Adventitious Root Development Research Articles

Response of growth and chlorophyll fluorescence parameters of mulberry seedlings to waterlogging stress

This study aimed to investigate the adaptive mechanisms of mulberry (Morus alba) to waterlogged conditions, with a specific focus on the development of adventitious roots (ARs), alteration of growth strategies, and adjustment of chlorophyll fluorescence parameters. To achieve this goal, 4-year-old potted mulberry plants were selected for research, and a waterlogging simulation method was implemented. Four treatments were established to investigate the effects of varying water conditions on leaf waterlogging damage, the number of ARs, plant height, chlorophyll fluorescence parameters, and proton motive force (pmf) parameters in mulberry plants. These treatments included the control group (CK), shallow submerged group (SS), half-submerged group (HS) and deep submerged group (DS). Our results showed that (1) The number of ARs in each group increased with increasing waterlogging time. (2) Waterlogging stress inhibited the height growth of mulberry, and the changes in plant height in the HS and DS groups were significantly lower than those in the CK and SS groups. (3) The maximum photochemical quantum yield (Fv/Fm) in the HS and DS groups decreased significantly under waterlogging stress. The nonphotochemical quenching (NPQt) of mulberry leaves in the submergence group increased significantly in the early stage of waterlogging stress, and the NPQt in the submergence group increased continuously with increasing waterlogging time. (4) Thylakoid conductivity to protons (gH+) in the leaves of mulberry decreased significantly under waterlogging stress, whereas the steady-state rate of proton flux (vH+) and total electrochromic shift (ECSt) increased significantly. The morphological, physiological, and ecological responses of mulberry plants to waterlogging stress include the timely generation of ARs at the stem base, the adjustment of plant growth strategies, and the repair of photosynthetic response centers in leaves through heat dissipation and thylakoid acidification mechanisms.

Regulatory mechanisms of miR171d-SCL6 module in the rooting process of Acer rubrum L.

MiR171d and SCL6 are induced by the plant hormone auxin. MiR171d negatively regulates the expression of SCL6, thereby regulating the growth and development of plant adventitious roots. Under natural conditions, it is difficult to induce rooting in the process of propagating Acer rubrum L. via branches, which seriously limits its wide application in landscaping construction. In this study, the expression of Ar-miR171d was downregulated and the expression of ArSCL6 was upregulated after 300mg/L indole-3-butyric acid (IBA) treatment. The transient interaction of Ar-miR171d and ArSCL6 in tobacco cells further confirmed their cleavage activity. Transgenic function verification confirmed that OE-Ar-miR171d inhibited adventitious root (AR) development, while OE-ArSCL6 promoted AR development. Tissue-specific expression verification of the ArSCL6 promoter demonstrated that it was specifically expressed in the plant root and leaf organs. Subcellular localization and transcriptional activation assays revealed that both ArSCL6 and ArbHLH089 were located in the nucleus and exhibited transcriptional activation activity. The interaction between the two was verified by bimolecular fluorescence complementarity (BIFC) experiments. These results help elucidate the regulatory mechanisms of the Ar-miR171d-ArSCL6 module during the propagation of A. rubrum and provide a molecular basis for the rooting of branches.

Genome-wide characterization, identification, and isolation of auxin response factor (ARF) gene family in maize

Auxin response factors (ARFs) are key regulators of numerous aspects of plant growth and development through mediating auxin signaling. In this study, we conducted a comprehensive genome-wide analysis of ZmARFs to identify and validate all auxin response factor genes in maize. These ZmARF genes were categorized into four distinct groups (I-IV) based on phylogenetic analysis, revealing seven sister pairs. We presented detailed information on gene sequences, structures, chromosome locations, and conserved motifs of ZmARFs. Through transient expression assays, we identified transcriptional activators or repressors among ZmARFs. Notably, our study demonstrated, for the first time, that ZmARF3 acts as a positive regulator of adventitious roots development in maize. This study not only provides basic insights into the maize ARF gene family but also sheds light on the specific functions of ZmARF3, paving the way for a more precise understanding of ZmARFs' roles in plant growth and development in maize.

