Lateral Meristems Research Articles

Vascular cambium stem cells: past, present and future.

Secondary xylem and phloem originate from a lateral meristem called the vascular cambium that consists of one to several layers of meristematic cells. Recent lineage tracing studies have shown that only one of the cambial cells in each radial cell file functions as the stem cell, capable of producing both secondary xylem and phloem. Here, we first review how phytohormones and signalling peptides regulate vascular cambium formation and activity. We then propose how the stem cell concept, familiar from apical meristems, could be applied tocambium studies. Finally, we discuss how this concept could set the basis for future research.

Growth periodicity in semi-deciduous tropical tree species from the Congo Basin.

In the tropics, more precisely in equatorial dense rainforest, xylogenesis is driven by a little distinct climatological seasonality, and many tropical trees do not show clear growth rings. This makes retrospective analyses and modeling of future tree performance difficult. This research investigates the presence, the distinctness, and the periodicity of growth ring for dominant tree species in two semi-deciduous rainforests, which contrast in terms of precipitation dynamics. Eighteen tree species common to both forests were investigated. We used the cambial marking technique and then verified the presence and periodicity of growth-ring boundaries in the wood produced between pinning and collection by microscopic and macroscopic observation. The study showed that all eighteen species can form visible growth rings in both sites. However, the periodicity of ring formation varied significantly within and between species, and within sites. Trees from the site with clearly defined dry season had a higher likelihood to form periodical growth rings compared to those from the site where rainfall seasonality is less pronounced. The distinctness of the formed rings however did not show a site dependency. Periodical growth-ring formation was more likely in fast-growing trees. Furthermore, improvements can be made by a detailed study of the cambial activity through microcores taken at high temporal resolution, to get insight on the phenology of the lateral meristem.

Single-cell resolution analysis reveals the preparation for reprogramming the fate of stem cell niche in cotton lateral meristem

BackgroundSomatic embryogenesis is a major process for plant regeneration. However, cell communication and the gene regulatory network responsible for cell reprogramming during somatic embryogenesis are still largely unclear. Recent advances in single-cell technologies enable us to explore the mechanism of plant regeneration at single-cell resolution.ResultsWe generate a high-resolution single-cell transcriptomic landscape of hypocotyl tissue from the highly regenerable cotton genotype Jin668 and the recalcitrant TM-1. We identify nine putative cell clusters and 23 cluster-specific marker genes for both cultivars. We find that the primary vascular cell is the major cell type that undergoes cell fate transition in response to external stimulation. Further developmental trajectory and gene regulatory network analysis of these cell clusters reveals that a total of 41 hormone response-related genes, including LAX2, LAX1, and LOX3, exhibit different expression patterns in the primary xylem and cambium region of Jin668 and TM-1. We also identify novel genes, including CSEF, PIS1, AFB2, ATHB2, PLC2, and PLT3, that are involved in regeneration. We demonstrate that LAX2, LAX1 and LOX3 play important roles in callus proliferation and plant regeneration by CRISPR/Cas9 editing and overexpression assay.ConclusionsThis study provides novel insights on the role of the regulatory network in cell fate transition and reprogramming during plant regeneration driven by somatic embryogenesis.

Exploring the Seasonal Dynamics and Molecular Mechanism of Wood Formation in Gymnosperm Trees.

Forests, comprising 31% of the Earth's surface, play pivotal roles in regulating the carbon, water, and energy cycles. Despite being far less diverse than angiosperms, gymnosperms account for over 50% of the global woody biomass production. To sustain growth and development, gymnosperms have evolved the capacity to sense and respond to cyclical environmental signals, such as changes in photoperiod and seasonal temperature, which initiate growth (spring and summer) and dormancy (fall and winter). Cambium, the lateral meristem responsible for wood formation, is reactivated through a complex interplay among hormonal, genetic, and epigenetic factors. Temperature signals perceived in early spring induce the synthesis of several phytohormones, including auxins, cytokinins, and gibberellins, which in turn reactivate cambium cells. Additionally, microRNA-mediated genetic and epigenetic pathways modulate cambial function. As a result, the cambium becomes active during the summer, resulting in active secondary xylem (i.e., wood) production, and starts to become inactive in autumn. This review summarizes and discusses recent findings regarding the climatic, hormonal, genetic, and epigenetic regulation of wood formation in gymnosperm trees (i.e., conifers) in response to seasonal changes.

