Early Stages Of Root Development Research Articles

Three RLKs integrate SHR-SCR and gibberellins to regulate root ground tissue patterning in Arabidopsis thaliana.

Precise regulation of cell division is essential for proper tissue patterning in multicellular organisms. In Arabidopsis, the ground tissue (GT) comprises cortex and endodermis in the early stages of root development. During GT maturation, additional periclinal cell divisions (PCDs) occasionally occur of the endodermis, generating a middle cortex (MC) layer between the cortex and endodermis. Although several regulatory proteins and phytohormones were identified to mediate GT patterning, such as SHORT-ROOT (SHR), SCARECROW (SCR), CYCLIND6;1 (CYCD6;1), and gibberellins (GAs), the interrelationship among these factors is not elucidated. Here, we report that three closely related receptor-like kinases (RLKs), ARH1, FEI1, and FEI2, play crucial roles in mediating a signal transduction pathway from the SHR-SCR module to GA to regulate GT patterning. Two independent triple mutants of these RLKs (tri-1 and tri-2) exhibit increased MC formation compared with wild type. Genetic analysis indicated that all three RLKs regulate MC formation mainly in a cell-autonomous manner. The transcription levels of these RLKs are negatively controlled by SHR and SCR. The altered GT patterns in shr and scr can be partially complemented by tri-1. GA biosynthesis is significantly reduced in the roots of tri-1. The excessive MC formation in tri-1 can be greatly suppressed by the exogenous application of GA3 or by the mutation of CYCD6;1. Our results demonstrate a signaling pathway involving SHR/SCR-ARH1/FEI1/FEI2-GA-CYCD6;1 to govern GT patterning in Arabidopsis thaliana.

Three-dimensional visualization of Hertwig's epithelial root sheath during tooth root development with the miniTESOS tissue clearing method.

Hertwig's epithelial root sheath (HERS) acts as a signaling center that regulates the size, shape, and number of tooth roots. Therefore, understanding the anatomical changes in HERS during development is crucial for investigating its effect on root formation. However, the three-dimensional morphology of HERS and its changes during tooth root development remain largely unknown due to the limitations of traditional histological techniques. We developed an improved tissue clearing method for mouse embryonic and early postnatal mandibles, designated as a mini Transparent Embedding Solvent System (miniTESOS), based on the Transparent Embedding Solvent System (TESOS). We applied this method to the K14-Cre;Ai14 mouse line to systematically investigate the spatiotemporal dynamics of HERS at the cellular level during the development of the roots of mandibular first molars (MM1) and mandibular second molars (MM2). Additionally, using MM1 as a model, we quantitatively investigated the spatiotemporal changes in HERS in the root bifurcation region during the development of two-rooted teeth. In the early stages of root development, differences in growth rates and developmental patterns between MM1 and MM2 were observed in the mesiodistal and buccolingual directions, from the initiation to the fusion of buccal and lingual HERS. In the elongation stage of two-rooted teeth, continuous HERS was found exclusively at the leading edge of the root, gradually decreasing in length as the root extended. In the root bifurcation area, HERS undergoes four developmental stages: initiation, elongation, contact, and complete fragmentation, each characterized by specific morphological features. This study improves the understanding of the alterations in HERS during root development and summarizes its developmental pattern in the root bifurcation region. The miniTESOS tissue clearing method provides a new strategy to investigate tooth development.

Radiographic outcomes and prognostic factors in nonvital immature permanent teeth after apexification with modified calcium hydroxide paste: a retrospective study.