Exogenous γ-aminobutyric acid enhanced salt-alkaline tolerance in mulberry trees through transcriptomic sequencing analysis

Soil salinization is a widespread abiotic stress in China and one of the most critical factors affecting agricultural production and food security. γ-Aminobutyric acid (GABA) is a non-protein amino acid widely found in vertebrates, plants, and microorganisms, regulating the nervous system as well as plant defense systems. Mulberry is rich in GABA and exhibits extensive adaptability to various environments. In this study, we explored the possibility of alleviating salinity and alkalinity stress in mulberry seedlings using GABA and elucidating the intrinsic mechanisms by which GABA enhances salt-alkaline tolerance in mulberry trees through transcriptomic sequencing analysis. The results showed that 1 mM exogenous GABA enhanced the activities of mulberry seeds under saline-alkali stress, significantly increased the activities of POD and CAT (P < 0.01), reduced the level of reactive oxygen species and the content of malondialdehyde in mulberry seedlings and facilitated the growth and development of adventitious roots of mulberry. Transcriptomic analysis showed that GABA promoted the development and growth of adventitious roots of mulberry under saline-alkali stress by regulating the synthesis and modification of the cell wall, phytohormone signal transduction, and the conversion of starch and monosaccharides. Furthermore, the expression of pathogen pattern recognition receptors on the cell membrane of mulberry root system cells increased, enhancing the defense ability of mulberry root system cells. It is suggested that MYB, PME, SBT, EXP, DIR, POD, and the ARR family of transcription factors could be used as the target genes for further in-depth research.

Laser wounding pattern in relation to vascular tissue development for the stimulation of adventitious root formation in rose cuttings

The stimulation of adventitious root formation from laser-wounded rose cuttings in our previous study suggests that exposing the phloem proximities is one of the most relevant aspects for a positive effect on rooting response. But, the specific dimensions that wound patterns must fulfill to optimize rooting promotion remain unknown. This study analyzed the effect of wounded area and wound perimeter of laser marking patterns on the development of phloem, xylem, and callus using cross sections of single-leaf cuttings of Rosa canina 'Pfänder'. Four distinct laser patterns were designed and marked along the cutting base. Among these, three patterns were based on longitudinal strips, while one pattern was characterized by small squares, resulting in two distinct wound area levels and four wound perimeter levels. Periodic evaluations of stem sections showed that the development of phloem and xylem was significantly influenced by the pattern's geometry. Larger dimensions of xylem were associated with patterns of greater area and a smaller perimeter, while an increase in phloem was related to patterns of longer perimeter distributed in smaller areas. The maximum rooting success in wounded cuttings reached 44% in contrast to 9% observed in the control group in the absence of additional wounds. The development of vascular tissue was significantly correlated with adventitious rooting, with phloem being more closely linked with a Pearson coefficient of 0.92 compared to 0.30 for xylem. Additionally, a negative Pearson coefficient of −0.92 between the ratio area: perimeter and adventitious root formation showed that laser patterns with large wounded area with less borders led to a reduced rooting response. The results provide evidence of how wounded tissue contributes to the intrinsic development of adventitious roots and reveal the importance of proper wound dimensions.

Physiological Age of Stock Plants Determines Phytohormonal Changes in Leafy Cuttings of Prunus subhirtella 'Autumnalis'

AbstractThe aim of this study was to investigate adventitious root formation in cuttings obtained from physiologically different old stock material. The ornamental cherry Prunus subhirtella ´Autumnalis´ was used for the experiment. We examined three stock plants, namely a physiologically mature stock plant (about 60 years old) and physiologically juvenile plants (21 years old), which were previously propagated by cuttings, semi-mature stock material and in vitro juvenile stock material. We also investigated the role of phytohormones in the induction phase of adventitious root (AR) formation depending on the physiological age of the stock plant and the time after cutting. High performance liquid chromatography coupled with mass spectrometry (HPLC–MS/MS) was used to identify and quantify the phytohormones. The difference in rooting and quality of the developed AR is observed between semi-mature stock and mature stock material. Cuttings from semi-mature plants rooted in 95.00% of cases, while cuttings from mature stock plants only rooted in 68.33%. The high concentration of strigolactones and jasmonic acid (JA) immediately after severance had an inhibitory effect on the development of adventitious roots, especially in cuttings of mature origin. The development of AR is positively influenced by the increase in indole-3-acetic acid (IAA) 4 h after cutting from the stock plant. Our results show that the formation of adventitious root formation depends on the concentration and ratio between different phytohormones.