From modeling the kinetics of cell enlargement to building tracheidograms of Larix gmelinii Rupr. (Rupr.) in the permafrost zone in Siberia

Boreal forest ecosystems are a crucial element in the global climate balance. In harsh environments functioning lateral meristems of trees are more regulated by the exogenous (included local climate) than endogenous factors. This information is encoded in the tree-ring structure which can be effectively decomposed by the process-based tree-ring growth simulations. Moreover, the process-based modeling can be used to describe non-linear processes linking climate variables with tree-ring formation. In this study, we applied the Vaganov-Shashkin model to simulate seasonal cell production and cell enlargement of Larix gmelinii Rupr. (Rupr.) growing in the permafrost zone of Central Siberia. We developed a procedure for calculating the radial cell diameter based on specific Gompertz function combined with the “instantaneous tracheidogram” approach to estimate effectively seasonal cell production and timing of cell enlargement under climate control. Simulated cell number and cell size matched well with direct xylogenesis observations. The developed procedure demonstrate strong relationships between seasonal simulated growth rate and measured tracheid radial size (the average correlation is 0.64, p < 0.01). A highly significant correlation (p < 0.01) between simulated and observed cell profiles was obtained for 71% of the growing seasons over the period 1950–2011. The strong exponential relationship (R2 = 0.67) was obtained between the day of the year (DOY) when cambial cell transfers into enlargement zone and simulated time intervals of cell enlargement. Based on the strong exponential relationship it was possible to reproduce the basic pattern of the observed tracheidograms over 1950–2011 with a systematic overestimation of final cell sizes at the beginning of the growing season, which will be possible to eliminate by using more anatomical data (trees) and longer period. The proposed approach of simulating intra-annual cell dynamics (cell production) has a great potential for studying how climate affects tree-ring formation.

Vascular Cambium—Between the Hammer and the Anvil: A Tensile Stress Hypothesis on the Mechanism of Radial Growth of Broadleaved Trees

The vascular cambium is the main lateral meristem responsible for the secondary growth of trees. There are a number of explicit and implicit assumptions behind this statement which allow questions to be raised about the mechanism underlying the radial growth of trees. Based on the hypothesis of the diurnal strains of plant organs, it is anticipated that the process of radial growth can be understood as an adaptation to the cyclically changing mechanical stress in the radial direction generated by the phloem during the 24 h day cycle. This qualitative hypothesis treats cambium as a tissue subjected to nighttime stretching and daytime compression in the radial direction. The proposed osmo-mechanical hypothesis of the radial growth of vascular cambium links the daily change in water status and the considerable daily strains in the xylem and phloem with the radial net expansion of a tree trunk. We highlight transpiration as a major factor influencing the secondary growth of woody plants. Thus, we indirectly relate all the biotic (e.g., insect infestation, fungi infections, injuries, shadowing, intra- and interspecies competition, parasitism, symbiosis, etc.) and abiotic (e.g., humidity, water availability, wind, injuries, shadowing, day length in a vegetative season, altitude, temperature, insolation, etc.) processes influencing transpiration with radial growth. In the proposed hypothesis, we also infer that differences in the strains in phloem and xylem are the direct source of tensile stress, tensile stress relaxation, compressive stress, and compressive stress relaxation in the vascular cambium. This sequence appears to be crucial in understanding both the process of the radial growth of trees and the formation of differential wood patterns, within the same genotype as well as in different genotypes. It also provides arguments for the discussion on the mechanisms regulating processes in the vascular cambium. It points out the important role of the variable mechanical stresses in the radial, circumferential, and axial directions and their interference in the development of this lateral meristem. Thus, this hypothesis supports the concept of the epigenetic and systemic regulation of intrinsic wood patterns and tree forms by environmental factors. The hypothesis is focused exclusively on broadleaved trees and symplastic growth. This limitation of the scope is due to a concern for clarity. In this form, the hypothesis provides an alternative explanation for a pure process of radial growth and paves the way for a better interpretation of such phenomena as earlywood and latewood formation. At the same time, this approach to the vascular cambium provides answers to many questions related to the generation of the mechanical conditions necessary for the occurrence of intrusive growth between tangential cell walls; this is of fundamental importance for fusiform initials readjustment, vessel element and fibre formation, ring-porous wood formation, etc.

