Rhizobia are symbiotic diazotrophs (prokaryotic organisms that carry out dinitrogen fixation) that form a symbiotic association with legumes. This association is symbiotic in that both the plant and rhizobia benefit. The plant supplies the rhizobia with energy in the form of amino acids and the rhizobia fix nitrogen from the atmosphere for plant uptake. The reduction of atmospheric dinitrogen into ammonia is the second most important biological process on earth after photosynthesis (Sylvia, 2005). The actual process of dinitrogen fixation can only be carried out by diazotrophs that contain the enzyme dinitrogenase. Nitrogen is the most critical nutrient needed to support plant growth. Unfortunately, atmospheric dinitrogen (78% of air we breathe) is extremely stable due to triple bonds which can only be broken by energy intensive ways. These include electrical N2 fixation by lightning where oxides of N come to ground with rain, the Haber-Bosch process in industrial fertilizer production, and biological N2 fixation in legumes by bacterial symbionts such as Rhizobium etli. Biological fixation of nitrogen was the leading form of annual nitrogen input until the last decade of the 20th century (Russelle, 2008). It is gaining attention once again as sustainability becomes a central focus to feed a world population of over 7 billion people.
Introduction :
Mycorrhizae are mutualistic symbiotic associations formed between the roots of higher plants and fungi.
Fungal roots were discovered by the German botanist A B Frank in the last century (1855) in forest trees such as pine.
In nature approximately 90% of plants are infected with mycorrhizae. 83% Dicots,79% Monocots and 100% Gymnosperms.
Convert insoluble form of phosphorous in soil into soluble form.
Mycorrhiza Biofertilizer is also known as VAM (Myco = Fungal + rrhiza = roots) adheres to plants rhizoids leading to development of hyphae. Hyphae boost development and spreading of white root in to soil leading to significant increase in rhizosphere. These hyphae further penetrate and form arbuscules within the root cortical. VAM fungi form a special symbiotic relationship with roots of plant that can enhance growth and survivability of colonized plants. Mycorrhiza Biofertilizer is very useful in organic farming as well as normal commercial farming
Introduction :
Mycorrhizae are mutualistic symbiotic associations formed between the roots of higher plants and fungi.
Fungal roots were discovered by the German botanist A B Frank in the last century (1855) in forest trees such as pine.
In nature approximately 90% of plants are infected with mycorrhizae. 83% Dicots,79% Monocots and 100% Gymnosperms.
Convert insoluble form of phosphorous in soil into soluble form.
Mycorrhiza Biofertilizer is also known as VAM (Myco = Fungal + rrhiza = roots) adheres to plants rhizoids leading to development of hyphae. Hyphae boost development and spreading of white root in to soil leading to significant increase in rhizosphere. These hyphae further penetrate and form arbuscules within the root cortical. VAM fungi form a special symbiotic relationship with roots of plant that can enhance growth and survivability of colonized plants. Mycorrhiza Biofertilizer is very useful in organic farming as well as normal commercial farming
he rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome.
The phyllosphere is a term used in microbiology to refer to the total above-ground portions of plants as habitat for microorganisms.
Biofertilizers definition, classification, bacterial biofertilizers, mass production of bacterial biofertilizers, prospects and constraints of biofertilizers production in hilly regions of Indian states. Liquid biofertilizers and its uses and advatages
Soils give a mechanical support to plants from which they extract nutrients. soil provides shelters for many animal types, from invertebrates such as worms and insects up to mammals like rabbits, moles, foxes and badgers. It also provides habitats colonised by a staggering variety of microorganisms. This module is about the microbial life in soils.
Microbial interactions are ubiquitous, diverse, critically important in the function of any biological community.
The most common cooperative interactions seen in microbial systems are mutually beneficial. The interactions between the two populations are classified according to whether both populations and one of them benefit from the associations, or one or both populations are negatively affected.
A creative way to learn about the bacteria Rhizobium with a touch of Bollywood. For young, science minds. This was a part of my college curriculum as I am studying Microbiology Hons.
he rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome.