To assess the radiographic outcomes and prognostic factors in nonvital immature permanent teeth after apexification with modified calcium hydroxide paste. Clinical and radiographic data were collected from 115 necrotic immature permanent teeth (71 caused by trauma and 44 caused by dens evaginatus) treated with apexification using a modified calcium hydroxide. Postoperative root morphology and changes in radiographic root area (RRA) on periapical radiographs were determined and statistically evaluated. Regression analysis was performed to identify factors associated with the outcomes of apexification. The average time for a calcified barrier formation was 10.66 ± 6.37months. The root morphology after apexification with calcium hydroxide + iodoform paste was similar to that previously described after calcium hydroxide apexification. Compared with the trauma cases, the dens evaginatus cases revealed more type I (40.91% vs 16.9%) and less type II morphology (45.45% vs 67.61%). Although the changes in RRA were limited, the dens evaginatus cases showed greater increment of RRA than the trauma cases (4.12% ± 5.58% vs 0.70% ± 5.21%, P < 0.001). A significant association was found between the preoperative stage of root development and postoperative percentage change in RRA (P < 0.001). Teeth caused by dens evaginatus had better outcomes after apexification than teeth caused by trauma. Early stages of root development were associated with superior radiographic outcomes. Apexification provided reliable outcomes in the treatment of immature teeth with pulp necrosis and apical periodontitis, even though the root development is limited. Treatment decision should be made with comprehensive evaluation of prognostic factors.

Pulp healing in immature replanted permanent teeth: A competing risk analysis.

Tooth displacement during avulsion causes total rupture of the pulp's neurovascular supply. Revascularization and pulp healing may occur in immature teeth, which gives rise to the recommendation that root canal treatment may not be required. The aim of this study was to evaluate the prognostic factors for the pulp's response after replantation of young permanent teeth. Records from 117 patients with 133 replanted permanent immature teeth were reviewed, and pulp outcomes were classified as healing (hard tissue deposition on the dentinal walls followed by narrowing of the pulp lumen or ingrowth of bone-like tissue inside the pulp canal) or non-healing (pulp necrosis with infection). The effect of clinical and demographic co-variates on the hazards of both outcomes was assessed performing a competing risk model. Pulp necrosis with infection was diagnosed in 78.2% of the teeth, and healing was observed in 12.8% of the teeth. A total of 12 teeth (9.0%) were censored due to prophylactic removal of the pulp or severe external root resorption caused by eruption of adjacent canines. The cs-Cox model demonstrated that the hazards of pulp healing increased in teeth with extra-alveolar periods <15min (csHR: 7.83, 95% CI 1.76-34.80, p=.01), while the hazards of pulp necrosis with infection decreased (csHR: 0.31, 95% CI: 0.10-0.92, p=.04). Teeth replanted with Moorrees' stages 4 and 5 of root development had higher hazards of pulp necrosis with infection than teeth with stage 2 of root development (csHR: 2.23, 95% CI 1.11-4.50, p=.03; csHR: 2.89, 95% CI: 1.40-5.95; p=.01). Pulp healing rarely occurred after replantation of young permanent teeth being associated with short extra-alveolar periods <15min. Early stages of root development decreased the hazards of pulp necrosis with infection.

A Linear Model to Describe Branching and Allometry in Root Architecture.

Root architecture is a complex structure that comprises multiple traits of the root phenotype. Novel platforms and models have been developed to better understand root architecture. In this methods paper, we introduce a novel allometric model, named rhizochron index (m), which describes lateral root (LR) branching and elongation patterns across the primary root (PR). To test our model, we obtained data from 16 natural accessions of Arabidopsis thaliana at three stages of early root development to measure conventional traits of root architecture (e.g., PR and LR length), and extracted the rhizochron index (m). In addition, we tested previously published datasets to assess the utility of the rhizochron index (m) to distinguish mutants and environmental effects on root architecture. Our results indicate that rhizochron index (m) is useful to distinguish the natural variations of root architecture between A. thaliana accessions, but not across early stages of root development. Correlation analyses in these accessions showed that m is a novel trait that partially captures information from other root architecture traits such as total lateral root length, and the ratio between lateral root and primary root lengths. Moreover, we found that the rhizochron index was useful to distinguish ABA effect on root architecture, as well as the mutant pho1 phenotype. We propose the rhizochron index (m) as a new feature of the root architectural system to be considered, in addition to conventional traits in future investigations.

