Ethylene inhibitors enhance in vitro root formation from apple shoot cultures

Ethylene Action Inhibition Improves Adventitious Root Induction in Adult Chestnut Tissues

Phase change refers to the process of maturation and transition from the juvenile to the adult stage. In response to this shift, certain species like chestnut lose the ability to form adventitious roots, thereby hindering the successful micropropagation of adult plants. While auxin is the main hormone involved in adventitious root formation, other hormones, such as ethylene, are also thought to play a role in its induction and development. In this study, experiments were carried out to determine the effects of ethylene on the induction and growth of adventitious roots. The analysis was performed in two types of chestnut microshoots derived from the same tree, a juvenile-like line with a high rooting ability derived from basal shoots (P2BS) and a line derived from crown branches (P2CR) with low rooting responses. By means of the application of compounds to modify ethylene content or inhibit its signalling, the potential involvement of this hormone in the induction of adventitious roots was analysed. Our results show that ethylene can modify the rooting competence of mature shoots, while the response in juvenile material was barely affected. To further characterise the molecular reasons underlying this maturation-derived shift in behaviour, specific gene expression analyses were developed. The findings suggest that several mechanisms, including ethylene signalling, auxin transport and epigenetic modifications, relate to the modulation of the rooting ability of mature chestnut microshoots and their recalcitrant behaviour.

Plant Growth-Promoting Rhizobacteria With ACC Deaminase Activity Enhance Maternal Lateral Root and Seedling Growth in Switchgrass

Switchgrass, a C4 plant with high potential as a bioenergy source, is unsteady in yield under sub-optimal conditions. Bacteria containing 1-aminocyclopropane-1-carboxylate synthase (ACC) deaminase can promote plant growth. We isolated bacteria containing ACC deaminase activity from switchgrass rhizosphere using an orthogonal matrix experimental design with four factors (bacterial liquid concentration, bacterial liquid treatment time, nitrogen content, and NaCl) to quantitatively investigate the effects and pairwise interactions on the seedling growth. Pseudomonas sp. Y1, isolated from the switchgrass cv. Blackwell rhizomes was selected. We optimized the inoculation bacterial concentration, treatment time, NaCl, and nitrogen concentration for the seedling growth. The optimal bacterial concentration, treatment time, NaCl, and nitrogen content was 0.5-1.25 OD at 600 nm, 3 h, 60-125 mM and 158 mg L-1, respectively. Pseudomonas sp. Y1 significantly increased the total root length, root surface, shoot length, and fresh and dry weight through an effective proliferation of the number of first-order lateral roots and root tips. This indicated that Pseudomonas sp. Y1 has a higher potential to be used as a plant growth-promoting rhizobacteria bacteria.

The role and proteomic analysis of ethylene in hydrogen gas-induced adventitious rooting development in cucumber (Cucumis sativus L.) explants

Previous studies have shown that both hydrogen gas (H₂) and ethylene (ETH) play positive roles in plant adventitious rooting. However, the relationship between H₂and ETH during this process has not been explored and remains insufficiently understood. In this study, cucumber (Cucumis sativus L.) was used to explore the proteomic changes in ETH-H₂-induced rooting. Our results show that hydrogen-rich water (HRW) and ethylene-releasing compound (ethephon) at proper concentrations promote adventitious rooting, with maximal biological responses occurring at 50% HRW or 0.5 µM ethephon. ETH inhibitors aminoethoxyvinylglycine (AVG) and AgNO₃ cause partial inhibition of adventitious rooting induced by H₂, suggesting that ETH might be involved in H₂-induced adventitious rooting. According to two-dimensional electrophoresis (2-DE) and mass spectrometric analyses, compared with the control, 9 proteins were up-regulated while 15 proteins were down-regulated in HRW treatment; four proteins were up-regulated while 10 proteins were down-regulated in ethephon treatment; and one protein was up-regulated while nine proteins were down-regulated in HRW+AVG treatment. Six of these differentially accumulated proteins were further analyzed, including photosynthesis -related proteins (ribulose-1,5-bisphosphate carall boxylase smsubunit (Rubisco), sedoheptulose-1,7-bisphosphatase (SBPase), oxygen-evolving enhancer protein (OEE1)), amino and metabolism-related protein (threonine dehydratase (TDH)), stress response-related protein (cytosolic ascorbate peroxidase (CAPX)), and folding, modification and degradation-related protein (protein disulfide-isomerase (PDI)). Moreover, the results of real-time PCR about the mRNA levels of these genes in various treatments were consistent with the 2-DE results. Therefore, ETH may be the downstream signaling molecule during H₂- induced adventitious rooting and proteins Rubisco, SBPase, OEE1, TDH, CAPX and PDI may play important roles during the process.

