Effects of node restriction on cadmium accumulation in eight Chinese wheat (Triticum turgidum) cultivars

Minimization of cadmium (Cd) accumulation in wheat is an effective method to prevent Cd-related health risks to humans. To understand the underlying mechanisms of restricting Cd transport, the role of nodes in Cd restriction was studied in eight Chinese wheat cultivars. The Cd accumulation differed significantly among the cultivars. The grain Cd concentrations were mainly dependent on the Cd concentrations in the roots and shoots. The Cd transport in the shoots controlled the wheat grain Cd accumulations. Nodes in the wheat stem have distinct functions in the transfer, distribution, and restriction of Cd. The node connected to the panicle showed the lowest translocation factors. The area of the vascular bundles, especially the diffuse vascular bundles, in the junctional node with the flag leaf was the key factor in restricting Cd transfer to the wheat grain. There was a significant relation between these areas and the grain Cd concentrations. The conclusion of this study is that screening or breeding cultivars with low Cd concentrations in the roots or with smaller areas of diffuse vascular bundles in the junctional nodes with the flag leaf is an effective strategy to decrease Cd concentration in wheat grains.

Dynamics of gene expression during development and expansion of vegetative stem internodes of bioenergy sorghum

BACKGROUND

Bioenergy sorghum accumulates 75% of shoot biomass in stem internodes. Grass stem internodes are formed during vegetative growth and elongate in response to developmental and environmental signals. To identify genes and molecular mechanisms that modulate the extent of internode growth, we conducted microscopic and transcriptomic analyses of four successive sub-apical vegetative internodes representing different stages of internode development of the bioenergy sorghum genotype R.07020.

RESULTS

Stem internodes of sorghum genotype R.07020 are formed during the vegetative phase and their length is enhanced by environmental signals such as shade and floral induction in short days. During vegetative growth, the first visible and youngest sub-apical internode was ~0.7 cm in length, whereas the fourth fully expanded internode was ~5 cm in length. Microscopic analyses revealed that all internode tissue types including pith parenchyma and vascular bundles are present in the four successive internodes. Growth in the first two sub-apical internodes occurred primarily through an increase in cell number consistent with expression of genes involved in the cell cycle and DNA replication. Growth of the 3rd internode was associated with an increase in cell length and growth cessation in the 4th internode was associated with up-regulation of genes involved in secondary cell wall deposition. The expression of genes involved in hormone metabolism and signaling indicates that GA, BR, and CK activity decreased while ethylene, ABA, and JA increased in the 3rd/4th internodes. While the level of auxin appears to be increasing as indicated by the up-regulation of ARFs, down-regulation of TIR during development indicates that auxin signaling is also modified. The expression patterns of transcription factors are closely associated with their role during the development of the vegetative internodes.

CONCLUSIONS

Microscopic and transcriptome analyses of four successive sub-apical internodes characterized the developmental progression of vegetative stem internodes from initiation through full elongation in the sorghum genotype R.07020. Transcriptome profiling indicates that dynamic variation in the levels and action of GA, CK, IAA, BR, ethylene, ABA, and JA modulate gene expression and growth during internode growth and development. This study provides detailed microscopic and transcriptomic data useful for identifying genes and molecular pathways regulating internode elongation in response to various developmental and environmental signals.

Lignin synthesis and accumulation in barley cultivars differing in their resistance to lodging

Since lignin greatly affects stem strength, which is an important agronomical trait, understanding the relationship between lodging resistance and lignin synthesis is important in barley breeding and selection processes. The aim of the study was to reveal the connection between physiological aspects of lignin synthesis and genetic background of barley cultivars with different lodging phenotype. Three barley cultivars Astor, Scarlett and Jaran were compared by measuring lignin, cellulose and total soluble phenolics content, phenylalanine ammonia-lyase activity (PAL) and expression of cinnamoyl-CoA reductase (CCR) and cinnamyl-alcohol dehydrogenase (CAD) in three lower internodes at flowering and grain filling stage. To assess their genetic background simple sequence repeats (SSR) markers, connected to lodging resistance and plant height, were analyzed. Compared to lodging susceptible cultivars Scarlett and Jaran, a lodging resistant cultivar Astor revealed different dynamics of lignin synthesis and deposition, showing higher PAL activity and total soluble phenolics content as well as higher expression of CCR and CAD genes in the second internode at grain filling stage. Analysis of SSR markers associated with quantitative trait loci (QTL) for lodging resistance revealed that Astor discriminates from Scarlett and Jaran by marker Bmag337 connected with elongation of the second internode. Lignification process is under a strong influence of genotype and environmental factors which determine lignin synthesis dynamics and deposition of lignin in the cell walls of barley.

