participation by both rhizosphere and endophytic diazotrophs (Baldani et al. 1997).
Several N 2 fixing bacteria such as Enterobacter cloacae, Erwinia herbicola, Klebsiella pneumoniae, Azotobacter vinelandi, Paenibacillus polymixa, Azospirillum
spp., Herbaspirillum spp., and Gluconacetobacter diazotrophicus colonize the sugarcane plant (Cavalcante and Döbereiner 1988; Olivares et al. 1996).
20.3 Biology of Diazotrophs and Interaction with Plants
Diazotrophic bacteria could fix gaseous nitrogen epiphytically or endophytically
from air and could supply that needed resource to the plants. In addition, they could
have other functions to benefit the plants such as not only producing IAA,
gibberelline, and cytokinin-like substances (Fuentes-Ramírez et al. 1993; Bastián
et al. 1998) but also promoting plant’s growth and inducing resistance to pest and
other abiotic stress like drought (Ji et al. 2014b). The genetics of diazotrophs are now
much elucidated on the interaction of plants with advanced biotechnology. The
biology of endophytes is summarized with the proposed mechanisms for endosymbiosis in Table 20.2 (Dent 2018 and Pinski et al. 2019).
Recently, plant microbiomes are a very hot topic to study. The microbiome of
plants includes the epiphytes and endophytes in all parts of plant tissues. Endophytic
bacteria primarily survive in the intercellular spaces due to an abundance of carbohydrates, amino acids, and other nutrients available from the plant. Some endophytes
are capable of intracellular colonization. Endophytic strains colonize various parts of
plants, including the roots, leaves, stems, flowers, and seeds. However, the roots of
plants are the part that endophytes reside the most abundantly, both in terms of the
microoganisms number and diversity (Pinski et al. 2019). Diazotrophic endophytes
which have the functions of nitrogen fixation are of special interest for agricultural
practice. Of them, the bacteria that have other benefits such as phosphate solubilities,
IAA and siderophore production, and antagonistic effects against pathogens are very
promising for the crops. The antagonistic effects of endophytes against phytopathogens are associated with the endophytes production of chitinase, protease, and
siderophores (Pinski et al. 2019). The enhanced resistance which endophytes provide to plants against environmental stresses might be due to the activity of deaminase 1-aminocyclopropane-1-carboxylate (ACC). This could decrease ethylene
production by degrading ACC, which is known as the precursor of ethylene leading
in the necrosis of cell (Kandel et al. 2017). Numerous studies have demonstrated that
endophytic bacteria could induce the resistance of plants to cold and drought, and
also stimulate plant immune systems in a process called priming (Liu et al. 2017;
Gagne-Bourque et al. 2015).
In the study of Ji et al. (2014b), rice seeds were inoculated with Bacillus subtilis
CB-R05 that possessed antagonistic effects against several fungal pathogens—it is a
diazotrophic bacteria marked with the green fluorescent protein (gfp) gene. The
pathogenesis-related (PR) proteins (PR2, PR6, PR15, and PR16) in rice inoculated
with CB-R05 were generally more strongly expressed in the rice leaves inoculated
20 The Diazotroph as an Endophyte and How a Diazotroph Interacts with Its. . .
395
Several N 2 fixing bacteria such as Enterobacter cloacae, Erwinia herbicola, Klebsiella pneumoniae, Azotobacter vinelandi, Paenibacillus polymixa, Azospirillum
spp., Herbaspirillum spp., and Gluconacetobacter diazotrophicus colonize the sugarcane plant (Cavalcante and Döbereiner 1988; Olivares et al. 1996).
20.3 Biology of Diazotrophs and Interaction with Plants
Diazotrophic bacteria could fix gaseous nitrogen epiphytically or endophytically
from air and could supply that needed resource to the plants. In addition, they could
have other functions to benefit the plants such as not only producing IAA,
gibberelline, and cytokinin-like substances (Fuentes-Ramírez et al. 1993; Bastián
et al. 1998) but also promoting plant’s growth and inducing resistance to pest and
other abiotic stress like drought (Ji et al. 2014b). The genetics of diazotrophs are now
much elucidated on the interaction of plants with advanced biotechnology. The
biology of endophytes is summarized with the proposed mechanisms for endosymbiosis in Table 20.2 (Dent 2018 and Pinski et al. 2019).
Recently, plant microbiomes are a very hot topic to study. The microbiome of
plants includes the epiphytes and endophytes in all parts of plant tissues. Endophytic
bacteria primarily survive in the intercellular spaces due to an abundance of carbohydrates, amino acids, and other nutrients available from the plant. Some endophytes
are capable of intracellular colonization. Endophytic strains colonize various parts of
plants, including the roots, leaves, stems, flowers, and seeds. However, the roots of
plants are the part that endophytes reside the most abundantly, both in terms of the
microoganisms number and diversity (Pinski et al. 2019). Diazotrophic endophytes
which have the functions of nitrogen fixation are of special interest for agricultural
practice. Of them, the bacteria that have other benefits such as phosphate solubilities,
IAA and siderophore production, and antagonistic effects against pathogens are very
promising for the crops. The antagonistic effects of endophytes against phytopathogens are associated with the endophytes production of chitinase, protease, and
siderophores (Pinski et al. 2019). The enhanced resistance which endophytes provide to plants against environmental stresses might be due to the activity of deaminase 1-aminocyclopropane-1-carboxylate (ACC). This could decrease ethylene
production by degrading ACC, which is known as the precursor of ethylene leading
in the necrosis of cell (Kandel et al. 2017). Numerous studies have demonstrated that
endophytic bacteria could induce the resistance of plants to cold and drought, and
also stimulate plant immune systems in a process called priming (Liu et al. 2017;
Gagne-Bourque et al. 2015).
In the study of Ji et al. (2014b), rice seeds were inoculated with Bacillus subtilis
CB-R05 that possessed antagonistic effects against several fungal pathogens—it is a
diazotrophic bacteria marked with the green fluorescent protein (gfp) gene. The
pathogenesis-related (PR) proteins (PR2, PR6, PR15, and PR16) in rice inoculated
with CB-R05 were generally more strongly expressed in the rice leaves inoculated
20 The Diazotroph as an Endophyte and How a Diazotroph Interacts with Its. . .
395