Shoot Organs Research Articles

The Biphasic Role of Cupper and Counteraction with <i>Azospirillum brasilense</i> Application on Growth, Metabolities, Osmotic Pressure and Mineral of Wheat Plant

The interactive effect of different Cu++ concentrations (5 mM, 10 mM, 20 mM and 25 mM) and treatments with biofertilizers Azospirillum brasilense on growth, metabolites, minerals and osmotic pressure of wheat plants was investigated. Shoots and roots of wheat plant were differentially response to Cu++ treatments, while shoot organ response positively to this treatment, root response negatively. The positive effect of Cu++ in shoot organ was concomitant with the increase in the production of fresh, dry matter, length and water content and this related with the accumulation of soluble sugar, soluble protein and mineral as a result of increasing osmotic pressure. On the other side, the negative effect of Cu++ on root organ was concomitant with the decrease in production of fresh, dry matter, length and water content that related with the reduction in the accumulation of soluble sugar and mineral with the insignificant change in osmotic pressure. Azospirillum brasilense inoculation increased the accumulation of soluble sugar and soluble protein which reflected an increase in the production of fresh, dry matter and water content with increasing values of osmotic pressure of the tested plants under Cu++ treatment. Finally, wheat plants response differentially to Cu++ treatment according to its organ and Azospirillum brasilense treatment improved wheat plant efficiency to tolerate the effect of Cu++ stress.

Structure and functioning of oil cavities in the shoot apex of Metrodorea nigra A. St.-Hil. (Rutaceae).

This study investigates the histology and subcellular features of secretory cavities during the development of the shoot apex of Metrodorea nigra A. St.-Hil. in order to better understand the functioning of these glands. This Rutaceae species is a very suitable model for studying secretory cavity life span, since the shoot apex exhibits both dormant and growth stages during its annual cycle. Shoot apices were collected during the dormant and growth stages from populations of M. nigra growing under natural conditions. Materials were processed using standard techniques for light and electron microscopy. The secretory cavities originate under the protodermis, and their initiation is restricted to the early developmental stage of shoot organs, which are protected by a hood-shaped structure. Secretory cavities have a multi-seriate epithelium surrounding a lumen that expands schizolysigenously. Oil production begins before lumen formation. When the shoot apex resumes development after the dormant stage, the glands remain active in oil secretion in the developing shoot apex and fully expanded leaves. The mature epithelial cells are flattened and exhibit very thin walls, large oil bodies, leucoplasts surrounded by endoplasmic reticulum, and mitochondria with unusual morphology. The tangential walls of the epithelial cells facing the lumen undergo continuous peeling. The vacuole extrusion appears to be the primary mode of release oil into the lumen, in an exocytotic way. The continuity of oil secretion is ensured by the replacement of the damaged inner epithelial cells by divisions in the parenchyma layer that surround the oil gland, likely a meristematic sheath.

Optical Properties of Berry Epicuticular Waxes in Four Georgian Grape Cultivars (Vitis vinifera L.)

The epidermis of plant shoot organs is generally covered by epicuticular waxes. The role of this layer isrelated mainly to the protection of the inner tissues from biotic and abiotic stresses. In this study, attentionis focused on the optical properties of the berry epicuticular waxes of the grapevine (Vitis vinifera L.) atfruit ripening. The reflectance of the berry surface was measured before and after chloroform treatmentsin four Georgian grape cultivars grown in northern Italy. Epicarp optical properties were underlinedat different wavelengths (341 to 1025 nm) for each cultivar. The results show that the berry waxes haveseveral optical properties; it is possible that their main eco-physiological effect is to provide specificprotection against different types of radiation. Besides the physiological aspects, the results are interestingalso from a technical point of view in the field of interpretation of reflectance measurements carried out bynon-invasive instruments.

Drought response transcriptomes are altered in poplar with reduced tonoplast sucrose transporter expression.