The Significance of Internode Length for Saltatory Conduction: Looking Back at the Age of 90

The development of peripheral nerve fibers involves interdependence between the timing of Schwann cell recruitment during myelination and elongation of the nerve. This adjusts the number and the length of internodes to the length of the fiber. Saltatory conduction in longer nerves involves longer saltations; this makes internode length the factor that determines conduction velocity, thereby adjusting impulse transmission in circuits of different lengths. Myelination increases conduction velocity by means of saltatory conduction but what determines the saltatory conduction is not so much the indispensable insulating adjunct of myelin as the length of the internodes that separate the excitable membrane segments. We have previously studied the development of the length and proportion of internodes in some detail. If the anatomical data are combined, the data fall in place for a revised understanding of conduction velocity and the system that adapts the conduction properties of peripheral nerves to fiber lengths and to body size.

Progression of motor axon dysfunction and ectopic Nav1.8 expression in a mouse model of Charcot-Marie-Tooth disease 1B

Mice heterozygously deficient for the myelin protein P0 gene (P0+/-) develop a slowly progressing neuropathy modeling demyelinating Charcot-Marie-Tooth disease (CMT1B). The aim of the study was to investigate the long-term progression of motor dysfunction in P0+/- mice at 3, 7, 12 and 20months. By comparison with WT littermates, P0+/- showed a decreasing motor performance with age. This was associated with a progressive reduction in amplitude and increase in latency of the plantar compound muscle action potential (CMAP) evoked by stimulation of the tibial nerve at ankle. This progressive functional impairment was in contrast to the mild demyelinating neuropathy of the tibial nerve revealed by histology. "Threshold-tracking" studies showed impaired motor axon excitability in P0+/- from 3months. With time, there was a progressive reduction in threshold deviations during both depolarizing and hyperpolarizing threshold electrotonus associated with increasing resting I/V slope and increasing strength-duration time constant. These depolarizing features in excitability in P0+/- as well as the reduced CMAP amplitude were absent in P0+/- NaV1.8 knockouts, and could be acutely reversed by selective pharmacologic block of NaV1.8 in P0+/-. Mathematical modeling indicated an association of altered passive cable properties with a depolarizing shift in resting membrane potential and increase in the persistent Na(+) current in P0+/-. Our data suggest that ectopic NaV1.8 expression precipitates depolarizing conduction failure in CMT1B, and that motor axon dysfunction in demyelinating neuropathy is pharmacologically reversible.

Common metabolic networks contribute to carbon sink strength of sorghum internodes: implications for bioenergy improvement

BACKGROUND

Sorghum bicolor (L.) is an important bioenergy source. The stems of sweet sorghum function as carbon sinks and accumulate large amounts of sugars and lignocellulosic biomass and considerable amounts of starch, therefore providing a model of carbon allocation and accumulation for other bioenergy crops. While omics data sets for sugar accumulation have been reported in different genotypes, the common features of primary metabolism in sweet genotypes remain unclear. To obtain a cohesive and comparative picture of carbohydrate metabolism between sorghum genotypes, we compared the phenotypes and transcriptome dynamics of sugar-accumulating internodes among three different sweet genotypes (Della, Rio, and SIL-05) and two non-sweet genotypes (BTx406 and R9188).

RESULTS

Field experiments showed that Della and Rio had similar dynamics and internode patterns of sugar concentration, albeit distinct other phenotypes. Interestingly, cellulose synthases for primary cell wall and key genes in starch synthesis and degradation were coordinately upregulated in sweet genotypes. Sweet sorghums maintained active monolignol biosynthesis compared to the non-sweet genotypes. Comparative RNA-seq results support the role of candidate Tonoplast Sugar Transporter gene (TST), but not the Sugars Will Eventually be Exported Transporter genes (SWEETs) in the different sugar accumulations between sweet and non-sweet genotypes.

