Growth Of Adventitious Roots Research Articles

Molecular Mechanisms of the miR396b-GRF1 Module Underlying Rooting Regulation in Acer rubrum L.

Rooting and root development in Acer rubrum have important effects on overall growth. A. rubrum does not take root easily in natural conditions. In this study, the mechanisms of the miR396b-GRF1 module underlying rooting regulation in A. rubrum were studied. The subcellular localization and transcriptional activation of miR396b and its target gene growth regulating factor 1 (GRF1) were investigated. These experiments showed that GRF1 was localized in the nucleus and had transcriptional activation activity. Functional validation experiments in transgenic plants demonstrated that overexpression of Ar-miR396b inhibited adventitious root growth, whereas overexpression of ArGRF1 increased adventitious root growth. These results help clarify the molecular regulatory mechanisms underlying adventitious root growth in A. rubrum and provide some new insights into the rooting rate in this species.

The Role of γ-Aminobutyric Acid (GABA) in the Occurrence of Adventitious Roots and Somatic Embryos in Woody Plants.

The occurrence of adventitious roots and somatic embryos is a crucial step in micropropagation that frequently limits the application of this technique in woody plants. Recent studies demonstrated that they can be negatively or positively regulated with γ-aminobutyric acid (GABA), which is a four-carbon non-proteinous amino acid that not only acts as a main inhibitory neurotransmitter in mammals. It has been reported that GABA affects plant growth and their response to stress although its mode of action is still unclear. This review dealt with the effects of GABA on adventitious root formation and growth as well as on somatic embryogenesis. Furthermore, we focused on discussing the interaction of GABA with phytohormones, such as auxin, ethylene, abscisic acid, and gibberellin, as well as with the carbon and nitrogen metabolism during adventitious root development. We suggested that research on GABA will contribute to the application of micropropagation in the recalcitrant fruit and forest species.

Transcription Factor IAA27 Positively Regulates P Uptake through Promoted Adventitious Root Development in Apple Plants.

Phosphate (P) deficiency severely limits the growth and production of plants. Adventitious root development plays an essential role in responding to low phosphorus stress for apple plants. However, the molecular mechanisms regulating adventitious root growth and development in response to low phosphorus stress have remained elusive. In this study, a mutation (C-T) in the coding region of the apple AUXIN/INDOLE-3-ACETIC ACID 27 (IAA27) gene was identified. MdIAA27T-overexpressing transgenic apple improved the tolerance to phosphorus deficiency, which grew longer and denser adventitious roots and presented higher phosphorous content than the control plants under low phosphorus conditions, while the overexpression of MdIAA27C displayed the opposite trend. Moreover, the heterologous overexpression of MdIAA27 in tobacco yielded the same results, supporting the aforementioned findings. In vitro and in vivo assays showed that MdIAA27 directly interacted with AUXIN RESPONSE FACTOR (ARF8), ARF26 and ARF27, which regulated Small Auxin-Up RNA 76 (MdSAUR76) and lateral organ boundaries domain 16 (MdLBD16) transcription. The mutation in IAA27 resulted in altered interaction modes, which in turn promoted the release of positive ARFs to upregulate SAUR76 and LBD16 expression in low phosphorus conditions. Altogether, our studies provide insights into how the allelic variation of IAA27 affects adventitious root development in response to low phosphorus stress.

Identification of the HAK gene family reveals their critical response to potassium regulation during adventitious root formation in apple rootstock

