Agriculture Reference
In-Depth Information
Soybean, Salinity and Drought
About one milliard hectares of agricultural soils are saline or subjected to some kind
of salinity, worldwide (Flowers and Yeo
1995
). Leguminous plants are classified
among sensitive or moderately tolerant plants to salinity (Lauchli
1984
). Legume's
tolerance to salinity differs among different species (Lu et al.
2009
) and usually un-
der salinity they excrete ion salt from the leaf or localized the salt in different parts
of the plant. Under high salinity rhizobium are not able to become dormant, and
hence must have the ability to tolerate high salt levels. Parameters including soil
fertility, N source, temperature, drought, relative humidity and physical properties
can affect plant growth under saline conditions (Velagaleti et al.
1990
; Munns
2002
;
Vercruysse et al.
2011
; Meilhoc et al.
2011
).
Higher concentration of salt in mature leaf, relative to the young leaf, results in
the senescence of mature leaf. Plant ability to allocate salt to the cellular vacuoles is
among the important parameters determining plant tolerance to salinity. The higher
the plant ability to allocate salt to the vacuoles the higher its tolerance to salinity
is. Plant hormones such as abscisic acid (ABA) can also regulate plant activities
under stress by for example controlling the stomatal activities (Wolf et al.
1990
;
Yang et al.
2012
). Salt adverse effects on plant growth under salinity also include
cytoplasm malfunctioning, membrane leakage, and loss of turgor and water.
Drought and salinity adversely influence legume-host plant symbiosis by affect-
ing the growth and survival of bacterium, delaying the infection process, suppress-
ing nodule functionality, decreasing the photosynthesis rate, plant growth and N
uptake in the host plant. There are usually interactions between drought/salinity and
rhizobium as there are bacterial strains, which are more tolerant and hence efficient
under stress. Physiological alterations under stress make the plants allocate more
carbon to their roots (Miransari and Smith,
2007
; Miransari et al.
2007
;
2008
).
Researchers hypothesized and proved that addition of genistein (4′,5,7-trihy-
droxyisoflavone), the plant to bacterium signal, under stress, enhanced the activa-
tion rate of bacterial Nod genes resulting in the increased production of nodulation
(Nod) factors by
Bradyrhizobium
japonicum
(Miransari et al.
2006
; Wang et al.
2012
) and hence faster formation of nodules (Zhang and Smith
1995
; Pan and Smith
1998a
;
b
). According to Miransari and Smith (
2007
,
2008
,
2009
) the effects of ge-
nistein became greater with time by more effectively influencing N-fixation and
hence plant growth and yield in the second sampling compared with the first sam-
pling. This also indicates that genistein persistence in soil is suitable.
Flavonoids are able to:
1. regulate the polar transport of auxin followed by the imbalance of auxin-cytoki-
nin and initiation of nodule meristem formation (Schmidt et al.
1994
),
2. enhance bacterial growth,
3. increase the production of Nod factors by bacteria as a result of higher Nod genes
activation, resulting in the alteration of root morphological properties including
root hair curling and bulging and eventual formation of root nodules by inducing
cellular division at different sites, and
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