Identification and Expression Profile of CLE41/44-PXY-WOX Genes in Adult Trees Pinus sylvestris L. Trunk Tissues during Cambial Activity

WUSCHEL (WUS)-related homeobox (WOX) protein family members play important roles in the maintenance and proliferation of the stem cells in the cambium, the lateral meristem that forms all the wood structural elements. Most studies have examined the function of these genes in angiosperms, and very little was known about coniferous trees. Pine is one of the most critical forest-forming conifers globally, and in this research, we studied the distribution of WOX4, WOX13, and WOXG genes expression in Pinus sylvestris L. trunk tissues. Further, we considered the role of TDIF(CLE41/44)/TDR(PXY) signaling in regulating Scots pine cambial activity. The distribution of CLE41/44-PXY-WOXs gene expression in Scots pine trunk tissues was studied: (1) depending on the stage of ontogenesis (the first group of objects); and (2) depending on the stage of cambial growth (the second group of objects). The first group of objects is lingonberry pine forests of different ages (30-, 80-, and 180-year-old stands) in the middle taiga subzone. At the time of selection, all the trees of the studied groups were at the same seasonal stage of development: the formation of late phloem and early xylem was occurring in the trunk. The second group of objects is 40-year-old pine trees that were selected growing in the forest seed orchard. We took the trunk tissue samples on 27 May 2022, 21 June 2022, and 21 July 2022. We have indicated the spatial separation expressed of PsCLE41/44 and PsPXY in pine trunk tissues. PsCLE41/44 was differentially expressed in Fraction 1, including phloem cells and cambial zone. Maximum expression of the PsPXY gene occurred in Fraction 2, including differentiating xylem cells. The maximum expression of the PsCLE41/44 gene occurred on 27 May, when the number of cells in the cambial zone was the highest, and then it decreased to almost zero. The PsPXY gene transcript level increased from May to the end of July. We found that the highest transcript level of the PsWOX4 gene was during the period of active cell proliferation in the cambial zone, and also in the trees with the cambial age 63 years, which were characterized by the largest number of cell layers in the cambial zone. In this study, we have examined the expression profiles of genes belonging to the ancient clade (PsWOXG and PsWOX13) in stem tissues in Scots pine for the first time. We found that, in contrast to PsWOX4 (high expression that was observed during the period of active formation of early tracheids), the expression of genes of the ancient clade of the WOX genes was observed during the period of decreased cambial activity in the second half of the growing season. We found that PsWOX13 expression was shifted to Fraction 1 in most cases and increased from the phloem side, while PsWOXG expression was not clearly bound to a certain fraction. Based on the data, the role of the CLE41/44-PXY-WOX signaling module in regulating P. sylvestris cambial growth is discussed.

Space-time analysis of the longitudinal variation in wood specific gravity of teak and its effect on tree growth and development

The space-time structure of a teak wood specific gravity (SG) dataset was analyzed using a mixed-effects model. Spatial correlation increased in space, a phenomenon attributable to the maturation of apical meristems, while the temporal correlation of vascular meristems decreased over time. The decay of temporal correlation over time was attributed to the diminishing crown effect on the later formed wood further away from the pith, morphogen gradient, and probably changing microenvironmental conditions. The Kronecker product was used to collect spatiotemporal data on the intricate dynamic process of the evolution of the apical and lateral meristems. The results showed that height and relative radial distance (RRD) (i.e., the flow of time with wood formation) were statistically significant factors, with their interaction showing no significance. The results confirm the usefulness of using the space-time approach to elucidate the interaction between the apical and lateral meristems, two major inherent biological systems that control tree growth and wood formation dynamics. To understand the origins of patterns that vary both temporally and spatially in the tree, future work should describe the variation of SG within the tree due to increasing height (space) and diameter (age) as a matrix; then the correlation function can be modelled.