Adventitious root formation is a bottleneck during vegetative proliferation. Potassium (K+) is an essential macronutrient for plants. K+ accumulation from the soil and its distribution to the different plant organs is mediated by K+ transporters named K+ transporter (KT), K+ uptake (KUP), or high-affinity K+ (HAK). This study aimed to identify members of the HAK gene family in apples and to characterize the effects of K+ supply on adventitious root formation and on the expression of HAK genes and the genes that putatively control auxin transport, signaling, and cell fate during adventitious root formation. In this study, 34 HAK genes (MdHAKs) were identified in the apple (Malus × domestica ‘Golden Delicious’) genome. A phylogenetic analysis divided MdHAKs into four clusters (I, II, III, and IV), comprising 16, 1, 4, and 13 genes, respectively. The syntenic relationships revealed that 62.5% of the total MdHAK genes arise from genomic duplication events. Chromosome location, domain structure, motif analysis, and physico-chemical characteristics were subsequently investigated. Furthermore, the application of K+ indicated the emergence of adventitious roots at 8 d and produced more adventitious roots at 16 d than the K+-free control (CK) treatment. In addition, various MdHAKs showed root-specific expression in B9 apple rootstock stem cuttings and enhanced expression during the initiation and emergence stages of adventitious root formation in response to K+ treatment. Additionally, K+ treatment enhanced the expression levels of MdPIN1, MdPIN2, and MdAUX1. Further data indicated that a higher expression of MdWOX11, MdLBD16, and MdLBD29 and of cell cycle-related genes contributed to the auxin-stimulated adventitious root formation in response to K+.

Adventitious root cultures of Arnebia euchroma: A sustainable alternative for the production of natural pigments

Arnebia euchroma is a valuable Himalayan herb, whose roots are savagely harvested from the wild to extract red naphthoquinone pigments with applications in food, cosmetic and pharmaceutical industries. The primary objective of this study was to induce A. euchroma adventitious roots and use the same for the production of naphthoquinone pigments. A number of media and auxin types were tried for the formation of adventitious roots from leaves of A. euchroma under in vitro conditions. The data showed 100% root induction on semi-solid Schenk & Hildebrandt (SH) medium fortified with 2.5 mg/L indole-3-butyric acid (IBA) after 4-weeks of culture. Thereafter, factors like inoculum density and sucrose concentration were optimized to maximize adventitious root growth and pigment production in liquid shake flask cultures. The results revealed a significantly high root biomass (7.00 ± 0.25 g/L dry weight (DW)) and pigment (192.92 ± 1.61 mg/g DW) yield in SH medium having 10 g/L inoculum density, 0.5 mg/L IBA and 5% sucrose concentration. In addition, the cultivation of adventitious roots in Balloon-Type Bubble Bioreactor (5 L cap.) was also done, which showed comparably lower root biomass (4.33 ± 0.09 g/L DW) yield to shake flask culturing, however, resulted in higher pigments accumulation (195.36 ± 1.95 mg/g DW). The chemical profile of in vitro induced adventitious roots cultivated in shake flask and bioreactor was also compared with parent plant rhizome using Ultra Performance Liquid Chromatography. As per the results, deoxyshikonin and β, β-dimethylacrylshikonin were found to be the key pigments in adventitious roots, although shikonin was not detectable which otherwise also present in parent plant rhizomes. Considering the shorter cultivation cycle (4-weeks) and regenerative potential of induced adventitious roots along with comparable metabolic profile, the developed process seems to be a feasible alternative for the production of natural pigments.

Agrobacterium-mediated transformation and in vitro evaluation of dehydration tolerance in transgenic tobacco harboring Ca-AFP gene

We have known that plant defensins have the main roles in biotic stress, especially antifungal activities. In addition, their functions on abiotic stress tolerance have been demonstrated on previous studies, but that information was still limited. Ca-AFP, a plant defensin gene derived from chickpea, was transformed into tobacco leaf disks by Agrobacterium method. After 16 weeks on selection media containing 15 mg/L hygromycin, some regeneration shoot lines were obtained. Four of them showed the positive bands on hpt gene and Ca-AFP gene by PCR screening. These lines were applied on in vitro evaluation of dehydration tolerance using rotary liquid culture, and the water-deficit stress was caused by 2% (w/v) PEG 6000. These four transgenic lines had better growth of adventitious roots (number of adventitious roots, total adventitious root length, and average of root length) and higher rate of biomass increase than the non-transgenic line. The result illustrated that the expression of Ca-AFP gene could mitigate the negative effect of water-deficit stress on transgenic tobacco lines under the in vitro stress condition. These transgenic tobacco lines are potential for water-deficit stress trials on greenhouse in the future.

