Substomatal Chambers Research Articles

Drought-stress tolerance potential in plum and prune rootstocks and cultivars (Prunus spp.) based on physiological and photosynthetical parameters

Drought stress and water crisis is a great limiting factor for the production of horticultural crops. The present study was carried out during 2021 and 2022 at Horticultural Science Research Institute, Kamalshahr, Karaj, Iran to identify the effect of drought stress in physiological and photosynthetic characteristics of Prunus spp. rootstocks and varieties of 4-year old Prunus spp. The factorial experiment was conducted in a completely randomized block design (CRBD) having 3 factors and 3 replications. Factors included 8 rootstocks, viz. Myrobalan 29C, Penta, Tetra, St. Julien, Mariana 2624, GF 677, GN 15 and Seedling as the first factor; 4 cultivars, viz. Greengage, Simka, NO 16 and Zochelo as the second factor; and drought stress conditions in two levels namely with interruption of irrigation for 14 days and without interruption of irrigation as the third factor. Drought stress decreased relative water content of leaves, stomatal conductance, transpiration, CO2 content in substomatal chamber, and water use efficiency. Zuchelo and Greengage varieties and GN 15 rootstock had the highest and Simka variety and Mariana 2624 and Myrobalan 29C rootstocks had the lowest stomatal exchanges and photosynthesis, respectively. Among the rootstocks; GN 15, GF 677 and Mariana 2624 showed better physiological stability under stress, and the most tolerant variety against drought stress was NO 16. Totally, grafting combination of cv. NO 16 and rootstock GN 15 has been identified as the most tolerant to drought stress.

Knock-out of SlDMR6-1 in tomato promotes a drought-avoidance strategy and increases tolerance to Late Blight

The DOWNY MILDEW RESISTANCE 6 (DMR6) protein is a 2-oxoglutarate (2OG) and Fe(II)-dependent oxygenase, involved in salicylic acid (SA) metabolism. SA is recognized as an abiotic stress-tolerance enhancer, and in tomato the inactivation of DMR6 was found increase its level and induce disease-resistance against several pathogens. By applying the CRISPR/Cas9 technique, we generated Sldmr6-1 tomato mutants and tested their tolerance to drought as well as to Late Blight. Wild-type tomato cultivar ‘San Marzano’ and its Sldmr6-1 mutants were subjected to water deprivation for 7 days. WT plants exhibited severe wilting, while T2Sldmr6-1 mutants showed turgid leaves and maintained higher Soil Relative Water Content. Eco-physiological measurements highlighted that Sldmr6-1 mutants adopted a water saving behavior reducing transpiration rate by decreasing stomatal conductance. Under drought stress the assimilation rate decreased as well, resulting in no alteration of the CO2 concentration in the sub-stomatal chamber and increasing the Water Use Efficiency. Furthermore, in Sldmr6-1 mutants the drought stress induced up-regulation of the anti-oxidant related genes SlAPX and SlGST as well as down-regulation of SlCYP707A2 gene, which is involved in ABA catabolism. At last we highlighted, for the first time in tomato, that Sldmr6-1 mutants exhibited a reduced susceptibility to Phytophthora infestans, the causal agent of Late Blight.

Mechanical advantage of subsidiary cells depends on the stomatal complex structure

Structural features of stomatal complexes influencing the mechanical advantage of subsidiary cells were studied. Light, scanning and transmission electron microscopy were used to research the morphology of Fagraea ceilanica stomatal complexes. Their guard cells are located on subsidiary cells. The walls of the subsidiary cells are thickened unevenly. The inner tangential walls are thin and most extensive as compared to other walls of these cells. The data obtained allowed a 3D model of F. ceilanica stomatal complex to be constructed. To elucidate the interaction between the guard and subsidiary cells during stomatal movements, we have applied modelling using the finite-element method. According to the modelling results, the mechanical advantage of the subsidiary cells depends on mutual location of the guard and subsidiary cells, uneven thickening, area and rigidity of the subsidiary cell walls and presence of substomatal chambers, into which the inner tangential walls of the subsidiary cells can bulge when turgor pressure in these cells increases. The modelling results were confirmed by the observed deformations in actual stomatal complex cells of F. ceilanica. The decrease in mechanical advantage of the subsidiary cells ensures stoma opening in the conditions of excessive saturation of the epidermis with water, for example, in the conditions of tropical rainforests.

