ in regulating crop growth and ameliorating abiotic stresses in this review. Furthermore, the influence of PBZ on numerous biochemical, physiological, and molecular processes is thoroughly investigated, resulting in increased crop yield.

Multifaceted effects of difenoconazole in tomato fruit ripening: Physiology, flavour and nutritional quality

Difenoconazole is widely used in crop growth, however, its effects on the quality of agricultural products are poorly studied. In this study, the application of difenoconazole on tomato plants could increase soluble sugar content, reduce organic acid and raise accumulation of nutrient-related metabolites during late fruit ripening. Consumer surveys in our study showed that the treatment of difenoconazole tomatoes group had higher sweetness and lower acidity, and those tomatoes were preferred by consumers. Alterations in fruit flavor-related attributes were at least in part corroborated by the abundance of transcripts related to sucrose (SlLin5, SlLin7, SlSuS2, SlSuS6, SlSPS1, SlSPS3) and organic acids (CS, ICDH, cMDH) anabolism. Furthermore, the difenoconazole also significantly promoted the expression of phytohormones synthesis genes, and consequently increased abscisic acid and ethylene levels. Our study not only provides theoretical support for the use of difenoconazole on tomatoes at the level of flavor quality and nutritional health, but also provides valuable information on the mechanism of triazole fungicides in the flavor quality of tomato fruits.

Foliar Application of Spermidine Alleviates Waterlogging-Induced Damages to Maize Seedlings by Enhancing Antioxidative Capacity, Modulating Polyamines and Ethylene Biosynthesis.

Waterlogging is a major threat to maize production worldwide. The exogenous application of spermidine is well known to enhance plant tolerance to abiotic stresses. The role of exogenous spermidine application in waterlogging tolerance in maize was investigated in this study. Two maize varieties (a waterlogging-tolerant variety: Xundan 20 (XD20) and a waterlogging-sensitive variety: Denghai 662 (DH662)) were subjected to waterlogging stress at the seedling stage, and then foliar spraying of 0.75 mM spermidine or purified water. Findings demonstrated lower chlorophyll content, reduced growth indices, considerable increase in superoxide anion (O2-) generation rate, and H2O2/malondialdehyde accumulation in the two maize varieties under waterlogging stress compared to the control treatment. However, the tolerance variety performed better than the sensitive one. Foliar application of spermidine significantly increased antioxidant enzyme activities under waterlogging stress. In addition, the application of spermidine increased polyamine levels and led to the reduction of ethylene levels under waterlogging. Consequences of spermidine application were most apparent for the waterlogging-sensitive cultivar DH662 under waterlogging than the waterlogging-tolerant variety XD20.

The volatilome response of fast-melting peaches to short low oxygen stress

Fast-melting peaches have a shelf life of only 3–4 d due to their rapid softening, and this poses a problem in marketing and consumer acceptability. A postharvest 22 h treatment at 20 °C of low oxygen (<1%) or 2 µl L−1 1-methylcyclopropene (1-MCP) was applied to delay softening. 1-MCP was ineffective, but the anaerobic stress delayed softening as expressed by texture measurements, ethylene levels, and chlorophyll index values. Taste panels showed a preference for untreated fruit of the same firmness as treated fruit, probably due to off-flavors volatiles evaporation. Nevertheless, consumer acceptance of treated fruit was high after 3 d at 20 °C and 4 d of cold storage, while control fruit was too soft to be sampled. Volatile compounds were analyzed on control and low oxygen-treated fruit following treatment and 48 h later. Forty-eight compounds were identified, and thirty-nine significantly differed among all four conditions. Eleven volatile compounds associated with anaerobic conditions increased in the low oxygen treatment after 72 h. However, the low oxygen treatment did not affect most ripening-related peach fruit volatiles, primarily lactones. It is hypothesized that these compounds diminished the perception of off-flavors associated with the anaerobic volatiles. This simple low oxygen treatment demonstrates promising results in delaying softening and extending the market life of fast-ripening peaches.