Genome-wide analysis of the WOX gene family and function exploration of RhWOX331 in rose (R. 'The Fairy').

WOXs are a class of plant-specific transcription factors that play key roles in plant growth and stress responses. However, the mechanism by which WOXs influence adventitious root development in Rosa hybrida remains unclear. In this study, RcWOX gene family in rose was identified and phylogenetically analyzed using bioinformatics analysis. A total of 381 RcWOX gene members were localized on seven chromosomes except of nine members. The main cis-acting elements involved in hormonal, light, developmental, and abiotic stress responses were identified in the promoters of RcWOX genes, suggesting their regulation by these signals. Nine RhWOX genes had significant different expression during rooting process of rose. RhWOX331, RhWOX308, RhWOX318 were positive with the formation of rose roots. RhWOX331 was positively involved in the formation of adventitious root primordia, which gene coding a transcription factor localized in the nucleus. The HOX conserved domain in the protein contributed to the self-activating activity of RhWOX331. We obtained genetically modified Arabidopsis to validate the function of RhWOX331. Overexpression of RhWOX331 gene alleviated the inhibition of root length of A. thaliana primary roots by high concentration of IBA and NPA, and significantly increased the number of lateral roots on the primary roots, as well as the height of A. thaliana plants. Additionally, RhWOX331 promoted adventitious root formation in A. thaliana and mitigated hormonal inhibition by exogenous 6-BA, NPA, and GA3. The RhWOX331 promoter contained cis-acting elements such as ABRE, Box 4 and CGTCA-motif et.al. GUS activity analysis showed that the gene acted at the cotyledon attachment site. Taken together, these studies identified a significant expansion of the RcWOX gene family, inferred roles of certain branch members in adventitious root formation, elucidated the function of RhWOX331 in adventitious root initiation, and laid the foundation for further research on the function of WOX gene family in roses.

Genome-Wide Identification and Analysis of the Aux/IAA Gene Family in Rosa hybrida—“The Fairy”: Evidence for the Role of RhIAA25 in Adventitious Root Development

Propagation of cuttings is the primary method of rose multiplication. Aux/IAA, early response genes to auxin, play an important role in regulating the process of adventitious root formation in plants. However, systematic research on the identification of RhAux/IAA genes and their role in adventitious root formation in roses is lacking. In this study, 34 RhAux/IAA genes were identified by screening the rose genome, distributed on seven chromosomes, and classified into three clades based on the evolutionary tree. An analysis of the cis-acting elements in the promoters of RhAux/IAA genes revealed the presence of numerous elements related to plant hormones, the light signal response, the growth and development of plants, and abiotic stress. RNA-seq analysis identified a key RhIAA25 gene that may play an important role in the generation of adventitious roots in roses. Subcellular localization, yeast self-activation, and tissue-specific expression experiments indicated that RhIAA25 encoded a nuclear protein, had no yeast self-activated activity, and was highly expressed in the stem. The overexpression of RhIAA25 promoted the elongation of the primary root in Arabidopsis but inhibited adventitious root formation. This study systematically identified and analyzed the RhAux/IAA gene family and identified a key gene, RhIAA25, that regulates adventitious root generation in roses. This study offers a valuable genetic resource for investigating the regulatory mechanism of adventitious root formation in roses.

GhMAX2 Contributes to Auxin-Mediated Fiber Elongation in Cotton (Gossypium hirsutum).

