Agriculture Reference
In-Depth Information
Fig. 15.1
Similarity in intra-
cellular boron concentrations
required to inhibit growth
in a range of cell types.
(Reprinted from Reid et al.
(
2004
) with permission)
Chara
shoots
Barley roots
Arabidopsis
culture
Barley culture
120
100
80
60
40
20
0
4
6
0
2
8
10
Boron (mM)
Fig. 15.2
Spatial sensitivity
of growth of wheat roots to
10 mM boron applied either
to the mature section of the
root or to the apical 5 mm.
Shading indicates regions
where boron was applied.
(Reprinted from Reid et al.
(
2004
) with permission)
0.8
0.6
0.4
0.2
0
Binding to the former three inhibits energy metabolism while binding to the latter
affects a number of developmental processes related to gene expression and protein
synthesis. Reid et al. (
2004
) examined the effect of increasing boron concentrations
on a range of cellular activities, and compared responses to tissue concentrations
at which toxicity symptoms were observed. Using barley seedlings, they found that
quite high concentrations (ca. 50 mM) were required to significantly inhibit respira-
tion, photosynthesis, protein synthesis and selected enzymes of energy metabolism
(malate dehyrogenase, isocitrate dehydrogenase) and acid phosphatase. This con-
trasted with the threshold concentration for visible toxicity symptoms to appear
in leaves of around 20 mM, which was still an order of magnitude higher than the
boron concentration at which inhibition of root growth occurred. Measurements of
growth of the giant alga
Chara,
and suspension cultures of
Arabidopsis
and barley
all showed a similar threshold for inhibition of growth of around 2 mM (Fig.
15.1
).
It was further established that inhibition of root growth only occurred if high con-
centrations were applied to the tip; no inhibition was observed if the chemical was
applied to the mature sections of the root (Fig.
15.2
) (Reid et al.
2004
).
The difference in sensitivity between mature and meristematic tissue suggested
that toxicity might be related either to cell expansion or cell division, possibly by
