Abstract
Endophytes are symptomless fungal and bacterial microorganisms found in almost all living plants. They are vital components of plant microbiomes. Endophytes affect plant growth and plant responses to pathogens, herbivores, and environmental change by producing a range of natural products having antifungal, antibacterial, and insecticidal properties. Endophytes have shown particular promise in agriculture particularly as beneficial crop inoculants and are known to enhance abiotic and biotic plant stress tolerance by increasing tolerance to drought and water stress, as well as tolerance to high temperature and high salinity. A better understanding of their plant growth-promoting mechanisms could simplify higher production of energy crops in a more sustainable manner even on marginal land and feed stocks for industrial processes, thus contribute to avoiding conflicts between food and energy production Many endophytes can be exploited to improve the efficiency of phytoremediation as they are found to be resistant to heavy metals and capable of detoxifying organic contaminants.
TopIntroduction
The term endophyte was originally defined by De Bary in 1866 as “Any organism occurring within plant tissues”. The word endophyte means in the plant (derived from the Greek-endon = within, phyton=plant) this term can be used for a wide spectrum of potential hosts inhabitants, e.g. bacteria, fungi, etc. (Stone et al., 2000).By definition, an endophytic fungus lives in mycelial form in biological association with living plant at least for some time. Endophytes are very diverse group which include endophytic bacteria and endophytic fungi (Raghukumar, 2008).There are approximately 300,000 plant species on earth and each plant is the host to one or more endophytes, and many of them may colonize certain hosts (Petrini, 1991). Endophytes are ubiquitous in nature as they have been recovered from plants adjusted to a wide range of ecosystems that include hot deserts, temperate, arctic tundra, tropical forests, grasslands and croplands (Arnold, 2007, 2008; Arnold & Lutzoni, 2007). They are present in all the major lineages of land plants (conifers and flowering plants, mosses and other non-vascular plants, ferns and other seedless plants) (Arnold, 2007). It has been estimated that there are at least 1 million endophytic fungal species which signifies the importance of fungal endophytes as vital constituents of fungal biodiversity (Ganley et al., 2004). These microorganisms reside in the intercellular spaces of plants with no antagonistic manifestation and exhibit a relationships with specific plants and produces bioactive substances (plant growth regulatory, antibacterial, antiviral, antifungal, insecticidal, etc.) enhance the growth and competitiveness of the host in nature (Shentu et al., 2014;Hardoim et al., 2015; Card et al., 2016). Some endophytes could be reliable sources of materials of the agricultural and pharmaceutical potential (Nisa et al., 2015). Endophytic microbes initiate the biological degradation of dead or dying host-plant which is necessary for nutrient recycling (Hungria et al., 2010). These microbes inhibit the plant without causing any harm and can ascertain a mutualistic association (Azovedo et al., 2000).
Key Terms in this Chapter
Phytoremediation: Also known as phytodegradation, it has been derived from ancient Greek f?t? ( phyto ), meaning “plant,” and Latin remedium , meaning “restoring balance,” refers to the process that use green plants and their microorganisms to either remove, breakdown, contain, or reduce toxic environmental contaminants.
Heavy Metals: Heavy metals are natural metallic components that have a high atomic weight and a density 5 times greater than water. They are generally toxic to organisms even as low level (e.g., lead, mercury, cadmium, etc.).
Bioremediation: Bioremediation is the process of using living organisms to remove, detoxify, breakdown or reduce the environmental contaminants from soil, water, and air.
Nitrogen Fixation: It is biological process by which atmospheric nitrogen (N 2 ) is converted into nitrogen components (ammonia and nitrates) which are plant nutrients. This process is carried out by specific bacteria in the root nodules of legumes such as beans.
Abiotic Stress: Abiotic stress may be defined as the antagonistic impact of non-living components on the biotic components in a definite environment (e.g., drought, flooding, high and low temperature).
Endophytes: Endophytes may be defined as microorganisms that reside or colonize the internal tissues of plants without causing any harmful effects.