CONCLUSIONS

Comparisons of the expression dynamics of carbon metabolic genes across the RNA-seq data sets identify several candidate genes with contrasting expression patterns between sweet and non-sweet sorghum lines, including genes required for cellulose and monolignol synthesis (CesA, PTAL, and CCR), starch metabolism (AGPase, SS, SBE, and G6P-translocator SbGPT2), and sucrose metabolism and transport (TPP and TST2). The common transcriptome features of primary metabolism identified here suggest the metabolic networks contributing to carbon sink strength in sorghum internodes, prioritize the candidate genes for manipulating carbon allocation with bioenergy purposes, and provide a comparative and cohesive picture of the complexity of carbon sink strength in sorghum stem.

High frequency plant regeneration with histological analysis of organogenic callus from internode explants of Asteracantha longifolia Nees

Asteracantha longifolia Nees is an ayurvedic medicinal herb. The internode explants of this plant were used for high frequency plant regeneration on Murashige and Skoog (MS) medium supplemented with various plant growth regulators (PGRs) in different concentrations. Apical meristem and leaf primordium formations were confirmed through microscopic analysis of histological sections of the organogenic callus tissues. The synergistic effect of α-naphthaleneacetic acid (NAA) 0.5 mg/l with N 6 benzyladenine (BA) 0.25 mg/l increased the percentage of explants response for callus induction while comparing other treatments. Various concentrations of NAA were also found to be best for explants response to callus induction than 2,4-dichlorophenoxyacetic acid (2,4-D). The callus morphology (color and texture) was different according to the growth regulators and their concentrations. The highest percentage of response per culture for shoot bud regeneration was noted for the concentration of NAA 0.5 mg/l with BA 2.0 mg/l, the same concentration effectively increased the number of shoots per culture. Different concentrations of indol-3-butyric acid (IBA) and NAA were used in half strength MS medium for in vitro rooting of regenerated shoots. The maximum percentage of shoot response for rooting and the highest number of root formations per shoot were observed on the medium containing 0.5 mg/l of IBA. The survival rate (86.7%) of the regenerated plants was noted after 20 days of transplantation.

Global transcriptome changes of elongating internode of sugarcane in response to mepiquat chloride

Background

Mepiquat chloride (DPC) is a chemical that is extensively used to control internode growth and create compact canopies in cultured plants. Previous studies have suggested that DPC could also inhibit gibberellin biosynthesis in sugarcane. Unfortunately, the molecular mechanism underlying the suppressive effects of DPC on plant growth is still largely unknown.

Results

In the present study, we first obtained high-quality long transcripts from the internodes of sugarcane using the PacBio Sequel System. A total of 72,671 isoforms, with N50 at 3073, were generated. These long isoforms were used as a reference for the subsequent RNA-seq. Afterwards, short reads generated from the Illumina HiSeq 4000 platform were used to compare the differentially expressed genes in both the DPC and the control groups. Transcriptome profiling showed that most significant gene changes occurred after six days post DPC treatment. These genes were related to plant hormone signal transduction and biosynthesis of several metabolites, indicating that DPC affected multiple pathways, in addition to suppressing gibberellin biosynthesis. The network of DPC on the key stage was illustrated by weighted gene co-expression network analysis (WGCNA). Among the 36 constructed modules, the top positive correlated module, at the stage of six days post spraying DPC, was sienna3. Notably, Stf0 sulfotransferase, cyclin-like F-box, and HOX12 were the hub genes in sienna3 that had high correlation with other genes in this module. Furthermore, the qPCR validated the high accuracy of the RNA-seq results.

Conclusion

Taken together, we have demonstrated the key role of these genes in DPC-induced growth inhibition in sugarcane.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07352-w.

Efficient regeneration and improved sonication-assisted Agrobacterium transformation (SAAT) method for Catharanthus roseus

Catharanthus roseus is an important medicinal plant known for its pharmacological qualities such as antimicrobial, anticancerous, antifeedant, antisterility, antidiabetic activities. More than 130 bioactive compounds like vinblastine, vindoline and vincristine have been synthesized in this plant. Extensive studies have been carried out for optimization regeneration and transformation protocols. Most of the protocol described are laborious and time-consuming. Due to sophisticated protocol of regeneration and genetic transformation, the production of these bioactive molecules is less and not feasible to be commercialized worldwide. Here we have optimized the efficient protocol for regeneration and transformation to minimize the time scale and enhance the transformation frequency through Agrobacterium and sonication-assisted transformation (SAAT) method. In this study, hypocotyl explants responded best for maximal production of transformed shoots. The callus percentage were recorded 52% with 1.0 mg L⁻¹ (BAP) and 0.5 mg L⁻¹ (NAA) while 80% shoot percentage obtained with 4.0 mg L⁻¹ (BAP) and 0.05 mg L⁻¹ (NAA). The microscopic studies revealed that the expression of GFP was clearly localized in leaf tissue of the C. roseus after transformation of pRepGFP0029 construct. Consequently, transformation efficiency was revealed on the basis of GFP localization. The transformation efficiency of SAAT method was 6.0% comparable to 3.5% as conventional method. Further, PCR analysis confirmed the integration of the nptII gene in the transformed plantlets of C. roseus.

