Roots Of Higher Plants Research Articles

Analysis of express sequence tags from Arbuscular Mycorrhizal fungi (AMF) express during the pre-symbiotic stage of the fungus

Arbuscular Mycorrhizal Fungi (AMF) are symbiotically associated with the roots of higher plants which enhance the overall nutritional status of plants. It is known that the overall growth and development of plants not only depend upon the performance of specific genotypes but their association is also affected by the various types of microbes. Therefore, the major aim of the study was the isolation and characterization of gene expression during the presymbiotic stage of AMF. In the present study, total RNA was extracted from spores of Rhizophagus irregularis grown under root organ culture (ROC). cDNA library was prepared and expressed sequence tag (EST) analysis was performed. Approximately 150 random clones were selected for EST sequencing analysis. Out of the 150 clones obtained, 1.5% carried inserts of the rRNA gene cluster. After excision, inserts from 72 randomly selected clones were sequenced. Database searches revealed that 74% of the clones had similarities to already known sequences. Putative genes for Ca2+-regulated symbiotic genes, cell cycle regulatory factors and precursors for lipid biosynthesis genes were discovered. A full-length mating gene was discovered using rapid amplification of cDNA ends (RACE). Studies revealed the presence of a putative mating type gene in mycorrhizal species that are evident in the sexual origin of AMF.

Properties and Characterization of Starch as a Natural Binder: A Brief Overview

This paper was reviewed about the properties and characterization of starch as a natural binders. Starch is one of the most abundant organic compounds and applied as a binder. The efficiency of binder are affected by the characteristic and properties of starch. The characteristics of starch are determined by the biological origin. Starch is composed of D-glucose in polysaccharides and it was isolated from leaves, stems, tubers, seeds, and roots of higher plants where it serves as an energy reserve. This review concentrates the several types of characterization which are structural properties, morphology properties, viscosity and functional group of starch. The X-ray diffraction result shows that the relative crystallinity decreased for modified starch compared with native starch while scanning electron microscope shows the modified starch slightly has rough surface compared with native starch. Nowadays, the concern on eco-environmental issues is increasing and this review has shown that starch is eco-environmental friendly binder that can be used in various application.

Influence of Local Isolates of Arbuscular Mycorrhizal Fungi on Growth and Some Physiological Performance of Zea mays Grown in Calcareous Soil as Affected by Phosphorus Levels

Arbuscular mycorrhizal fungi (AMF) are among plant-symbiotic fungi with higher plant roots. The applicability of AMF poses a strategy to minimize the deleterious effect of abiotic stress to enhance plant tolerance. Phosphorus is an essential macronutrient for plants, can cause toxic effects at low levels. Our target was to determine the mitigation effect of local inoculum of AMF on growth and metabolic activity of Zea mays under phosphorus levels. Phosphorus deficiency disturbed physiological performance however, AMF mitigated negative effects by enhancing the dry weight significantly (P < 0.05), P content and alkaline phosphatase in calcareous soil amended with P concentrations (from 15 to 120 mg P kg-1 soil), compared with non-inoculated plant. The maximum H+-ATPase activity was 28.13 µmol Pi-1ngP-1min in leaves of Zea mays in AM- inoculated soil and amended with 60 mg P kg-1soil. AMF enhanced antioxidant enzyme activities, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) together with their substrates glutathione (GSH) and ascorbic acid (AA), with concurrent reduction of lipid peroxidation and hydrogen peroxide content. Highest mycorrhizal colonization (88%) recorded in maize grown in 60 mg P kg-1 soil. Established data on morphological characters revealed AMF local isolates belong to four native spores related to genus Glomus, Acaulospora, Scutellospora and Entrophospora. Analysis of the genetic material confirmed that spores were related to Glomus mosseae and Acaulospora spinose. These findings demonstrate that root colonization by local AMP inoculum could ameliorate the phosphorus deficiency in calcareous soils collected from Southwestern coast of Egypt

Effect of the diverse combinations of useful microbes and chemical fertilizers on important traits of potato.