Transgenic Populus tremula x alba (717-1B4) plants with reduced expression of a tonoplast sucrose efflux transporter, PtaSUT4, exhibit reduced shoot growth compared to wild type (WT) under sustained mild drought. The present study was undertaken to determine whether SUT4-RNAi directly or indirectly altered poplar predisposition and/or response to changes in soil water availability. While sucrose and hexose levels were constitutively elevated in shoot organs, expression responses to drought were most altered in the root tips of SUT4-RNAi plants. Prior to any drought treatment, constitutively elevated transcript levels of abscisic acid biosynthetic genes and bark/vegetative storage proteins suggested altered metabolism in root tips of RNAi plants. Stronger drought-stimulation of stress-inducible genes encoding late-embryogenesis-abundant proteins in transgenic roots was consistent with increased vulnerability to soil drying. Transcript evidence suggested an RNAi effect on intercellular water trafficking by aquaporins in stem xylem during soil drying and recovery. Co-expression network analysis predicted altered integration of abscisic acid sensing/signaling with ethylene and jasmonate sensing/signaling in RNAi compared to WT roots. The overall conclusion is that steepened shoot-root sugar gradient in RNAi plants increased sensitivity of root tips to decreasing soil water availability.

Modelling N and Dry Matter Partitioning between Leaf and Stem of Wheat under Varying N Supply

AbstractThe fraction of dry matter and nitrogen (N) allocated to leaves is of high importance for wheat crop simulators, because it has an impact on N demand, evapotranspiration, light interception and light use efficiency. For the vegetative phase of wheat, a robust empiric description of the influence of N nutrition status (NNI) on this pattern is still pending. We investigated the influence of NNI on leaf: stem partitioning of wheat (Triticum aestivum L.), until end of leaf growth. The evaluation based on N rate experiments (0–320 kg N ha−1) from three subsequent seasons (2003/4 to 2005/6), with five modern bread wheat cultivars, carried out near Kiel (northern Germany). A previously published model was adapted for describing the influence of NNI on dry matter partitioning. Starting from the allometric leaf: stem relationship of situations with NNI ≥1, a correction term was used, to describe the partitioning under varying N supply. The correction term assumes a linear increase of the stem fraction, proportional to the difference between a NNI threshold and actual NNI. The allometric partitioning was found to shift towards stem fraction, if the NNI falls below 1.38. The slope of the relative increase was determined with 0.6. Both dimensionless parameters of the correction term were found to be highly significant. The second aim was to quantify how N status impacts the N allocation between shoot organs. Dry matter‐based N dilution curves were fitted for stem (plateau power) and leaf (plateau linear), for situations with sufficient N supply (NNI ≥1). The ‘expected’ shoot N demand was calculated as a function of observed dry matter and N dilution for both organs. The N deficit was defined as difference between expected and observed shoot N. Plotting stem against shoot N deficit reveals that 63 % of the shoot deficit was allocated to the stem (R2 = 0.98). Implications for crop modelling are discussed.

Light Signaling Regulates Tulip Organ Growth and Ethylene Production in a Tissue-Specific Manner

Premise of research. Plants growing under physical or leaf canopy shade often exhibit increases in shoot growth that allow for additional exposure to irradiance from sunlight. These shaded plants also usually exhibit an accelerated flowering, though the effect of shade light on growth of flower organs has not been well studied. These growth changes in shoot organs induced by shade light signaling are regulated in a negative manner by ethylene in a number of plant species; that is, shading reduces shoot ethylene production, thereby increasing shoot growth.Methodology. Tulip (Tulipa gesneriana L., Liliaceae) plants were selected as a model system, one where floral organ development occurs in the bulb before exposure to shade light. This allows any effects of shade light signaling on floral organ growth to be uncoupled from effects on development. Therefore, following a period of low temperature, tulip bulbs were exposed to simulated sunlight with and without physical or canopy shade.Pivotal results. Both a ...