The phyllosphere is a term used in microbiology to refer to the total above-ground portions of plants as habitat for microorganisms.
Biofertilizers definition, classification, bacterial biofertilizers, mass production of bacterial biofertilizers, prospects and constraints of biofertilizers production in hilly regions of Indian states. Liquid biofertilizers and its uses and advatages
Soils give a mechanical support to plants from which they extract nutrients. soil provides shelters for many animal types, from invertebrates such as worms and insects up to mammals like rabbits, moles, foxes and badgers. It also provides habitats colonised by a staggering variety of microorganisms. This module is about the microbial life in soils.
Microbial interactions are ubiquitous, diverse, critically important in the function of any biological community.
The most common cooperative interactions seen in microbial systems are mutually beneficial. The interactions between the two populations are classified according to whether both populations and one of them benefit from the associations, or one or both populations are negatively affected.
A creative way to learn about the bacteria Rhizobium with a touch of Bollywood. For young, science minds. This was a part of my college curriculum as I am studying Microbiology Hons.
Nitrogen-fixing bacteria, microorganisms capable of transforming atmospheric nitrogen into fixed nitrogen (inorganic compounds usable by plants). More than 90 percent of all nitrogen fixation is effected by these organisms, which thus play an important role in the nitrogen cycle.
Two kinds of nitrogen-fixing bacteria are recognized. The first kind, the free-living (nonsymbiotic) bacteria, includes the cyanobacteria (or blue-green algae) Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium. The second kind comprises the mutualistic (symbiotic) bacteria; examples include Rhizobium, associated with leguminous plants (e.g., various members of the pea family); Frankia, associated with certain dicotyledonous species (actinorhizal plants); and certain Azospirillum species, associated with cereal grasses.
The symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate formation of root nodules, enlargements of plant cells and bacteria in intimate association. Within the nodules the bacteria convert free nitrogen to ammonia, which the host plant utilizes for its development. To ensure sufficient nodule formation and optimum growth of legumes (e.g., alfalfa, beans, clovers, peas, soybeans), seeds are usually inoculated with commercial cultures of appropriate Rhizobium species, especially in soils poor or lacking in the required bacterium.
Defensins: Antimicrobial peptide for the host plant resistancesnehaljikamade
Since the beginning of the 90s lots of cationic plant, cysteine-rich antimicrobial peptides (AMP) have been studied. However, Broekaert et al. (1995) only coined the term “plant defensin,” after comparison of a new class of plant antifungal peptides with known insect defensins. From there, many plant defensins have been reported and studies on this class of peptides encompass its activity toward microorganisms and molecular features of the mechanism of action against bacteria and fungi. Plant defensins also have been tested as biotechnological tools to improve crop production through fungi resistance generation in organisms genetically modified (OGM). Its low effective concentration towards fungi, ranging from 0.1 to 10 μM and its safety to mammals and birds makes them a better choice, in place of chemicals, to control fungi infection on crop fields. Herein, is a review of the history of plant defensins since their discovery at the beginning of 90s, following the advances on its structure conformation and mechanism of action towards microorganisms is reported. This review also points out some important topics, including: (i) the most studied plant defensins and their fungal targets; (ii) the molecular features of plant defensins and their relation with antifungal activity; (iii) the possibility of using plant defensin(s) genes to generate fungi resistant GM crops and biofungicides; and (iv) a brief discussion about the absence of products in the market containing plant antifungal defensins.
Plant phenolics are secondary metabolites that encompass several classes structurally diverse of natural products biogenetically arising from the shikimate-phenylpropanoids-flavonoids pathways. Plants need phenolic compounds for pigmentation, growth, reproduction, resistance to pathogens and for many other functions. Therefore, they represent adaptive characters that have been subjected to natural selection during evolution. Plants synthesize a greater array of secondary compounds than animals because they cannot rely on physical mobility to escape their predators and have therefore evolved a chemical defence against such predators. This article, after a short review of plant phenols and polyphenols as UV sunscreens, signal compounds, pigments, internal physiological regulators or chemical messengers, examines some findings in chemical ecology concerning the role of phenolics in the resistance mechanisms of plants against fungal pathogens and phytophagous insects.
RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression, typically by causing the destruction of specific mRNA molecules. Historically, it was known by other names, including co-suppression, post-transcriptional gene silencing (PTGS), and quelling. Only after these apparently unrelated processes were fully understood did it become clear that they all described the RNAi phenomenon. Andrew Fire and Craig C. Mello shared the 2006 Nobel Prize in Physiology or Medicine for their work on RNA interference in the nematode worm Caenorhabditis elegans, which they published in 1998. Since the discovery of RNAi and its regulatory potentials, it has become evident that RNAi has immense potential in suppression of desired genes. RNAi is now known as precise, efficient, stable and better than antisense technology for gene suppression. Two types of small ribonucleic acid (RNA) molecules – microRNA (miRNA) and small interfering RNA (siRNA) – are central to RNA interference. RNAs are the direct products of genes, and these small RNAs can bind to other specific messenger RNA (mRNA) molecules and either increase or decrease their activity, for example by preventing an mRNA from producing a protein. RNA interference has an important role in defending cells against parasitic nucleotide sequences – viruses and transposons. It also influences development.
The simplest virions consist of two basic components: nucleic acid (single- or double-stranded RNA or DNA) and a protein coat, the capsid, which functions as a shell to protect the viral genome from nucleases and which during infection attaches the virion to specific receptors exposed on the prospective host cell.
Soil organic matter has long been recognized as one of the most important components in maintaining soil fertility, soil quality, and agricultural sustainability. The soil zone strongly influenced by plant roots, the rhizosphere, plays an important role in regulating soil organic matter decomposition and nutrient cycling. Processes that are largely controlled or directly influenced by roots are often referred to as rhizosphere processes. These processes may include exudation of soluble compounds, water uptake, nutrient mobilization by roots and microorganisms, rhizosphere-mediated soil organic matter decomposition, and the subsequent release of CO2 through respiration. Rhizosphere processes are major gateways for nutrients and water. At the global scale, rhizosphere processes utilize approximately 50% of the energy fixed by photosynthesis in terrestrial ecosystems, contribute roughly 50% of the total CO2 emitted from terrestrial ecosystems, and mediate virtually all aspects of nutrient cycling. Therefore, plant roots and their rhizosphere interactions are at the center of many ecosystem processes. However, the linkage between rhizosphere processes and soil organic matter decomposition is not well understood. Because of the lack of appropriate methods, rates of soil organic matter decomposition are commonly assessed by incubating soil samples in the absence of vegetation and live roots with an implicit assumption that rhizosphere processes have little impact on the results. Our recent studies have overwhelmingly proved that this implicit assumption is often invalid, because the rate of soil organic matter decomposition can be accelerated by as much as 380% or inhibited by as much as 50% by the presence of live roots. The rhizosphere effect on soil organic matter decomposition is often large in magnitude and significant in mediating plant-soil interactions.
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into various chemical forms as it circulates among the atmosphere and terrestrial and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is nitrogen, making it the largest pool of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
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Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
2. Rhizobium is a genus of Gram negative soil bacteria that fix
nitrogen.Rhizobium forms an endosymbiotic nitrogen
fixing association with roots of legumes and Parasponia.
3. The bacteria colonize plant cells within root
nodules where they convert atmospheric nitrogen
into ammonia and then provide organic nitrogenous
compounds such as glutamine or ureides to the plant.
The plant in turn provides the bacteria with organic
compounds made by photosynthesis.
This mutually beneficial relationship is true of all of
the rhizobia, of which the Rhizobium genus is a typical
example.
4. Kingdom: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Order: Rhizobiales
Family: Rhizobiaceae
Genus:
Rhizobium
Frank 1889
Beijerinck in the Netherlands was the first to isolate and cultivate
a microorganism from the nodules of legumes in 1888. He named itBacillus
radicicola, which is now placed in Bergey's Manual of Determinative
Bacteriology under the genus Rhizobium.
6. Rhizobia are nitrogen-fixing bacteria that form root nodules on legume
plants.