Metabolic Changes Induced by Silver Ions in Carlina acaulis

Silver is one of the most toxic heavy metals for plants, inducing various toxic symptoms and metabolic changes. Here, the impact of Ag(I) on Carlina acaulis physiology and selected metabolites was studied using two Ag concentrations (1 or 10 µM) after 14 days of exposure. The higher concentration of Ag(I) evoked reduction of growth, while 1 µM Ag had a growth-promoting effect on root biomass. The translocation factor (<0.04) showed that Ag was mainly retained in the roots. The 1 µM Ag concentration increased the level of low-molecular-weight organic acids (LMWOAs), while 10 µM Ag depleted these compounds in the roots. The increased concentration of Ag(I) elevated the accumulation of phytochelatins (PCs) in the roots and reduced glutathione (GSH) in the shoots (but not in the roots). At 1 µM, Ag(I) elevated the level of phenolic and triterpene acids, while the 10 µM Ag treatment increased the carlina oxide content in the roots. The obtained results indicate an alteration of metabolic pathways of C. acaulis to cope with different levels of Ag(I) stress. Our data imply that the intracellular binding of Ag(I) and nonenzymatic antioxidants contribute to the protection against low concentrations of Ag ions.

Uptake and Transformation of Silver Nanoparticles and Ions by Rice Plants Revealed by Dual Stable Isotope Tracing

Knowledge on the uptake and transformation of silver nanoparticles (AgNPs) and Ag⁺ ions by organisms is critical for understanding their toxicity. Herein, the differential uptake, transformation, and translocation of AgNPs and Ag⁺ ions in hydroponic rice ( Oryza sativa L.) is assessed in modified Hewitt (with Cl^- ions, HS(Cl)) and Hogland solutions (without Cl^- ions, HS) using dual stable isotope tracing (¹⁰⁷AgNO₃ and ¹⁰⁹AgNPs). After coexposure to ¹⁰⁷Ag⁺ ions and ¹⁰⁹AgNPs at 50 μg L^-1 (as Ag for both) for 14 days, a stimulatory effect was observed on root elongation (increased by 68.8 and 71.9% for HS(Cl) and HS, respectively). Most of the Ag⁺ ions (from ¹⁰⁷Ag⁺ ions and ¹⁰⁹AgNPs) were retained on the root surface, while the occurrence of AgNPs (from ¹⁰⁹AgNPs and ¹⁰⁷Ag⁺ ions) was observed in the root, suggesting the direct uptake of AgNPs and/or reduction of Ag⁺ ions. Higher fractions of Ag⁺ ions in the shoot suggest an in vivo oxidation of AgNPs. These results demonstrated the intertransformation between Ag⁺ ions and AgNPs and the role of AgNPs as carriers and sources of Ag⁺ ions in organisms, which is helpful for understanding the fate and toxicology of Ag.

Transcriptome profiling of genes involved in induced systemic salt tolerance conferred by Bacillus amyloliquefaciens FZB42 in Arabidopsis thaliana

Plant growth-promoting Bacillus amyloliquefaciens FZB42 induces systemic salt tolerance in Arabidopsis and enhances the fresh and dry weight. However, the underlying molecular mechanism that allows plants to respond to FZB42 and exhibit salt tolerance is largely unknown. Therefore, we performed large-scale transcriptome sequencing of Arabidopsis shoot tissues grown under salt stress with or without FZB42 inoculation by using Illumina sequencing to identify the key genes and pathways with important roles during this interaction. In total, 1461 genes were differentially expressed (FZB42-inoculated versus non-inoculated samples) at 0 mM NaCl, of which 953 were upregulated and 508 downregulated, while 1288 genes were differentially expressed at 100 mM NaCl, of which 1024 were upregulated and 264 were downregulated. Transcripts associated with photosynthesis, auxin-related, SOS scavenging, Na+ translocation, and osmoprotectant synthesis, such as trehalose and proline, were differentially expressed by FZB42 inoculation, which reduced the susceptibility to salt and facilitated salt adaptation. Meanwhile, etr1-3, eto1, jar1-1, and abi4-102 hormone-related mutants demonstrated that FZB42 might induce plant salt tolerance via activating plants ET/JA signaling but not ABA-dependent pathway. The results here characterize the plant transcriptome under salt stress with plant growth-promoting bacteria inoculation, thereby providing insights into the molecular mechanisms responsible for induced salt tolerance.

