Auxin Concentration Research Articles

Relationship between submergence of graft union and auxin accumulation of grafted mango trees under flooded conditions

ABSTRACT In recent years, many fields have been affected by floods. In mango trees, grafted trees are more susceptible to flood damage than seedling trees, When the graft union is submerged. In this study, the translocation of substances, especially auxin, through the graft union was investigated to clarify the causes of death in mango trees when the trunk was submerged up to the graft union. After approximately 1 month of flooding, changes were observed in root respiration, carbon dioxide release from the trunk, and leaf stomatal conductance. The auxin content in the scion increased significantly from 19.5 ng g−1 dry weight (DW) in the control to 122.1 ng g−1 (DW) in the flooded treatment. Nevertheless, no significant increase in auxin content was observed in the rootstock. In addition, there was no pectin degradation, leading to the death of the grafted mango trees. Auxin accumulation induces expansins, which are cell wall proteins that loosen the cell wall structure and are involved in structural changes in cell wall polysaccharides. Therefore, submergence of the graft union may inhibit auxin translocation between the scion and rootstock, resulting in pectin degradation in the scion bark and leading to tissue breakdown and death of the mango tree.

Effects of humic acid on the root growth and its interaction with coated diammonium phosphate on yield of wheat

Coated diammonium phosphate (CDAP) and humic acid (HA) have improved crop phosphorus fertilizer use efficiency. However, the effects of different phosphorus concentrations and HA incorporation on wheat and their potential mechanisms are unknown. This study aimed to elucidate the impact of varying phosphorus concentrations and HA applied in combination with coated phosphate fertilizers on wheat growth and its yield. An incubation experiment was performed using different phosphorus (P) concentrations (P0%, P1%, P10%, and P100% in Hoagland nutrient solution) combined with two HA content (0 and 0.1 g L−1). Finally, the wheat pot experiments were presented with two HA application rates (0 and 45 kg ha−1) and two P levels (60 and 75 kg P2O5 ha−1) under the condition that two forms of P fertilizer (CDAP and diammonium phosphate (DAP)) were comprised. At the same P rate, the auxin (IAA) and cytokinin (CTK) content in wheat seedlings of HA-added treatments was increased by 11.30%- 40.33% and 12.03%-29.21%, respectively, compared with the HA-free treatment. The CDAP combined with HA that improved the wheat growth and increased the yield and P use efficiency (PUE) by 2.7%-4.3% and 6.7-7.1 percentage points. Furthermore, the interactions between the types of P fertilizer (DAP, CDAP) and the application rate of HA were recorded as being significant (p < 0.01) for the wheat yield. In conclusion, as an environmentally friendly fertilizer, the combination of CDAP and HA increased enhanced root growth, and then maximized yields and PUE, which is important for P resource conservation and environmental protection.

Biochemical and physiological effects of propagule type and auxin concentration on adventitious root formation in novel Jasmine genotypes

Jasmine is primarily propagated through asexual methods, and bio-stimulants can improve soil fertility around plant roots. Some jasmine genotypes are mainly propagated through cuttings; however, the rooting process is slow and inconsistent. Specific jasmine genotypes are primarily propagated through cuttings, but the rooting process is slow and uneven. This study evaluated the regeneration potential of stem cuttings by investigating the effects of auxins and various propagule types on adventitious root formation, along with associated biochemical changes. A field experiment conducted by the Department of Floriculture and Landscaping at TNAU, Coimbatore, Tamil Nadu, from December 2023 to June 2024, during the winter monsoon, investigated the rooting of stem cuttings in three Jasminum genotypes using auxin. Stem cuttings of J. sambac Double Flower type (DF), J. grandiflorum White Flower type (WF) and a new cultivar of J. multiflorum CO.1 Winter Jasmine (CO.1 WJ) were treated with three Indole-3-Butyric Acid (IBA) concentrations (0.5, 1, 1.5 g L-1) and distilled water as control. Utilizing a Factorial, Completely Randomized Design for terminal and semi-hardwood cuttings, the study found that rooting hormone significantly enhanced root formation and stem and shoot growth. Semi-hardwood cuttings of J. sambac (DF) treated with 1g L-1 IBA had the highest rooting rate (88.60%), number of roots (9.34), root length (12.74 cm), shoot length (10.26 cm) and number of leaves (6.60). The highest rooting rate of 48.15% was obtained from the terminal cuttings of J. grandiflorum (WF) that had been treated with 1g L-1 IBA, in addition to other parameters such as number of roots (13.52), root length (12.03 cm), shoot length (14.30 cm), and number of leaves (13.48). On the other hand, J. multiflorum (CO.1 WJ) recorded the highest rooting rate of 72.23%, root number of 16.52, root length of 17.22 cm, shoot length of 14.14 cm and number of leaves, which was pegged at 31.70 when terminal cuttings were treated with 1g L-1 IBA. The current findings indicate that the application of auxins is crucial for promoting early root initiation and achieving higher rooting success, making it advantageous for vegetative propagation.