Most of these bacterial species are in the Rhizobiacae family in the alpha-
proteobacteria and are in either the Rhizobium, Mesorhizobium, Ensifer,
or Bradyrhizobium genera.
However recent research has shown that there are many other rhizobial
species in addition to these.
In some cases these new species have arisen through lateral gene transfer
of symbiotic genes. The list below is not 'official' by any means, and it is
merely my compilation and interpretation of the literature.
An alternative list is maintained by the "ICSP Subcommittee on the
taxonomy of Rhizobium and Agrobacterium".
7. Class: Alphaproteobacteria
Order: Rhizobiales
Family: Rhizobiaceae
Rhizobium alamii Rhizobium freirei
Rhizobium alkalisoli Rhizobium galegae
Rhizobium azibense Rhizobium gallicum
Rhizobium calliandrae Rhizobium giardinii
Rhizobium cauense Rhizobium grahamii
Rhizobium cellulosilyticum Rhizobium hainanense
Rhizobium daejeonense Rhizobium halophytocola
Rhizobium endophyticum Rhizobium herbae
Rhizobium etli Rhizobium huautlense
Rhizobium fabae Rhizobium indigoferae
The genus Rhizobium (Frank 1889) was the first named (from
Latin meaning 'root living'), and for many years this was a
'catch all' genus for all rhizobia. Some species were later moved
in to new genera based on phylogenetic analyses. It currently
consists of 49 rhizobial species (and 11 non rhizobial species).
9. Class: Alphaproteobacteria
Order: Rhizobiales
Family: Phyllobacteriaceae
The genus Mesorhizobium was described by Jarvis et al.
in 1997. Several Rhizobium species were transferred to
this genus. It currently consists of 21 rhizobia species
(and 1 non-rhizobial species).
Mesorhizobium abyssinicae Mesorhizobium chacoense
Mesorhizobium albiziae Mesorhizobium ciceri
Mesorhizobium alhagi Mesorhizobium erdmanii
Mesorhizobium amorphae Mesorhizobium gobiense
Mesorhizobium australicum Mesorhizobium hawassense
Mesorhizobium camelthorni Mesorhizobium huakuii
Mesorhizobium caraganae Mesorhizobium jarvisii
11. class: Alphaproteobacteria
order: Rhizobiales
family: Rhizobiaceae
The Sinorhizobium genus was described by Chen et al. in 1988.
However some recent studies show that Sinorhizobium and the
genus Ensifer (Casida, 1982) belong to a single taxon. Ensiferis the
earlier heterotypic synonym (it was named first) and thus takes
priority (Young, 2003). This means that all Sinorhizobium spp. must
be renamed as Ensifer spp. according to the Bacteriological code.
There has been some discussion in the literature
if Ensifer or Sinorhizobium is correct Young (2010), this website
follows the opinion of the Judicial Commission, and will use Ensifer.
The genus currently consists of 17 species.
13. class: Alphaproteobacteria
order: Rhizobiales
family: Bradyrhizobiaceae
The Bradyrhizobium genus was described by Jordan
in 1982. It currently consists of 9 rhizobia species
(and 1 non rhizobial species).
Bradyrhizobium canariense Bradyrhizobium japonicum
Bradyrhizobium cytisi Bradyrhizobium jicamae
Bradyrhizobium denitrificans Bradyrhizobium liaoningense
Bradyrhizobium elkanii Bradyrhizobium pachyrhizi
Bradyrhizobium iriomotense Bradyrhizobium yuanmingense
14. class: Betaproteobacteria
order: Burkholderiales
family: Burkholderiaceae
The Burkholderia genus currently contains
seven named rhizobial members and others
as Burkholderia sp.
Burkholderia caribensis
Burkholderia cepacia
Burkholderia mimosarum
Burkholderia nodosa
Burkholderia phymatum
Burkholderia sabiae
Burkholderia tuberum
15. class: Alphaproteobacteria
order: Rhizobiales
family: Phyllobacteriaceae
The Phyllobacterium genus currently contains
three rhizobial species.