Optimum Moisture Conditions for English Lavender Cuttings Are Drier for Root Development than Shoot Development

Providing proper moisture conditions is critical for successful cutting propagation. This study aimed to investigate the optimal substrate moisture level for enhancing the survival and rooting rates of Lavandula angustifolia cuttings. Apical cuttings of L. angustifolia were propagated under four irrigation thresholds (−1.0, −2.5, −5.0, and −10.0 kPa) over six weeks. At the final harvest, cuttings grown at −2.5 kPa demonstrated the highest survival rate (83.3%), and those grown at −10.0 kPa demonstrated a mortality > 50%. A high rooting percentage (53.0 and 47.2%) was observed in cuttings grown at −1.0 and −2.5 kPa, while the lowest rooting percentage (<10%) was present in those grown at −10.0 kPa. Adventitious root formation and root growth occurred within a month for all treatments, except for the −10.0 kPa treatment; the general root growth was similar among treatments at the final harvest. Shoot growth was negligible in all treatments until four weeks, and it increased rapidly with increasing substrate moisture levels after the formation of adventitious roots. The adventitious root system was established within four weeks, which was followed by accelerated leaf and shoot growth. The optimal substrate moisture level for high survival and rooting of English lavender cuttings was approximately −2.5 kPa, but higher moisture tension at −1.0 kPa could enhance the shoot growth after adventitious roots are established.

The Pyramiding of Three Key Root Traits Aid Breeding of Flood-Tolerant Rice.

Flooding is constantly threatening the growth and yield of crops worldwide. When flooding kicks in, the soil becomes water-saturated and, therefore, the roots are the first organs to be exposed to excess water. Soon after flooding, the soil turns anoxic and the roots can no longer obtain molecular oxygen for respiration from the rhizosphere, rendering the roots dysfunctional. Rice, however, is a semi-aquatic plant and therefore relatively tolerant to flooding due to adaptive traits developed during evolution. In the present review, we have identified three key root traits, viz. cortical aerenchyma formation, a barrier to radial oxygen loss and adventitious root growth. The understanding of the physiological function, the molecular mechanisms, and the genetic regulation of these three traits has grown substantially and therefore forms the backbone of this review. Our synthesis of the recent literature shows each of the three key root traits contributes to flood tolerance in rice. One trait, however, is generally insufficient to enhance plant tolerance to flooding. Consequently, we suggest comprehensive use of all three adaptive traits in a pyramiding approach in order to improve tolerance to flooding in our major crops, in general, and in rice, in particular.

STUDY ON in vitro INDUCTION OF ROOTING AND CHANGES IN ENDOGENOUS HORMONE CONTENT OF Lagerstroemia indica ‘ZIJINGLING’

Different media had different effects on the induction of rooting of Lagerstroemia indica ‘Zijingling’. The aims of this study were to identify the best rooting medium, determine the changes in endogenous hormone content in aseptic seedlings of ‘Zijingling’, and then analyze its role in the rooting process, to improve the rooting rate. Using a test tube seedling of ‘Zijingling’ as the experimental material, the tissue cells were observed via paraffin sectioning, and the changes in endogenous hormone content during the rooting process were determined using high-performance liquid chromatography. The results showed that 1/2 MS Medium had the most significant effect on rooting in the basic medium. The promoting effects of different auxins on rooting decreased in magnitude in the order 3-Indolebutyric acid (IBA) > Naphthalene acetic acid (NAA)> Indole-3-aceticacid (IAA). The optimal rooting medium was 1/2 MS + 0.6 mg L-1 IBA+ 15 g L-1 sucrose + 5 g L-1 agar + 200 mg L-1 activated carbon , and the highest induction rate of adventitious roots was 92.5%. The rooting of ‘Zijingling’ is classified as a primordial type of induced rooting. Exogenous IBA content promoted an increase in endogenous IAA and Gibberellic acid (GA3) contents. High contents of IAA, GA3, and Abscisic acid (ABA) and low content of Zeatin riboside (ZR) promoted the growth of adventitious roots, whereas high contents of IAA and ZR, and low contents of GA3 and ABA were required for the induction of root primordia. High levels of IAA/ZR and low levels of IAA/ABA promoted the differentiation of root primordia. However, low levels of IAA/ZR and high levels of IAA/ABA promoted adventitious root elongation.