Axillary Meristem Development in Plants

Abstract: The shoot apical meristem of seed plants gives rise to the above-ground parts of the plants during development, including leaves, stems, and lateral meristems. Among them, two types of meristems, axillary meristem and vascular cambium, support the main lateral growth. In this review, we will discuss the regulatory network of lateral growth, focusing on recent progress made mainly in Arabidopsis thaliana, tomato and maize, including the identification of genes and their roles in controlling lateral meristems. In addition, we will summarize the latest evidence about how meristem affects yield-related traits, and discuss the strategies for modulating meristem regulatory genes so as to increase crop yield in agriculture.

BHLH heterodimer complex variations regulate cell proliferation activity in the meristems of Arabidopsis thaliana

Root, shoot, and lateral meristems are the main regions of cell proliferation in plants. It has been proposed that meristems might have evolved dedicated transcriptional networks to balance cell proliferation. Here, we show that basic helix-loop-helix (bHLH) transcription factor heterodimers formed by members of the TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHW) subclades are general regulators of cell proliferation in all meristems. Yet, genetics and expression analyses suggest specific functions of these transcription factors in distinct meristems, possibly due to their expression domains determining heterodimer complex variations within meristems, and to a certain extent to the absence of some of them in a given meristem. Target gene specificity analysis for heterodimer complexes focusing on the LONELY GUY gene targets further suggests differences in transcriptional responses through heterodimer diversification that could allow a common bHLH heterodimer complex module to contribute to cell proliferation control in multiple meristems.

Genome-wide analysis of long non-coding RNAs in shoot apical meristem and vascular cambium in Populus tomentosa

Shoot apical and lateral meristems play essential roles in the formation and development of primary and secondary growth in plants. A delicate regulatory mechanism is needed to maintain homeostatic balance between the primary and secondary growth, as well as the self-renewal of meristems with the rate of cell division and differentiation of new meristems. However, little is known about the roles of long non-coding RNAs (lncRNAs) in the regulation of maintenance and differentiation of primary and secondary growth in Populus, especially in the cambium division and differentiation into secondary xylem. Here, 1298 lncRNAs were identified both in the apical meristem and vascular cambium, with 80 lncRNAs being expressed only in shoot apical meristem and 45 only in vascular cambium. There are 410 differentially expressed lncRNAs in shoot apical meristem and vascular cambium, among which 271 lncRNAs were up-regulated and 139 were down-regulated in cambium. The GO enrichment analysis revealed that differentially expressed lncRNAs mainly influenced the expression of lncRNAs related to the ribosome pathway, plant hormone signal pathway and photosynthesis pathway. The differentially expressed lncRNAs mainly target mRNA through cis-regulation in the vascular cambium. In addition, six key lncRNAs and also their significantly upregulated target genes were identified. Theses target genes are involved in plant secondary metabolites, cellulose and lignin synthesis, hormone and signal transduction. In addition, six key lncRNAs were identified, their significantly upregulated target genes are related to plant secondary metabolites, cellulose and lignin synthesis, hormone and signal transduction. Investigating lncRNA–mRNA interactions, we further found some genes that may be related to the development of vascular cambium, such as domain-containing transcription factors, cellulose synthesis genes, calcium dependent protein kinase 2, cytokinin receptor 1, glycosyl transferase and polyphenol oxidase. Our findings provide new insights into the lncRNA-mRNA networks in the development of vascular cambium of secondary growth in Populus.

Damaged Dickinsonia specimens provide clues to Ediacaran vendobiont biology.

