Endophytes are abundant in plants and studies are continuously emanating on their ability to protect plants from pathogens that cause diseases especially in the field of agriculture. The advantage that endophytes have over other biocontrol agents is the ability to colonize plant's internal tissues. Despite this attributes, a deep understanding of the mechanism employed by endophytes in protecting the plant from diseases is still required for both effectiveness and commercialization. Also, there are increasing cases of antibiotics resistance among most causative agents of diseases in human beings, which calls for an alternative drug discovery using natural sources. Endophytes present themselves as a storehouse of many bioactive metabolites such as phenolic acids, alkaloids, quinones, steroids, saponins, tannins, and terpenoids which makes them a promising candidate for anticancer, antimalarial, antituberculosis, antiviral, antidiabetic, anti-inflammatory, antiarthritis, and immunosuppressive properties among many others, even though the primary function of bioactive compounds from endophytes is to make the host plants resistant to both abiotic and biotic stresses. Endophytes still present themselves as a peculiar source of possible drugs. This study elucidates the mechanisms employed by endophytes in protecting the plant from diseases and different bioactivities of importance to humans with a focus on endophytic bacteria and fungi.
In this review, we briefly describe the biological application of PGPR for purposes of phytoremediating heavy metals. We address the agronomic practices that can be used to maximize the remediation potential of plants. Plant roots have limited ability ability mental from soil, mainly because metals have low solubility in the soil solution. The phytoavailability of metal is closely tired to the soil properties and the metabolites that are released by PGPR (e.g., siderophores, organ acids, and plant growth regulators). The role played by PGPR may be accomplished by their direct effect on plant growth dynamics, or indirectly by acidification, chelation, precipitation, or immobilization of heavy metals in the rhizosphere. From performing this review we have formed the following conclusions: The most critical factor is determining how efficient phytoremediation of metal-contaminated soil will be is the rate of uptake of the metal by plants. In turn, this depends on the rate of bioavailability. We know from our review that beneficial bacteria exist tha can alter metal bioavailability of plants. Using these beneficial bacteria improves the performance of phytoremediation of the metal-contaminated sites. Contaminated sites are often nutrient poor. Such soil can be nutrient enriched by applying metal-tolerant microbes that provide key needed plant nutrients. Applying metal-tolerant microbes therefore may be vital in enhancing the detoxification of heavy-metal-contaminated soils (Glick 2003). Plant stress generated by metal-contaminated soils can be countered by enhancing plant defense responses. Responses can be enhanced by alleviating the stress-mediated impact on plants by enzymatic hydrolysis of ACC, which is intermediate in the biosynthetic pathway of ethylene. These plant-microbe partnerships can act as decontaminators by improving phytoremediation. Soil microorganisms play a central role in maintaining soil structure, fertility and in remediating contaminated soils. Although not yet widely applied, utilizing a plant-microbe partnership is now being recognized as an important tool to enhance successful phytoremediaton of metal-contaminated sites. Hence, soil microbes are essential to soil health and sustainability. The key to their usefulness is their close association with, and positive influence on, plant growth and function. To capitalize on the early success of this technique and to improve it, additional research is needed on successful colonization and survival of inoculums under field conditions, because there are vital for the success of this approach. In addition, the effects of the interaction of PGPR and plant root-mediated process on the metal mobilization in soil are required, to better elucidate the mechanism that underlines bacterial-assisted phytoremediation is important. Finally, applying PGPR-associated phytoremediation under field conditions is important, because, to date, only locally contaminated sites have been treated with this technique, by using microbes cultured in the laboratory.
Pathogen affects plant growth, host health and productivity. Endophytes, presumed to live inside the plant tissues, might be helpful in sustaining the future of agriculture. Although recent studies have proven that endophytes can be pathogenic, commensal, non-pathogenic, and/or beneficial, this review will focus on the beneficial category only. Beneficial endophytes produce a number of compounds which are useful for protecting plants from environmental conditions, enhancing plant growth and sustainability, while living conveniently inside the hosts. The population of endophytes is majorly controlled by location, and climatic conditions where the host plant grows. Often the most frequently isolated endophytes from the tissues of the plant are fungi, but sometimes greater numbers of bacteria are isolated. Beneficial endophytes stand a chance to replace the synthetic chemicals currently being used for plant growth promotion if carefully explored by researchers and embraced by policymakers. However, the roles of endophytes in plant growth improvement and their behavior in the host plant have not been fully understood. This review presents the current development of research into beneficial endophytes and their effect in improving plant growth.
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