Study of Probiotics as Biostimulants and Biofortifiers in Seed Germination

Germination is a bioprocessing technique used by the food industry to improve the nutrient content of seeds. Imbibition is considered a crucial stage for optimal plant development. In this research, four different groups of seeds were studied to evaluate the effect of using probiotics during the imbibition phase on the germination process, as well as on the microbiological quality, as specified by Mexican regulations. The efficiency of probiotic production was also determined. Regarding the results, most seeds achieved a germination rate between 90–100%, with seeds inoculated with probiotics reaching a higher rate. This increase was related to the concentration of auxins. Importantly, the lowest levels of CFU/g counts for coliforms and fungi were found in the treated sprouts. Additionally, the sprouts exhibited values greater than 1 × 106 CFU/g of probiotics. The imbibition of certain types of seeds with probiotics with Lactiplantibacillus plantarum and Saccharomyces boulardii increases the germination speed, as well as the biomass obtained, which suggests that it may be an alternative to treatments in the agricultural industry for greater production.

Accumulation of podophyllotoxin in the root culture of Hyptis suaveolens (L.) Poit: A potential natural lignan for clinically useful anticancer drugs

Podophyllotoxin (PTOX) is a natural antiviral, antirheumatic and anticancer molecule, but it is expensive to chemically synthesize. The present study aimed to evaluate growth and PTOX accumulation in root cultures of Hyptis suaveolens treated with different concentrations of auxins, vitamins and myo-inositol. Root cultures grown in liquid medium supplemented with different concentrations of indole-3-butyric acid (IBA), 1-naphthaleneacetic acid (NAA), vitamins and myo-inositol were used to measure biomass production and PTOX content. PTOX quantitation was performed via high-performance liquid chromatography with diode-array detection (HPLC-DAD) using a newly developed analytical method after successful validation. Root culture in MS medium supplemented with 1 mg L−1 IBA +0.5 mg L−1 NAA resulted in the highest root dry weight (248.76 mg) and the highest PTOX concentration in the roots (179.97 μg g−1 root). The roots cultured in liquid MS medium supplemented with 1 mg L−1 IBA +0.5 mg L−1 NAA presented the greatest increase in root biomass and PTOX content. This adequate balance of vitamin and myo-inositol supplementation in liquid MS culture medium increased the root dry weight and PTOX content.

Single-Base Methylome Analysis of Sweet Cherry (Prunus avium L.) on Dwarfing Rootstocks Reveals Epigenomic Differences Associated with Scion Dwarfing Conferred by Grafting