Recently reported specimens of the enigmatic Ediacaran fossil Dickinsonia from Russia show damage and repair that provides evidence of how they grew, and of their biological affinities. Marginal and terminal areas of wilting deformation are necrotic zones separating regenerated growth, sometimes on two divergent axes, rather than a single axis. Necrotic zones of damage to Dickinsonia are not a thick scar or callus, like a wound or amputation. Nor are they smooth transitions to a regenerated tail or arm. The wilted necrotic zone is most like damage by freezing, salt, or sunburn of leaves and lichens, compatible with evidence of terrestrial habitat from associated frigid and gypsic paleosols. Dickinsonia did not regrow by postembryonic addition of modules from a subterminal or patterned growth zone as in earthworms, myriapods, trilobites, crustaceans, and lizards. Rather Dickinsonia postembryonic regrowth from sublethal damage was from microscopic apical and lateral meristems, as in plants and lichens. Considered as fungal, Dickinsonia, and perhaps others of Class Vendobionta, were more likely Glomeromycota or Mucoromycotina, rather than Ascomycota or Basidiomycota.

Efficiency of Microfertilizer Oracle Multicomplex in Corn Cultivation Technology

In recent years, the use of all types of fertilizers has sharply decreased, which negatively affected the state of the agroecosystem, its stability and constancy, therefore, it is extremely important to replenish nutrients, including microelements, to maintain the stability of yields. The increasing attention of scientists and industrialists deserves the question of the use of micronutrient fertilizers in the plant nutrition system, as an important element of the technology of growing crops. It is especially important to study the various forms, types and timing of their introduction. The article presents the research results for 2019-2021 according to the effect of microfertilizer Oracle multicomplex (1.5 l/ha) applied foliarly during the development phases of plants of the mid-early hybrid Orzhitsa 237 MB (VVSN 13-15, VVSN 16-18, VVSN 59) against the background of mineral nutrition – N150P90K90. It has been established that on gray forest surface-gley soils of the Western Forest-Steppe zone, a high grain yield of the mid-early corn hybrid (FAO 200-299) of the Orzhitsa 237 MV ripeness group was provided both by favorable weather conditions and by the influence of the Oracle multicomplex. Foliar application of the Oracle multicomplex microfertilizer in the phase BBCH 13-15 (3-5 leaves) increased the yield increase versus control (without micronutrient fertilization) by 0.82 t/ha, by meeting the needs of plants of this period in available forms of phosphorus, nitrogen, zinc, when panicle axes were laid on the tops of the shoots, and lateral apical meristems (future cobs) formed in the leaf axils. The highest yield by 1.19 t/ha was obtained with foliar application of micronutrient fertilizer in the phase of 6-8 leaves (VVSN 16-18). In this phase, panicle flowers, pollen grains in the stamens, the number of ears and grains in a row were laid, therefore, the content of S, Ca, Mg, Mn, Zn in the fertilizer positively influenced the formation of the reproductive organs of maize plants. Under the influence of micronutrient fertility introduced into the phase of full panic appearance (VVSN 59), blooming and pollution of maize effectively taken place, which ensured an increase in grain yield – 1.27 t/ha. The difference in this indicator between the VVSN 16-18 and VVSN 59 phases was unreliable (0.09 t/ha). Balanced nutrition of plants with macroelements (N150P90K90 with a gradual introduction of nitrogen) and micro – Mn, Cu, Zn, Fe, Co, S, Mo contributed to the formation of a 55-59 g higher weight of 1000 grains. The total yield of the coarse and medium grain fractions was 91.5-92.1%, the fine one decreased by 30.6%

Isolation and Functional Characterization of a LEAFY Gene in Mango (Mangifera indica L.).