Basis of ontogenetic and evolutionary transformations of thecate hydroids

The high diversity of spatial organization of shoots in colonies of thecate hydroids (Cnidaria, Hydroidomedusa, Leptomedusae) is determined by their modular organization, which is characterized by the cyclic morphogenesis in the colony. It is attempted to show that evolutionary and ontogenetic changes in the spatial organization of hydroids of this group are based on the allometric growth of modules of colony shoots. An increase in size of a developing module provides prerequisites for earlier initiation of the growing tips of succeeding moduls (heterochrony). In some cases, heterochronies determined transition from cyclic to acyclic morphogenesis. The earlier emergence of new growing tips allowed integration of several primary modules into secondary modules, resulting among other things in changes in relative positions of primary modules (heterotopy). In complex colonies, these changes are traced in the ontogeny of a single colony.

HANABA TARANU (HAN) Bridges Meristem and Organ Primordia Boundaries through PINHEAD, JAGGED, BLADE-ON-PETIOLE2 and CYTOKININ OXIDASE 3 during Flower Development in Arabidopsis.

Shoot organ primordia are initiated from the shoot apical meristem and develop into leaves during the vegetative stage, and into flowers during the reproductive phase. Between the meristem and the newly formed organ primordia, a boundary with specialized cells is formed that separates meristematic activity from determinate organ growth. Despite interactions that have been found between boundary regulators with genes controlling meristem maintenance or primordial development, most boundary studies were performed during embryogenesis or vegetative growth, hence little is known about whether and how boundaries communicate with meristem and organ primordia during the reproductive stage. We combined genetic, molecular and biochemical tools to explore interactions between the boundary gene HANABA TARANU (HAN) and two meristem regulators BREVIPEDICELLUS (BP) and PINHEAD (PNH), and three primordia-specific genes PETAL LOSS (PTL), JAGGED (JAG) and BLADE-ON-PETIOLE (BOP) during flower development. We demonstrated the key role of HAN in determining petal number, as part of a set of complex genetic interactions. HAN and PNH transcriptionally promote each other, and biochemically interact to regulate meristem organization. HAN physically interacts with JAG, and directly stimulates the expression of JAG and BOP2 to regulate floral organ development. Further, HAN directly binds to the promoter and intron of CYTOKININ OXIDASE 3 (CKX3) to modulate cytokinin homeostasis in the boundary. Our data suggest that boundary-expressing HAN communicates with the meristem through the PNH, regulates floral organ development via JAG and BOP2, and maintains boundary morphology through CKX3 during flower development in Arabidopsis.

ATML1 and PDF2 Play a Redundant and Essential Role in Arabidopsis Embryo Development.

The epidermis of shoot organs in plants develops from the outermost layer (L1) of the shoot apical meristem. In Arabidopsis, a pair of homeobox genes, ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1) and PROTODERMAL FACTOR2 (PDF2), play a role in regulating the expression of L1-specific genes. atml1-1 pdf2-1 double mutants show striking defects in the differentiation of shoot epidermal cells. However, because atml1-1 and pdf2-1 have a T-DNA inserted downstream of the respective homeobox sequences, these alleles may not represent null mutations. Here we characterized additional mutant alleles that have a T-DNA insertion at different positions of each gene. Double mutants of a strong atml1-3 allele with each pdf2 allele were found to cause embryonic arrest at the globular stage. Although with low frequency, all double mutant combinations of a weak atml1-1 allele with each pdf2 allele germinated and showed phenotypes defective in shoot epidermal cell differentiation. We further confirmed that transgenic induction of PDF2 fused to the Drosophila Engrailed repressor domain temporarily interferes with epidermal cell differentiation in the wild-type background. These results indicate that ATML1 and PDF2 act redundantly as a positive regulator of shoot epidermal cell differentiation and at least one copy of these genes is essential for embryo development.