The belowground soil environment is an active space for microbes, particularly Arbuscular Mycorrhizal Fungi (AMF) and P hosphate Solubilizing Bacteria (PSB) that can colonize with roots of higher plants. In the present experiment, we evaluated the combination of microbial inoculants with the different doses of urea and superphosphate in a complete randomized block design (CRBD). Three different doses of urea and superphosphate were tested, i.e., recommended dose, 75% of the recommended dose and 125% of the recommended dose, independently and in combination with three microbial groups viz. Glomus mosseae (AMF), Bacillus subtilis (PSB) and Nitrifying microorganisms (Nitrosomonas + Nitrobacter, NN). Overall, there were 16 treatment combinations used, and studied the number of tubers per plant, the weight of tubers, moisture content, and the number of nodes per tubers which were best in treatment comprising of AMF + PSB + NN + 75% of urea + superphosphate. From our results, it is suggested for the growers to use a lesser quantity of fertilizers from the recommended dose along with some bioinoculants to maintain the soil fertility and also to achieve the yield targets by decreasing the cost of chemical fertilizers.

Crosstalk amongst phytohormones from planta and PGPR under biotic and abiotic stresses

Phytohormones are endogenously produced organic substances indispensable for regulating plant growth and yield and also play major role in inducing tolerance to plants against various biotic and abiotic stresses. The convergence points among hormone signal transduction cascades are considered as cross-talk which are crucial for plant development as well as for plant responses to biotic and abiotic stresses. Hormones interact by activating either a second messenger or through a phosphorylation cascade. These transduction cascades lead to the regulation of gene expression that directly affects the biosynthesis or action of different hormones and developmental processes in coordination with multiple stimuli. Hormone synthesis, signal transduction, perception and cross-talk create a complex network. Interaction of plant growth promoting rhizobacteria (PGPR) which form intimate association with the roots of higher plants also modulate the level of endogenous phytohormones and demonstrate a new paradigm for hormonal interaction. The ratio of hormones changes with ontogeny of plant and the specific ratio of growth promoting and growth inhibiting hormones determine the response of plants. Furthermore, the sensitivity of plant tissue to each hormone changes with the exposure to stresses. This review is a compilation of the interactions between phytohormones and plant development. The cross talk between different hormones under abiotic and biotic stresses will be enumerated. Hormone and stress-responsive cis elements and the trans-regulation capabilities of miRNAs for the coordination of multiple hormonal responses will be discussed. Finally the role of PGPR will be evaluated under various environmental stresses with particular emphasis on phytohormone production and its interaction with host plant physiology. PGPR provides cross protective properties through improvement in defense mechanism controlling pathogen resistance through induced systemic resistance (ISR) and alleviating abiotic stress through influencing the phytohormones metabolism. PGPR isolates from stressed soil/stressed host plants impart tolerance to plants against abiotic and biotic stresses by modulating the production of phytohormones and alteration in their sensitivity to respond. Bacteria communicate with each other through quorum sensing molecules which also regulate gene expression and phytohormone production. The intricate relationship between other microbes/fungi and their residual effects on plant rhizosphere phytohormones need further investigation for better understanding of bacterial coordination with plants.

Organic Acids Exuded From Roots Increase the Available Potassium Content in the Rhizosphere Soil: A Rhizobag Experiment in Nicotiana tabacum

Organic acid secretion from higher plant roots into the rhizosphere soil plays an important role in nutrient acquisition and metal detoxification; however, their precise functions and the related mechanisms in abiotic stress tolerance remain poorly understood. Tobacco is an important crop plant, so thoroughly elucidating these factors in tobacco is of high priority. In the present study, the activation effect on soil potassium (K), contents of exuded organic acids, and physiological changes in the roots of various tobacco varieties under both normal K supply and K-deficiency stress were investigated. Our results showed that one high-K variety (ND202) exhibited a significantly higher total content of organic acids in the root exudates and the highest available K content in the rhizosphere soil, compared with two common ones (K326 and NC89). Moreover, the high-K tobacco variety was less affected in terms of root vigor under K-deficiency stress, and displayed greater increases in the activities of the stress-resistant enzymes consisting of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Taken together, these results provide evidence that tobacco roots exude large amounts of organic acids to increase the available K content in the rhizosphere soil and improve the utilization rate of soil K.