Strigolactones (SLs) represent a new group of phytohormones that play a pivotal role in the regulation of plant shoot branching and the development of adventitious roots. In cotton (Gossypium hirsutum, Gh), SLs play a crucial role in the regulation of fiber cell elongation and secondary cell wall thickness. However, the underlying molecular mechanisms of SL signaling involved in fiber cell development are largely unknown. In this study, we report two SL-signaling genes, GhMAX2-3 and GhMAX2-6, which positively regulate cotton fiber elongation. Further protein-protein interaction and degradation assays showed that the repressor of the auxin cascade GhIAA17 serves as a substrate for the F-box E3 ligase GhMAX2. The in vivo ubiquitination assay suggested that GhMAX2-3 and GhMAX2-6 ubiquitinate GhIAA17 and coordinately degrade GhIAA17 with GhTIR1. The findings of this investigation offer valuable insights into the roles of GhMAX2-mediated SL signaling in cotton and establish a solid foundation for future endeavors aimed at optimizing cotton plant cultivation.

Physiological, Cellular, and Transcriptomic Analyses Provide Insights into the Tolerance Response of Arundo donax to Waterlogging Stress

Arundo donax is widely used as an ornamental plant in landscape gardening because of its adaptability to varying degrees of waterlogged conditions. However, to date, little information is available about the adaptive mechanism of A. donax under waterlogging stress. The results showed that long-term mild waterlogging efficiently induced the formation of adventitious roots (ARs) and further promoted root aerenchyma development, and that the activity of antioxidant enzymes (SOD, POD, and CAT) in Ars also was greatly enhanced after waterlogging. At the transcriptomic level, the expression of genes related to apoptosis, the regulation of cell division, ethylene biosynthesis, alginate synthesis, auxin signaling pathways, and anaerobic respiration was mostly up-regulated after the occurrence of waterlogging stress but genes involved in the abscisic acid signaling pathways were partly down-regulated, which indicated a preferential and favorable transcriptional response in regulating adventitious root development. Taken together, this study definitely advances our knowledge of the morphological, physiological, and transcriptomic responses of A. donax under waterlogging stress and sheds new lights on its adaptive mechanisms.

Raffinose catabolism enhances maize waterlogging tolerance by stimulating adventitious root growth and development.

Raffinose mitigates plant heat, drought, and cold stresses; however, whether raffinose contributes to plant waterlogging tolerance is unknown. The maize raffinose synthase mutant zmrafs-1 had seedlings that lack raffinose, generated fewer and shorter adventitious roots, and were more sensitive to waterlogging stress, while overexpression of the raffinose synthase gene, ZmRAFS, increased raffinose content, stimulated adventitious root formation, and enhanced waterlogging tolerance of maize seedlings. Transcriptome analysis of null segregant seedlings compared with zmrafs-1, particularly when waterlogged, revealed that the expression of genes related to galactose metabolism and the auxin biosynthetic pathway were up-regulated by raffinose. Additionally, indole-3-acetic acid content was significantly decreased in zmrafs-1 seedlings and increased in ZmRAFS-overexpressing seedlings. Inhibition of the hydrolysis of raffinose by 1-deoxygalactonojirimycin decreased the waterlogging tolerance of maize seedlings, the expression of genes encoding proteins related to auxin transport-related genes, and the indole-3-acetic acid level in the seedlings, indicating that the hydrolysis of raffinose is necessary for maize waterlogging tolerance. These data demonstrate that raffinose catabolism stimulates adventitious root formation via the auxin signaling pathway to enhance maize waterlogging tolerance.

A Small Auxin-Up RNA Gene, IbSAUR36, Regulates Adventitious Root Development in Transgenic Sweet Potato.

Small auxin-upregulated RNAs (SAURs), as the largest family of early auxin-responsive genes, play important roles in plant growth and development processes, such as auxin signaling and transport, hypocotyl development, and tolerance to environmental stresses. However, the functions of few SAUR genes are known in the root development of sweet potatoes. In this study, an IbSAUR36 gene was cloned and functionally analyzed. The IbSAUR36 protein was localized to the nucleus and plasma membrane. The transcriptional level of this gene was significantly higher in the pencil root and leaf.This gene was strongly induced by indole-3-acetic acid (IAA), but it was downregulated under methyl-jasmonate(MeJA) treatment. The promoter of IbSAUR36 contained the core cis-elements for phytohormone responsiveness. Promoter β-glucuronidase (GUS) analysis in Arabidopsis showed that IbSAUR36 is highly expressed in the young tissues of plants, such as young leaves, roots, and buds. IbSAUR36-overexpressing sweet potato roots were obtained by an efficient Agrobacterium rhizogenes-mediated root transgenic system. We demonstrated that overexpression of IbSAUR36 promoted the accumulation of IAA, upregulated the genes encoding IAA synthesis and its signaling pathways, and downregulated the genes encoding lignin synthesis and JA signaling pathways. Taken together, these results show that IbSAUR36 plays an important role in adventitious root (AR) development by regulating IAA signaling, lignin synthesis, and JA signaling pathways in transgenic sweet potatoes.