MsmiR156 affects global gene expression and promotes root regenerative capacity and nitrogen fixation activity in alfalfa.

MicroRNA156 (miR156) regulates a network of downstream genes to affect plant growth and development. We previously generated alfalfa (Medicago sativa) plants that overexpress homologous miR156 (MsmiR156OE), and identified three of its SPL target genes. These plants exhibited increased vegetative yield, delayed flowering and longer roots. In this study, we aimed to elucidate the effect of miR156 on the root system, including effect on nodulation and nitrogen fixation. We found that MsmiR156 overexpression increases root regeneration capacity in alfalfa, but with little effect on root biomass at the early stages of root development. MsmiR156 also promotes nitrogen fixation activity by upregulating expression of nitrogenase-related genes FixK, NifA and RpoH in roots inoculated with Sinorrhizobium meliloti. Furthermore, we conducted transcriptomics analysis of MsmiR156OE alfalfa roots and identified differentially expressed genes belonging to 132 different functional categories, including plant cell wall organization, peptidyl-hypusine synthesis, and response to water stress. Expression analysis also revealed miR156 effects on genes involved in nodulation, root development and phytohormone biosynthesis. The present findings suggest that miR156 regulates root development and nitrogen fixation activity. Taken together, these findings highlight the important role that miR156 may play as a tool in the biotechnological improvement of alfalfa, and potentially other crops.

Comparison of stem cell behaviors between indigenous high and low-CD24 percentage expressing cells of stem cells from apical papilla (SCAPs).

CD24 was suggested as a marker to SCAPs and has been reported for a decade. CD24 has been shown to involve stem cell activities such as self-renewal, proliferation and differentiation. However, the percentage variations of CD24 positive cells were reported among the studies. It is possible that this variation may affect these SCAPs behaviors. In this study, the variation was confirmed. To elucidate the influence of CD24 positive cells quantity on SCAPs stem cell behaviors, the 3 cell lines with the most maximum and the least numbers of CD24 positive cells (High-CD24 and Low-CD24 group) were selected to study. Both groups expressed the same mesenchymal stem cell markers and negative to hematopoietic marker. High-CD24 group demonstrated less self-renewal capacity by lower colony-forming-unit count and pluripotency marker gene expressions. However, cell proliferation was not different. In contrast, osteogenic and adipogenic differentiation were better than Low-CD24 group. The early stage of root development demonstrated higher CD24 expressing cells than later stage. In conclusion, quantity of CD24 expressing cells influenced SCAPs self-renewal and multi-lineage differentiation but did not influence on cell proliferation. Stage of root development influenced to CD24 expressing cell numbers.

Pulp Revascularization after Repositioning of Impacted Incisor with a Dilacerated Root and a Detached Apex

Severely impacted and dilacerated incisors are rarely considered for surgical exposure because they may not respond favorably to orthodontic extrusion. These incisors are often extracted, resulting in the need for tooth replacement; however, prosthetic solutions are limited in growing patients. Transalveolar autotransplantation of an impacted incisor may be the only method to preserve the natural tooth and maintain the shape of the alveolus. The severely impacted upper central incisor (#9) with a developing root was diagnosed in a 9-year-old girl. The unfavorable tooth position and dilaceration of its root made orthodontic extrusion of the impacted incisor impossible. Initial orthodontic space opening at the recipient site was performed before the surgery. Transalveolar transplantation of the impacted incisor to its normal position was performed to avoid tooth extraction. The incisor was later aligned using fixed orthodontic appliances. At the 5-year follow-up, the transplanted incisor presented features that were typical of a revascularized tooth (ie, obliteration of root canal but a positive response to vitality tests). Healthy periodontal tissues and continued root development were also noted. However, the root apex, which separated from the transplant at the time of the surgery, continued formation in its initial position. Transalveolar transplantation of an unfavorably impacted upper central incisor with a dilacerated root is a successful treatment, which stands the test of time. The early stage of root development allowed revascularization of the tooth despite dilaceration of the root and detachment of its apex.