Austropuccinia psidii infection changes stomatal dynamics and leaf gas exchange of guava leaves: A physio-histopathological assessment

This study aimed to characterise the life cycle of Austropuccinia psidii, the causal agent of myrtle rust, in guava cv. Paluma and to determine how this pathogen affects gas exchange in diseased leaves. The pathogen formed appressoria on ordinary epidermal cells and intercellular hyphae and intracellular branched lobe-shaped haustoria in parenchyma cells. In the stem, hyphae grew in the cortical region and crossed between tracheary cells, reaching the medullary region. In the leaf, hyphae colonised the intercellular spaces of the main vein and mesophyll and the substomatal chamber. Colonisation of the substomatal chamber by A. psidii changed the stomatal dynamics and leaf gas exchange. The stomatal response to light was slower and had a smaller amplitude in diseased guava leaves. Consequently, impaired stomatal movement induced by A. psidii is an additional factor changing the performance of plants under abiotic stress.

Adaptative Strategies in Gymnocalycium Species (Cactaceae) and the Presence of Ectomycorrhizae Associated with Survival in Arid Environments.

The Cactaceae family makes use of different strategies, both physiological and biochemical, for anatomical adjustments that allow them to grow and reproduce in arid environments. Morphological studies of Gymnocalycium have been scarce, and the anatomy and phytochemistry are still largely unknown. The aim of the present work was to analyze the structural, physiological, and biochemical features of Gymnocalycium marianae and G. oenanthemum, two endemic species of arid regions in Argentina. The anatomic structure, biomass, and photosynthetic pigments, as well as phenolic compound contents, were analyzed in the stem, spine, and root of both species. G. marianae showed stems with deeper substomatal chambers and a more developed photosynthetic tissue than G. oenanthemum. The spines of G. oenanthemum showed higher biomass, thicker epidermal and subepidermal cell walls, and a higher content of phenolic compounds than those of G. marianae. Ectomycorrhizae were observed for the first time in roots in both species. Roots of G. marianae showed high colonization, biomass, and content of phenolic compounds. Both species showed abundant mucilaginous fibers in the stem and root. Finally, these results show the strategies associated with the survival in xeric environments of two cacti species at risk of extinction. They could be useful for the development of ex situ conservation programs.

Anatomical adaptations in the stem of Discocactus catingicola (Cactaceae) to the highly threatened ironstone outcrops from southeastern Brazil

The geosystems known as “cangas” are composed of ferruginous concretions and are characterized by being subjected to elevated temperatures and by having highly acidic, shallow, unfertile soils. The extremely harsh environmental conditions therein limit the occupation of cangas to a restricted number of species, such as Discocactus catingicola. We aimed to analyze the stem anatomy of D. catingicola occurring on cangas in order to assess which structural traits provide the species with an adaptive advantage to these geosystems. Stem samples were subjected to protocols of cross-sectioning, epidermal dissociation and lugol histochemical detection, and were then analyzed under light microscopy. Stems have a uniseriate epidermis and a thick cuticle. Paracytic stomata occur at the same level of pavement cells. Conspicuous substomatal chambers extend through the entire hypodermis height. The two-layered, collenchymatous hypodermis has a high amount of calcium oxalate inclusions in the form of prismatic crystals. Stem structure is also composed of a water-storing chlorenchyma, a starch and water storage parenchyma, and wide-band tracheids. Our findings revealed the occurrence of xeromorphic adaptive characters in D. catingicola which provide the species with its adaptive success in ironstone outcrops. The description of these anatomical traits in D. catingicola make up a pioneer report, thus being of great importance for future research on ecological plant anatomy not only of Cactaceae species but also of other unrelated xerophytes. We expect our work will assist researchers in the fields of anatomy, taxonomy and systematics of Cactaceae. Future research investigating the anatomy of D. catingicola populations occurring on ecosystems other than the lateritic cangas should provide a helpful comparative basis for evaluating the species degree of phenotypic plasticity.