The carbohydrate elicitor Riclinoctaose facilitates defense and growth of potato roots by inducing changes in transcriptional and metabolic profiles

Promoting both root growth and defense is conducive to the production of potatoes (Solanum tuberosum L.), while the role of elicitors in this topic hasn’t been fully understood. To investigate the effect of Riclinoctaose (RiOc) on root growth and defense, potato tissue cuttings were cultivated with different concentration of RiOc (0, 50, 200 mg/L) for 5 weeks and changes in root morphology, transcription, enzymatic and metabolomic profiles were monitored over time. The results indicated that RiOc triggered the salicylic acid (SA)-mediated defense response and facilitated the growth of adventitious and lateral roots in a dose- and time-dependent manner. MPK3/MPK6, SA- and auxin-signaling pathways and transcription factors such as WUS, SCR and GRAS4/GRAS9 participated in this process. Moreover, the 1H NMR based metabolome profiling demonstrated that potato roots altered the primary metabolism to respond to the RiOc elicitation and efficiency in production and allocation of defense and growth-related metabolites was improved. After 5-week treatment, the level of glucose, N-acetylglucosamine, glutamine, asparagine, isoleucine, valine, 3-hydroxyisovalerate and ferulate increased, while acetate, acetoacetate, fucose, and 2-hydroxyphenylacetate declined. In conclusion, RiOc played dual roles in activating the SA-mediated defense response and in promoting growth of potato roots by inducing changes in root transcription and metabolism.

Histological, Morpho-Physiological, and Biochemical Changes during Adventitious Rooting Induced by Exogenous Auxin in Magnolia wufengensis Cuttings

Magnolia wufengensis, a rare ornamental tree species, is now in a huge gap between market demand and actual supply of seedlings. As cutting propagation is one of the most important means to solve the shortage of seedling supply, this study developed an efficient cutting propagation procedure of M. wufengensis, revealed the morphological and histological changes of adventitious root formation, and explored the rhythm correlation between rooting process and physiological and biochemical changes. Cuttings pre-treated with NAA:IBA (2:1) exhibited the best rooting performance. Anatomical analysis demonstrated that adventitious root primordia of M. wufengensis were initiated from cambial and parenchyma cells of xylem, with no relationship to the callus formed on the epidermis. The rooting process of M. wufengenis can be divided into four periods: induction phase (0–8 dap) (dap means days after planting), initiation phase (8–13 dap), expression phase (13–18 dap), and extension phase (18–28 dap). NAA:IBA (2:1) induced the accumulations of 3-indoleacetic-acid and increased the contents of peroxidase and polyphenol-oxidase near the wounding at induction phase. The initiation phase, with the first histological modifications to the formation of meristemoids, correspond to the increase of peroxidase, polyphenol-oxidase, and soluble protein contents. The synergistic reaction of low 3-indoleacetic-acid and high levels of gibberellins and zeatin also stimulates the initiation phase. In the expression and extension phase, high activities of polyphenol-oxidase, IAA-oxidase, and increased contents of soluble protein co-stimulate the emergence and outgrowth of adventitious roots. The present study not only provides optimized protocol by application of auxin combination but also presents insights in the histological, morpho-physiological, and biochemical changes in stem cuttings of M. wufengensis.