LEAFY (LFY) plays an important role in the flowering process of plants, controlling flowering time and mediating floral meristem differentiation. Owing to its considerable importance, the mango LFY gene (MiLFY; GenBank accession no. HQ585988) was isolated, and its expression pattern and function were characterized in the present study. The cDNA sequence of MiLFY was 1152 bp, and it encoded a 383 amino acid protein. MiLFY was expressed in all tested tissues and was highly expressed in flowers and buds. Temporal expression analysis showed that MiLFY expression was correlated with floral development stage, and two relative expression peaks were detected in the early stages of floral transition and floral organ differentiation. Moreover, 35S::GFP-MiLFY fusion protein was shown to be localized to the nucleus of cells. Overexpression of MiLFY in Arabidopsis promoted early flowering and the conversion of lateral meristems into terminal flowers. In addition, transgenic plants exhibited obvious morphological changes, such as differences in cauline leaf shape, and the number of lateral branches. When driven by the MiLFY promoter, GFP was highly expressed in leaves, floral organs, stems, and roots, during the flowering period. Exogenous gibberellin (GA3) treatment downregulated MiLFY promoter expression, but paclobutrazol (PPP333) upregulated it. Bimolecular fluorescence complementation (BiFC) assays showed that the MiLFY protein can interact with zinc-finger protein 4 (ZFP4) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (MiSOC1D). Taken together, these results indicate that MiLFY plays a pivotal role in controlling mango flowering, and that it is regulated by gibberellin and paclobutrazol.

Apomictic fern fathers: an experimental approach to the reproductive characteristics of sexual, apomict, and hybrid fern gametophytes.

Apomixis and hybridization are two essential and complementary factors in the evolution of plants, including ferns. Hybridization combines characteristics from different species, while apomixis conserves features within a lineage. When combined, these two processes result in apo-sex hybrids. The conditions leading to the formation of these hybrids are poorly understood in ferns. We cultivated spores from 66 fern samples (43 apomicts, 7 apo-sex hybrids, and 16 sexuals), and measured their development in vitro over 16 weeks. We evaluated germination, lateral meristem formation rates, sexual expression, and production of sporophytes and then compared ontogenetic patterns among the three groups. The three examined groups formed antheridia (male gametangia) but differed in overall gametophyte development. Sexual species created archegonia (female, 86% of viable samples), but no sporophytes. Apomicts rarely created nonfunctional archegonia (8%) but usually produced apogamous sporophytes (75%). Surprisingly, apomictic and sexual species showed similar development speed. The sexually reproducing parents of viable studied hybrids formed about twice as many meristic gametophytes as the apomictic parents (39% vs. 20%, respectively). We present the most thorough comparison of gametangial development of sexual and apomictic ferns, to date. Despite expectations, apomictic reproduction might not lead to earlier sporophyte formation. Apomicts produce functional sperm and thus can contribute this type of gamete to their hybrids. The development patterns found in the parents of hybrids indicate a possible increase of hybridization rates by antheridiogens. The apo-sex hybrids always inherit the apomictic reproductive strategy and are thus capable of self-perpetuation.

Кора ассимиляционных побегов кустарника спиреи Бовера (Spiraea beauverdiana S.K. Schneid.): структурные изменения в условиях вулканогенного стресса на южных Курильских островах и полуострове Камчатка

The article analyzes the bark of annual assimilation shoots of the Beauverd spirea shrub (Spiraea beauverdiana S.K. Schneid., Rosaceae Juss.) growing under the stressful conditions of volcanic and post-volcanic activity in the Kuril Islands (Kunashir, Iturup) and the Kamchatka Peninsula. The combination of negative environmental factors under the conditions of fumarolic, gas-hydrothermal activity and on pyroclastic deposits in volcanogenic landscapes causes disturbance in the activity of the lateral meristems of the stem – phellogen and vascular cambium. Under the conditions of volcanic stress, the functional activity of these meristems can be both constant and intermittent during the growing season, or may be completely absent (temporary dormancy of meristems). As a result of combinations of different functional activity of meristems in assimilation shoots and in their individual sections, different anatomical structures of the cortex can form in S. beauverdiana. Based on the totality of structural and functional features, we identified three types of anatomical organization of the one-year-old cortex in S. beauverdiana from volcanic habitats, which are visualized by light microscopy in the form of contrasting anatomical patterns. We believe the structural changes in the one-year-old crust formed as a result of the unstable activity of the phellogen and vascular cambium under the influence of volcanic stress, to be adaptive.