Spore abundance and morphological root modifications of arbuscular mycorrhizal fungi-infected black pepper (&lt;em&gt;Piper nigrum&lt;/em&gt; L) plants in reddish brown latesolic soil of Matale in Sri Lanka

Arbuscular Mycorrhizae (AM) is a symbiotic association between fungi and roots of higher plants, which enhances plant growth and production. Black pepper (Piper nigrum L: Family Piperaceae), the second most valuable spice crop in Sri Lanka, is also identified as a host crop of mycorrhizae. However, existing indigenous AM species, their spore abundance and root colonization is not yet well studied or documented. Therefore, the present study was conducted to collect data on AM spore density and morphological features of modified roots due to infection of existing AM species in black pepper fields. Rhizosphere soils of randomly selected, 20 well-grown black pepper plants in RBL soils of Matale in Sri Lanka were evaluated for pH, moisture and major nutrients while AM spore abundance and AM colonization in stained roots were examined microscopically. The soil pH (4.7-5.9), total N (0.18-0.23 %), and organic C (1.57-1.75%) levels in study sites were preferable for biological activities while variability was observed in available P (4.4-29 ppm), exchangeable K (188-788 ppm) and volumetric moisture (9.8-24%). The AM spore (size &gt;50 μm) density in examined soils were high and ranged from 1600-9000 spores kg-1 soil. Both live (slight yellowish to dark brown in colour) and dead (black) spores were present and globular or spherical in shape without any special hyphal attachments. About 95% of examined roots were infected with AM with modifications such as arbuscules or vesicles or both. Networks of non-septate, extra-radical hyphae and branched intra-radical hyphae could be seen. Arbuscules observed were in different maturity and highly branched. Both inter or intracellular vesicles found were oval or ellipsoid in shape. Thus, most of the mature black pepper plants in RBL soils of Matale were found infected with indigenous vesicular arbuscular mycorrhizae (VAM) and morphological features of their spores, hyphae, arbuscules and vesicles were similar to fungi of order Glomerales, which consisted with Glomus spp.

Functional groups of soil fungi decline under grazing

Fungi play vital roles in organic matter decomposition, and mineralisation of phosphorus and nitrogen, are significant plant and animal pathogens, and major mutualistic symbionts with the roots of higher plants. Despite their importance, relatively little is known about the effects of livestock grazing on different functional groups of fungi. We used structural equation modelling to examine how grazing by domestic livestock and native herbivores, and aridity, plant cover and soil carbon influenced four functional groups of soil fungi (ectomycorrhizal fungi, arbuscular mycorrhizal fungi, dung saprobes, plant pathogens) from three microsites (tree, shrub, grass) at 54 woodland sites across 0.4 million km2 of dryland in eastern Australia. Structural equation modelling showed that aridity influenced fungi indirectly by affecting different herbivores and by changing plant cover, which had different effects on different fungal groups. Rabbit grazing had a direct negative effect on ectomycorrhizal and arbuscular mycorrhizal fungi, most likely by disrupting hyphal networks through soil disturbance. Increased cattle grazing was directly positively associated with fungal dung saprobe abundance, and indirectly, negatively associated with dung saprobes by suppressing the positive effects of soil carbon. Sheep had direct and indirect negative effects on the abundance of plant pathogens. Grazing was always an important predictor of the relative abundance of all fungal groups, either directly or indirectly. Thus, overgrazing is likely to have substantial effects on a range of important soil processes controlled by these microorganisms. Overall, our work indicates that increasing grazing, linked to on-going land use intensification to support a growing global population, will have major impacts on fungal functional groups.

