Agriculture Reference
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4. increase root exudates of isoflavonoids (Verma et al.
1992
; Zhang and Smith
1995
; Corradini et al.
2011
).
Under stress root growth is less affected than nodulation (Abd-Alla et al.
1998
;
Miransari and Smith
2007
), because under stress plant must spend more energy to
alleviate the stress rather than developing a symbiotic association with the soil mi-
crobes (Miransari and Smith
2007
; Miransari et al.
2007
,
2008
). Nodules are tissues
with a high energy requirement and hence a part of energy produced by plant must
be allocated to nodules for different activities such as respiration and development
(Zhang and Smith
1995
).
Under stress different concentrations of genistein ranging from 5 to 20 µM were
tested and proved to be effective. In addition, the highest concentration of genis-
tein (20 µM) did not adversely affect bacterial N fixation and hence plant growth.
Results indicated that with increasing the level of stress genistein became more ef-
fective. The mathematical equations used to relate genistein concentration to nodu-
lation and plant growth indicated that the most effective concentration of genistein
ranged from 5 to 11 µM. Using multivariate equations, it is possible to predict the
most optimum concentration of genistein under stress with respect to plant response
to genistein affecting plant growth and yield production under field and greenhouse
conditions (Miransari and Smith
2007
).
During drought stress, water deficiency can adversely affect plant growth and
yield production. Plant roots absorb water, which moves solutes to different plant
parts for utilization and assimilation, and nutrients from the surrounding soil. Water
is necessary for cellular expansion and development by producing the necessary
turgor for cell growth. During the process of evapo-transpiration, water is evapo-
rated from plant leaf creating the necessary potential for the uptake of water and nu-
trients by plant roots and their movement to different parts of the plant. Hence, with
respect to the importance of water in plant its deficiency can significantly decrease
plant growth and yield production (Asbjornsen et al.
2011
).
Under drought plant utilizes different mechanisms to alleviate the stress. Such
mechanisms result in the adjustment of plant growth and production of organic
compounds as osmoprotectants regulating cellular water potential and the uptake
of nutrients. The morphological and physiological alterations in plant growth under
drought can alleviate the stress up to some extent. Yamaghuchi et al. (
2010
) indi-
cated that different parts of soybean primary roots respond differently to drought
stress. They attributed such a response to the regulation of phenypropanoid metabo-
lism in different parts of the roots and hence the biosynthesis of isoflavonoids. How-
ever, contrary to this alteration, the production of caffeoyl-CoA
O
-methyltransferse,
which is responsible for the production of lignin, highly increased resulting in the
inhibition of root growth in the specific parts. In addition, different proteins were
produced in the water stressed part of roots to alleviate the oxidative stress.
There are some responsive genes, being induced under salinity. For example, Li
et al. (
2008
) found that a protein, which is homologous to oxysterol binding protein
in soybean, was expressed under salinity stress resulting in cotyledon senescence.
Under salinity, the isomer of a pathogenic related protein, as a responsive protein to
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