Plant grafting using dwarfing rootstocks is one of the important cultivation measures in the sweet cherry (Prunus avium) industry. In this work, we aimed to explore the effects of the dwarfing rootstock “Pd1” (Prunus tomentosa) on sweet cherry ‘Shuguang2’ scions by performing morphological observations using the paraffin slice technique, detecting GA (gibberellin) and IAA (auxin) contents using UPLC-QTRAP-MS (ultra-performance liquid chromatography coupled with a hybrid triple quadrupole-linear ion trap mass spectrometer), and implementing integration analyses of the epigenome and transcriptome using whole-genome bisulfite sequencing and transcriptome sequencing. Anatomical analysis indicated that the cell division ability of the SAM (shoot apical meristem) in dwarfing plants was reduced. Pd1 rootstock significantly decreased the levels of GAs and IAA in sweet cherry scions. Methylome analysis showed that the sweet cherry genome presented 15.2~18.6%, 59.88~61.55%, 28.09~33.78%, and 2.99~5.28% methylation at total C, CG, CHG, and CHH sites, respectively. Shoot tips from dwarfing plants exhibited a hypermethylated pattern mostly due to increased CHH methylation, while leaves exhibited a hypomethylated pattern. According to GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis, DMGs (differentially methylated genes) and DEGs (differentially expressed genes) were enriched in hormone-related GO terms and KEGG pathways. Global correlation analysis between methylation and transcription revealed that mCpG in the gene body region enhanced gene expression and mCHH in the region near the TSS (transcription start site) was positively correlated with gene expression. Next, we found some hormone-related genes and TFs with significant changes in methylation and transcription, including SAURs, ARF, GA2ox, ABS1, bZIP, MYB, and NAC. This study presents a methylome map of the sweet cherry genome, revealed widespread DNA methylation alterations in scions caused by dwarfing rootstock, and obtained abundant genes with methylation and transcription alterations that are potentially involved in rootstock-induced growth changes in sweet cherry scions. Our findings can lay a good basis for further epigenetic studies on sweet cherry dwarfing and provide valuable new insight into understanding rootstock–scion interactions.

AUXIN RESPONSE FACTOR 2 mediates repression of strawberry receptacle ripening via auxin-ABA interplay.

Cultivated strawberry (Fragaria × ananassa) is a popular, economically important fruit. The ripening of the receptacle (pseudocarp), the main edible part, depends on endogenously produced abscisic acid (ABA) and is suppressed by the high level of auxin produced from achenes (true fruit) during early development. However, the mechanism whereby auxin regulates receptacle ripening through inhibiting ABA biosynthesis remains unclear. Here, we identified AUXIN RESPONSE FACTOR 2 (FaARF2), which showed decreased expression with reduced auxin content in the receptacle, leading to increased ABA levels and accelerated ripening. Dual-luciferase, yeast one-hybrid, and electrophoretic mobility shift assays demonstrated that FaARF2 could bind to the AuxRE element in the promoter of 9-CIS-EPOXYCAROT-ENOID DIOXYGENASE 1 (FaNCED1), a key ABA biosynthetic gene, to suppress its transcriptional activity. Transiently overexpressing FaARF2 in the receptacles decreased FaNCED1 expression and ABA levels, resulting in inhibition of receptacle ripening and of development of quality attributes, such as pigmentation, aroma, and sweetness. This inhibition caused by overexpressing FaARF2 was partially recovered by the injection of exogenous ABA; conversely, transient silencing of FaARF2 using RNA interference produced the opposite results. The negative targeting of FaNCED1 by FaARF2 is a key link between auxin-ABA interactions and regulation of strawberry ripening.

GhMAC3e is involved in plant growth and defense response to Verticillium dahliae.

GhMAC3e expression was induced by various stresses and hormones. GhMAC3e may regulate plant growth by influencing auxin distribution, and play important roles in Verticillium wilt resistance via mediating SA signaling. The MOS4-Associated Complex (MAC) is a highly conserved protein complex involved in pre-mRNA splicing and spliceosome assembly, which plays a vital role in plant immunity. It comprises key components such as MOS4, CDC5, and PRL1. MAC3A/B, as U-box E3 ubiquitin ligases, are crucial for various plant processes including development, stress responses, and disease resistance. However, their roles in cotton remain largely unknown. In this study, we first cloned the GhMAC3e gene from cotton and explored its biological functions by using virus-induced gene silencing (VIGS) in cotton and transgenic overexpression in Arabidopsis. The results showed that GhMAC3e is ubiquitously expressed in cotton tissues and could be induced by salt stress, Verticillium dahliae (VD) infection, PEG, ABA, ETH, GA3, MeJA, and SA. Silencing GhMAC3e retarded primary stem growth and reduced biomass of cotton coupled with the reduced auxin content in the petioles and veins. Silencing GhMAC3e up-regulated expression of cell growth-related genes GhXTH16 and Gh3.6, while down-regulated GhSAUR12 expression. Ectopic expression of GhMAC3e in Arabidopsis significantly enhanced its resistance to Verticillium wilt (VW) in terms of decreased pathogen biomass and lowered plant mortality. Overexpression of GhMAC3e dramatically upregulated AtPR1 by around 15 fold and more than 262 fold under basal and VD inoculation condition, respectively. This change was not associated with the expression of GhNPR1. In conclusion, GhMAC3e may not only regulate plant growth by influencing auxin distribution and growth-related gene expression, but also play important roles in VW resistance via mediating SA signaling independent of NPR1 transcription level.