New Insights on Alternative Hosts of Xanthomonas vasicola pv. vasculorum, the Causal Agent of Bacterial Leaf Streak of Maize

Bacterial leaf streak (BLS) of maize (Zea mays), caused by the bacterium Xanthomonas vasicola pv. vasculorum (Xvv), was first reported in Brazil in 2018. In this study, we evaluated 52 species of cultivated plants, cover crops, forage, and grasses that are used in succession or crop rotation with maize, and weeds with natural occurrence in maize-producing regions, to determine their potentials as alternative hosts for Xvv. We investigated (i) the pathogenicity of Xvv based on symptom development, (ii) epiphytic colonization of the bacterium in asymptomatic plants, and (iii) bacterial colonization in plant tissues using scanning electron microscopy (SEM) in symptomatic and asymptomatic species. Ten species, all belonging to the Poaceae family, presented symptoms after Xvv infection, including Avena sativa (cvs. IPR Afrodite and IPR Esmeralda), A. strigosa (cv. IPR 161), Hordeum vulgare (cv. BRS Cauê), Oryza sativa (cv. IPR 117), Brachiaria brizantha (Brizantha and cv. Marandu), Digitaria horizontalis, D. insularis, Echinochloa colonum, Eleusine indica, and Sorghum arundinaceum. Furthermore, epiphytic colonization by Xvv was observed in 23 asymptomatic species. Scanning micrographs revealed that Xvv cells and their aggregates were distributed throughout the leaf surface. In addition, bacterial colonization in the intercellular tissues of the substomatal chambers of white oat, black oat, and maize was observed across the tissue fractures. Despite showing typical symptoms of Xvv infection, SEM examination revealed evidence of Xvv colonization only on the leaf surface of rice. In asymptomatic species, such as rye, sorghum, and millet, a low number of bacterial cells were found on the leaf surface. However, no evidence of internal tissue colonization was observed in millet fractures, suggesting that Xvv survives only epiphytically in this species.

Large lipid droplets of the guard cells are dynamic organelles of the functioning stomata of Fagraea ceilanica

Fagraea ceilanica is an evergreen epiphyte, a large shrub or a small tree. Its native range is tropical and subtropical Asia. Light, scanning and transmission electron microscopy were used to study the development and structure of its stomatal complexes. They are anisocytic or helicocytic. The absence of typical chloroplasts, the presence of complex-shaped mitochondria, the diurnal formation and destruction of large lipid droplets (LDs) are structural features of F. ceilanica guard cells. The plastids of these cells have few peripheral thylakoids and contain large starch grains. The plastids of subsidiary cells are typical chloroplasts with large grana. Stomata are functional. The data obtained indicate the relation between the filling of the guard cells with LDs and the opening of stomata. The measuring of stomatal conductance revealed its slow lowering in the cut-off leaves. The leaves of F. ceilanica are protected from rapid water loss by the formation of mucilage from wall components of spongy tissue cells. Their walls facing the substomatal chamber are covered with a mucilaginous layer.