Holocene vegetation signals in the Alashan Desert of northwest China revealed by lipid molecular proxies from calcareous root tubes

AbstractIn the hinterland of deserts, it is difficult to reconstruct paleovegetation using fossil pollen because of the low pollen concentration. Therefore, an efficient method is needed to reconstruct the paleovegetation of desert regions. In this study, 34 Holocene calcareous root tube (CRT) samples were collected from the Alashan Desert in northwest China, and lipid molecular proxies from CRTs were selected to address this deficiency. The results show that n-alkanes mainly maximized at C27, C29, and C16, and that the carbon preference index is close to 1. Thus, the sources of n-alkanes from CRTs were the roots of higher plants and microorganisms, and thus changes in n-alkanes from CRTs could reveal variations in vegetation cover. The n-alkane Cmax of long-chain n-alkanes (C&gt;25) in CRTs, maximizing at C27, indicated that vegetation in the Alashan Desert was characterized by shrub vegetation during the Holocene. Changes in the ratio of (C27+C29)/(C31+C33) indicated that the biomass of shrub vegetation increased during the period 7–2 cal ka BP. Moreover, the relative concentration of short-chain to long-chain n-alkanes decreased from 7 to 2 cal ka BP, suggesting that the effective moisture decreased during that period.

THE COMPARATIVE CHARACTERISTIC OF MYCOLOGICAL STRUCTURE OF TECHNOGENIC TERRITORIES OF SULFURIC QUARRIES IN LVIV REGION

The largest technogenic territories in Western Ukraine were formed during mining of native sulfur in the Carpathian sulfur pool. Posttechnogenic landscapes have appeared on site of mining complexes. Mining was accompanied by a number of negative environmental consequences: pollution hydrogen sulfide, sulfur dioxide, sulfur dust; withdrawal from economic use of thousands of hectares of land; discharging mineral waters into rivers; depletion of drinking water; activation of karst processes; landslides near settlements; flooding, accumulation of waste. Therefore, after the close of quarry the main task was to eliminate existing negative processes in this area and restore degraded lands, by technical and biological reclamation. This scheme of dumps reclamation system is the basis for phytomeliorative activities for landscaping areas and improves soil fertility. So, our study aims at conducting a comparative analysis of the impact of generated in different parts technogenic soils of mycological complexes on reproduction of devastated land within Podorozhne, Yavoriv and Novoyavoriv sulfur quarries. Our study has revealed that soil fungal complexes actively interact with roots of higher plants, bacteria, and help speed up the process of destruction of organic matter in the surface layers of technogenic soils, contributing to strengthening the stability of plant communities to the impact of various negative factors, which creates favourable conditions for the implementation of important plant phytomeliorative functions. Furthermore, the analysis of similarity in species composition of micobiota at Sorensa-Czekanowski rate shows that the greatest similarity of species of fungi is recorded between edafotop of Yavoriv sulfur quarry (II) and Novyj Rozdil sulfur quarry (III) – S = 1,92. The greatest difference in species composition between micobiota is found in edafotop in Podorozhne sulfur quarry (I) and Novyj Rozdil sulfur quarry – S = 1,11. In this case quite different microassociations are formed. Indices of species diversity of micromycetes confirm that the most diverse species composition of micobiota is characterised by edafotop of Novyj Rozdil sulfur quarry (III) – H = 3.12, and the most simplified species composition was edafotop of Podorozhne sulfur quarry (I) – N = 1.47. Shannon ratio is quite low in all variants except edafotop III, indicating that the recovery and enrichment of micromycetes composition of soils on experimental plots of Novyj Rozdil sulfur quarry. To summarise, the results of correlation analysis of micromycetes biota in every research facility during three growing season (2014-2016) showed that in areas within Novyj Rozdil and Yavoriv sulfur quarries had formed highly organized complex of soil micromycetes compared to Podorozhne sulfur quarry that differ by structural types due to the different stages of succession. It should be also noted that in Novyj Rozdil sulfur quarry territories formed highly organized complex of soil micromycetes. Group similarity dendrogram described in the case of Yavoriv sulfur quarry showed strong correlation between species, forming clusters of 3-5 species.

The influence of arbuscular mycorrhizal fungi inoculation on yam (Dioscorea spp.) tuber weights and secondary metabolite content.