Phytohormonal balance and differential gene expression in chronically irradiated Scots pine populations from the chernobyl affected zone.

The impact of chronic radiation exposure on phytohormone content and expression of phytohormone- and stress-related genes of Scots pine in the zone affected by the Chernobyl accident was studied. Needle samples were collected from three plots with contrasting levels of radioactive contamination in the Polesye State Radiation-Ecological Reserve, Republic of Belarus, and two reference plots in the Kozeluzhsky forest in June 2022. The experimental plots were located within the artificial plantations of Scots pine established in 1982, before the accident in 1986. The activity of radionuclides 137Cs, 90Sr, 241Am, 238Pu, and 239+240Pu in soil and needles ensured dose rates ranging from 3.3 to 87 mGy × year-1, while at the reference plots, the range was 0.7‒0.8 mGy × year-1. Concentrations of plant hormones, including indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), zeatin, and abscisic acid (ABA) in needles were evaluated using high-performance liquid chromatography (HPLC). We demonstrate that chronic radiation exposure is a significant stress factor that affects both phytohormonal balance and the expression of some important phytohormone- and stress-related genes. We found a tendency toward decreased ABA and auxin concentrations in trees from plots contaminated with radionuclides. The ratio (IAA + IBA + zeatin)/ABA was drastically raised at the most contaminated plots Masany and Kulazhin, reflecting the functional rearrangements of cellular metabolism that ensure plant adaptation under chronic radiation exposure. Changes in gene expression indicated modulation of ABA and Ca2+ signalling pathways, decreased potential of zeatin biosynthesis, and activation of heat shock proteins biosynthesis.

Polyacrylamide Regulated Phytohormone Balance and Starch Degradation to Promote Seed-Potato Sprouting and Emergence

Potatoes are typically seeded as tubers, and their slow sprouting significantly impacts production. Therefore, the effects of polyacrylamide (20 g·L−1, 30 g·L−1, and 40 g·L−1) as a seed potato dressing on sprouting, seedling growth, and biomass were investigated. The phytohormone content, respiratory intensity, and starch metabolism enzyme activity were analyzed to elucidate the physiological mechanisms involved. The sprouting rate significantly increased after 20 g·L−1 and 30 g·L−1 treatments by 40.63% and 15.63%, respectively. The sprouting energy was the highest (52.0%) at 20 g·L−1, 7.67 times higher than the control. The 20 g·L−1 and 30 g·L−1 treatments also promoted emergence and growth, with the emergence rate increasing by 18.18% and 27.27% and growth increasing by over 8.1% and 11.9%, respectively. These effects were related to changes in phytohormone content and accelerated starch conversion. After treatment, the auxin and cytokinin contents in the apical buds increased significantly at the germination initiation stage, and during the germination and vigorous growth phases, the auxin, cytokinin, and gibberellin contents increased. Polyacrylamide treatment activated α-amylase and promoted starch degradation, increasing soluble sugar content to provide nutrients and energy for sprouting. This study provides a promising approach for promoting potato tuber sprouting and seedling growth.