Phyllobacterium trifolii
Phyllobacterium ifriqiyense
Phyllobacterium leguminum
16. class: Alphaproteobacteria
order: Rhizobiales
family: Methylobacteriaceae
The Azorhizobium genus was described by Dreyfus et al.
in 1988. It currently consists of 2 species.
Azorhizobium caulinodans
Azorhizobium doebereinerae
20. Root nodules occur on the roots of plants (primarily Fabaceae) that
associate with symbiotic nitrogen-fixing bacteria.
Undernitrogen-limiting conditions, capable plants form a symbiotic
relationship with a host-specific strain of bacteria known as rhizobia.
This process has evolved multiple times within the Fabaceae, as well
as in other species found within the Rosidclade.
The Fabaceae include legume crops such as beans and peas.
Within legume nodules, nitrogen gas from the atmosphere is
converted into ammonia, which is then assimilated into amino
acids (the building blocks of proteins), nucleotides (the building
blocks of DNA and RNA as well as the important energy
molecule ATP), and other cellular constituents such
as vitamins, flavones, and hormones.
21. Cross section though a soybean (Glycine max'Essex') root nodule. The
bacterium, Bradyrhizobium japonicum, colonizes the roots and
establishes a nitrogen fixing symbiosis. This high magnification image
shows part of a cell with single bacteroids within their symbiosomes. In
this image, endoplasmic reticulum, dictysome and cell wall can be seen.
22. Their ability to fix gaseous nitrogen makes legumes an ideal
agricultural organism as their requirement for nitrogen
fertilizer is reduced.
Indeed high nitrogen content blocks nodule development as
there is no benefit for the plant of forming the symbiosis. The
energy for splitting the nitrogen gas in the nodule comes from
sugar that is translocated from the leaf (a product
of photosynthesis).
Malate as a breakdown product of sucrose is the direct carbon
source for the bacteroid. Nitrogen fixation in the nodule is very
oxygen sensitive.
Legume nodules harbor an iron containing protein
called leghaemoglobin, closely related to animal myoglobin, to
facilitate the conversion of nitrogen gas to ammonia.
23. Legume family
Plants that contribute to nitrogen fixation include the legume family – Fabaceae –
with taxa such as kudzu, clovers, soybeans, alfalfa, lupines, peanuts, and rooibos.
They containsymbiotic bacteria called rhizobia within the nodules, producing
nitrogen compounds that help the plant to grow and compete with other plants.
When the plant dies, the fixed nitrogen is released, making it available to other
plants and this helps to fertilize the soil.
The great majority of legumes have this association, but a few genera
(e.g.,Styphnolobium) do not.
In many traditional and organic farming practices, fields are rotated through
various types of crops, which usually includes one consisting mainly or entirely of
clover or buckwheat (non-legume family Polygonaceae), which are often referred
to as "green manure".
Inga alley farming relies on the leguminous genus Inga, a small tropical, tough-
leaved, nitrogen-fixing tree.[4]
24. Non-leguminous
Although by far the majority of plants able to form
nitrogen-fixing root nodules are in the legume
family Fabaceae, there are a few exceptions:
•Parasponia, a tropical genus in the Cannabaceae also
able to interact with rhizobia and form nitrogen-fixing
nodules
•Actinorhizal plants such as alder and bayberry can also
form nitrogen-fixing nodules, thanks to a symbiotic
association with Frankiabacteria. These plants belong to
25 genera[6] distributed among 8 plant families.
The ability to fix nitrogen is far from universally present
in these families. For instance, of 122 genera in
the Rosaceae, only 4 genera are capable of fixing
nitrogen. All these families belong to
the orders Cucurbitales, Fagales, and Rosales, which
together with the Fabalesform a clade of eurosids.
A sectioned alder tree
root nodule.
25. Two main types of nodule have been described: determinate and
indeterminate.
Determinate nodules are found on certain tribes of tropical legume such as
those of the genera Glycine (soybean), Phaseolus (common bean),
and Vigna. and on some temperate legumes such as Lotus.