Isolation and Functional Analysis of Chalcone Isomerase Gene from Purple-Fleshed Sweet Potato

Chalcone isomerase (CHI, EC 5.5.1.6) is one of the essential enzymes in the anthocyanin biosynthetic pathway catalyzing the stereospecific isomerization of chalcones into their corresponding (2S)-flavanones. A full-length cDNA of CHI (844 bp in length) was isolated from purple-fleshed sweet potato [Ipomoea batatas (L.) Lam] cv. Yamakawamurasaki, designated IbCHI, containing a 732-bp open reading frame encoding a 243 amino acid polypeptide. Sequence alignment showed that the coding region of IbCHI gene is highly homologous with CHIs from other plant species and has four conserved amino acid residues (Thr50, Tyr108, Asn115, and Ser192) essential for CHI active sites. Phylogenetic analysis revealed that IbCHI was clustered into type I CHI group. Southern blotting showed that there were multicopies of IbCHI gene in I. batatas genome and IbCHI gene showed significant restriction fragment length polymorphism among different I. batatas cultivars. Overexpression of the IbCHI gene in Arabidopsis tt5 mutant fully complemented the pigmentation phenotype of the seed coat, cotyledon, and hypocotyl, indicating that the IbCHI gene encoded a fully functional CHI protein for anthocyanin and proanthocyanidin biosynthesis. The expression patterns of IbCHI and other anthocyanin biosynthesis-related genes (IbCHS, IbF3H, IbDFR, and IbANS) matched the accumulation patterns of anthocyanin in the thick roots and mature storage roots of different cultivars of sweet potato. However, in the fibrous roots, only IbCHI expressed obviously higher in purple-fleshed cultivar than white-fleshed cultivar, while IbCHS and IbDFR exhibited the opposite expression trends, and IbF3H and IbANS expressed almost equally in purple- and white-fleshed cultivars. The findings suggest that IbCHI is a key enzyme in the anthocyanin biosynthetic pathway of sweet potato, which is responsible for the activation of anthocyanin biosynthesis in the early stage of root development.

Regenerative Endodontic Treatment of an Immature Permanent Tooth at an Early Stage of Root Development: A Case Report

IntroductionRegenerative endodontic treatment (RET) has been used in treating nonvital immature permanent tooth whose root formation ranged from approximately two-thirds of the full root length to almost completely developed root with open apex at least 1.1 mm in diameter according to the reported cases. However, this case report was to introduce RET in an affected tooth at an early stage of root development. MethodsThe premolar #29 in an 8-year-old girl had pulpal necrosis and apical periodontitis caused by the fracture of dens evaginatus. Its root was at the beginning of formation. Copious hemorrhagic drainage was observed after preparing of an access cavity. The canal was irrigated with 3% NaOCl solution, sterile normal saline, and chlorhexidine. Root dressing with triple antibiotic was then performed and left for 4 weeks. We used a K-file to create bleeding into the canal after flushing and drying the root canal. Mineral trioxide aggregate was carefully placed over the formed blood clot. ResultsClinical examination at 1, 3, 6, 9, and 12 months revealed an asymptomatic tooth. Radiographic examination revealed resolution of periapical radiolucency, increased thickening of the canal wall, and lengthening of the root, which demonstrated the continual development of the tooth root. Noticeably, the first-month postoperative radiograph showed radiopaque image in the root canal like an isolated island, which was gradually obvious during follow-up. Cone-beam computed tomography revealed that the calcification was attached with dentin wall in buccolingual direction, and the root canal was not completely obliterated. ConclusionsRET is feasible for a tooth at an early stage of root development that has necrotic pulp and periapical lesion.