Respon Pertumbuhan Bibit Single Bud Tanaman Aglaonema Varietas Donna Carmen Terhadap Aplikasi Zat Pengatur Tumbuh dan Pupuk Daun

Ornamental plants now become a trend among the public. The hobby of growing ornamental plants causes the demand for ornamental plant is increased day by day, especially the Aglaonema ornamental plant. In general, the propagation of Aglaonema plants is carried out by using separation of tillers and stem cuttings of 4-7 segments. Due to the high demand for Aglaonema plants, a new method of plant propagation is needed, in order to produce more plants in a short time, by using the single bud nursery method. Aglaonema stem cuttings are difficult to do because Aglaonema plants has bud's dormancy period. Dormancy of Aglaonema plant buds is triggered by apical dominance. The way to break bud dormancy on Aglaonema cuttings is using zpt auxin (Rootone-f). In addition, plants also need nutrients to grow, by providing fertilizer. Fertilization for ornamental plants generally uses foliar fertilizer (Gandasil D). This research was conducted using a Randomized Block Design (RBD) which consisted of 2 factors, the first factor zpt auxin (Rootone-f) which consisted of 4 levels (0 ppm, 100 ppm, 200 ppm, 300 ppm), and the second factor was Gandasil D foliar fertilizer which consisted of 3 treatment levels (0 g/l, 1 g/l, 2 g/l) so there are 12 treatment combinations. Each combination was repeated 3 times, thus forming 36 experimental units. The data were analyzed by analysis of variance (ANOVA) to determine the effect of the treatment and those whose effects were significantly different were further tested using the Ducan Multiple Range (DMRT) with a 95% confidence level. The combination of auxin zpt treatment (Rootone-f) with a concentration of 200 ppm and Gandasil D foliar fertilizer with a concentration of 2 g/l showed the best treatment combination on the parameters of observing fresh weight of Aglaonema plants. The concentration of zpt auxin (Rootone-f) 200 ppm gave the highest average value of shoot length, number of leaves, root length, and number of roots of Aglaonema plants. The concentration of Gandasil D 2 g/l foliar fertilizer gave the highest average leaf length and leaf width of Aglaonema plants.

Plant growth promoting signatory volatiles emitted by a drought-tolerant bacterium Bacillus altitudinis FD48 and its role in moisture stress alleviation in rice (Oryza sativa L.)

Increasing evidence implies that bacterial volatile organic compounds (bVOCs) play a significant role in plant-microbe interaction. Plant associated bacteria produces plant growth modulating volatiles elicits induced systemic tolerance (IST) in plants against a multitude of abiotic stress. Induction of IST and plant growth promotion by signatory bVOCs of Bacillus altitudinis FD48 against drought are reported in this study. The rice seedlings exposed to bVOCs blends of FD48 showed a one-fold increase in whole plant biomass and auxin content (3 µmol g-1 FW) under induced moisture stress. The effect of bVOCs highly depends on the inoculum load. Higher inoculum quantity (100 µL) is detrimental to plant growth. bVOCs produced by FD48 profiled at different growth intervals in GC–MS-ATD revealed a total of 40 bioactive compounds both under stress (PEG 6000) and non-stressed conditions. Interestingly, potential plant growth-promoting compounds such as 1-Hexanol, 2,3-butanediol, dimethyl disulfide, benzene, butanoic acid, pentadecane, and acetic acid are more pronounced. Few compounds produced under non-stress were found to increase during stress (example, 2,3-Butanediol, and acetic acid). This study unraveled the significant biosynthetic pathways induced by FD48 bVOC blends, such as pyruvate metabolism, tryptophan metabolism, sulfur metabolism, fatty acid biosynthesis, and ethanol degradation that anchors in abating moisture stress. Hence, it can be concluded that PGPB B. altitudinis FD48 produced bVOCs could be potential orchestrators of induced systemic tolerance in plants against moisture stress.

An integrated targeted metabolome of phytohormones and transcriptomics analysis provides insight into the new generation of crops: Polygonatum kingianum var. grandifolium and Polygonatum kingianum.