Arbuscular mycorrhizal fungi (AMF) are widely distributed in nature. They live in the roots of higher plants, in a symbiotic relationship. In this study, five commercial species of yams (Dioscorea spp.) were inoculated with six species of AMF, Glomus clarum, G. etunicatum, G. fasciculatum, Gigaspora sp., G. mosseae, and Acaulospora sp., in field cultivation conditions to investigate the influence of AMF inoculation on tuber weights and secondary metabolite content in yam tubers. The results showed that mycorrhizae formation rates ranged from 63.33% to 90%. G. etunicatum inoculation treatment increased the tube weights of the five species of yam tubers by 39%, 35%, 20%, 56%, and 40% for Tainung 1, Tainung 2, Ercih, Zihyuxieshu, and Tainung 5, respectively. The content of secondary metabolites, such as polyphenols, flavonoids, and anthocyanin, was significantly increased by the AMF treatment in tuber flesh and peel of all the tested yam species. Specifically, the maximums exchange of secondary metabolite contents increased to 40%, 42%, and 106% for polyphenols, flavonoids, and anthocyanin, respectively, in the tuber fresh. This study revealed that different species of yam had varying degrees of affinity with various AMF species; selecting effective AMF species is necessary to facilitate yam growth and improve the quality and quantity of yam tubers.

Screening of sorghum genotypes and biochemical changes for resistance to damage caused by Macrophomina phaseolina

Charcoal rot, caused by Macrophomina phaseolina, is the most common yield reducing constraint in sorghum. In the present study, eight cultivars of Sorghum bicolor were screened against M. phaseolina to determine its effects on several growth parameters as well as the content of phenols, salicylic acid (SA), total protein and peroxidase activity and were examined for their relationship, with disease resistance. Out of the eight cultivars tested, PJ-1430 was the most resistant and SU-1080, the most susceptible. The roots of plants were more affected by the pathogen than the shoots. The cultivar PJ-1430 produced a higher plant root and shoot dry mass and was associated with higher polyphenols, SA, peroxidases and thus sustained less oxidative damage whereas SU-1080 experienced maximum oxidative damage, so was considered susceptible to charcoal rot. A positive relationship was observed among various biochemical parameters and disease resistance of cultivars PJ-1430 and SU-1080.

NPKS uptake, sensing, and signaling and miRNAs in plant nutrient stress.

Sessile nature of higher plants consequently makes it highly adaptable for nutrient absorption and acquisition from soil. Plants require 17 essential elements for their growth and development which include 14 minerals (macronutrients: N, P, K, Mg, Ca, S; micronutrients: Cl, Fe, B, Mn, Zn, Cu, Ni, Mo) and 3 non-mineral (C, H, O) elements. The roots of higher plants must acquire these macronutrients and micronutrients from rhizosphere and further allocate to other plant parts for completing their life cycle. Plants evolved an intricate series of signaling and sensing cascades to maintain nutrient homeostasis and to cope with nutrient stress/availability. The specific receptors for nutrients in root, root system architecture, and internal signaling pathways help to develop plasticity in response to the nutrient starvation. Nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) are essential for various metabolic processes, and their deficiency negatively effects the plant growth and yield. Genes coding for transporters and receptors for nutrients as well as some small non-coding RNAs have been implicated in nutrient uptake and signaling. This review summarizes the N, P, K, and S uptake, sensing and signaling events in nutrient stress condition especially in model plant Arabidopsis thaliana and involvement of microRNAs in nutrient deficiency. This article also provides a framework of uptake, sensing, signaling and to highlight the microRNA as an emerging major players in nutrient stress condition. Nutrient-plant-miRNA cross talk may help plant to cope up nutrient stress, and understanding their precise mechanism(s) will be necessary to develop high yielding smart crop with low nutrient input.

Functions of Nitric Oxide (NO) in Roots during Development and under Adverse Stress Conditions.