Beneficial microbial species and metabolites alleviate soybean oxidative damage and increase grain yield during short dry spells

Short dry spells are an important grain yield constraint in tropical regions. Plant growth-promoting bacteria (PGPB) and their metabolites can mitigate the impact of drought stress by promoting changes in plant metabolism, physiology, and biochemistry. However, the effects of PGPB on soybean [Glycine max (L.) Merril] under drought stress in tropical regions have not been established. The experiments were carried out under tropical field conditions with short dry spells. Therefore, in this study we used a three-factorial trial to evaluate the effects of bacterial consortium consisting of N2-fixing Bradyrhizobium japonicum (strain SEMIA 5079) and Bradyrhizobium diazoefficiens (strain SEMIA 5080), the biocontrol agent Bacillus subtilis (strain QST 713), and the plant growth-promoting Azospirillum brasilense (strains Ab-V5 and Ab-V6) with or without application of microbial secondary metabolites (MSM, rhizobial metabolites enriched in lipo-chitooligosaccharides (LCOs)) during two growing seasons. Photosynthetic pigments, gas exchange parameters, antioxidant enzyme activity and proline concentrations in leaves, nodulation, plant growth development and grain yield were evaluated. The bacterial consortium comprising Bradyrhizobium spp., A. brasilense strains and MSM application increased the contents of chlorophyll a (14.5 %), chlorophyll b (30.8 %), total chlorophyll (17.2 %), and total carotenoids (27.3 %) compared with Bradyrhizobium spp. treatment alone. This consortium also increased the net photosynthetic rate (17.7 %), stomatal conductance (56.5 %), internal CO2 concentration in the substomatal chamber (8.3 %), and transpiration (44 %) compared with plants that received the standard inoculation (Bradyrhizobium spp. only), while reducing the leaf contents of hydrogen peroxide (−18.8 %) and proline (−29.4 %), lipid peroxidation (−15.9 %), and the activities of superoxide dismutase (−18.2 %), catalase (−21.2 %), and ascorbate peroxidase (−19.1 %). Taken together, the results indicate that a beneficial bacterial consortium comprising Bradyrhizobium spp. and A. brasilense strains combined with MSM application can alleviate oxidative damage during dry spells. Furthermore, this consortium improved soybean nodulation, plant growth development, and grain yield by up to 12.2 %.

Influence of Polyethylene Glycol on Leaf Anatomy, Stomatal Behavior, Water Loss, and Some Physiological Traits of Date Palm Plantlets Grown In Vitro and Ex Vitro.

Few reports explain the mechanism of PEG action on stomatal behavior and anatomical structure and analyze the photosynthetic pigments of in vitro date palm plantlets for better tolerance to ex vitro exposure. The main challenge for in vitro micropropagation of date palm techniques remains restricted to high survival rates and vigorous growth after ex vitro transplantation. In vitro hardening is induced by Polyethylene glycol PEG (0.0, 10, 20, 30 g L−1) for 4 weeks. Leaf anatomy, stomatal behavior, water loss %, photosynthetic pigments, and reducing sugars were examined in date palm plantlets (Phoenix dactylifera L.) cv. (Sewi) after 4 weeks from in vitro PEG treatment and after 4 weeks from ex vitro transplanting to the greenhouse. Leaf anatomy and the surface ultrastructure of in vitro untreated leaves showed a thin cuticle layer, wide opened malfunctioning stomata, and abnormal leaf anatomy. Furthermore, addition of PEG resulted in increasing cuticle thickness, epicuticular wax depositions, and plastids density, improving the stomatal ability to close and decreasing the stomatal aperture length while reducing the substomatal chambers and intercellular spaces in the mesophyll. As a result, a significant reduction in water loss % was observed in both in vitro and ex vitro PEG treated leaves as compared to untreated ones, which exhibited rapid wilting when exposed to low humidity for 4 h. PEG application significantly increased Chlorophylls a, b and carotenoids concentrations, especially 10, 20 g L−1 treatments, which were sequentially reflected in increasing the reducing sugar concentration. However, leaves of plantlets treated with PEG at 30 g L−1 became yellow and had necrosis ends with death. In vitro hardening by 20 g L−1 PEG increased the survival rate of plantlets to 90% after ex vitro transfer compared to 63% recorded for the untreated plantlets. Therefore, this application provides normal date palm plantlets developed faster and enhances survival after ex vitro transfer.