Huangjing is becoming a new generation of crop. Polygonatum kingianum var. grandifolium (XHJ) is a variant of P. kingianum (DHJ), and they are treated as Huangjing. Unlike other Polygonatum species, the rhizome bud of XHJ can germinate both in spring and autumn, which contributes to its high rhizome yield. However, the molecular mechanism of the autumn shooting of XHJ was still unknown. In the present study, cellular observation, comparative targeted metabolome of phytohormones, and transcriptome analysis between XHJ and DHJ in autumn were conducted. Interestingly, 'Diterpenoid biosynthesis' (ko00904) and 'Plant hormone signal transduction' (ko04075) were commonly enriched by differentially accumulated phytohormones (DAPs) and differentially expressed genes (DEGs) in all tissues, which indicated the high auxin content, low cytokinin (CTK) content, and low abscisic acid/gibberellin (ABA/GA) ratio might contribute to the XHJ rhizome buds' differentiation and germination in autumn. Moreover, according to the weighted gene co-expression network analysis (WCGNA), transcript factors (TFs) related to auxin, CTK, GA, and jasmonic acid (JA) metabolism were screened, such as AP2/ERFs, WRKY, and NAC, which deserve further research. In conclusion, we comprehensively illustrated the mechanism of XHJ natural autumn shooting through cytological, metabolic, and transcriptomic analysis, which improves our understanding of the high yield of XHJ rhizomes and the diversity of shooting mechanisms in Polygonatum to lay the foundation for the further development of the Huangjing industry.

A nitrogen-responsive cytokinin oxidase/dehydrogenase regulates root response to high ammonium in rice.

Plant root system is significantly influenced by high soil levels of ammonium nitrogen, leading to reduced root elongation and enhanced lateral root branching. In Arabidopsis, these processes have been reported to be mediated by phytohormones and their downstream signaling pathways, while the controlling mechanisms remain elusive in crops. Through a transcriptome analysis of roots subjected to high/low ammonium treatments, we identified a cytokinin oxidase/dehydrogenase encoding gene, CKX3, whose expression is induced by high ammonium. Knocking out CKX3 and its homologue CKX8 results in shorter seminal roots, fewer lateral roots, and reduced sensitivity to high ammonium. Endogenous cytokinin levels are elevated by high ammonium or in ckx3 mutants. Cytokinin application results in shorter seminal roots and fewer lateral roots in wild-type, mimicking the root responses of ckx3 mutants to high ammonium. Furthermore, CKX3 is transcriptionally activated by type-B RR25 and RR26, and ckx3 mutants have reduced auxin content and signaling in roots under low ammonium. This study identified RR25/26-CKX3-cytokinin as a signal module that mediates root responses to external ammonium by modulating of auxin signaling in the root meristem and lateral root primordium. This highlights the critical role of cytokinin metabolism in regulating rice root development in response to ammonium.

Determination and Analysis of Endogenous Hormones and Cell Wall Composition between the Straight and Twisted Trunk Types of Pinus yunnanensis Franch

Pinus yunnanensis Franch., one of the pioneer species of wild mountain afforestation in southwest China, plays an essential role in the economy, society and environment of Yunnan Province. Nonetheless, P. yunnanensis’ trunk twisting and bending phenomenon has become more common, which significantly restricts its use and economic benefits. In order to clarify the compositional differences between the straight and twisted trunk types of P. yunnanensis and to investigate the reasons for the formation of twisted stems, the present study was carried out to dissect the macroscopic and microscopic structure of the straight and twisted trunk types of P. yunnanensis, to determine the content of cell wall components (lignin, cellulose, hemicellulose), determine the content of endogenous hormones, and the expression validation of phytohormone-related differential genes (GA2OX, COI1, COI2) and cell wall-related genes (XTH16, TCH4). The results showed that the annual rings of twisted trunk types were unevenly distributed, eccentric growth, insignificant decomposition of early and late wood, rounding and widening of the tracheid cells, thickening of the cell wall, and reduction of the cavity diameter; the lignin and hemicellulose contents of twisted trunk types were higher; in twisted trunk types, the contents of gibberellin (GA) and jasmonic acid (JA) increased, and the content of auxin (IAA) was reduced; the GA2OX were significantly down-regulated in twisted trunk types, and the expressions of the genes associated with the cell wall, COI1, COI2, TCH4 and XTH16, were significantly up-regulated. In conclusion, the present study found that the uneven distribution of endogenous hormones may be an important factor leading to the formation of twisted trunk type of P. yunnanensis, which adds new discoveries to reveal the mechanism of the genesis of different trunk types in plants, and provides a theoretical basis for the genetic improvement of forest trees.