AcdS gene of Bacillus cereus enhances salt tolerance of seedlings in tobacco (Nicotiana tabacum L.)

Previous studies show that 1-aminocyclopropane-1-carboxylate (ACC) deaminase can facilitate the growth and stress tolerance of hosts by reducing ethylene levels. In this study, the acdS gene encoding ACC deaminase from Bacillus cereus (HK012) was cloned and transformed into tobacco (Nicotiana tabacum L.) by the leaf disc method using Agrobacterium. Molecular detection and physiological analysis of the transgenic tobacco plants were performed. Our results showed the acdS gene was integrated into the tobacco genome and fluorescence microscopy showed that the fusion protein was located on the cell membrane of tobacco root. Compared with control, the transgenic plants showed increases in plant height, root length, dry weight, fresh weight and chlorophyll content; and significant increases in the concentration of proline of 55.15% and 42.7% under salt stress conditions (150 mmol L−1 and 300 mmol L−1 NaCl, respectively). The superoxide dismutase, peroxidase, catalase and ACC deaminase activities of transgenic tobacco were higher than those of control tobacco at 150 and 300 mmol L−1 salt concentrations. Transgenic tobacco seedlings expressing the acdS gene of B. cereus HK012 showed higher salt tolerance than the control plants. The obtained results suggest that the acdS gene of B. cereus can be used to promote salt tolerance in glycophytes by using biotechnology strategies.

Altered brassinolide sensitivity1 Regulates Fruit Size in Association with Phytohormones Modulation in Tomato

BRs (Brassinosteroids) regulate many essential pathways related to growth, cell elongation, cell expansion, plant architecture, and fruit development. The potential exogenous application of BR-derivatives has been proven to stimulate plant growth and development, including quality attributes of fruits, whereas its biosynthesis inhibition has shown the opposite effect. In this study, BR-insensitive tomato mutants were used to reveal the potential function of BR signaling in the regulation of fruit development to elaborate the regulatory mechanism of BR signaling in tomato fruits. The BR-signaling mutant exhibited a typical dwarf phenotype and reduced vegetative growth, fruit size, and weight. Microscopic and transcriptional evaluation of the abs1 mutant fruits implies that reduced cell size and number are responsible for the phenotypic variations. Additionally, we also found that the altered content of phytohormones, such as auxin, gibberellin, cytokinin, and ethylene levels, contributed to altered fruit development. Moreover, fruit growth and cell development-specific gene expression levels were downregulated in BR-insensitive plants; culminating in reduced cell size, cell number, and cell layers. These findings provide insight into physio-chemical changes during fruit development in response to BR-insensitivity.

The HY5 transcription factor negatively regulates ethylene production by inhibiting ACS1 expression under blue light conditions in pear

Ethylene is the main factor controlling fruit ripening of pear (Pyrus ussuriensis). Ethylene production rate is negatively correlated with fruit shelf life; therefore, it is important to decrease the ethylene levels for optimal fruit storage. Here, we observed that blue light treatment could inhibit ethylene production and promote the expression of ELONGATED HYPOCOTYL 5 (PuHY5), a basic leucine zipper domain (bZIP) transcription factor. The following studies showed that PuHY5 could bind to the promoter of ACC synthase 1 (PuACS1), a rate-limiting enzyme in ethylene biosynthesis, and inhibit its expression. For pears in which PuHY5 was silenced, the ethylene production and PuACS1 expression were much higher than those in the control fruit. These results demonstrated that blue light inhibited ethylene production through the induction of PuHY5 in pear. Our finding provides a new method for prolonging fruit shelf life.