These determinate nodules lose meristematic activity shortly after initiation,
thus growth is due to cell expansion resulting in mature nodules which are
spherical in shape.
Another types of determinate nodule is found in a wide range of herbs,
shrubs and trees, such as Arachis (peanut).
These are always associated with the axils of lateral or adventitious roots and
are formed following infection via cracks where these roots emerge and not
using root hairs. Their internal structure is quite different from those of the
soybean type of nodule.
26. Indeterminate nodules are found in the majority of legumes from
all three sub-families, whether in temperate regions or in the
tropics.
They can be seen in papilioinoid legumes such
as Pisum (pea), Medicago (alfalfa), Trifolium (clover),
and Vicia (vetch) and all mimosoid legumes such as acacias
(mimosas), the few nodulated caesalpinioid legumes such as
partridge pea they earned the name "indeterminate" because
they maintain an active apical meristem that produces new cells
for growth over the life of the nodule.
This results in the nodule having a generally cylindrical shape,
which may be extensively branched.
Because they are actively growing, indeterminate nodules
manifest zones which demarcate different stages of
development/symbiosis.
29. Zone I—the active meristem. This is where new nodule tissue is formed
which will later differentiate into the other zones of the nodule.
Zone II—the infection zone. This zone is permeated with infection
threads full of bacteria. The plant cells are larger than in the
previous zone and cell division is halted.
Interzone II–III—Here the bacteria have entered the plant cells, which
contain amyloplasts. They elongate and begin terminally
differentiating into symbiotic, nitrogen-fixing bacteroids.
Zone III—the nitrogen fixation zone. Each cell in this zone contains a
large, central vacuole and the cytoplasm is filled with fully
differentiated bacteroids which are actively fixing nitrogen. The
plant provides these cells with leghemoglobin, resulting in a distinct
pink color.
30. Zone IV—the senescent zone. Here plant cells and their
bacteroid contents are being degraded.
The breakdown of the heme component of leghemoglobin
results in a visible greening at the base of the nodule.
This is the most widely studied type of nodule, but the details
are quite different in nodules of peanut and relatives and some
other important crops such as lupins where the nodule is
formed following direct infection of rhizobia through the
epidermis and where infection threads are never formed.
Nodules grow around the root, forming a collar-like structure.
In these nodules and in the peanut type the central infected
tissue is uniform, lacking the uninfected ells seen in nodules of
soybean and many indeterminate types such as peas and
clovers.
31. Legumes release compounds called flavonoids from their roots, which
trigger the production of nod factors by the bacteria.
When the nod factor is sensed by the root, a number of biochemical
and morphological changes happen: cell division is triggered in the root
to create the nodule, and the root hair growth is redirected to wind
around the bacteria multiple times until it fully encapsulates 1 or more
bacteria.
The bacteria encapsulated divide multiple times, forming a
microcolony. From this microcolony, the bacteria enter the developing
nodule through a structure called an infection thread, which grows
through the root hair into the basal part of the epidermis cell, and
onwards into the root cortex; they are then surrounded by a plant-
derived membrane and differentiate into bacteroids that fix nitrogen.
32.
33. Nodulation is controlled by a variety of processes, both external (heat, acidic
soils, drought, nitrate) and internal (autoregulation of nodulation, ethylene).
Autoregulation of nodulation controls nodule numbers per plant through a
systemic process involving the leaf. Leaf tissue senses the early nodulation
events in the root through an unknown chemical signal, then restricts further
nodule development in newly developing root tissue.
The Leucine rich repeat (LRR) receptor kinases (NARK in soybean (Glycine
max); HAR1 in Lotus japonicus, SUNN in Medicago truncatula) are essential
for autoregulation of nodulation (AON). Mutation leading to loss of function
in these AON receptor kinases leads to supernodulation or hypernodulation.
Often root growth abnormalities accompany the loss of AON receptor kinase
activity, suggesting that nodule growth and root development are
functionally linked. Investigations into the mechanisms of nodule formation
showed that theENOD40 gene, coding for a 12–13 amino acid protein [41], is
up-regulated during nodule formation [3].