The Application Timing of a Cytokinin B-Mo-based Product Affects the Characteristics of Rooted Cuttings and Nonstructural Carbohydrates of Coleus (Plectranthus scutellarioides cv. Wild Lime) during Adventitious Root Development

A large group of horticulture species are propagated vegetatively through shoot-tip cuttings harvested from stock plants and planted to form adventitious roots. Adventitious rooting leads to establishing a carbohydrate sink in the region of root regeneration that is highly dependent on energy and carbon skeletons. We hypothesized that the timing of exogenous applications of cytokinin (CK) and boron (B)–molybdenum (Mo)-based products during adventitious root development can affect the flow of sugars from leaves to sinks, carbon allocation to the adventitious roots, and the quality of rooted cuttings. During this project, we aimed to determine if the application time of a CK/B-Mo-based product during the adventitious root development of unrooted cuttings would impact the source-to-sink relationship and, hence, affect plug growth and quality. A sink-strengthening commercial product based on cytokinin, B, and Mo was applied at four plug development stages plus a negative control as follows: T1, plants without product (control); T2, sticking stage (starting 24 hours after the sticking); T3, callus formation stage; T4, root development stage; and T5, toning stage. The root and shoot lengths and dry matter, number of leaves, leaf chlorophyll content, root-to-shoot ratio (based on dry matter), and nonstructural carbohydrate contents were measured. The timing of the application of the product impacted the root development, quality of the cuttings, and nonstructural carbohydrate content. Product application during the adventitious root dedifferentiation and induction phases (T2) resulted in the shortest root and shoot lengths, lowest dry matter accumulation, lowest nonstructural carbohydrate contents, and some phytotoxicity. Application during the initiation phase (T3) resulted in greater root length, total dry matter, and total soluble sugar contents compared with the control. Application during the expression phase (T4) resulted in the largest root length and mass and the highest sucrose contents. Applying the product when the roots had grown and reached all the edges of the growing media (T5) did not have any benefits compared with the control. This study provides new insights into the application timing of exogenous CKs, B, and Mo to generate a well-toned rooted coleus cutting and potential explanations in relation to nonstructural carbohydrate metabolism.

The Slow Growth of Adventitious Roots in Tetraploid Hybrid Poplar (Populus simonii × P. nigra var. italica) May Be Caused by Endogenous Hormone-Mediated Meristem Shortening.

Polyploidization produces abundant phenotypic variation. Little is currently known about adventitious root (AR) development variation due to polyploidization. In this study, we analyzed the morphological, cytological, and physiological variations in AR development between tetraploid and diploid Populus plants during in vitro rooting culture. Compared to the diploids, the AR formation times and rooting rates of the tetraploids' stem explants had non-significant changes. However, the tetraploid ARs exhibited significantly slower elongation growth than the diploid ARs. Cytological observation showed that the tetraploid ARs were characterized by shorter root meristems and reduced meristem cell numbers, suggesting the reasons for the slow AR elongation. Analysis of hormones and related metabolites during AR development demonstrated that the total auxin, cytokinin, and jasmonic acid contents were significantly lower in the tetraploid ARs than in those of the diploids, and that the ratio of total auxins to total CKs at 0 h of AR development was also lower in the tetraploids than in the diploids, whereas the total salicylic acid content of the tetraploids was consistently higher than that of the diploids. qPCR analysis showed that the expression levels of several hormone signaling and cell division-related genes in the tetraploid ARs significantly differed from those in the diploids. In conclusion, the slow elongation of the tetraploid ARs may be caused by the endogenous hormone-mediated meristem shortening. Our findings enhance the understanding of polyploidization-induced variation in AR development of forest trees.

