Mobility and distribution of boron in plants and effects on reproductive growth and yield

Authors : Richard BELL

Pages : 175-183

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Publication Date : 2017-12-30

Article Type : Review Paper

Abstract :Most boron (B) behaviour in plants can be explained by complexation of B in cell walls and membranes which links the consequences of B deficiency to the disruption of cell wall and membrane function. Many symptoms of B deficiency reflect the localised and timely need for B for stabilisation of cell walls in tissues with expanding cells, e.g. flowers, fruit, root tips and shoot meristems. The internal B requirement of tissues for adequate function is determined by the abundance of rhamnogalacturonan-II (RG-II) which complexes B in the cell wall. Reproductive plant parts appear to be particularly at risk from low B supply, in part because they require relatively high concentrations of B compared to vegetative tissues.  When external B concentrations are adequate to high, the uptake and distribution of B in plants can be largely explained by the uptake of water and its movement within the plant. However, under marginal and deficient external B concentrations, channels and transporters exert significant control of the uptake and distribution of B within the plant. Channels and transporters in roots promote uptake and loading of B into the xylem. For flowers, pollen and seed, with low rates of transpiration, channels and transporters are probably involved in their B acquisition under low external supply. The mobility of B in the phloem is variable among species. In most plants, B is immobile in the phloem and growing tissues rely substantially on B supplied through the xylem or by xylem-to-phloem transfer. However, if present in the phloem, B-complexing compounds, notably sugar alcohols, allow free mobility of B in the phloem so that B can be retranslocated within the plant of those species especially under deficient supply. 
Keywords : Boron complexing, Boron requirements, Cell wall, Deficiency symptoms, Pectin, RG II, Sugar alcohols

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