Agriculture Reference
In-Depth Information
important agronomic impact (Gupta
1979
). In soils with high percolatory water,
B is easily leached downward in the soil and hence it is not readily available for
plants (Blevins and Lukaszewski
1998
). Adequate B nutrition is required for high
production as well as for quality of crops. B deficiency results in biochemical,
metabolic and physiological abnormalities, and causes diverse disease symptoms in
plants and hence adequate supply is a critical challenge for plant nutrition.
In the last 10 years, several roles have been demonstrated for B in plant function,
including as a cell wall component, an involvement in membrane structure and
integrity, and involvement in metabolic process (Bola˜os et al.
2004
). To date, one
of the most accepted roles of B in plant physiological function is the formation of an
ester with one apiose residue of rhamnogalacturonan
(RG II) in the cell wall
(Kobayashi et al.
1996
), which is essential for maintaining cell wall permeability
and also for rigidity (Fleischer et al.
1999
; Ryden et al.
2003
). Moreover, B
deficiency led to a decrease of gene transcription of various hydrolytic enzymes
such as xyloglucan endotransglucosylase/hydrolases (XTHs), expansins, pectin
methylesterases, and pectin lyases in
Arabidopsis
roots (Camacho-Crist´bal
et al.
2002
). These enzymes play key roles in cell wall loosening, necessary for
cell elongation (Cosgrove
1999
). Camacho-Cristobal et al. (
2011
) suggested an
influence of B in transcriptional level regulation of genes, which are responsible for
cell wall synthesis and its modification.
Many research reports suggested roles of B in plasma membrane transport
processes, and in membrane integrity by cross-linking the membrane molecules
containing hydroxlated ligands such as glycoproteins and glycolipids (Goldbach
et al.
2001
;Wimmeretal.
2009
). The membrane potential in
Daucus carota
is
changed under limited B (Blaser-Grill et al.
1989
) and activity of the proton-
pumping ATPase was reduced in
Helianthus annuus
roots (Ferrol and Donaire
1992
). Similarly, it has been reported that B deficiency alters plasma membrane
permeability for ions and other solutes (Wang et al.
1999
; Carmen Rodriguez
Hernandez et al.
2013
).TheimpactofBonionfluxescanbemediatedbydirect
or indirect effects of B on plasma membrane-bound proton-pumping ATPase
(Cara et al.
2002
). The activity of the K
+
stimulated ATPase in B-deficient maize
roots was considerably lower than in control plants (Pollard et al.
1977
). These
results indicated that the action of B could be associated with membrane com-
ponents. It is still unclear whether B directly interacts with membrane proteins or
indirectly modifies membrane properties with subsequent changes in enzymatic
activities.
The literature indicates possible roles of B in several other metabolic func-
tions. For instance, it has been shown that B deficiency causes qualitative and
quantitative changes in phenol metabolism (Pandey and Archana
2012
; Hajiboland
et al.
2013
). Additionally B deficiency affects nitrogen metabolism (Bola˜os
et al.
1994
). B-deficient plants showed lower nitrate reductase activity and enhanced
amounts of nitrate; these observations strongly suggest a role of B in the de
novo synthesis of the nitrate reductase protein or facilitation of nitrate absorption
(Ruiz et al.
1998
).
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