The free radical molecule, nitric oxide (NO), is present in the principal organs of plants, where it plays an important role in a wide range of physiological functions. Root growth and development are highly regulated by both internal and external factors such as nutrient availability, hormones, pattern formation, cell polarity and cell cycle control. The presence of NO in roots has opened up new areas of research on the role of NO, including root architecture, nutrient acquisition, microorganism interactions and the response mechanisms to adverse environmental conditions, among others. Additionally, the exogenous application of NO throughout the roots has the potential to counteract specific damages caused by certain stresses. This review aims to provide an up-to-date perspective on NO functions in the roots of higher plants.

Phosphoproteome and proteome analyses reveal low-phosphate mediated plasticity of root developmental and metabolic regulation in maize (Zea mays L.)

Phosphate (Pi) deficiency has become a significant challenge to worldwide agriculture due to the depletion of accessible rock phosphate that is the major source of cheap Pi fertilizers. Previous research has identified a number of diverse adaptive responses to Pi starvation in the roots of higher plants. In this study, we found that accelerated axile root elongation of Pi-deprived maize plants resulted from enhanced cell proliferation. Comparative phosphoproteome and proteome profiles of maize axile roots were conducted in four stages in response to Pi deficiency by multiplex staining of high-resolution two dimensional gel separated proteins. Pro-Q DPS stained gels revealed that 6% of phosphoprotein spots displayed changes in phosphorylation state following low-Pi treatment. These proteins were involved in a large number of metabolic and cellular pathways including carbon metabolism and signal transduction. Changes in protein abundance of a number of enzymes indicated that low-Pi induced a number of carbon flux modifications in metabolic processes including sucrose breakdown and other downstream sugar metabolic pathways. A few key metabolic enzymes, including sucrose synthase (EC 2.4.1.13) and malate dehydrogenase (EC 1.1.1.37), and several signaling components involved in protein kinase or phosphatase cascades, auxin signaling and 14-3-3 proteins displayed low-Pi responsive changes in phosphorylation state or protein abundance. A variety of key enzymes and signaling components identified as potential targets for phosphorylation provide novel clues for comprehensive understanding of Pi regulation in plants. Protein phosphorylation, coordinating with changes in protein abundance, is required for maize root metabolic regulation and developmental acclimation to Pi starvation.

The physiology of channel‐mediated K+ acquisition in roots of higher plants

K(+) channels are among the best-characterized classes of membrane protein in plants. Nevertheless, in-planta demonstrations of traits emerging from molecular characterizations have often been insufficient or lacking altogether. Such linkages are, however, critical to our basic understanding of plant nutrition and to addressing 'real-world' issues that are faced in environmental and agricultural settings. Here, we cover some of the recent advances in K(+) acquisition with particular focus on voltage-gated K(+) channel functioning and regulation in roots, and highlight where linkages to in-planta behavior have been successfully made and, conversely, where such linkages are yet to be made.

Biocontrol by plant growth promoting rhizobacteria against black scurf and stem canker disease of potato caused by Rhizoctonia solani

Non-pathogenic soil bacteria living in association with roots of higher plants enhance their adaptive potential and thus could be beneficial for their growth. Here, we present the current status of the use of Bacillus subtilis in biocontrol. Rhizobacteria are found in the rhizosphere. Plant growth promoting rhizobacteria (PGPR) strains, such as Bacillus and Pseudomonas, were isolated by using Nutreint dextrose Agar medium or Potato Dextrose Agar medium. The selection of PGPR strains was done by duel culture methods against the potato pathogens. The interaction of PGPR (Bacillus) with potato seeds or vegetative parts show promising antagonism by virtue of producing siderophore and antibiotics against black scurf and stem canker diseases of potato caused by Rhizoctonia solani, thereby resulting in increase of potato yield. The effectiveness of PGPR strain (Bacillus spp.) in improving the yield of potato in greenhouse conditions and in the field was observed.