Taxonomic history, comparative morphology, and variation in Astrophytum myriostigma and its subspecies tulense (Cactaceae)

Astrophytum myriostigma subsp. myriostigma and subsp. tulense are distinguished by both vegetative and reproductive characters. The stem of the nominotypical subspecies is broad and depressed becoming broadly cylindrical in age, reaching a known maximum height of ca. 52 cm. In subsp. tulense, the stem is relatively slen-der and columnar and can reach a maximum height of ca. 90 cm. Both taxa show variation in the angle and profile of the ribs. In the nominotypical subspecies, the ribs are usually obtuse with a rounded or angular profile, or moderately acute with an angular profile. In subsp. tulense, the ribs are typically moderately to very acute with an angular profile. There are exceptions to these generalities. Both taxa have a modal number of five ribs, and both have the tendency to insert additional ribs with age, although the tendency seems more pronounced in subsp. tulense.&#x0D; The flower of the nominotypical subspecies differs from that of subsp. tulense in having a significantly larger mean perianth diameter (P &lt;= 0.01), a significantly higher mean number of stigma lobes (P &lt;= 0.05), and more tepal rows (3–5 vs. 1–3). The color of the tepals is pale yellow to whitish yellow in subsp. tulense, but brighter yellow or golden yellow in the nominotypical subspecies. The seeds of the nominotypical subspecies are significantly larger (P &lt;= 0.01) than the seeds of subsp. tulense.&#x0D; Morphological variation was studied in nine populations of the subsp. myriostigma and six populations of the subsp. tulense. The nominotypical subspecies displays rib angle and rib profile differences among individual plants within a population. Plants with a depressed stem and obtuse, rounded ribs are predominant at some localities. At other localities, plants with more moderately acute, angular ribs are predominant, or at least common. Populations of subsp. tulense show individual variation in stem morphology. The stem varies from attenuated (tapered) to non-attenuated and from relatively slender (diameter ca. 20% of height) to relatively broad (diameter ca. 77% of height).&#x0D; The plants from near Mama León and adjacent localities in Tamaulipas, have very robust stems and are the least typical of the columnar subspecies. The rela-tionships of this population to other columnar populations warrant further study. The population near Las Tablas, San Luis Potosí, shows considerable variation in the stem and rib morphology. Some plants resemble the nominotypical subspecies whereas others are similar morphologically to subsp. tulense. The perianth diameter is intermediate between those of the two subspecies. The evidence suggests that this is an area of past or ongoing hybridization between the two taxa; the question of hybridization warrants further investigation.&#x0D; Attenuated and non-attenuated stems are the result of differential rates of vertical and lateral growth due to cellular activity in the apical and lateral meristems, respectively. The attenuated (tapered) stem is produced by a gradually increasing lateral growth rate which remains slower than the vertical rate. A non-attenuated stem is produced by the lateral growth rate exceeding the vertical rate early in development, then stabilizing at some point and not surpassing the vertical rate.

Revisiting the anatomy of the monocot cambium, a novel meristem

Main conclusionThe monocot cambium is semi-storied, and its cells do not undergo rearrangement.The monocot cambium is a lateral meristem responsible for secondary growth in some monocotyledons of Asparagales. It is an unusual meristem, not homologous with the vascular cambia of gymnosperms and non-monocotyledonous angiosperms. Owing to the limited information available on the characteristics of this meristem, the aim of this study was to survey the structure of the monocot cambium in order to clarify the similarities and dissimilarities of this lateral meristem to the vascular cambium of trees. Using the serial sectioning analysis, we have studied the monocot cambium of three species of arborescent monocotyledons, i.e., Quiver Tree Aloe dichotoma, Dragon Tree Dracaena draco, and Joshua Tree Yucca brevifolia, native to different parts of the world. Data showed that in contrast to the vascular cambium, the monocot cambium is composed of a single type of short initials that vary in shape, and in tangential view display a semi-storied pattern. Furthermore, the cells of the monocot cambium do not undergo rearrangement. The criteria used in identifying monocot cambium initial cell are also discussed.

A Heterozygous Genotype-Dependent Branched-Spike Wheat and the Potential Genetic Mechanism Revealed by Transcriptome Sequencing.