Comparison of transcriptome and metabolome analysis revealed cold-resistant metabolic pathways in cucumber roots under low-temperature stress in root zone.

Low ground temperature is a major factor limiting overwintering in cucumber cultivation facilities in northern alpine regions. Lower temperatures in the root zone directly affect the physiological function of the root system, which in turn affects the normal physiological activity of plants. However, the importance of the ground temperature in facilities has not attracted sufficient attention. Therefore, this study tested the cucumber variety Jinyou 35 under three root zone temperatures (room temperature, 20-22°C; suboptimal temperature, 13- 15°C; and low temperature, 8-10°C) to investigated possible cold resistance mechanisms in the root of cucumber seedlings through hormone, metabolomics, and transcriptomics analyses. The results showed that cucumber roots were subjected to chilling stress at different temperatures. Hormone analysis indicated that auxin content was highest in the roots. Jasmonic acid and strigolactone participated in the low-temperature stress response. Auxin and jasmonate are key hormones that regulate the response of cucumber roots to low temperatures. Phenolic acid was the most abundant metabolite in cucumber roots under chilling stress. Additionally, triterpenes may play an important role in chilling resistance. Differentially expressed genes and metabolites were significantly enriched in benzoxazinoid biosynthesis in the room temperature vs. suboptimal temperature groups and the room temperature vs. low temperature groups. Most differentially expressed transcription factor genes in AP2/ERF were strongly induced in cucumber roots by both suboptimal and low-temperature stress conditions. These results provide guidance for the cultivation of cucumber in facilities.

The MdIAA29-MdARF4 complex plays an important role in balancing plant height with salt and drought stress responses.

Breeding dwarf apple (Malus domestica) varieties is a recent trend in agriculture because such varieties are easy to maintain and have high yields; however, dwarf apple trees generally have poor stress tolerance. Balancing apple plant height and stress response has been an important breeding goal. In this study, aux/indole-3-acetic acid 29 gene in apple (MdIAA29) overexpression lines (#1, #2, #3) had reduced plant height by 39%, 31%, and 35%, respectively, suitable for close planting applications. Surprisingly, the dwarf MdIAA29-overexpression lines also showed increased plant tolerance to salt and drought stresses. Further analysis showed that MdIAA29 inhibited the regulation of auxin response factor 4 (ARF4) on Gretchen Hagen 3.9 (GH3.9) gene and 9-cis-epoxycarotenoid dioxygenase 3 (NCED3) gene in apple and changed the contents of auxin and abscisic acid in different tissues, thus achieving a balance between plant height and stress tolerance. In addition, we also found that MdIAA7 enhanced the inhibitory effect of MdIAA29 on MdARF4. In brief, the MdIAA29-MdARF4 complex significantly impacts the height of apple plants and their ability to respond to salt and drought stress.

Dual-Mediated Roles of H+-ATPase in Alleviating the Phytotoxicity of Imazethapyr to Nontarget Wheat.

The regulation solutions and mechanisms of reducing pesticide phytotoxicity to nontarget plants are not well-defined and detailed. Here, we have proposed a new detoxification strategy to control the toxic effects of herbicide imazethapyr (IM) induced in wheat seedlings from the perspective of the plasma membrane (PM) H+-ATPase. We found that the changes in PM H+-ATPase activity have a regulatory effect on the phytotoxic effects induced by IM in plants. Treatment with PM H+-ATPase activators restored the reduced auxin content and photosynthetic efficiency caused by IM, thereby promoting plant growth. Application of a PM H+-ATPase inhibitor further reduced phosphorus content and significantly increased 2,4-dihydroxy-7-methoxy-2H,1,4-benzoxazin-3(4H)one (DIMBOA) and jasmonic acid levels. These effects indicate that auxin and DIMBOA may regulate plant growth trends and detoxification effects mediated by PM H+-ATPase. This work opens a new strategy for regulating herbicide toxicity to nontarget plants from the PM H+-ATPase.