Control of patterning, growth, and differentiation by floral organ identity genes

In spite of the different morphologies of sepals, petals, stamens, and carpels, all these floral organs are believed to be modified versions of a ground-state organ similar to the leaf. Modifications of the ground-state developmental programme are orchestrated by different combinations of MADS-domain transcription factors encoded by floral organ identity genes. In recent years, much has been revealed about the gene regulatory networks controlled by the floral organ identity genes and about the genetic pathways that control leaf development. This review examines how floral organ identity is connected with the control of morphogenesis and differentiation of shoot organs, focusing on the model species Arabidopsis thaliana. Direct links have emerged between floral organ identity genes and genes involved in abaxial-adaxial patterning, organ boundary formation, tissue growth, and cell differentiation. In parallel, predictive models have been developed to explain how the activity of regulatory genes can be coordinated by intercellular signalling and constrained by tissue mechanics. When combined, these advances provide a unique opportunity for revealing exactly how leaf-like organs have been 'metamorphosed' into floral organs during evolution and showing crucial regulatory points in the generation of plant form.

The conflict between cell proliferation and expansion primarily affects stem organogenesis in Arabidopsis.

Plant shoot organs such as stems, leaves and flowers are derived from specialized groups of stem cells organized at the shoot apical meristem (SAM). Organogenesis involves two major processes, namely cell proliferation and differentiation, whereby the former contributes to increasing the cell number and the latter involves substantial increases in cell volume through cell expansion. Co-ordination between the above processes in time and space is essential for proper organogenesis. To identify regulatory factors involved in proper organogenesis, heavy-ion beam-irradiated de-etiolated (det) 3-1 seeds have been used to identify striking phenotypes in the A#26-2; det3-1 mutant. In addition to the stunted plant stature mimicking det3-1, the A#26-2; det3-1 mutant exhibited stem thickening, increased floral organ number and a fruit shape reminiscent of clavata (clv) mutants. DNA sequencing analysis demonstrated that A#26-2; det3-1 harbors a mutation in the CLV3 gene. Importantly, A#26-2; det3-1 displayed cracks that randomly occurred on the main stem with a frequency of approximately 50%. Furthermore, the double mutants clv3-8 det3-1, clv1-4 det3-1 and clv2-1 det3-1 consistently showed stem cracks with frequencies of approximately 97, 38 and 35%, respectively. Cross-sections of stems further revealed an increase in vascular bundle number, cell number and size in the pith of clv3-8 det3-1 compared with det3-1. These findings suggest that the stem inner volume increase due to clv mutations exerts an outward mechanical stress; that in a det3-1 background (defective in cell expansion) resulted in cracking of the outermost layer of epidermal cells.

Plant Growth and Morphogenesis under Different Gravity Conditions: Relevance to Plant Life in Space.

The growth and morphogenesis of plants are entirely dependent on the gravitational acceleration of earth. Under microgravity conditions in space, these processes are greatly modified. Recent space experiments, in combination with ground-based studies, have shown that elongation growth is stimulated and lateral expansion suppressed in various shoot organs and roots under microgravity conditions. Plant organs also show automorphogenesis in space, which consists of altered growth direction and spontaneous curvature in the dorsiventral (back and front) directions. Changes in cell wall properties are responsible for these modifications of growth and morphogenesis under microgravity conditions. Plants live in space with interesting new sizes and forms.

Photosynthetic performance and biochemical adjustments in two co-occurring Mediterranean evergreens, Quercus ilex and Arbutus unedo, differing in salt-exclusion ability.

The responses to mild root zone salinity stress were investigated in two co-occurring Mediterranean woody evergreens, Quercus ilex L. and Arbutus unedo L., which differ in morpho-anatomical traits and strategies to cope with water deficit. The aim was to explore their strategies to allocate potentially toxic ions at organism level, and the consequential physiological and biochemical adjustments. Water and ionic relations, gas exchange and PSII performance, the concentration of photosynthetic pigments, and the activity of antioxidant defences, were measured. Q. ilex displayed a greater capacity to exclude Na+ and Cl- from the leaf than A. unedo, in part as a consequence of greater reductions in transpiration rates. Salt-induced reductions in CO2 assimilation resulted in Q. ilex suffering from excess of light to a greater extent than A. unedo. Consistently, in Q. ilex effective mechanisms of nonphotochemical quenching, also sustained by the lutein epoxide-lutein cycle, operated in response to salinity stress. Q. ilex also displayed a superior capacity to detoxify reactive oxygen species (ROS) than A. unedo. Our data suggest that the ability to exclude salt from actively growing shoot organs depends on the metabolic cost of sustaining leaf construction, i.e. species-specific leaf life-span, and the relative strategies to cope with salt-induced water stress. We discuss how contrasting abilities to restrict the entry and transport of salt in sensitive organs relates with species-specific salt tolerance.