Adventitious Root Culture—An Alternative Strategy for Secondary Metabolite Production: A Review

Medicinal plants are valuable sources of botanical drugs, extracts and pure compounds. Although several species can be propagated or collected, the access to herbal material is limited in certain cases. The protection of natural habitats and biodiversity demands new sources to provide plant secondary metabolites of medical importance. Adventitious root culture is used to harvest the secondary metabolites from the medicinally important plants, thereby offering an alternative to collection and propagation of medicinal plants. In this review, we comprehensively summarize the previously published data on the use of adventitious root cultures for numerous therapeutic plants. Adventitious roots showed elevated growth rates and production of pharmaceutically important metabolites under sterilized condition with optimized plant-growth regulators in culture media. In the present study, major influencing factors, such as the stages involved in the process of adventitious root formation, medium composition and type of growth regulators, specifically the effect of different auxins on the initiation and formation of roots, are discussed. Elicitation strategies using biotic (yeast extracts, chitosan and pectin) and abiotic factors (MJ, SA, CuSO4, AgNO3, NaCl) that affect the in vitro growth of adventitious roots and the role of bioreactors, which are new advancements in the scale-up process, are also highlighted. The development of adventitious root cultures for the production of secondary metabolites of medicinal importance is a perspective that is advantageous from ecological and economical aspects as well.

Salicylic Acid Enhances Adventitious Root and Aerenchyma Formation in Wheat under Waterlogged Conditions.

The present study investigated the role of salicylic acid (SA) in regulating morpho-anatomical adaptive responses of a wheat plant to waterlogging. Our pharmacological study showed that treatment of waterlogged wheat plants with exogenous SA promotes the formation axile roots and surface adventitious roots that originate from basal stem nodes, but inhibits their elongation, leading to the formation of a shallow root system. The treatment also enhanced axile root formation in non-waterlogged plants but with only slight reductions in their length and branch root formation. Exogenous SA enhanced the formation of root aerenchyma, a key anatomical adaptive response of plants to waterlogging. Consistent with these results, waterlogging enhanced SA content in the root via expression of specific isochorismate synthase (ICS; ICS1 and ICS2) and phenylalanine ammonia lyase (PAL; PAL4, PAL5 and PAL6) genes and in the stem nodes via expression of specific PAL (PAL5 and PAL6) genes. Although not to the same level observed in waterlogged plants, exogenous SA also induced aerenchyma formation in non-waterlogged plants. The findings of this study furthermore indicated that inhibition of ethylene synthesis in SA treated non-waterlogged and waterlogged plants does not have any effect on SA-induced emergence of axile and/or surface adventitious roots but represses SA-mediated induction of aerenchyma formation. These results highlight that the role of SA in promoting the development of axile and surface adventitious roots in waterlogged wheat plants is ethylene independent while the induction of aerenchyma formation by SA requires the presence of ethylene.

Nitrate Application Induces Adventitious Root Growth by Regulating Gene Expression Patterns in Apple Rootstocks

Nitrate Application Induces Adventitious Root Growth by Regulating Gene Expression Patterns in Apple Rootstocks

Effectiveness of stimulating treatment cuttings of privet common (Ligustrum vulgare L.) with biologically active preparations

The effectiveness of the use biologically active substances in the rooting of cuttings privet common (Ligustrum vulgare L.) in its introduction in the region of Nizhny Novgorod was studied. The processes of callus adventitious root formation were studied. The research target was an arboretum collection of common privet in Nizhny Novgorod State Agricultural Academy with geographical coordinates 56°19′43” N, 44°00′O7” E and an altitude of 141 m above sea level. Tested nine industrially produced biologically active preparations widely used in tree and forest nurseries to increase the efficiency of rooting cuttings. The positive effect of cutting treatment with biologically active preparations was confirmed. A significant intensity of callus formation was recorded in the variants with profistim (98.50±1.05%) and extrasol (96.50±0.76%). A noticeable increase in the number of adnexal roots was caused by the use of the drugs heteroauxin (24.55±1.08 pcs.) and ferovit (22.00±1.38 pcs.). The best results for the total length of adventive roots were obtained after the use of heteroauxin (266.92±16.71 cm) and ecofus (272.22±14.42 cm). The effectiveness of bioactive drugs in stimulating regeneration processes on privet cuttings, increasing in the intensity of callus formation and the rate of linear growth of adventitious roots has been proven.