Early response of willow to increasing silver concentration exposure

This is a preliminary hydroponic study to test willow sensitivity to silver nitrate, a highly toxic chemical compound. We grew willow cuttings for a period of three weeks in the presence of increasing AgNO(3) concentrations and assessed the response in terms of growth and physiology. We found that AgNO(3) is generally extremely harmful to willow. AgNO(3) concentration as high as 0.027 muM may result in a significant reduction of biomass productivity and a decrease in stomatal conductance over the first week of exposure. However, willows seem able to adapt to high AgNO(3) concentrations on a longer timeline.

Ethylene emission and PR protein synthesis in ACC deaminase producing Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.) challenged with Ralstonia solanacearum under greenhouse conditions

Bacteria of genus Methylobacterium have been found to promote plant growth and regulate the level of ethylene in crop plants. This work is aimed to test the induction of defense responses in tomato against bacterial wilt by stress ethylene level reduction mediated by the ACC deaminase activity of Methylobacterium strains. Under greenhouse conditions, the disease index value in Methylobacterium sp. inoculated tomato plants was lower than control plants. Plants treated with Methylobacterium sp. challenge inoculated with Ralstonia solanacearum (RS) showed significantly reduced disease symptoms and lowered ethylene emission under greenhouse condition. The ACC and ACO (1-aminocyclopropane-1-carboxylate oxidase) accumulation in tomato leaves were significantly reduced with Methylobacterium strains inoculation. While ACC oxidase gene expression was found higher in plants treated with R. solanacearum than Methylobacterium sp. treatment, PR proteins related to induced systemic resistance like β-1,3-glucanase, PAL, PO and PPO were increased in Methylobacterium sp. inoculated plants. A significant increase in β-1,3-glucanase and PAL gene expression was found in all the Methylobacterium spp. treatments compared to the R. solanacearum treatment. This study confirms the activity of Methylobacterium sp. in increasing the defense enzymes by modulating the ethylene biosynthesis pathway and suggests the use of methylotrophic bacteria as potential biocontrol agents in tomato cultivation.

Current trends and future prospects of biotechnological interventions through tissue culture in apple

Apple (Malus domestica Borkh.), which is a widely cultivated, important economic fruit crop with nutritive and medicinal importance, has emerged as a model horticultural crop in this post-genomic era. Apple cultivation is heavily dependent on climatic condition and is susceptible to several diseases caused by fungi, bacteria, viruses, insects, etc. Extensive research work has been carried out to standardize tissue culture protocols and utilize them in apple improvement. We review the in vitro shoot multiplication, rooting, transformation and regeneration methodologies in apple and tabulate various such protocols for easy reference. The utility and limitation of transgenesis in apple improvement have also been summarized. The concepts of marker-free plants, use of non-antibiotic resistance selectable markers, and cisgenic and intragenic approaches are highlighted. Furthermore, the limitations, current trends and future prospects of tissue culture-mediated biotechnological interventions in apple improvement are discussed.

Micropropagation of apple--a review

Micropropagation of apple has played an important role in the production of healthy, disease-free plants and in the rapid multiplication of scions and rootstocks with desirable traits. During the last few decades, in apple, many reliable methods have been developed for both rootstocks and scions from a practical, commercial point of view. Successful micropropagation of apple using pre-existing meristems (culture of apical buds or nodal segments) is influenced by several internal and external factors including ex vitro (e.g. genotype and physiological state) and in vitro conditions (e.g., media constituents and light). Specific requirements during stages of micropropagation, such as the establishment of in vitro cultures, shoot multiplication, rooting of microshoots and acclimatization are summarized in this review. New approaches for increasing shoot multiplication and rooting for apple and current use of micropropagated plantlets as tools in basic and applied research are also discussed.

Comparative effectiveness of Pseudomonas and Serratia sp. containing ACC-deaminase for improving growth and yield of wheat (Triticum aestivum L.) under salt-stressed conditions

Ethylene synthesis is accelerated in response to various environmental stresses like salinity. Ten rhizobacterial strains isolated from wheat rhizosphere taken from different salt affected areas were screened for growth promotion of wheat under axenic conditions at 1, 5, 10 and 15 dS m(-1). Three strains, i.e., Pseudomonas putida (N21), Pseudomonas aeruginosa (N39) and Serratia proteamaculans (M35) showing promising performance under axenic conditions were selected for a pot trial at 1.63 (original), 5, 10 and 15 dS m(-1). Results showed that inoculation was effective even in the presence of higher salinity levels. P. putida was the most efficient strain compared to the other strains and significantly increased the plant height, root length, grain yield, 100-grain weight and straw yield up to 52, 60, 76, 19 and 67%, respectively, over uninoculated control at 15 dS m(-1). Similarly, chlorophyll content and K(+)/Na(+) of leaves also increased by P. putida over control. It is highly likely that under salinity stress, 1-aminocyclopropane-1-carboxylic acid-deaminase activity of these microbial strains might have caused reduction in the synthesis of stress (salt)-induced inhibitory levels of ethylene. The results suggested that these strains could be employed for salinity tolerance in wheat; however, P. putida may have better prospects in stress alleviation/reduction.