Comparison of Maize (Zea mays L.) F1-Hybrid and Parental Inbred Line Primary Root Transcriptomes Suggests Organ-Specific Patterns of Nonadditive Gene Expression and Conserved Expression Trends

The phenomenon of heterosis describes the increased agronomic performance of heterozygous F(1) plants compared to their homozygous parental inbred plants. Heterosis is manifested during the early stages of root development in maize. The goal of this study was to identify nonadditive gene expression in primary roots of maize hybrids compared to the average expression levels of their parental inbred lines. To achieve this goal a two-step strategy was used. First, a microarray preselection of nonadditively expressed candidate genes was performed. Subsequently, gene expression levels in a subset of genes were determined via high-throughput quantitative real-time (qRT)-PCR experiments. Initial microarray experiments identified 1941 distinct microarray features that displayed nonadditive gene expression in at least 1 of the 12 analyzed hybrids compared to the midparent value of their parental inbred lines. Most nonadditively expressed genes were expressed between the parental values (>89%). Comparison of these 1941 genes with nonadditively expressed genes identified in maize shoot apical meristems via the same experimental procedure in the same genotypes revealed significantly less overlap than expected by pure chance. This finding suggests organ-specific patterns of nonadditively expressed genes. qRT-PCR analyses of 64 of the 1941 genes in four different hybrids revealed conserved patterns of nonadditively expressed genes in different hybrids. Subsequently, 22 of the 64 genes that displayed nonadditive expression in all four hybrids were analyzed in 12 hybrids that were generated from four inbred lines. Among those genes a superoxide dismutase 2 was expressed significantly above the midparent value in all 12 hybrids and might thus play a protective role in heterosis-related antioxidative defense in the primary root of maize hybrids. The findings of this study are consistent with the hypothesis that both global expression trends and the consistent differential expression of specific genes contribute to the organ-specific manifestation of heterosis.

Temporal and Spatial Expression of Genes Involved in Anthocyanin Biosynthesis during Sweet Potato (Ipomoea batatas[L.] Lam.) Root Development

To elucidate the gene regulation of pigmentation in sweet potato, expressions of the genes involved in anthocyanin biosynthesis were investigated in correlation with the accumulation of the anthocyanins during plant development. Fragments of the anthocyanin biosynthetic pathway genes involved in the central flavonoid pathway, including those for chalcone synthase (CHS), chalcone isomerase (CHI), flavone 3‐hydroxylase (F3H), dihydroflavonol 4‐reductase (DFR), anthocyanidin synthase (ANS), and UDPG‐flavonoid‐3‐0‐glucosyltransferase (UF3GT) were investigated in sweet potato, and their expressions were characterized in various tissues and developmental stages in both purple‐ and yellow‐fleshed varieties. Transcription patterns of the anthocyanin biosynthetic genes show accumulation at the early stages of root development (10–30 d after planting), followed by a decline. The anthocyanin biosynthetic genes were expressed throughout all stages of root development, wherein their expressions were activated at the stages corresponding to anthocyanin accumulation. Quantification of total anthocyanin content in various sweet potato tissues showed that the anthocyanin content of the purple‐fleshed variety was highly concentrated in all root types except in the lateral roots, while in the yellow‐fleshed variety, anthocyanin content was highest in the pigmented roots. The anthocyanin content at the different developmental stages of the sweet potato plant is highest during the early stages of development (10–30 d after planting), which is in accordance with the transcription levels of the anthocyanin biosynthetic genes.

Manifestation of heterosis during early maize (Zea mays L.) root development

Heterosis is typically detected in adult hybrid plants as increased yield or vigor compared to their parental inbred lines. Only little is known about the manifestation of heterosis during early postembryonic development. Objective of this study was to identify heterotic traits during early maize root development. Four German inbred lines of the flint (UH002 and UH005) and dent (UH250 and UH301) pool and the 12 reciprocal hybrids generated from these inbred lines were subjected to a morphological and histological analysis during early root development. Primary root length and width were measured daily in a time course between 3 and 7 days after germination (DAG) and displayed average midparent heterosis (MPH) of 17-25% and 1-7%, respectively. Longitudinal size of cortical cells in primary roots was determined 5 DAG and displayed on average 24% MPH thus demonstrating that enlarged primary roots of hybrids can mainly be attributed to elongated cortical cells. The number of seminal roots determined 14 DAG showed on average 18% MPH. Lateral root density of all tested hybrids was determined 5 DAG. This root trait showed the highest degree of heterosis with an average MPH value of 51%. This study demonstrated that heterosis is already manifesting during the very early stages of root development a few days after germination. The young root system is therefore a suitable model for subsequent molecular studies of the early stages of heterosis manifestation during seedling development.

