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A. Ghasemnezhad et al.
6.1 Introduction
To understand why endophytes have received great attention in the field of antimicrobial research, there is a need to examine their intended role in nature. Microbial
groups residing in plant tissue have been identified as symbiotic or pathogenic (Larran
et al. 2016; Martinez-Klimova et al. 2017). According to Wilson (1995), endophyte
(Gr. Endon, within; Phyton, plant) is an organism that lives within the plant.
Usually, the organisms found inside the plant are fungi and bacteria. Endophytic
host plants show no signs of disease symptoms at least during the endophytic phase of
their life cycle (Wilson 1995). Endophytic fungi are found in all plant families worldwide and almost in all climatic conditions (Larran et al. 2016; Martinez-Klimova
et al. 2017; Santoyo et al. 2016). Microbes enter plant tissues through wounds or
roots or the creation of wounds by secreting enzymes such as pectolytic and cellulolytic enzymes. It is unclear, why plants and endophytes co-exist or why plants do
not defend themselves against internal colonization (Martinez-Klimova et al. 2017;
Wilson 1995) yet to be understood. So far, the relationship between plant co-existence
and endophyte seems to be beneficial to both parties and has dual advantages. It is
beneficial for endophyte due to plant nutrients and habitat while for the plant because
of the protection against pathogens, increased nutrient uptake, plant growth promotion (Martinez-Klimova et al. 2017; Santoyo et al. 2016) and stress resistance (Larran
et al. 2016) Bacterial endophytes facilitate the acquisition of essential mineral nutrients through the environment such as nitrogen, phosphorus, and iron (Zhang et al.
2006; Gangwar et al. 2014) and also produce vitamins or modulate phytohormone
levels in the plant because of their nature of producing auxin, cytokinin, gibberellins,
etc. (Santoyo et al. 2016).
Endophytes increase the root volume of the plant (Zhang et al. 2006), and increased
plant growth thus, may eliminate the cellular apoptosis caused by the pathogen
infection (Alvin et al. 2014). However, according to Hyde and Suetong (2008), more
research is yet to be done to confirm the beneficial properties of endophytes toward
plants. Endophytic plants are believed to be healthier than non-endophytic plants
(Zhang et al. 2006), because endophytes produce metabolites that promote plant
growth and protect the plant, act against insects, pests, and plant diseases (Golinska
et al. 2015; Abdalla and Matasyoh 2014). Since, the natural products of endophytes
act as antimicrobial, antifungal, anticancer, and antioxidant agents as reported by
Zhang et al. (2006), hence, secondary metabolites produced by endophytes might be
useful in the pharmaceutical industries (Golinska et al. 2015) (Table 6.1; Fig. 6.1).
Endophytes are capable of biosynthesis of some chemical compounds like their
host plant, possibly as an adaptor to the host micro-environment (Zhang et al. 2006).
The most common example is taxol, but several other anticancer compounds such
as comptotcin and podophylotoxine have also been reported (Alvin et al. 2014).
Endophytes secrete antibiotics and hydrolytic enzymes to prevent the colonization
of plant pathogenic microbes or to prevent insects and nematodes penetration and
produce metabolites capable of activating the plant defense mechanism or enhancing
plant growth (Fig. 6.2).
A. Ghasemnezhad et al.
6.1 Introduction
To understand why endophytes have received great attention in the field of antimicrobial research, there is a need to examine their intended role in nature. Microbial
groups residing in plant tissue have been identified as symbiotic or pathogenic (Larran
et al. 2016; Martinez-Klimova et al. 2017). According to Wilson (1995), endophyte
(Gr. Endon, within; Phyton, plant) is an organism that lives within the plant.
Usually, the organisms found inside the plant are fungi and bacteria. Endophytic
host plants show no signs of disease symptoms at least during the endophytic phase of
their life cycle (Wilson 1995). Endophytic fungi are found in all plant families worldwide and almost in all climatic conditions (Larran et al. 2016; Martinez-Klimova
et al. 2017; Santoyo et al. 2016). Microbes enter plant tissues through wounds or
roots or the creation of wounds by secreting enzymes such as pectolytic and cellulolytic enzymes. It is unclear, why plants and endophytes co-exist or why plants do
not defend themselves against internal colonization (Martinez-Klimova et al. 2017;
Wilson 1995) yet to be understood. So far, the relationship between plant co-existence
and endophyte seems to be beneficial to both parties and has dual advantages. It is
beneficial for endophyte due to plant nutrients and habitat while for the plant because
of the protection against pathogens, increased nutrient uptake, plant growth promotion (Martinez-Klimova et al. 2017; Santoyo et al. 2016) and stress resistance (Larran
et al. 2016) Bacterial endophytes facilitate the acquisition of essential mineral nutrients through the environment such as nitrogen, phosphorus, and iron (Zhang et al.
2006; Gangwar et al. 2014) and also produce vitamins or modulate phytohormone
levels in the plant because of their nature of producing auxin, cytokinin, gibberellins,
etc. (Santoyo et al. 2016).
Endophytes increase the root volume of the plant (Zhang et al. 2006), and increased
plant growth thus, may eliminate the cellular apoptosis caused by the pathogen
infection (Alvin et al. 2014). However, according to Hyde and Suetong (2008), more
research is yet to be done to confirm the beneficial properties of endophytes toward
plants. Endophytic plants are believed to be healthier than non-endophytic plants
(Zhang et al. 2006), because endophytes produce metabolites that promote plant
growth and protect the plant, act against insects, pests, and plant diseases (Golinska
et al. 2015; Abdalla and Matasyoh 2014). Since, the natural products of endophytes
act as antimicrobial, antifungal, anticancer, and antioxidant agents as reported by
Zhang et al. (2006), hence, secondary metabolites produced by endophytes might be
useful in the pharmaceutical industries (Golinska et al. 2015) (Table 6.1; Fig. 6.1).
Endophytes are capable of biosynthesis of some chemical compounds like their
host plant, possibly as an adaptor to the host micro-environment (Zhang et al. 2006).
The most common example is taxol, but several other anticancer compounds such
as comptotcin and podophylotoxine have also been reported (Alvin et al. 2014).
Endophytes secrete antibiotics and hydrolytic enzymes to prevent the colonization
of plant pathogenic microbes or to prevent insects and nematodes penetration and
produce metabolites capable of activating the plant defense mechanism or enhancing
plant growth (Fig. 6.2).