5 Fluorescent Pseudomonads …
111
Fe
3+ are the two interconvertible forms of iron; pH, salinity, and alkalinity influence
the conversion of Fe
2+ and Fe
3+ . Iron combines with phosphates, carbonates, calcium
magnesium, and hydrogen ions and its limitation increases due to its non-solubility
corresponding to salinity. The downregulation of iron transportation in response
to salinity may lead to iron limitation (Cotsaftis et al. 2011). Another context of a
reduction in iron availability is the inhibition of proton pumps required for the uptake
processes (Rabhi et al. 2007).
5.7 Avoidance of Iron Limitation in Saline Soils
Plants under iron deficiency exhibit various mechanisms to avoid the Iron limitation. This is also including root exudates and phytosiderophores production. Bacterial siderophores are more efficient when compared to phytosiderophores and efficient siderophores have been observed in different genera of plant growth-promoting
rhizobacteria which can avoid deleterious phytopathogens (Dileep 2012). The root
exudate secretions and other metabolites include amino acids, organic acids, and
phenolic compounds which lower pH of the soil and avoid to interfere iron availability. These root exudates attract the PGPRs to the rhizosphere regions by root
colonization and chemotaxis, thus facilitate to chelate iron (Singh et al. 2010; Aeron
et al. 2020). The iron-siderophore complexes, having membrane receptors, can easily
access the Iron. Iron limitation in saline soils can be alleviated through the inoculation
of halo-tolerant PGPR as given in Fig.5.1.
5.8 Fluorescent Pseudomonads—A Sustainable Solution
for Iron Limitation in Saline Soils
The effective strategy for avoiding Iron limitation by the application of P. fluorescens,
P. stuzeri on Tomato (Tank and Saraf 2010), on common bean by P. fluorescens
(Younesi and Moradi 2014); Growth promotion reports on Groundnut by P. fluorescens (Saravanakumar and Samiyappan 2007), and in Peanut (Sharma et al.2016)
and various other crop plants (Maheshwari 2011; Maheshwari et al. 2013).
In a case study, saline tolerant fluorescent pseudomonads are collected from the
saline Pokkali rice field, with an average 5.9 pH and 5.0 T.S.S (Total soluble salt).
Pokkali is a salt-tolerant, GI tagged rice variety; cultivated in saline soils. The primary
screening of the organism, by its ability to fluorescence under UV light. The King’s
B medium (Peptone 20 g; MgSO 4 .7H 2 O 1.5 g; K 2 HPO 4 1.5 g; Agar 15 g; Distilled
water 1L) is modified by varying concentrations of NaCl to screen the salt tolerance
of the organism. Selected strains are inoculated in iron-deficient, synthetic, succinate
medium (Mayer and Abdallah 1978), incubated for 48 h at 30 °C. The culture supernatants were centrifuged at 10000 rpm for 20 min. The supernatants were filtered
111
Fe
3+ are the two interconvertible forms of iron; pH, salinity, and alkalinity influence
the conversion of Fe
2+ and Fe
3+ . Iron combines with phosphates, carbonates, calcium
magnesium, and hydrogen ions and its limitation increases due to its non-solubility
corresponding to salinity. The downregulation of iron transportation in response
to salinity may lead to iron limitation (Cotsaftis et al. 2011). Another context of a
reduction in iron availability is the inhibition of proton pumps required for the uptake
processes (Rabhi et al. 2007).
5.7 Avoidance of Iron Limitation in Saline Soils
Plants under iron deficiency exhibit various mechanisms to avoid the Iron limitation. This is also including root exudates and phytosiderophores production. Bacterial siderophores are more efficient when compared to phytosiderophores and efficient siderophores have been observed in different genera of plant growth-promoting
rhizobacteria which can avoid deleterious phytopathogens (Dileep 2012). The root
exudate secretions and other metabolites include amino acids, organic acids, and
phenolic compounds which lower pH of the soil and avoid to interfere iron availability. These root exudates attract the PGPRs to the rhizosphere regions by root
colonization and chemotaxis, thus facilitate to chelate iron (Singh et al. 2010; Aeron
et al. 2020). The iron-siderophore complexes, having membrane receptors, can easily
access the Iron. Iron limitation in saline soils can be alleviated through the inoculation
of halo-tolerant PGPR as given in Fig.5.1.
5.8 Fluorescent Pseudomonads—A Sustainable Solution
for Iron Limitation in Saline Soils
The effective strategy for avoiding Iron limitation by the application of P. fluorescens,
P. stuzeri on Tomato (Tank and Saraf 2010), on common bean by P. fluorescens
(Younesi and Moradi 2014); Growth promotion reports on Groundnut by P. fluorescens (Saravanakumar and Samiyappan 2007), and in Peanut (Sharma et al.2016)
and various other crop plants (Maheshwari 2011; Maheshwari et al. 2013).
In a case study, saline tolerant fluorescent pseudomonads are collected from the
saline Pokkali rice field, with an average 5.9 pH and 5.0 T.S.S (Total soluble salt).
Pokkali is a salt-tolerant, GI tagged rice variety; cultivated in saline soils. The primary
screening of the organism, by its ability to fluorescence under UV light. The King’s
B medium (Peptone 20 g; MgSO 4 .7H 2 O 1.5 g; K 2 HPO 4 1.5 g; Agar 15 g; Distilled
water 1L) is modified by varying concentrations of NaCl to screen the salt tolerance
of the organism. Selected strains are inoculated in iron-deficient, synthetic, succinate
medium (Mayer and Abdallah 1978), incubated for 48 h at 30 °C. The culture supernatants were centrifuged at 10000 rpm for 20 min. The supernatants were filtered