Growth and dry matter partitioning in sugar beet plants (Beta vulgaris L.) under moderate drought

Growth response of sugar beet plants to drought stress applied at different growth stages has been investigated. Cessation of watering imposed moderate water stress and resulted in the reduction of the relative water content of young and old leaves maximally by 6%. However, water content in taproot was more drastically decreased than in the shoot. Water withholding reduced dry matter accumulation and leaf assimilatory expansion when imposed at successive growth stages, especially in the case of earlier stress application. Substantial change in distribution pattern was observed when stress affected foliar development, more than 80% of dry matter was accumulated in the taproots. Water shortage negatively influenced both taproot and sugar yield by 16&amp;ndash;52%, depending on the stress timing in the season. Drought stress did not change the sucrose concentration but when occurred in foliar and early stage of root development, decreased the contents of important non-sugar compounds like potassium and -amino-N solutes in the final yield. Overall, data concerning the different water status in particular organs implies that a hydrodynamic equilibrium does not exist within the sugar beet plant as a response to water stress. Drought imposed on the earlier stage, most drastically influenced plant growth and final yield. When water stress occurs at the end of crop cycle, sugar beet plants had a higher ability to recovery their growth.

Ultrastructure of early mineral deposition during hyaline layer formation in rat molars

There is no consensus on whether the first mineralized layer, the hyaline layer, that is juxtaposed to root dentine is a variety of dentine or cementum or even a tissue of epithelial origin. Some suggest that there is no intermediate tissue between the acellular extrinsic fibre cementum (AEFC) and the root dentine. Here, to study hyaline layer formation and mineralization we examined by transmission electron microscopy the early stages of root development in upper molars from 10 to 13 day old Wistar rats. In addition to conventionally processed material, undemineralized and unstained sections were examined, which showed the deposition of fine mineral crystals in contact with the mineralized surface of root dentine. Early mineralization of the hyaline layer occurred in the region of the inner basement membrane, which persisted between the inner cellular layer of Hertwig's epithelial root sheath and the outer mineralized root dentine. When the root sheath began its fragment, collagen fibrils from the developing periodontal ligament began to insert into the mineralising hyaline layer, which was 0.5–0.8 μm wide. As the fragmentation of the root sheath HERS increased, more collagen fibrils appeared intermingled with the mineralising hyaline layer. In more advanced stages, when the hyaline layer had become fully mineralized and the formation of the AEFC began, the hyaline layer could no longer be identified. Thus, the hyaline layer is clearly discernible at early stages of periodontal development. Subsequently, it is masked by intermingling of cementum and dentine and therefore it is not possible to detect it in the formed roots of rat molars.

The effect of chloride and nitrogen on nitrate accumulation and yield in beetroot (Beta vulgaris var. conditiva)

A pot and a field experiment were conducted to evaluate the effects of different nitrogen and chloride fertilizer levels on the nitrate content of beetroot. The yield and dry matter content were also determined. Sulphate fertilization was used as a control to chloride fertilization. There was a considerable decrease in the nitrate content of beetroots during the growing season. High nitrogen fertilization caused nitrate accumulation in both experiments. Chloride had a significant decreasing effect on the nitrate accumulation towards the middle of the growing period in the pot experiment. In the field experiment, chloride also decreased nitrate accumulation towards the middle of the growing period, soon after additional application of ammonium nitrate limestone (13.8 % NH4-N; 13.7 % NO3-N). Chloride tends to decrease nitrate accumulation only at an early stage of root development when nitrate is not the only source of nitrogen in the soil. The yield was higher on high nitrogen supply, in the pot experiment also on chloride application. Nitrogen decreased the dry matter content, but chloride had this effect only in the field experiment.