Study of the effect of the gene ERECTA2 on the development of Arabidopsis thaliana shoot

The role of the gene ER2 in plant development has been studied by the analysis of the erecta2 (er2) mutant of Arabidopsis thaliana (L.) Heynh. It was shown that the mutation er2 provides pleiotropic effect on the development of all aboveground organs. It induces shortening and thickening of the stem, leaves and all flower organs, though it does not change the sensitivity to gibberellin. Changes in the morphology of the shoot organs are due to the changes in cell polarity. The cells get wider and shorter compared to the wild type. It was found that the gene ER2 is located in the lower arm of the chromosome 1. It complementarily interacts with the gene ER that plays an important role in the control of intercellular interactions.

Polarity, Continuity, and Alignment in Plant Vascular Strands

Plant vascular cells are joined end to end along uninterrupted lines to connect shoot organs with roots; vascular strands are thus polar, continuous, and internally aligned. What controls the formation of vascular strands with these properties? The "auxin canalization hypothesis"-based on positive feedback between auxin flow through a cell and the cell's capacity for auxin transport-predicts the selection of continuous files of cells that transport auxin polarly, thus accounting for the polarity and continuity of vascular strands. By contrast, polar, continuous auxin transport-though required-is insufficient to promote internal alignment of vascular strands, implicating additional factors. The auxin canalization hypothesis was derived from the response of mature tissue to auxin application but is consistent with molecular and cellular events in embryo axis formation and shoot organ development. Objections to the hypothesis have been raised based on vascular organizations in callus tissue and shoot organs but seem unsupported by available evidence. Other objections call instead for further research; yet the inductive and orienting influence of auxin on continuous vascular differentiation remains unique.

Needles and seed cones of Pinus premassoniana sp. nov., and associated pollen cone from the upper Miocene in East China

A long shoot with needles and two immature seed cones, and some isolated organs of shoot, needles and seed cones from the late Miocene Shengxian Formation in Zhejiang Province, East China are described. A detailed comparison of the gross morphology and cuticle micromorphology of needles and seed cones with previously published Cenozoic fossils and related extant pine species reveals that the present fossils can be identified as a new species, Pinus premassoniana sp. nov., which has the closest affinity with extant Pinus massoniana. A pollen cone with copious bisaccate pollen grains from the same locality is identified as an indeterminate species of subgenus Pinus. The pollen grains show a verrucate external sculpture on the corpus and sacci and an alveolae internal structure in the sacci. The fossil needle cuticles and pollen cone of the genus Pinus from China are reported for the first time. The modern distribution indicates that P. premassoniana sp. nov. should also live under a warm and humid climate. Hitherto, there is no any reliable fossil record that has an affinity with the extant P. massoniana. The occurrence of the present fossils suggests that P. premassoniana has existed in East China since at least in the late Miocene.

Phytostimulation of Poplars and Arabidopsis Exposed to Silver Nanoparticles and Ag+ at Sublethal Concentrations