丛枝菌根提高宿主植物抗旱性分子机制研究进展

Arbuscular mycorrhizal(AM) symbiosis,a ubiquitous symbiotic association established between AM fungi and roots of higher plants in most terrestrial ecosystems,is essentially important for plant adaptation to various environmental stresses,such as nutrient deficiency,environmental pollution and drought,etc.Many studies proved the positive influences of AM on plant drought tolerance and made efforts to uncover the underlying mechanisms: for plant individuals,AM fungi could stimulate plant physiological responses to drought stress;at the ecosystem level,AM fungi could interact with host plant to adapt to an adverse environment.However,systematic study is still necessary to reveal the fundamental role of AM fungi in improving plant drought tolerance. In this mini-review we summarized recent research progresses in the involvements of AM fungi in regulation of plant drought tolerance related genes,such as LEA encoding late embryogenesis-abundant proteins,P5CS encoding △1-pyrroline-5-carboxylate synthetase,MIPs encoding major intrinsic proteins,and NCED encoding 9-cis-epoxycarotenoid dioxygenase.As seen in reports,AM fungi could up-or down-regulate these genes under drought stresses,however,there were conflicting results as for the mycorrhizal effects on gene expressions in different experiments.In most cases,this could be attributed to incomparable experimental conditions,considering that 1) not all members in a gene family had been examined in each experiment;2) different symbiotic associations(plant-AM fungus combinations) might exert different strategies to resist drought stresses,and each fungal species/strain might exhibit different capacity to assist host plant against environmental adversities;3) gene expression varies in different plant tissues at different plant developmental stages.Obviously,it is still necessary to carry out further research for a better understanding of AM regulation of drought tolerance related genes in host plants,and model plants and AM fungal strains might be ideal choices to make sure of comparable results from different experiments. In addition to a full discussion on the insufficiency of previous studies,we also introduced the advances of proteomics in AM physiology and proposed perspectives for future research by the end of this review.

CELL-CELL INTERACTION IN THE EUKARYOTE-PROKARYOTE MODEL OF THE MICROALGAE CHLORELLA VULGARIS AND THE BACTERIUM AZOSPIRILLUM BRASILENSE IMMOBILIZED IN POLYMER BEADS(1).

Cell-cell interaction in the eukaryote-prokaryote model of the unicellular, freshwater microalga Chlorella vulgaris Beij. and the plant growth-promoting bacterium Azospirillum brasilense, when jointly immobilized in small polymer alginate beads, was evaluated by quantitative fluorescence in situ hybridization (FISH) combined with SEM. This step revealed significant changes, with an increase in the populations of both partners, cluster (mixed colonies) mode of colonization of the bead by the two microorganisms, increase in the size of microalgae-bacterial clusters, movement of the motile bacteria cells toward the immotile microalgae cells within solid matrix, and formation of firm structures among the bacteria, microalgae cells, and the inert matrix that creates a biofilm. This biofilm was sufficiently strong to keep the two species attached to each other, even after eliminating the alginate support. This study showed that the common structural phenotypic interaction of Azospirillum with roots of higher plants, via fibrils and sheath material, is also formed and maintained during the interaction of this bacterium with the surface of rootless single-cell microalgae.

A quick incorporation of 13N into the soluble high-molecular compound in rice (Oryza sativa L.) roots by application of 13N-labeled nitrate/nitrite

The nitrate/nitrite response, which occurs within minutes for the gene expression of the primary nitrogen metabolism in higher-plant roots, has almost been described, but the intermediate signaling molecule that exerts in signal transduction remains to be elucidated. It is hypothesized that the constitutively present signaling molecule may bind quickly to exogenously applied nitrate/nitrite to transduce the nitrate/nitrite signal. To examine the quick binding of nitrate/nitrite to high-molecular compounds, which may include intermediate signaling molecules, in the roots of the rice plant (Oryza sativa L.), the segmented roots of rice seedlings were exposed to nitrogen-13 (13N)-labeled nitrate/nitrite for either 2 or 5 min at 25°C. The supernatant of the Tris-buffer root extract was separated by a desalting pre-packed column. The incorporation of 13N into the high-molecular fraction was identified by 13N feeding for 2 min, and by 13N feeding for 5 min, however, the amount of 13N incorporation was not increased. Although the findings are preliminary, it was clearly demonstrated that 13N-labeled nitrate/nitrite was quickly incorporated into a limited amount of the soluble high-molecular compound(s). The formation of NO x -bound proteins, which may play a role in nitrate/nitrite signal transduction, is discussed.