Gas exchanges, growth and production of okra cultivated with saline water and silicon fertilization

Excess salts in water and/or soil are a critical factor that adversely affects the physiology and growth, besides limiting the production of crops in the semiarid region of Northeast Brazil. One way to reduce the effect of salt stress on plants is by using silicon (Si) fertilization. In this context, the objective of this study was to evaluate the gas exchange, growth, and production of okra cv. Valença as a function of irrigation with saline water and Si doses. The experiment was conducted in a greenhouse in the municipality of Pombal - PB, Brazil. The experimental design adopted was randomized blocks in a 5 × 2 factorial scheme corresponding to five levels of electrical conductivity of water ECw (0.3, 1.0, 1.7, 2.4, and 3.1 dS m-1) and two doses of Si fertilization (100 and 200 g of Si per plant), with four replicates. Salt stress increased the intercellular concentration of CO2 in the substomatal chamber and reduced the CO2 assimilation rate, instantaneous carboxylation efficiency, growth, and production of okra plants. Intrinsic water use efficiency and average weights of okra fruits were not influenced by irrigation with saline water and Si doses. The supply of 200 g Si per plant reduced the deleterious effect of salt stress on stomatal conductance and leaf area of okra, at 45 days after sowing but did not increase production.

A New Species of Brachyphyllum from the Crato Formation (Lower Cretaceous), Araripe Basin, Brazil

The Araripe Basin, located in the Northeast of Brazil, contains many fossils. Among these, the gymnosperms stand out, especially species of the fossil taxon Brachyphyllum. It encompasses conifer shoots with helically arranged scale-like, adpressed leaves whose length does not exceed the width. This foliage morphotype was widely distributed during the Mesozoic, and species accommodated in this genus can be attributed to different families if their anatomical characters are taken into consideration. In the Araripe basin, specifically in the Crato and Romualdo formations, Brachyphyllum obesum is frequently found and was attributed to the family Araucariaceae based on leaf epidermal and xylem characters. In this work, we describe a new species from the Crato Formation (Lower Cretaceous), Brachyphyllum sattlerae sp. nov., based on the following morphological and anatomical features: sub-main shoots with lateral branches oppositely disposed and almost exclusively decussately arranged leaves; scarious leaf margins; rugose abaxial leaf surfaces; non-papillate epidermal cells; stomata distributed in longitudinal rows except close to the leaf margins and scarce at the leaf base; stomatal openings obliquely oriented; and hypodermis with a sinuous pattern around the substomatal chamber. Some of these features are distinctive of Araucariaceae, which indicates that B. sattlerae sp. nov. also belongs to this family.

Mucilaginous Secretions in the Xylem and Leaf Apoplast of the Swamp Palm Mauritia flexuosa L.f. (Arecaceae).

Mauritia flexuosa palms inhabit wetland environments in the dry, seasonal Brazilian savanna (Cerrado) and produce mucilaginous secretions in the stem and petiole that have a medicinal value. The present study sought to characterize the chemical natures of those secretions and to describe the anatomical structures involved in their synthesis. Chemical analyzes of the secretions, anatomical, histochemical analyses, and electron microscopy studies were performed on the roots, stipes, petioles, and leaf blades. Stipe and petiole secretions are similar, and rich in cell wall polysaccharides and pectic compounds such as rhamnose, arabinose, xylose, mannose, galactose, and glucose, which are hydrophilic largely due to their hydroxyl and carboxylate groups. Mucilaginous secretions accumulate in the lumens of vessel elements and sclerenchyma fibers of the root, stipe, petiole, and foliar veins; their synthesis involves cell wall loosening and the activities of dictyosomes. The outer faces of the cell walls of the parenchyma tissue in the mesophyll expand to form pockets that rupture and release pectocellulose substances into the intercellular spaces. The presence of mucilage in the xylem, extending from the roots to the leaf veins and continuous with the leaf apoplast, and sub-stomatal chambers suggest a strategy for plant water economy.