LCMS and GCMS for the screening of alkaloids in natural and in vitro extracts of Leucojum aestivum

HPLC coupled to a mass spectrometer (MS) was used for the analysis of galanthamine and lycorine in natural extracts of Leucojum aestivum and in their in vitro cultures grown with a precursor (ACC), inhibitors (AgNO(3), STS), or an absorber (KMnO(4)) of ethylene. The maximum galanthamine (0.002%) and lycorine (0.02%) concentrations in tissue cultures were obtained in the presence of KMnO(4). GCMS was used to investigate underivatized alkaloid mixtures from L. aestivum. Seven alkaloids were identified in in vivo bulbs. KMnO(4) led to the highest diversity of alkaloids in tissue culture extracts.

Characterization of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing Methylobacterium oryzae and interactions with auxins and ACC regulation of ethylene in canola (Brassica campestris)

The possible interaction of the plant hormones auxin and ethylene and the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing bacteria on ethylene production in canola (Brassica campestris) in the presence of inhibitory concentrations of growth regulators were investigated. The effects of auxin (indole-3-acetic acid and 2,4-dichlorophenoxy acetic acid), auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid, ethylene precursor 1-aminocyclopropane-1-carboxylate and ethylene synthesis inhibitor L-alpha-(2-aminoethoxyvinyl)glycine hydrochloride on root elongation were concentration dependent. Exogenous addition of growth regulators influences the enzyme activities of ethylene production and we have presented here evidences that support the hypothesis that inhibitory effects of auxin on root elongation are independent of ethylene. Additionally, we have proved that inoculation of ACC deaminase containing Methylobacterium oryzae sequester ACC exuded from roots and hydrolyze them lowering the concentration of ACC in root exudates. However, the inhibitory actions of exogenous additions of auxins could not be ameliorated by bacterial inoculation that reduces ethylene concentration in canola seedlings.

Regulation of ethylene levels in canola (Brassica campestris) by 1-aminocyclopropane-1-carboxylate deaminase-containing Methylobacterium fujisawaense

We report the presence of ACC deaminase in Methylobacterium fujisawaense and its lowering of ethylene levels and promotion of root elongation in canola seedlings under gnotobiotic conditions. To test a part of the previous model proposed for ACC deaminase producing bacteria with Methylobacterium, ACC levels and various enzyme activities were monitored in canola. Lower amounts of ACC were present in the tissues of seeds treated with M. fujisawaense strains than in control seeds treated with MgSO(4). Though the increased activities of ACC synthase in the tissue extracts of the treated seedlings might be due to bacterial indole-3-acetic acid, the amount of ACC was reduced due to bacterial ACC deaminase activity. The activities of ACC oxidase, the enzyme catalyzing conversion of ACC to ethylene remained lower in M. fujisawaense treated seedlings. This consequently lowered the ethylene in plants and prevented ethylene inhibition of root elongation. Our results collectively suggest that Methylobacterium commonly found in soils, as well as on the surfaces of leaves, seeds, and in the rhizosphere of a wide variety of plants could be better exploited to promote plant growth.

Determination of 1-aminocycopropane-1-carboxylic acid (ACC) to assess the effects of ACC deaminase-containing bacteria on roots of canola seedlings

Previously, it was proposed that plant growth-promoting bacteria that possess the enzyme, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, can reduce the amount of ethylene produced by a plant and thereby promote root elongation. To test this model, canola seeds were imbibed in the presence of the chemical ethylene inhibitor, 2-aminoethoxyvinyl glycine (AVG), various strains of plant growth-promoting bacteria, and a psychrophilic bacterium containing an ACC deaminase gene on a broad host range plasmid. The extent of root elongation and levels of ACC, the immediate precursor of ethylene, were measured in the canola seedling roots. A modification of the Waters AccQ*Tag Amino Acid Analysis Method(tm) was used to quantify ACC in the root extracts. It was found that, in the presence of the ethylene inhibitor, AVG, or any one of several ACC deaminase-containing strains of bacteria, the growth of canola seedling roots was enhanced and the ACC levels in these roots were lowered.