Aerenchyma Formation in Adventitious Roots of Tall Fescue and Cocksfoot under Waterlogged Conditions

The formation of aerenchyma in adventitious roots is one of the most crucial adaptive traits for waterlogging tolerance in plants. Pasture grasses, like other crops, can be affected by waterlogging, and there is scope to improve tolerance through breeding. In this study, two summer-active cocksfoot (Dactylis glomerata L.) cultivars, Lazuly and Porto, and two summer-active tall fescue (Lolium arundinaceum Schreb., syn. Festuca arundinacea Schreb.) cultivars, Hummer and Quantum II MaxP, were selected to investigate the effects of waterlogging on root growth and morphological change. Cultivars were subjected to four periods of waterlogging treatments (7, 14, 21 and 28 days), while comparable plants were kept under free drained control conditions. The experiment was arranged as a split–split plot design, with waterlogging treatments (waterlogged, control) considered as main plots, time periods (days of waterlogging) as subplots and cultivars as sub-subplots. Plants began to show signs of waterlogging stress 14–21 days after the onset of waterlogging treatments. There were no significant differences in shoot biomass between the waterlogged and control plants of any cultivar. However, waterlogging significantly reduced root dry matter in all cultivars, with greater reduction in cocksfoot (56%) than in tall fescue (38%). Waterlogging also led to increased adventitious root and aerenchyma formation in both species. Cocksfoot cultivars showed a greater increase in adventitious roots, while tall fescue cultivars had a greater proportion of aerenchyma. Both cultivars within each species showed similar responses to waterlogging treatments. However, an extended screening program is needed to identify whether there are varietal differences within species, which could be used to discover genes related to aerenchyma or adventitious root formation (waterlogging tolerance) for use in breeding programs.

Dynamic Hormone Gradients Regulate Wound-Induced de novo Organ Formation in Tomato Hypocotyl Explants

Plants have a remarkable regenerative capacity, which allows them to survive tissue damage after biotic and abiotic stresses. In this study, we use Solanum lycopersicum ‘Micro-Tom’ explants as a model to investigate wound-induced de novo organ formation, as these explants can regenerate the missing structures without the exogenous application of plant hormones. Here, we performed simultaneous targeted profiling of 22 phytohormone-related metabolites during de novo organ formation and found that endogenous hormone levels dynamically changed after root and shoot excision, according to region-specific patterns. Our results indicate that a defined temporal window of high auxin-to-cytokinin accumulation in the basal region of the explants was required for adventitious root formation and that was dependent on a concerted regulation of polar auxin transport through the hypocotyl, of local induction of auxin biosynthesis, and of local inhibition of auxin degradation. In the apical region, though, a minimum of auxin-to-cytokinin ratio is established shortly after wounding both by decreasing active auxin levels and by draining auxin via its basipetal transport and internalization. Cross-validation with transcriptomic data highlighted the main hormonal gradients involved in wound-induced de novo organ formation in tomato hypocotyl explants.

Salt Stress Affects Plastid Ultrastructure and Photosynthetic Activity but Not the Essential Oil Composition in Spearmint (Mentha spicata L. var. crispa “Moroccan”)

High levels of soil salinity affect plant growth, reproduction, water and ion uptake, and plant metabolism in a complex manner. In this work, the effect of salt stress on vegetative growth, photosynthetic activity, and chloroplast ultrastructure of spearmint (Mentha spicata L. var. crispa “Moroccan”) was investigated. After 2 weeks of low concentration treatments (5, 25, and 50 mM NaCl) of freshly cut shoots, we observed that the stem-derived adventitious root formation, which is a major mean for vegetative reproduction among mints, was completely inhibited at 50 mM NaCl concentration. One-week-long, high concentration (150 mM NaCl) salt stress, and isosmotic polyethylene glycol (PEG) 6000 treatments were compared in intact (rooted) plants and freshly cut, i.e., rootless shoots. Our data showed that roots have an important role in mitigating the deleterious effects of both the osmotic (PEG treatment) and specific ionic components of high salinity stress. At 50 mM NaCl or above, the ionic component of salt stress caused strong and irreversible physiological alterations. The effects include a decrease in relative water content, the maximal and actual quantum efficiency of photosystem II, relative chlorophyll content, as well as disorganization of the native chlorophyll-protein complexes as revealed by 77 K fluorescence spectroscopy. In addition, important ultrastructural damage was observed by transmission electron microscopy such as the swelling of the thylakoid lumen at 50 mM NaCl treatment. Interestingly, in almost fully dry leaf regions and leaves, granum structure was relatively well retained, however, their disorganization occurred in leaf chloroplasts of rooted spearmint treated with 150 mM NaCl. This loss of granum regularity was also confirmed in the leaves of these plants using small-angle neutron scattering measurements of intact leaves of 150 mM NaCl-stressed rooted plants. At the same time, solid-phase microextraction of spearmint leaves followed by gas chromatography and mass spectrometry (GC/MS) analyses revealed that the essential oil composition of spearmint was unaffected by the treatments applied in this work. Taken together, the used spearmint cultivar tolerates low salinity levels. However, at 50 mM NaCl concentration and above, the ionic components of the stress strongly inhibit adventitious root formation and thus their clonal propagation, and severely damage the photosynthetic apparatus.