Two new species in a new genus and a critical revision of Brachybasidiaceae (Exobasidiales, Basidiomycota) in honor of Franz Oberwinkler

The Brachybasidiaceae are a family of 22 known species of plant-parasitic microfungi belonging to Exobasidiales, Basidiomycota. Within this family, species of the largest genus Kordyana develop balls of basidia on top of stomatal openings. Basidial cells originate from fungal stroma filling substomatal chambers. Species of Kordyana typically infect species of Commelinaceae. During fieldwork in the neotropics, fungi morphologically similar to Kordyana spp. were found on Goeppertia spp. (syn. Calathea spp., Marantaceae), namely on G. panamensis in Panama and on G. propinqua in Bolivia. These specimens are proposed as representatives of a genus new to science, Marantokordyana, based on the distinct host family and molecular sequence data of ITS and LSU rDNA regions. The specimens on the two host species represent two species new to science, M. oberwinkleriana on G. panamensis and M. boliviana on G. propinqua. They differ by the size and shape of their basidia, molecular sequence data of ITS and LSU rDNA regions, and host plant species. In the past, the understanding of Brachybasidiaceae at order and family level was significantly improved by investigation realized by Franz Oberwinkler and his collaborators at the University of Tübingen, Germany. On species level, however, our knowledge is still very poor due to incomplete species descriptions of several existing names in literature, scarceness of specimens, as well as sequence data lacking for many taxa and for further barcode regions. Especially species of Kordyana and species of Dicellomyces are in need of revision.Graphical

Leaf and scape anatomy of Leiothrix Ruhland (Eriocaulaceae) from a taxonomic and ecological perspective

Leiothrix is endemic to South America with 47 species, only two of which do not occur in Brazil. Its distinguishing characters are habit, dialypetalous or gamopetalous corolla of the male flowers and presence or not of pseudovivipary. According to Ruhland's monograph (1903) there are five subgenera. Recent molecular and morphological analyses of the family show the genus to be monophyletic, but infrageneric relationships are not well established. The study objective was to investigate leaf and scape anatomy of representatives of the four subgenera that occur in Brazil in order to contribute to the taxonomy and better understand the plants' environmental adaptations. Leiothrix anatomy is similar to that of other Eriocaulaceae genera: leaves and scapes have a single-layered epidermis, collateral vascular bundles are surrounded by a double sheath, leaves have stomata only on the abaxial side, and scapes have alternating vascular bundles of larger and smaller size. Leiothrix subg. Rheocaulon is monospecific, leaves have a single vascular bundle, scapes lack ribs, the epidermal cells have slightly thickened walls, and the cortex contains collenchyma and chlorophyllous parenchyma. In L. subg. Eleutherandra the leaf epidermis cell walls have homogeneous thickening at the margins, specialized substomatal chambers, a hypodermis, and sclerenchymatous extensions of the vascular bundle sheaths. Most taxa of L. subg. Calycocephalus have smaller vascular bundle sheath extensions facing both surfaces and ribbed scapes. Species from Minas Gerais have a hypodermis and up to seven leaf vascular bundles; those from Bahia lack a hypodermis and have more than seven leaf vascular bundles. L. subg. Stephanophyllum has scapes with a cylindric multilayered pericycle with thickened and lignified cell walls. These anatomical structures partly corroborate the subgenera proposed by Ruhland, suggest the existence of other infrageneric groups and reflect the environmental adaptations of the studied species.

How does a C3 epiphytic tank bromeliad respond to drought?