Low intensity repetitive transcranial magnetic stimulation enhances remyelination by newborn and surviving oligodendrocytes in the cuprizone model of toxic demyelination

In people with multiple sclerosis (MS), newborn and surviving oligodendrocytes (OLs) can contribute to remyelination, however, current therapies are unable to enhance or sustain endogenous repair. Low intensity repetitive transcranial magnetic stimulation (LI-rTMS), delivered as an intermittent theta burst stimulation (iTBS), increases the survival and maturation of newborn OLs in the healthy adult mouse cortex, but it is unclear whether LI-rTMS can promote remyelination. To examine this possibility, we fluorescently labelled oligodendrocyte progenitor cells (OPCs; Pdgfrα-CreER transgenic mice) or mature OLs (Plp-CreER transgenic mice) in the adult mouse brain and traced the fate of each cell population over time. Daily sessions of iTBS (600 pulses; 120 mT), delivered during cuprizone (CPZ) feeding, did not alter new or pre-existing OL survival but increased the number of myelin internodes elaborated by new OLs in the primary motor cortex (M1). This resulted in each new M1 OL producing ~ 471 µm more myelin. When LI-rTMS was delivered after CPZ withdrawal (during remyelination), it significantly increased the length of the internodes elaborated by new M1 and callosal OLs, increased the number of surviving OLs that supported internodes in the corpus callosum (CC), and increased the proportion of axons that were myelinated. The ability of LI-rTMS to modify cortical neuronal activity and the behaviour of new and surviving OLs, suggests that it may be a suitable adjunct intervention to enhance remyelination in people with MS.

Cessation of annual apical growth and partial death of cambium in stem of Abies sachalinensis under intensive shading

This study evaluated variation in the height at which absent rings and internodes were detected along stem of Abies sachalinensis trees grown under shade for 39 years. Eight sample trees planted in 1974 under a secondary forest in Japan were felled in 2013 and analyzed. A. sachalinensis is a monopodial species in which it is possible to measure annual apical growth using the distinct internodes. We applied microscopic analysis on 154 stem disks from the stem base to the top to evaluate the cessation of apical and radial growth caused by intensive shading. Cessation of apical stem growth for one or more years was found in 6 out of 8 sample trees. We termed this phenomenon as "absent internode". In addition, the absent growth rings were detected more frequently in the lower part of sample stems, and the number of absent rings at the stem base did not correspond with the number of absent internodes in the six trees. From cellular level observation, the five suppressed trees had no living cambial cells at the stem base but had living cells at the stem top. The cessation of the apical and radial growth did not occur synchronously but did occur independently under a shade environment in A. sachalinensis.

Accumulation of mutations in the AP2 homoeologs causes suppression of anther extrusion with altered spike and culm development in hexaploid wheat

Cleistogamy or closed flowering is a widely used trait in barley (Hordeum vulgare) breeding because it reduces the risk of fungal infection in florets at anthesis. Cleistogamy in barley is caused by a point mutation within the microRNA172 (miR172) target site of the Cly1 gene, which encodes the Apetala2 (AP2) transcription factor. Because cleistogamy is not apparent in cultivars of hexaploid wheat (Triticum aestivum), a strategy to develop cleistogamous wheat was proposed by inducing point mutations in all three AP2 homoeologs, which are the wheat orthologs of barley Cly1. In this study, we investigated the effects of miR172 target site mutations on wheat cleistogamy using double mutants by combining three previously obtained mutant alleles (AP2-A1, D1 and D2) in a near-isogenic background. The AP2-D2 allele had the greatest effect on reducing the anther extrusion rate and lodicule size compared with the other two mutant alleles. The double mutant containing the AP2-A1 and AP2-D2 alleles had a much greater suppression of anther extrusion by reducing the lodicule size than the single AP2-D2 mutant, suggesting cumulative effects of the two mutant alleles. In addition, both single and double mutants exhibited compact spikes and shorter plant heights due to reduced rachis and culm internodes in the upper parts. The presence or absence of the wild-type AP2-B homoeolog had no significant effect on phenotype. This study provides insights into the cumulative effects of mutant AP2 alleles in suppressing open flowering and provides a basis for further research on the development of complete cleistogamy in hexaploid wheat.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01458-9.