Stay-green trait ameliorates combined heat and drought stress in wheat

The present study was carried out during rabi 2017-18 at ICAR-Indian Agricultural Research Institute, New Delhi to investigate the effect of stay-green trait on grain yield in wheat under combined heat and drought stress. Two high stay green (GCP 6 and GCP 33) and two low stay green (GCP 23 and GCP 30) Recombinant Inbred Lines (RILs) of wheat along with their parents (HI1500/DBW43) were grown in field conditions under timely sown with irrigation (control) and without irrigation (drought stress), and late sown with irrigation (heat stress) and without irrigation (combined heat and drought stress). High stay-green RILs showed the reduced levels of abscisic acid and ethylene production during anthesis stage under heat, drought and combined stress conditions as compared to low stay green RILs. Furthermore, there was significantly better yield was observed in high stay-green RILs as compared to low stay-green RILs. Thus our study concludes that stay-green traits improve the yield in wheat under combined heat and drought stress condition by delaying the senescence through reduced levels of abscisic acid and ethylene.

Molecular dissection of rose and Botrytis cinerea pathosystems affected by ethylene

Botrytis cinerea (B. cinerea) is a necrotrophic pathogen that causes significant growth and postharvest commercial losses in cut roses. Postharvest disease severity is affected by ethylene levels during transport and storage conditions. In this study, we identified the relationship between ethylene, fungal growth, and ethylene inhibitors during B. cinerea infection in cut ‘Pink Beauty’ roses. The results suggest that cut rose susceptibility to gray mold disease is associated with the developmental stage of flowers, especially the level of senescence, which is stimulated by ethylene biosynthesis in petals. The mRNA levels of ethylene biosynthesis genes in petals were related to the severity of gray mold; however, their expression levels decreased when the cut roses were completely macerated by B. cinerea. B. cinerea infections in cut flowers activated ethylene biosynthesis and signaling pathways, leading to the activation of RhERFs in the petals. Ethylene regulated the development of B. cinerea infections in the cut flowers directly by binding to the receptors or indirectly by promoting the ethylene response in the host tissues. The suppression of ethylene responses in petals and inhibition of the fungal histidine kinase receptor of B. cinerea by 1-methylcylopropene (1-MCP) made cut rose flowers resistant to such necrotrophic pathogens. We also established a working model for ethylene binding and plant and fungus actions in the rose-B. cinerea pathosystem. Understanding the relationship between ethylene and gray mold disease in cut roses and the interaction between ethylene inhibitors and B. cinerea will help improve postharvest treatments for reducing B. cinerea damage in cut flowers.

Crosstalk of Cytokinin with Ethylene and Auxin for Cell Elongation Inhibition and Boron Transport in Arabidopsis Primary Root under Boron Deficiency

Several studies have shown the role of phytohormones in the regulation of root growth of Arabidopsis plants under boron (B) deficiency. Ethylene and auxin play an important role in the control of Arabidopsis primary root cell elongation under short-term B deprivation, whereas cytokinins regulate root growth inhibition under B deficiency by controlling meristem cell proliferation. In this work, we study the possible interaction among cytokinin, ethylene, and auxin in the primary root response to B-deprivation treatment, as well as their possible role in B uptake and transport. Wild type (WT) and two mutants related to auxin and ethylene (aux1 and acs11) Arabidopsis plants were grown in control (10 µM B) or B starvation (0 µM B) treatment, in the absence or presence of trans-zeatin, and their primary root growth was analyzed. The possible interaction between these hormones was also studied by analyzing AUX1 gene expression in the acs11 mutant and ACS11 gene expression in the aux1 mutant. The GUS reporter lines ARR5::GUS, IAA2::GUS, and EBS::GUS were used to observe changes in cytokinin, auxin, and ethylene levels in the root, respectively. The results of this work suggest that cytokinin inhibits root cell elongation under B deficiency through two different mechanisms: (i) an ethylene-dependent mechanism through increased expression of the ACS11 gene, which would lead to increased ethylene in the root, and (ii) an ethylene-independent mechanism through decreased expression of the AUX1 gene, which alters auxin signaling in the meristematic and elongation zones and stele. We also report that changes in the expression of several B transporters occur in response to auxin, ethylene, and cytokinin that may affect the plant B content.