Abstract Intermittent water availability characterizes the canopy habitat, but few studies have focused on how C3 epiphytic bromeliads deal with drought. In this context, we investigated how water deficits affect the photosynthetic responses of the epiphytic bromeliad Vriesea gigantea regarding its physiological and anatomical traits that can minimize the effects of stomatal closure. In a controlled experiment in which bromeliads were submitted to 21 days of drought, we demonstrated a reduction in the leaf water content followed by strong reductions in net CO2 exchange and the efficiency of the photochemical system. However, there were increases in the yield of non-photochemical quenching and the activities of hydrophilic antioxidants. We observed substomatal chambers connected with air channels reaching the chlorophyllous parenchyma. Our findings indicate that the low net CO2 exchange and the energy imbalance possibly increased the cyclic transport of electrons and activated the thermal dissipation of energy to avoid damage to the photosynthetic apparatus. Additionally, the aeration channels may passively store CO2 to facilitate its re-assimilation. Because most epiphytic bromeliads are C3 plants and drought is frequent in the canopy, we speculate that some attributes of V. gigantea may occur in other C3 species, favouring their radiation in the epiphytic environment.

Vegetative anatomy and mycorrhizal morphology of Schoenorchis nivea (Lindl.) Schltr., (Orchidaceae) and their adaptive significance

The anatomical description of the vegetative parts (leaf, leaf sheath, stem and root) and mycorrhizal morphology of Schoenorchis nivea (Lindl.) Schltr., belonging to the subfamily Epidendroideae of Orchidaceae was investigated. Leaves were amphistomatic covered by 10-12 μm thick cuticle, stomata paracytic with small and irregular substomatal chambers. Mesophyll homogenous, composed of thin-walled chlorenchymatous cells. Banded water-storage cells abundant in the mesophyll and the largest vascular bundle occurred at the centre of the leaf. The leaf sheath has both adaxial and abaxial epidermis covered with cuticle, homogenous mesophyll, water-storage cells, raphides and vascular bundles. The stem is surrounded by a uniseriate epidermis, cortex consisting of thick-walled fibers and collateral vascular bundles scattered in the ground tissue. Cortical proliferation was evident in S. nivea stem. Root hairs present in root regions were in contact with the substratum. Root hairs frequently branched at their tips. Root possess 2-3 layered velamen, ∩-thickened exodermal cells, O-thickened uniseriate endodermis, and cortex of thin-walled parenchymatous cells containing raphides and water-storage cells. Cover cells present. Xylem arches are 9-11, with vascular tissues embedded in sclerenchymatous cells. Pith composed of thick-walled sclerenchymatous cells with intercellular space. The stomatal characteristics in leaf, the size of water-storage cells and vascular bundles exhibited significant variation in different plant parts. Intact and degenerating pelotons of orchid mycorrhizal fungi were observed in the root cortical cells. The observations of the present study clearly indicate that S. nivea possesses several anatomical adaptations to thrive in epiphytic habitats.

Structural Characterization of Mint (Mentha x villosa Huds) Stem and Leaf

Aims: The objective of this study was to identify the structural characteristics of the shoots of Mentha x villosa Huds and also, identify the main structures responsible for the production of active principles.
 Methodology: The analyzes were performed with stems and leaves from adult and healthy plants, which presented a uniform morphological pattern. The materials selected for the anatomical analyzes were fixed in FAA for 24 hours and after this period conditioned in 70% alcohol. Cross-sections and paradermic sections were manually made with a cutting blade. For sections analysis, 1% sodium hypochlorite was used for discoloration and safranine 10% dye for tissue staining.
 Results: The leaf of Mentha x villosa Huds presents asymmetric mesophyll, formed by palisade and lacunar parenchyma, and uniseriate epidermis. The diacytic stomata are located on the abaxial surface of the leaves with different sizes, all having a substomatal chamber. On both sides of leaves, glandular trichomes were observed in great quantity. The leaf midrib is formed by a large vascular bundle, with xylem facing the adaxial surface and phloem facing the abaxial surface. The stem presents uniseriate epidermis and below it can be found one or two layers of colenchyma. The vascular bundle consists of four main xylem points, and externally to it is found the phloem, which gives the quadrangular shape to the stem. Mentha x villosa Huds has characteristics that are common to aromatic species of the Lamiaceae family, which makes its characterization and differentiation difficult, as for example, its secretory structures which do not have taxonomic importance for differentiation on this species, since they are similar in other species of the same family.
 Conclusion: However, Mentha x villosa has a larger number of cell layers in the lacunar parenchyma, which is an important characteristic for the differentiation of species.

