Breif study on endophytes-bacteria and fungi:their role in plant growth promotion and secondary metabolite production

1. ENDOPHYTES

2. ❏ Endophytes are endosymbionts, often a bacterium or fungus that lives
within a plant. For these organisms, all or part of their life cycle occurs within
their hosts, without causing any apparent symptoms of disease. They are
ubiquitous in nature.
❏ It was originally defined by De Bary in 1866 as “ Any organism occurring
within plant tissues.

3. The relationship between plants and endophyte can be mutualistic or
commensal
❏ A mutualistic relationship means that both the endophyte and the plant
host benefit from the presence of the endophyte
❏ A commensal relationship means the endophyte benefits, while the plant host
is unharmed

4. Endophytic fungi in plants
● Fungi that live inside a host plant are called endophytic fungi. The
presence of endophytic fungi in plants depends on several factors
including the host, the environment, the availability of nutrients, and the
presence of other microorganisms.
● Fungal endophytes primarily found in abundance are ascomycetes
whereas basidiomycetes and dueteromyctesare rarely found.

5. Endophytic Bacteria
● It is mainly defined as those bacteria that can be isolated from surface
disinfected plant tissue or extractedfrom within the plant and that do not
visibly harm the plant
● More than 200 genera from 16 phyla of bacterial species have been
reported to be associated with endophytes and among them, most of the
species belong to the phyla Actinobacteria, Proteobacteria,and
Firmicutes
● The diversity of endophytic bacteria ranges from gram-positive to gram-
negative bacteria

6. Role of endophytes in plant growth promotion
1. Direct growth promotion
a) Biological nitrogen fixation
* It is the second important biological process after
photosynthesis. It is restricted to prokaryotic organisms.
* Endophytic bacteria which form intimate association with plants
are capable of fixing nitrogen in various crops forming nodule
like structures.
* So the interior of plants are rich in carbon while low in oxygen,
which gives favourable condition for N fixation.
* Endophytic fungi and bacteria protect it from competition with
other microbes and are supplied with nutrients from the host.

7. b) Phosphate solubilisation
* Phosphorous is one of the main macronutrients required for
plant growth and needed in higher amount. So several
endophytic bacteria and fungi have the capacity to solubilize
insoluble inorganic phosphorous compounds and make them
available for plant’s uptake.

8. c) Siderophores synthesis
* It is having low molecular weight iron binding compound that
are produced by soil microorganisms
* The siderophore are synthesized by microbes which chelate Fe3+
and transport it back to their cell where it becomes available for
microbial growth
* The endophytic bacteria which promotes the growth can act as
a biofertilizer or biocontrol

9. d) Phytohormone (IAA) production
* Diverse fungi or bacteria species possess the ability to produce
several types of plant growth regulators or phytohormones such
as auxins, cytokinins, gibberellins etc.
* Production of Indole acetic acid is common among many genera
of bacteria and fungi
* Indole acetic acid enhances cell division and differentiation
which eventually increases the root length and root hair, so this
helps in absporbing more nutrients which stimulate plant
growth.

10. 2. Indirect growth promotion
Biological control of plant pathogens
* Biological control agents (BCA): they mainly control or reduce the
incidence and severity of the plant diseases.
* Pseudomonas and Bacilli species are the predominant bacterial
biological control agents whereas Trichoderma species is the most
important fungal biological control agent

11. Secondary metabolites
● It plays a vital role in the functioning of plants as the defence compound
or as the signalling molecule during ecological interactions and environmental
stresses.
● It acts as – antimicrobial, anticancerous, phytohormone and its precursor,
vitamin (B12), bioprotectants
Some examples of secondary metabolites are:
Alkaloids, steroids, terpenoids and phenols
Therapeutic application: antimicrobial and anticancerous

12. Alkaloids
* Nitrogen containing compounds having low molecular weight
* Used in the pharmaceutical industry due to their biological activity
* They are derived from amino acids through decarboxylation – (eg.
tryptophan)
* Exhibit high antiviral and antifungal properties
* Bacillus thuringiensis, Bacillus cereus are isolated from Pinellia ternata

13. Terpenoids
* They are biosynthetically derived from isoprene units
* Approximately 50,000 terpenoids are there, like monoterpenes,
serquiterpenes etc. Out of this, about 400 types are derived from plants,
fungi and bacteria

14. Phenols
* It has an important role in biological activities including as antioxidants,
anticarcinogens and antimicrobials
* Dietary polyphenols present in the gut (intestine) helps in the inhibition
of pathogenic bacteria (lactobacilli and bifidobacteria)

15. ⮚ Pestaloptiosis neglecta, an endophytic fungus of Cupressus torulosa is
considered to be a promising source of phenols, flavonoids, terpenoids,
alkaloids, tannins, carbohydrates, and saponin.

16. Gilmaniella Sp. an endophytic fungus, stimulate Atractylodes lancea to
produce volatile oils such as -caryophyllene, zingibereae, -
caryophyllene oxide, etc.
● Among this, the antioxidants are bioactive compounds that help in
preventing diseases and also help to maintain good health.
● ⮚Capsaicin is a bioactive compound found in red chilli peppers. It is often
used as a pain relief medication and has anticancerous properties.

17. Alternaria alternata: An endophytic fungus isolatedfrom, Capsicum
annum which produces capsaicin.
Phytohormone and defence enzymes
Phytohormones are signalmolecules that coordinate cellularactivities and
control plant growth and development. It regulates the responses of various
stresses
● IAA- Indole Acetic Acid (naturallyoccurring phytohormone)
- Bacillus thuringiensis, Bacilluscereus(endophytes)

18. - The endophyticbacteria can cause a significant reduction in up or down
regulation of the stress inducible genes
Abscisic acid (ABA) and Gibberellins
- Azospirillum lipoferum
- Abscisic acid is a plant stress hormone, responsible for many kinds of
stress including water stress, salt stressetc.
Salicylic acid
- It is a criticalhormone involved in various process, such as seed
germination, root initiation, stomatalclosure etc. besides the plants
power to tolerate to biotic and abiotic stress