A long-term study of 370 autotransplanted premolars. Part IV. Root development subsequent to transplantation

The purpose of the present study was to analyse the extent of root development subsequent to transplantation in a material of 370 transplanted premolars. Before transplantation, the grafts were classified according to stage of root development (i.e. quarters of root length and constriction of the apical foramen) and length of tooth development (measured in mm from the cusp tip to the apical foramen). At radiographic controls the extent of root formation was registered. These figures were compared to the final tooth length of 288 non-transplanted premolars from the present material as well as to tooth length determinations of 534 premolars extracted for orthodontic purposes. Furthermore, intra-individual and inter-individual differences in tooth length were examined in a skull material with 40 pairs of premolars. These method studies indicated that root growth was probably determined genetically with great right-left accuracy and variation related to location of premolar (maxilla or mandible) and sex. A statistical analysis of the transplant material revealed that stage as well as length of tooth development assessed prior to transplantation were significantly related to final tooth length after transplantation. In most cases of transplantation performed at early stages of root development, a reduction in the final root length was seen. When a qualitative analysis of root development was performed in teeth with incomplete root formation at the time of transplantation, and where a homologous non-transplanted premolar was present, it was found that 14 per cent showed total arrest of root formation, 65 per cent partial arrest whereas 21 per cent showed no arrest (i.e. normal root formation). Premolars in ectopic position in the mandible before transplantation showed a significantly reduced root growth compared to matched pairs with normal position of the tooth graft. The present study indicated that no, partial or total damage to the Hertwig's epithelial root sheath was probably the explanatory factor for variations in root growth.

Changes in the numbers of antibiotic-resistant rhizobia in the soil and rhizosphere of field grown Vigna mungo CV. Regur

A streptomycin-resistant variant, of CB756 was used as seed inoculum to follow population changes in rhizosphere and soil of black gram ( Vigna mungo cv. Regur) by direct plating onto an antibiotic agar medium. The number of viable rhizobia decreased from the initial level added to the soil at sowing. There was a further decrease during the early stages of root development, which was followed by a substantial increase in the rhizosphere population, and this increase continued for the duration of the experiment. Very little consistent change in soil numbers occurred until after plant senescence and nodule and root decay, which coincided with an increase in the soil numbers of CB756str r. Movement of the inoculum strain in the soil and rhizosphere from the seed inoculum was estimated by measuring lateral and vertical distribution of nodules on the root system.

In vitro Studies of Adventitious Rooting in Convolvulus sepium L.

Root production in excised nodes and internodes of Convolvulus sepium is reported All auxin-like compounds promoted rooting In the presence of indoleacetic acid (IAA), gibberellin and kinetin were inhibitory to rooting Early stages of root development were particularly sensitive to gibberellin inhibition The number of adventitious roots induced by IAA was significantly less in nodal sections. Removal of the foliar organs increased the rooting competence of nodal sections to levels comparable with internodes Methanolic extracts of nodes with intact axillary bud and leaf revealed a root inhibitor active in the mung-bean bioassay Thin-layer chromatography of these extracts showed that the inhibitor has Rf values of 0 53-0 73 Assays of fractions obtained after the removal of the foliar organs did not show inhibition

FURTHER STUDIES OF THE TERMINAL OXIDASES IN THE EMBRYOS AND YOUNG ROOTS OF BARLEY

In a previous paper (James, I953), evidence was presented that was taken to show that about 8o % of the embryos' respiratory transfer of electrons to oxygen passes through the cytochrome system. The root tips of seedlings about iO days old provided no such evidence; but gave strong indications that the function of the missing cytochrome enzyme was undertaken by ascorbic oxidase. It therefore seemed desirable to investigate the early stages of root development, and to discover whether the root tips lacked the cytochrome system from the start, or whether it failed during the first few days of growth. An investigation, using methods similar to those previously employed, was carried out with root tips during the first fortnight of their development.