Unraveling Key Factors for Hypoxia Tolerance in Contrasting Varieties of Cotton Rose by Comparative Morpho-physiological and Transcriptome Analysis.

The cotton rose (Hibiscus mutabilis) is a plant species commonly found in tropical and subtropical regions. It is remarkably resilient to waterlogging stress; however, the underlying mechanism behind this trait is yet unknown. This study used hypoxia-tolerant "Danbanhong" (DBH) and more hypoxia-sensitive "Yurui" (YR) genotypes and compared their morpho-physiological and transcriptional responses to hypoxic conditions. Notably, DBH had a higher number of adventitious roots (20.3) compared to YR (10.0), with longer adventitious roots in DBH (18.3 cm) than in YR (11.2 cm). Furthermore, the formation of aerenchyma was 3-fold greater in DBH compared to YR. Transcriptomic analysis revealed that DBH had more rapid transcriptional responses to hypoxia than YR. Identification of a greater number of differentially expressed genes (DEGs) for aerenchyma, adventitious root formation and development, and energy metabolism in DBH supported that DBH had better morphological and transcriptional adaptation than YR. DEG functional enrichment analysis indicated the involvement of variety-specific biological processes in adaption to hypoxia. Plant hormone signaling transduction, MAPK signaling pathway and carbon metabolism played more pronounced roles in DBH, whereas the ribosome genes were specifically induced in YR. These results show that effective multilevel coordination of adventitious root development and aerenchyma, in conjunction with plant hormone signaling and carbon metabolism, is required for increased hypoxia tolerance. This study provides new insights into the characterization of morpho-physiological and transcriptional responses to hypoxia in H. mutabilis, shedding light on the molecular mechanisms of its adaptation to hypoxic environments.

Variation in Root System Architecture Response to Arsenic during Establishment and Onset of Storage Root Formation in Two Sweetpotato (Ipomoea batatas L.) Cultivars

The primary objective of this work was to generate species-specific information about root architectural adaptations to simulated natural levels of arsenic (As) during the establishment phase and onset of storage root formation in sweetpotato. Cultivars Bayou Belle and Beauregard were grown on sand substrate and provided with 0.5X Hoagland’s nutrient solution with varying levels of As (0, 5, 10, or 15 mg⋅L−1). During the first experiment, entire root systems were sampled at 5, 10, and 15 days, corresponding to key adventitious root developmental stages. Compared with the untreated controls at 15 days, ‘Bayou Belle’ and ‘Beauregard’ provided with 15 mg⋅L−1 As showed respective increases in the following root architectural attributes: 168% and 130% in main root length; 168% and 98% in lateral root length; and 140% and 50% in lateral root density. A second experiment was performed to produce storage root samples at 50 days. Storage root length, width, and length/width ratio did not vary with As levels. The accumulation of As in storage roots increased with increasing As levels. The results support the hypothesis that natural As levels stimulate adventitious root development in sweetpotato in a cultivar-dependent manner. The observations are consistent with findings of other species that show similar growth stimulation at low As levels. This is the first report of sweetpotato root system architecture responses to experimental levels of As that are known to be present in agricultural soils. Standardization of experimental procedures and understanding of root system adaptations to natural levels of As could lead to a more systematic exploitation of genome-wide techniques and characterization of the molecular basis of reduced As uptake in plants.

Identification and functional analysis of a CbSHR homolog in controlling adventitious root development in Catalpa bungei

Identification and functional analysis of a CbSHR homolog in controlling adventitious root development in Catalpa bungei

Transcriptome analysis of waterlogging-induced adventitious root and control taproot of Mentha arvensis.

