Agriculture Reference
In-Depth Information
Chapter 15
Boron Toxicity and Tolerance in Crop Plants
Robert J. Reid
1 Introduction
Boron (B) is an essential plant nutrient required in relatively small quantities for
normal plant growth. In many respects, boron is the most difficult of plant nutrients
to manage, principally due to the fact that it is the only essential nutrient that nor-
mally exists as a neutral solute, boric acid. Combined with its small size, this lack
of charge allows it to pass easily through membranes and as a result, its distribution
within the plant can be hard to control. Both boron deficiency and boron toxicity are
common in agricultural crops. The deficiency can be easily corrected by its fertilisa-
tion, but toxicity is much more difficult to manage. This review examines the role
of boron in plants, possible targets for toxicity, and the mechanisms by which some
plants have developed tolerance to excess boron.
2 Functions of Boron in Plants
The essentiality of boron for plant growth was established by Warington in 1923,
but it took many decades to understand which processes depended on boron. The
first clue came from the discovery that boron was strongly bound in plant cell walls
(Tanaka
1967
) and that the boron content was well correlated with the amount of
pectic polysaccharide in cell walls (Matoh
1997
,
2000
). From these latter studies, it
is now well established that boron plays an important structural role as a component
of the rhamnogalacturonan II (RGII) complex that links cell wall polysaccharides.