Cytological and histochemical evaluations reveal roles of the cotyledonary petiole in the germination and seedling development of Mauritia flexuosa (Arecaceae)

The cotyledonary petiole (CP) completely envelops the embryo axis during embryogenesis in Arecaceae. There is little information available, however, on the roles of that structure in seed germination and initial seedling development-crucial plant life cycle phases. The study therefore sought to evaluate the roles of CP in the germination and post-seminal development of the recalcitrant seeds of Mauritia flexuosa, an ecologically and economically important neotropical palm. The CP and the embryo/vegetative axis were evaluated during germination and initial seedling development using standard morphological, anatomical, histochemical, and ultrastructural methodologies. Evaluations of dormant seeds incubated for 60days were also performed. The CP (a) promotes seedling protrusion in the germination, extending the embryo axis outside the seed; (b) protects the vegetative axis through the development of coating rich in phenolic compounds and lignin; (c) participates in reserve translocation, with the conversion of its own proteinaceous/mucilaginous reserves into transitional starch, as well as acting in the transport of endospermic reserves; (d) favors aeration, with the formation of pathways among stomata, substomatal chambers, and intercellular spaces; (e) controls seedling morphogenesis by modulating the curvature of the vegetative axis; and (f) contributes to overcoming seed bank dormancy through cytological alterations (protein synthesis and mitochondrial proliferation). The cotyledonary petiole of palms is a unique and multifunctional structure among angiosperms, with crucial roles in germination and seedling establishment.

Beneficial Linkages of Endophytic Burkholderia anthina MYSP113 Towards Sugarcane Growth Promotion

Microbial agents are the best alternative to the chemical fertilizers that promote the plant growth in an eco-friendly manner. This study was intended to characterize Burkholderia anthina strain MYSP113 and to evaluate its mechanisms linked to sugarcane growth promotion. The morphological, biochemical, and molecular characterization (gyrB and recA) results identified the bacteria as B. anthina. To determine the plant bacterial association, MYSP113 strain was tagged with a plasmid-bear green fluorescent protein (gfp) gene, and the tagged strain was inoculated to the sugarcane (variety GXB-9), and bacterial colonization analyzed by confocal laser fluorescence microscopy. The results revealed that strain MYSP113 had root-colonizing abilities, and colonization was detected at the root and leaves maturation zones. Bacteria entered the roots via cracks at the surfacing site of the roots and disrupted epidermis. Bacterial cells were observed in the substomatal chambers of leaves. Furthermore, to evaluate the mechanisms related to sugarcane growth promotion and bacterial competence in soil and plant, greenhouse experiment performed, and bacterial competence, plant growth parameters, and phytoenzymes, and hormones were assessed with or without MYSP113. We examined bacterial competence in soil and plant via qPCR and direct plant count at 45 and 90 DAI, and results recommended that strain MYSP113 has the ability to colonize in sugarcane rhizosphere and in the aerial part of the plant. Furthermore, strain MYSP113 significantly induced the plant fresh weight, dry weight, and chlorophyll content of sugarcane seedlings at 45 and 90 days after inoculation. Additionally, strain MYSP113 triggered chitinase, cellulose, indole acetic acid, and abscisic acid production in the plant roots and aerial parts, and these results signifying that bacterial inoculation modulates the plant metabolism and boost the health. The present study concluded that strain MYSP113 has beneficial linkages with the sugarcane plant, and it would be utilized as a bioinoculant in future.