The present study reports differentially expressed transcripts in the waterlogging-induced adventitious root (AR) of Mentha arvensis; the identified transcripts will help to understand AR development and improve waterlogging stress response. Waterlogging notably hampers plant growth in areas facing waterlogged soil conditions. In our previous findings, Mentha arvensis was shown to adapt better in waterlogging conditions by initiating the early onset of adventitious root development. In the present study, we compared the transcriptome analysis of adventitious root induced after the waterlogging treatment with the control taproot. The biochemical parameters of total carbohydrate, total protein content, nitric oxide (NO) scavenging activity and antioxidant enzymes, such as catalase activity (CAT) and superoxide dismutase (SOD) activity, were enhanced in the adventitious root compared with control taproot. Analysis of differentially expressed genes (DEGs) in adventitious root compared with the control taproot were grouped into four functional categories, i.e., carbohydrate metabolism, antioxidant activity, hormonal regulation, and transcription factors that could be majorly involved in the development of adventitious roots. Differential expression of the upregulated and uniquely expressing thirty-five transcripts in adventitious roots was validated using qRT-PCR. This study has generated the resource of differentially and uniquely expressing transcripts in the waterlogging-induced adventitious roots. Further functional characterization of these transcripts will be helpful to understand the development of adventitious roots, leading to the resistance towards waterlogging stress in Mentha arvensis.

Abiotic Stress Responses in Woody Plants: Morphological, Physiological, and Anatomical Features

Abiotic stressors may have intricate and varied impacts on the growth and development of forest trees. This article provides a comprehensive summary of the effects of abiotic stressors, such as flood, drought, severe temperature, salt, heavy metal, combination stresses, and microplastics, on the morphological, physiological, and anatomical features of woody plants. The focus is particularly on evaluating these effects from the viewpoint of the xylem. During abiotic stress, the ability of xylem to transport water declines, which is linked to the control of leaf stomata and the suppression of aquaporin (AQP) function. Concurrently, woody plants maintain control over the dimensions and structure of their roots and leaves in order to achieve a harmonious equilibrium between water intake and evaporation. The anatomical characteristics are modified as well, including increased density of leaf stomata, smaller conduits, and thicker cell walls. Furthermore, various types of stressors elicit distinct responses in plants. For instance, flooding leads to the development of adventitious roots and aeration tissues, while forest fires cause irreparable damage to the xylem. Low temperatures result in tissue freezing, salt stress hinders ion absorption, and exposure to heavy metals induces biological toxicity. Woody plants' growth may be periodically enhanced in conditions of drought, floods, and exposure to heavy metals. The impact of combined stress on the physiological, morphological, and anatomical characteristics of woody plants is not only cumulative. The underlying mechanism behind this phenomenon requires additional investigation, particularly in natural or near-natural environments.

Characterization and genetic differences analysis in adventitious roots development of 38 Populus germplasm resources.

To select poplar clones with excellent adventitious roots development (ARD) and deepen the understanding of its molecular mechanism, a comprehensive evaluation was conducted on 38 Populus germplasm resources with cuttings cultured in the greenhouse. Genetic differences between poplar clones with good ARD and with poor ARD were explored from the perspectives of genomics and transcriptomics. By cluster analysis of the seven adventitious roots (AR) traits, the materials were classified into three clusters, of which cluster I indicated excellent AR developmental capability and promising breeding potential, especially P.×canadensis 'Guariento', P. 'jingtong1', P. deltoides 'Zhongcheng5', P. deltoides 'Zhongcheng2'. At the genomic level, the cross-population composite likelihood ratio (XP-CLR) analysis identified 1944 positive selection regions related to ARD, and variation detection analysis identified 3426 specific SNPs and 687 specific Indels in the clones with good ARD, 3212 specific SNPs and 583 specific Indels in the clones with poor ARD, respectively. Through XP-CLR, variation detection, and weighted gene co-expression network analysis based on transcriptome data, eight major putative genes associated with poplar ARD were primary identified, and a co-expression network of eight genes was constructed, it was discovered that CSD1 and WRKY6 may be important in the ARD. Subsequently, we confirmed that SWEET17 had a non-synonymous mutation at the site of 928,404 in the clones with poor ARD, resulting in an alteration of the amino acid. After exploring phenotypic differences and the genetic variation of adventitious roots development in different poplar clones, this study provides valuable reference information for future poplar breeding and genetic improvement.