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.

Opportunities for Improving Waterlogging Tolerance in Cereal Crops—Physiological Traits and Genetic Mechanisms

Waterlogging occurs when soil is saturated with water, leading to anaerobic conditions in the root zone of plants. Climate change is increasing the frequency of waterlogging events, resulting in considerable crop losses. Plants respond to waterlogging stress by adventitious root growth, aerenchyma formation, energy metabolism, and phytohormone signalling. Genotypes differ in biomass reduction, photosynthesis rate, adventitious roots development, and aerenchyma formation in response to waterlogging. We reviewed the detrimental effects of waterlogging on physiological and genetic mechanisms in four major cereal crops (rice, maize, wheat, and barley). The review covers current knowledge on waterlogging tolerance mechanism, genes, and quantitative trait loci (QTL) associated with waterlogging tolerance-related traits, the conventional and modern breeding methods used in developing waterlogging tolerant germplasm. Lastly, we describe candidate genes controlling waterlogging tolerance identified in model plants Arabidopsis and rice to identify homologous genes in the less waterlogging-tolerant maize, wheat, and barley.

Shaping the root system: the interplay between miRNA regulatory hubs and phytohormones.

The root system commonly lies underground, where it provides anchorage for the aerial organs, as well as nutrients and water. Both endogenous and environmental cues contribute to the establishment of the root system. Among the endogenous cues, microRNAs (miRNAs), transcription factors, and phytohormones modulate root architecture. miRNAs belong to a subset of endogenous hairpin-derived small RNAs that post-transcriptionally control target gene expression, mostly transcription factors, comprising the miRNA regulatory hubs. Phytohormones are signaling molecules involved in most developmental processes. Some miRNAs and targets participate in more than one hormonal pathway, thereby providing new bridges in plant hormonal crosstalk. Unraveling the intricate network of molecular mechanisms underlying the establishment of root systems is a central aspect in the development of novel strategies for plant breeding to increase yield and optimize agricultural land use. In this review, we summarize recent findings describing the molecular mechanisms associated with the interplay between miRNA regulatory hubs and phytohormones to ensure the establishment of a proper root system. We focus on post-embryonic growth and development of primary, lateral, and adventitious roots. In addition, we discuss novel insights for future research on the interaction between miRNAs and phytohormones in root architecture.

The Effect of Different Levels of Indole-3-butyric Acid (IBA) and Naphthaleneacetic acid (NAA) on the Rooting of The Effect of Different Levels of Indole-3-butyric Acid (IBA) and Naphthaleneacetic acid (NAA) on the Rooting of Pear Stem CuPear Stem Cutting

The Effect of Different Levels of Indole-3-butyric Acid (IBA) and Naphthaleneacetic acid (NAA) on the Rooting of The Effect of Different Levels of Indole-3-butyric Acid (IBA) and Naphthaleneacetic acid (NAA) on the Rooting of Pear Stem CuPear Stem Cutting

Abscisic Acid as an Emerging Modulator of the Responses of Plants to Low Oxygen Conditions.

Different environmental and developmental cues involve low oxygen conditions, particularly those associated to abiotic stress conditions. It is widely accepted that plant responses to low oxygen conditions are mainly regulated by ethylene (ET). However, interaction with other hormonal signaling pathways as gibberellins (GAs), auxin (IAA), or nitric oxide (NO) has been well-documented. In this network of interactions, abscisic acid (ABA) has always been present and regarded to as a negative regulator of the development of morphological adaptations to soil flooding: hyponastic growth, adventitious root emergence, or formation of secondary aerenchyma in different plant species. However, recent evidence points toward a positive role of this plant hormone on the modulation of plant responses to hypoxia and, more importantly, on the ability to recover during the post-hypoxic period. In this work, the involvement of ABA as an emerging regulator of plant responses to low oxygen conditions alone or in interaction with other hormones is reviewed and discussed.