The increasing likelihood of silver nanoparticle (AgNP) releases to the environment highlights the importance of understanding AgNP interactions with plants, which are cornerstones of most ecosystems. In this study, poplars (Populus deltoides × nigra) and Arabidopsis thaliana were exposed hydroponically to nanoparticles of different sizes (PEG-coated 5 and 10 nm AgNPs, and carbon-coated 25 nm AgNPs) or silver ions (Ag(+), added as AgNO₃) at a wide range of concentrations (0.01 to 100 mg/L). Whereas all forms of silver were phytotoxic above a specific concentration, a stimulatory effect was observed on root elongation, fresh weight, and evapotranspiration of both plants at a narrow range of sublethal concentrations (e.g., 1 mg/L of 25 nm AgNPs for poplar). Plants were most susceptible to the toxic effects of Ag(+) (1 mg/L for poplar, 0.05 mg/L for Arabidopsis), but AgNPs also showed some toxicity at higher concentrations (e.g., 100 mg/L of 25 nm AgNPs for poplar, 1 mg/L of 5 nm AgNPs for Arabidopsis) and this susceptibility increased with decreasing AgNP size. Both poplars and Arabidopsis accumulated silver, but silver distribution in shoot organs varied between plant species. Arabidopsis accumulated silver primarily in leaves (at 10-fold higher concentrations than in the stem or flower tissues), whereas poplars accumulated silver at similar concentrations in leaves and stems. Within the particle subinhibitory concentration range, silver accumulation in poplar tissues increased with exposure concentration and with smaller AgNP size. However, compared to larger AgNPs, the faster silver uptake associated with smaller AgNPs was offset by their toxic effect on evapotranspiration, which was exerted at lower concentrations (e.g., 1 mg/L of 5 nm AgNPs for poplar). Overall, the observed phytostimulatory effects preclude generalizations about the phytotoxicity of AgNPs and encourage further mechanistic research.

Morphogenesis and structural organization of shoots of two life forms of Scutellaria supinа L.

Morphogenesis and structural organization of shoots two life forms S. supina L. in the different habitat conditions were studied.

Rose bush leaf and internode expansion dynamics: analysis and development of a model capturing interplant variability.

Rose bush architecture, among other factors, such as plant health, determines plant visual quality. The commercial product is the individual plant and interplant variability may be high within a crop. Thus, both mean plant architecture and interplant variability should be studied. Expansion is an important feature of architecture, but it has been little studied at the level of individual organs in rose bushes. We investigated the expansion kinetics of primary shoot organs, to develop a model reproducing the organ expansion of real crops from non-destructive input variables. We took interplant variability in expansion kinetics and the model's ability to simulate this variability into account. Changes in leaflet and internode dimensions over thermal time were recorded for primary shoot expansion, on 83 plants from three crops grown in different climatic conditions and densities. An empirical model was developed, to reproduce organ expansion kinetics for individual plants of a real crop of rose bush primary shoots. Leaflet or internode length was simulated as a logistic function of thermal time. The model was evaluated by cross-validation. We found that differences in leaflet or internode expansion kinetics between phytomer positions and between plants at a given phytomer position were due mostly to large differences in time of organ expansion and expansion rate, rather than differences in expansion duration. Thus, in the model, the parameters linked to expansion duration were predicted by values common to all plants, whereas variability in final size and organ expansion time was captured by input data. The model accurately simulated leaflet and internode expansion for individual plants (RMSEP = 7.3 and 10.2% of final length, respectively). Thus, this study defines the measurements required to simulate expansion and provides the first model simulating organ expansion in rosebush to capture interplant variability.

Emerging Role of the Ubiquitin Proteasome System in the Control of Shoot Apical Meristem FunctionF

The shoot apical meristem (SAM) is a population of undifferentiated cells at the tip of the shoot axis that establishes early during plant embryogenesis and gives rise to all shoot organs throughout the plant's life. A plethora of different families of transcription factors (TFs) play a key role in establishing the equilibrium between cell differentiation and stem cell maintenance in the SAM. Fine tuning of these regulatory proteins is crucial for a proper and fast SAM response to environmental and hormonal cues, and for development progression. One effective way to rapidly inactivate TFs involves regulated proteolysis by the ubiquitin/26S proteasome system (UPS). However, a possible role of UPS-dependent protein degradation in the regulation of key SAM TFs has not been thoroughly investigated. Here, we summarize recent evidence supporting a role for the UPS in SAM maintenance and function. We integrate this survey with an in silico analysis of publicly-available microarray databases which identified ubiquitin ligases that are expressed in specific areas within the SAM, suggesting that they may regulate or act downstream of meristem-specific factors.