Developmental Dynamics of Intercalary Meristem and Pith Cavity in Rice Stems

In rice, internode elongation is a critical aspect of plant development and agricultural productivity. Previous morphological and histochemical studies using [3H]thymidine have visualized the cell division zone (intercalary meristem) in internodes. However, it has remained unclear how the intercalary meristem forms during stem development. In addition, while a pith cavity forms in the central part of the rice stem, the spatiotemporal relationship between pith cavity formation and intercalary meristem development is not well understood. Therefore, we performed histological analysis of intercalary meristem and pith cavity development using C9285, a deepwater rice variety that shows internode elongation from the vegetative growth stage. We classified the developmental stages of the stem into four stages based on the analysis of pith cavity formation using Trypan blue, Calcein-AM, and MitoRed staining, and visualized dividing cells using the Click-iT EdU imaging assay. In Stage 1, no pith cavity was formed. Vertical cell rows were observed between above the axillary bud attachment and the upper node, suggesting anticlinal divisions that lead to internode formation in the early stage of stem development. In Stage 2, the first pith cavity formed in the pith of the foot, which is the region of axillary bud attachment. Compared to cell division in the internode, that in the foot was significantly activated resulting in slight elongation from Stage 1 to Stage 2. In Stage 3, cell division in the foot ceased, while active cell division at the base of the internode led to significant vertical elongation. The second pith cavity formed due to cell death in the pith of the internode. In Stage 4, the two pith cavities connected to form a single large pith cavity. Although the intercalary meristem maintained cell division activity, the number of cell divisions decreased. Based on these results, we propose a model for stem development that involves two phases of elongation regulation: primary elongation involving slight elongation in the foot, and secondary elongation involving significant internode elongation due to the activation of cell division and cell elongation in the intercalary meristem. This is the first study to anatomically elucidate the spatiotemporal relationship between intercalary meristem development and pith cavity formation in rice stem development. It provides new insights for future research on rice stem development and studies of other grass species.

Mechanical stimulation reprograms the sorghum internode transcriptome and broadly alters hormone homeostasis

Stem structural failure, or lodging, affects many crops including sorghum, and can cause large yield losses. Lodging is typically caused by mechanical forces associated with severe weather like high winds, but exposure to sub-catastrophic forces may strengthen stems and improve lodging resistance. The responses of sorghum internodes at different developmental stages were examined at 2 and 26 h after initiating moderate mechanical stimulation with an automated apparatus. Transcriptome profiling revealed that mechanical stimulation altered the expression of over 900 genes, including transcription factors, cell wall-related and hormone signaling-related genes. IAA, GA₁ and ABA abundances generally declined following mechanical stimulation, while JA increased. Weighted Gene Co-expression Network Analysis (WGCNA) identified three modules significantly enriched in GO terms associated with cell wall biology, hormone signaling and general stress responses, which were highly correlated with mechanical stimulation and with biomechanical and geometrical traits documented in a separate study. Additionally, mechanical stimulation-triggered responses were dependent on the developmental stage of the internode and the duration of stimulation. This study provides insights into the underlying mechanisms of plant hormone-regulated thigmomorphogenesis in sorghum stems. The critical biological processes and hub genes described here may offer opportunities to improve lodging resistance in sorghum and other crops.

Evolution of the sporophyte shoot axis and functions of TALE HD transcription factors in stem development

The stem is one of the major organs in seed plants and is important for plant survival as well as in agriculture. However, due to the lack of clear external landmarks in many species, its developmental and evolutionary processes are understudied compared to other organs. Recent approaches tackling these problems, especially those focused on KNOX1 and BLH transcription factors belonging to the TALE homeodomain superfamily have started unveiling the patterning process of nodes and internodes by connecting previously accumulated knowledge on lateral organ regulators. Fossil records played crucial roles in understanding the evolutionary process of the stem. The aim of this review is to introduce how the stem evolved from ancestorial sporophyte axes and to provide frameworks for future efforts in understanding the developmental process of this elusive but pivotal organ.