254
C. García-Latorre et al.
gene encoding nitrate reductase, activating also the uptake of trace elements (Mo, B,
Fe, Zn, and Mn) in the rhizosphere (Su et al. 2016, 2019).
The higher nutrient uptake in endophyte-infected plants occurred due to the endophytic borne secretion of substances that facilitate the mineral uptake by plant roots.
In this scenario, Curvularia geniculata (Tracy and Earle) Boedijn has been found to
secrete enzymes exhibiting P solubilization in sufficient amounts so as to enhance
plant growth and development (Priyadharsini and Muthukumar 2017). On the other
hand, the release of root exudates containing some phenolic compounds secreted by
Epichloë endophytes, were found to increase the P solubility in soil, increasing the
P uptake and the subsequent P concentration in the plants (Malinowski et al. 1998).
Similar studies have also reported an increased capability to bind Cu in the rhizosphere of endophyte-infected plants (Malinowski et al. 2004). Increment of P and
other mineral solubilization occurred due to the secretion of substances by root endophytes which acidifies the soil, thus P becomes more available in the soil solution by
its conversion from insoluble phosphates or other insoluble fertilizers (Aciego and
Brookes 2009; Narsian and Patel 2000).
Special mention deserves (DSE) which have been found to make mineral nutrients
available by facilitating access to complex C, N, and P present in the soil for their
host plant (Mandyam 2008). Such an effect could be explained by the production of
hydrolytic enzymes by the endophyte, which could induce the release of nutrients to
be uptaked by plants. Long back, Jumpponen and Trappe (1998) reported the uptake
of organic compounds (amino acids, small peptides, etc.) by DSE fungi, which might
be transferred directly to host plants, resulting in more efficient use of organic nutrient
resources (Reeve et al. 2008). As stated earlier, DSE and mycorrhizal fungi establish
a kind of symbiosis with several plant taxa, where hyphae grow endophytically in
roots, extending their mycelia into the soil, to acquire nutrients and to mobilize them
to plants (Marschner and Dell 1994). Thus, interactions between DSE and host plants
improved plant fitness due to an increment in the N and P transfer and uptake, and
nutrient provision to host plants (Gasoni and De Gurfinkel 1997; Usuki and Narisawa
2007). A few of these mechanisms are summarized in Table 11.2.
Most of these results have been found to be considerably variable depending
on the host plant, fungal strains, and environmental conditions (Haselwandter and
Read 1982; Jumpponen 2001; Svenningsen et al. 2018). Thus varying results
are obtained under different environmental conditions as observed in rice with
Phomopsis liquidambari, where analyzing the transcript levels of several genes in
endophyte-infected tissues, it was found that the genes with higher transcript levels,
OsAMT1;1, OsAMT1;3, OsAMT2;2, OsAMT3;2, OsAMT3;2 and Os- NRT2;1
increased under low-N conditions (Li et al. 2018).
11.4 Plant Growth Under Alleviation of Stress Conditions
The accumulation of mineral salts in soils has become nowadays one of the most
serious and growing environmental problems in arid and semi-arid areas causing
C. García-Latorre et al.
gene encoding nitrate reductase, activating also the uptake of trace elements (Mo, B,
Fe, Zn, and Mn) in the rhizosphere (Su et al. 2016, 2019).
The higher nutrient uptake in endophyte-infected plants occurred due to the endophytic borne secretion of substances that facilitate the mineral uptake by plant roots.
In this scenario, Curvularia geniculata (Tracy and Earle) Boedijn has been found to
secrete enzymes exhibiting P solubilization in sufficient amounts so as to enhance
plant growth and development (Priyadharsini and Muthukumar 2017). On the other
hand, the release of root exudates containing some phenolic compounds secreted by
Epichloë endophytes, were found to increase the P solubility in soil, increasing the
P uptake and the subsequent P concentration in the plants (Malinowski et al. 1998).
Similar studies have also reported an increased capability to bind Cu in the rhizosphere of endophyte-infected plants (Malinowski et al. 2004). Increment of P and
other mineral solubilization occurred due to the secretion of substances by root endophytes which acidifies the soil, thus P becomes more available in the soil solution by
its conversion from insoluble phosphates or other insoluble fertilizers (Aciego and
Brookes 2009; Narsian and Patel 2000).
Special mention deserves (DSE) which have been found to make mineral nutrients
available by facilitating access to complex C, N, and P present in the soil for their
host plant (Mandyam 2008). Such an effect could be explained by the production of
hydrolytic enzymes by the endophyte, which could induce the release of nutrients to
be uptaked by plants. Long back, Jumpponen and Trappe (1998) reported the uptake
of organic compounds (amino acids, small peptides, etc.) by DSE fungi, which might
be transferred directly to host plants, resulting in more efficient use of organic nutrient
resources (Reeve et al. 2008). As stated earlier, DSE and mycorrhizal fungi establish
a kind of symbiosis with several plant taxa, where hyphae grow endophytically in
roots, extending their mycelia into the soil, to acquire nutrients and to mobilize them
to plants (Marschner and Dell 1994). Thus, interactions between DSE and host plants
improved plant fitness due to an increment in the N and P transfer and uptake, and
nutrient provision to host plants (Gasoni and De Gurfinkel 1997; Usuki and Narisawa
2007). A few of these mechanisms are summarized in Table 11.2.
Most of these results have been found to be considerably variable depending
on the host plant, fungal strains, and environmental conditions (Haselwandter and
Read 1982; Jumpponen 2001; Svenningsen et al. 2018). Thus varying results
are obtained under different environmental conditions as observed in rice with
Phomopsis liquidambari, where analyzing the transcript levels of several genes in
endophyte-infected tissues, it was found that the genes with higher transcript levels,
OsAMT1;1, OsAMT1;3, OsAMT2;2, OsAMT3;2, OsAMT3;2 and Os- NRT2;1
increased under low-N conditions (Li et al. 2018).
11.4 Plant Growth Under Alleviation of Stress Conditions
The accumulation of mineral salts in soils has become nowadays one of the most
serious and growing environmental problems in arid and semi-arid areas causing