Gallic acid regulates primary root elongation via modulating auxin transport and signal transduction.

Gallic acid is an important secondary metabolite in plants, with great value in medicine, food, and chemical industry. However, whether and how this widely existing natural polyphenolic compound affects the growth and development of plants themselves remains elusive. In this study, we revealed that exogenous application of gallic acid has a dual effect on the elongation of primary root in Arabidopsis. While lower concentrations of gallic acid slightly stimulate primary root growth, excessive gallic acid profoundly reduces primary root length and root meristem size in a dose-dependent manner, probably via suppressing cell division in root meristem as indicated by CYCB1;1::GUS. Moreover, as suggested by the DR5::GFP line analysis and confirmed by the LC-MS assay, auxin contents in root tips were dramatically decreased upon excessive gallic acid treatment. Additional application of IAA partially rescued the shortened primary root and root meristem upon excessive gallic acid treatment, suggesting that auxin is required for excessive gallic acid-caused root growth inhibition. Then, we further revealed that excessive gallic acid down-regulated the expression of auxin transporters PIN1, PIN2, PIN3, and PIN7, and triple mutant pin1 pin3 pin7 exhibited a reduced sensitivity to gallic acid treatment. Meanwhile, excessive gallic acid decreased the degradation of AXR3/IAA17 protein as revealed by HS::AXR3NT-GUS reporter line. Auxin signaling mutant tir1 afb2 afb3 and axr3-3 were also less sensitive to excessive gallic acid treatment in terms of primary root length and root meristem size. Taken together, these findings suggested that excessive gallic acid inhibits primary root growth by modulating auxin transport and signaling in Arabidopsis.

Phosphate solubilization potential of PSB: an advance approach to enhance phosphorous availability for phytostimulation.

Rhizosphere engineering approach is considered a quantum leap in plant sciences. The current study focused on investigating rhizobacterial efficiency to mobilize bioavailable phosphate from insoluble-phosphate source. Four efficient phosphate-solubilizing bacterial isolates, i.e., Pseudomonas songnenensis (GR3), Stutzerimonas stutzeri (HH2), Bacillus bingmayongensis (KH3), and Achromobacter aegrifaciens (MH1) were selected for the current study. Interactions between various physiological parameters and phosphate solubilization efficiency of isolates revealed that glucose significantly facilitated phosphorus solubilization at 37 ℃, with media having pH 7 and 0.5% phosphorous. Additionally, positive correlation among P-solubilization potential, acids produced, and pH was observed. Plant microbe-interaction analysis was performed to evaluate the efficiency of these bacterial isolates on various morpho-physiological responses of Zea mays L. For this purpose, various concentrations of tricalcium phosphate (TCP) (0, 10, 20, 30, 40, and 50mM) were applied to plants in the presence and absence of bacterial isolates. The results showed that lower phosphate levels (10 and 20mM) trigger shoot development and improve plant weight and leaf formation whereas higher phosphate concentrations (30mM and above) stimulated the development of longer root system. The bacterial isolates, KH3 and HH2, were observed as efficient phosphate-solubilizing bacteria (PSB) that positively stimulated various plant growth and biochemical attributes over untreated plants. At lower phosphate levels, substantial increase of 92, 65, and 200% in shoot length, fresh weight, and number of leaves was recorded with bacterial isolate HH2, whereas, at 30mM TCP, increase of 165% was observed in root length of plants treated with bacterial isolate KH3 compared to control. Similarly, at lower phosphate levels, increment of 57.3, 76.7, and 217% in phosphate, protein, and auxin content was recorded in plants treated with bacterial isolate HH2, and increase of 188.8% in total soluble carbohydrates was observed in plants treated with bacterial isolate KH3 as compared to control. Contrarily, increment in total chlorophyll content was most substantial (207%) by the bacterial isolate KH3 when provided with 30mM TCP. Hence, the current study reviled that the use of these phosphates (KH3 and HH2)-solubilizing PGPR, as an efficient phytostimulator used for crop production in the replacement of chemical fertilizers, is carcinogenic and deteriorating our eco-system.