Simple SummaryThis paper reported a novel type of branched spike wheat from a natural mutation event. The branched spike was controlled by a heterozygous genotype. The genetic patterns showed that gametophytic male sterility probably contributed to the heterozygous genotype responsible for the branched spike trait. Expressional levels and Wheat FRIZZY PANICLE (WFZP) sequencing between the mutant with the branched spike and the wild-type with the normal spike showed that WFZP was not the causal gene for the branched spike. Data from transcriptome sequencing indicated that carbohydrate metabolism might be involved in the formation of the branched spike trait.Wheat (Triticum aestivum L.) spike architecture is an important trait associated with spike development and grain yield. Here, we report a naturally occurring wheat mutant with branched spikelets (BSL) from its wild-type YD-16, which has a normal spike trait and confers a moderate level of resistance to wheat Fusarium head blight (FHB). The lateral meristems positioned at the basal parts of the rachis node of the BSL mutant develop into ramified spikelets characterized as multiple spikelets. The BSL mutant shows three to four-day longer growth period but less 1000-grain weight than the wild type, and it becomes highly susceptible to FHB infection, indicating that the locus controlling the BSL trait may have undergone an intensively artificial and/or natural selection in modern breeding process. The self-pollinated descendants of the lines with the BSL trait consistently segregated with an equal ratio of branched and normal spikelets (NSL) wheat, and homozygotes with the BSL trait could not be achieved even after nine cycles of self-pollination. Distinct segregation patterns both from the self-pollinated progenies of the BSL plants and from the reciprocal crosses between the BSL plants with their sister NSL plants suggested that gametophytic male sterility was probably associated with the heterozygosity for the BSL trait. Transcriptome sequencing of the RNA bulks contrasting in the two types of spike trait at the heading stage indicated that the genes on chromosome 2DS may be critical for the BSL trait formation since 329 out of 2540 differentially expressed genes (DEGs) were located on that chromosome, and most of them were down-regulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that carbohydrate metabolism may be involved in the BSL trait expression. This work provides valuable clues into understanding development and domestication of wheat spike as well as the association of the BSL trait with FHB susceptibility.

Padronização de um protocolo para assepsia de segmentos nodais de Phalaenopsis para clonagem in vitro

Plantbiotechnologysan área ofhighimportancesinceit has forobtainingplantorganismswithcharacteristics superior tothosealreadyonthemarket. Cloningisoneofthetolos that forthisfunction, throughit, organismswithcharacteristicsofinterest are selected and this individual ismultiplied, ensuringthattheregeneratedplants are geneticallyidenticaltothedesiredmatrix, establishing a standardization. Knowingthatthe ornamental plants sector contributessignificantlytotheeconomy and amongthemostesteemed ornamental plantsamongBrazilians, there are orchidswhichhaveacquired cultural visibility and a largenumberofcollectors in recentyears. Theobjectiveofthepresentworkwastoestablishanefficientassepsisprotocolfor lateral meristems and toobtain clones oftheorchidofthegenusPhalaenopsis. Formethodology, aiming at thestandardization o fan asepsisprotocol, 4 treatmentsweredeveloped and testedwithdifferentcombinations (concentration x time) ofagentssuch as sodiumhypochlorite, alcohol, copper, tween and washingtheexplantswithsteriledistilled wáter formeristemsoftheorchidofthegenusPhalaenopsis. Themeristems, alsoknown as lateral bud, were removed fromthestemoftheseedlings, fromtheir floral stems. As forobtained clones, theexperimentcarriedoutconsistedofinoculatingthemeristems, after anasepsisprocess, in Knudson culture media, containingdifferentcombinationsofgrowthregulators, usinganauxin and cytokinin. Theresultsobtained show that, no asepsistreatmentstested in thiswork, presentedsignificant and positive results, so itwasnot posible toestablish, as yet, anasepsisprotocolfor lateral meristemoforchidsofthegenusPhalaenopsis. Sinceallmeristemssufferedcontamination and oxidation. Therefor, itwasnotyet posible toobtain clones, usingthismethodology. Thisworkserves as aninitialbasis, forfutureresearch, regardingcloningthroughmeristems in Phalaenopsis.