Integrated multi-omics analysis uncovers roles of mdm-miR164b-MdORE1 in strigolactone mediated inhibition of adventitious root formation in apple

Adventitious root (AR) formation is important for the vegetative propagation. The effects of strigolactones (SLs) on AR formation have been rarely reported, especially in woody plants. In this study, we first verified the inhibitory effects of SLs on AR formation in apple materials. Transcriptome analysis identified 12,051 differentially expressed genes over the course of AR formation, with functions related to organogenesis, cell wall biogenesis or plant senescence. WGCNA suggests SLs might inhibit AR formation through repressing the expression of two core hub genes, MdLAC3 and MdORE1. We further verified that enhanced cell wall formation and accelerated senescence were involved in the AR inhibition caused by SLs. Combining small RNA and degradome sequencing, as well as a dual-luciferase sensor system, we identified and validated three negatively correlated miRNA–mRNA pairs, including mdm-miR397–MdLAC3 involved in secondary cell wall formation, and mdm-miR164a/b–MdORE1 involved in senescence. Finally, we have experimentally demonstrated the role of mdm-miR164b–MdORE1 in SLs-mediated inhibition of AR formation. Overall, our findings not only propose a comprehensive regulatory network for the function of SLs on AR formation, but also provide novel candidate genes for the potential genetic improvement of AR formation in woody plants using transgenic or CRISPR technology.

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.

De novo transcriptome analysis provides insights into formation of in vitro adventitious root from leaf explants of Arnebia euchroma

Background Adventitious root formation is considered a major developmental step during the propagation of difficult to root plants, especially in horticultural crops. Recently, adventitious roots induced through plant tissue culture methods have also been used for production of phytochemicals such as flavonoids, anthocyanins and anthraquinones. It is rather well understood which horticultural species will easily form adventitious roots, but the factors affecting this process at molecular level or regulating the induction process in in vitro conditions are far less known. The present study was conducted to identify transcripts involved in in vitro induction and formation of adventitious roots using Arnebia euchroma leaves at different time points (intact leaf (control), 3 h, 12 h, 24 h, 3 d, 7 d, 10 d and 15 d). A. euchroma is an endangered medicinal Himalayan herb whose root contains red naphthoquinone pigments. These phytoconstituents are widely used as an herbal ingredient in Asian traditional medicine as well as natural colouring agent in food and cosmetics. Results A total of 137.93 to 293.76 million raw reads were generated and assembled to 54,587 transcripts with average length of 1512.27 bps and N50 of 2193 bps, respectively. In addition, 50,107 differentially expressed genes were identified and found to be involved in plant hormone signal transduction, cell wall modification and wound induced mitogen activated protein kinase signalling. The data exhibited dominance of auxin responsive (AUXIN RESPONSE FACTOR8, IAA13, GRETCHEN HAGEN3.1) and sucrose translocation (BETA-31 FRUCTOFURANOSIDASE and MONOSACCHARIDE-SENSING protein1) genes during induction phase. In the initiation phase, the expression of LATERAL ORGAN BOUNDARIES DOMAIN16, EXPANSIN-B15, ENDOGLUCANASE25 and LEUCINE-rich repeat EXTENSION-like proteins was increased. During the expression phase, the same transcripts, with exception of LATERAL ORGAN BOUNDARIES DOMAIN16 were identified. Overall, the transcriptomic analysis revealed a similar patterns of genes, however, their expression level varied in subsequent phases of in vitro adventitious root formation in A. euchroma. Conclusion The results presented here will be helpful in understanding key regulators of in vitro adventitious root development in Arnebia species, which may be deployed in the future for phytochemical production at a commercial scale.

NnLAC17, a Gene Related to Lignin Synthesis, is Involved in Adventitious Root Formation in the Seedlings of Lotus (Nelumbo Nucifera Gaertn)

BarkgroundAdventitious roots (ARs), which are considered as an important member of root system, have an unmatched status in plant growth and metabolism due to the degeneration of primary roots in lotus. The regulation of AR formation was previously revealed and multiple factors were recognized to be involved in this biological process. ResultsIn the present study, we sought to assess the effect of sucrose on AR formation. Based on our results, lignin metabolism, which is regulated by the sucrose signal transduction pathway, is involved in AR development. The lignification degree of the AR primordium was weaker in plants treated with 20 g/L sucrose than in control plants. However, based on the microstructural observation of the AR developmental process, 50 g/L sucrose promoted the lignification process. Lignin content, including monomer and polymer lignin, was determined in the present study. Compared with control plants, the monomer (containing 30%–45% S type and 55%–70% G type) and polymer lignin contents were lower in plants treated with 20 g/L sucrose and higher in plants treated with 50 g/L sucrose. The precursors of monomer lignin were identified in four libraries of differential developmental stages in seedlings using LC-MS/MS technique. The contents of four metabolites, including p-coumaric acid, caffeate, sinapinal aldehyde and ferulic acid for monomer lignin synthsis were lower in the GL50 library than in the GL20 library. Further analysis revealed that the gene expression of these four metabolites had no novel difference in the GL50/GL20 libraries. However, NnLAC17, a gene involved in polymer lignin synthesis, had a higher expression in the GL50 library than in the GL20 library. ConclusionsTherefore, NnLAC17 was cloned, and the overexpression of NnLAC17 was found to directly result in a decrease in AR number in transgenic Arabidopsis plants. These findings suggest that NnLAC17, which is relevant to lignin synthesis, is involved in AR formation in lotus seedlings.