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EC number: 215-125-8
CAS number: 1303-86-2
Concentrations of B (µg B/g) were measusred
in leaves, whole shoots, straw, grain, shoots and roots. An overview of
the added B concentrations in soils, the concentrations in plant
material and the BCF values are summarized below. Riley et al did not
calculate BCF values. Based on the data presented the BCF's can be
B conc. in leaves (µg/g)
B conc. in grain (µg/g)
The authors reported BCF values < 0.1 and
noted that liver and blood residues were eliminated within 1 day on a
Boron accumulates rapidly in adult mallard
liver and is estimated to take 2.8d to reach 95% of its asymptotic
level. On a dry-weight basis, B in adult liver in the control, 450 -,
and 900 -ppm B treatments groups was 2, 15, and 27 ppm, respectively.
Dry-weight concentrations of B in eggs were
0.6, 22, and 38 ppm in the B control, and 450- and 900 -ppm treatment
Values for different varieties:
Kawa (n=7): substrate (wood waste) -
31 mg-B/kg, stem - 29 mg B/kg, and leaf - 827 mg B/kg.
Toa (n=6): substrate (wood waste) -
36 mg-B/kg, stem - 22 mg B/kg, and leaf - 1012 mg B/kg
Yeogi (n=8): substrate (wood waste) -
28 mg-B/kg, stem - 20 mg B/kg, and leaf - 776 mg B/kg.
Boron is known to
be a critical element for the normal growth and productivity of
terrestrial plants. Boron is required in plants for normal metabolic
functioning of sugar transport, cell wall synthesis, lignification,
carbohydrate metabolism, RNA metabolism, respiration, indole acetic acid
(growth regulator) metabolism, phenol metabolism, the integrity of
membranes, and the pollination process (Marschner, 1995). There is a
certain minimum requirement of boron for a plant. However, there are
considerable interspecies differences in the levels required for optimal
growth. Monocotyledons generally require less than dicotyledons (Gupta
et al, 1985).
varies with stage of growth and the concentration varies among the plant
parts (Gupta et al., 1985). Plants also are known to change soil pH
locally by root exudates to enhance uptake of essential nutrients
(Reimann et al., 2001, WHO 1998).
mechanism has long been debated. It was first suggested that boron moves
to the root surface in the soil solution by mass flow and enters the
roots by passive diffusion (Bingham et al., 1970). However this concept
has been challenged by Bowen (1968, 1969, 1972), Bowen and Nissen
(1977), and Reisenauer et al (1973). They indicated that boron is
actively absorbed in ionic form particularly when the boron
concentration in soil is low (Gupta et al, 1985). This has been
confirmed by more recent studies, which provided evidence for channel-
and/or transporter-mediated boron transport systems (Tukano et al.,
2005). The isolation of the boron transporter in BOR1-1 mutant plants
showed elevated sensitivity to boron deficiency, especially in young
growing organs in shoots. BOR1 is a membrane protein that belongs to the
bicarbonate transporter superfamily (Takano et al., 2002; Frommer et al.,
Takano et al
(2005) found that the activity of the BOR1 plasma membrane transporter
for boron in plant is regulated (endocytosis and degradation) by boron
availability, to avoid accumulation of toxic levels of boron in shoots
under high boron supply, while protecting the shoot from boron
deficiency under boron limitation.
Once in the
plant, boron is passively carried in the transpiration stream to the
leaves where the water evaporates and boron accumulates. This explains
why boron concentrations are generally lower in roots, stems, and fruits
than in leaves (WHO 1998). Once assimilated by the plant, boron becomes
one of the least mobile micronutrients (Wolg 1940, Eaton 1944, Dible and
Berger, 1952). Since boron is not readily transported from old to young
plant parts, the earliest deficiency symptoms are found in young parts
while the earliest toxicity symptoms are found in the old plant parts
(Gupta et al, 1985).
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