Short‐ and Long‐distance Transport of Boric Acid in Plants

Abstract

SUMMARYT'he molecular weight and ether-water partition coefficient of boric acid are consistent with a Pj5,oH)3 i"^ plant cell membranes of at least 10^* cm s~^. This permeability coefficient is high enough to account for the measured magnitude of boric acid fiuxes at manj' plant cell membranes. The use of active transport of boric acid to maintain B distribution across a membrane away from thermodynamic equilibrium is consequently likely to be energetically expensive. The content of m-diols (with which boric acid can form complexes) in cell walls and inside the cells varies widely between different plant species without any obvious correlation with either total B content or with the B content at which deficiency (in B-requirers) or toxicitj^ symptoms are manifested. B distribution at the cell level depends on the relative extents of passive permeation, active transport and cw-diol formation; regulations may be in response to total mtracellular B rather than free boric acid.The net uptake of boric acid by intact \-ascular land plants is influenced by the rate of traiispiration; while transport of B zvitliiti the xylem is probably directly proportional to the rate of transpiration, neither whole plant B uptake nor transfer from root tissue into the xylem exhibit such a simple relationship. Redistribution of B in the piiloem from transpirational termini is very limited. This limitation could result from the toxicity of B (which requires a low B concentration in the translocation stream relative to other nutrients and to sinl-: requirements) or to 'counter-current distribution' of B fron"i the phloem to the adjacent xyleiri stream (low in B) throiifih the B-permeable sieve-tube plasmalemma.Tlie transport of B is discussed in relation to the evolution of multi-cellular algae and of vascular land plants.

Boron mobility in eucalyptus clones

“…Boron has historically been considered a nutrient with low phloem mobility (Oertli & Richardson, 1971;Epstein, 1972;Raven 1980). Consistent with this idea is the observation that B deficiency in plants leads to the development of symptoms that appear initially in rapidly growing tissues.…”

Extração e exportação de nutrientes em cultivares de batata: II - micronutrientes

“…O teor foliar de B observado nas cultivares Mondial, Ágata e Asterix foi superior ao relatado como adequado (25 a 50 mg kg -1 ) por Lorenzi et al (1997) (Fernandes et al, 2010) e da remobilização desses elementos para as regiões de crescimento. Já a quantidade de B e Mn presente nesse órgão permaneceu relativamente constante, apesar da diminuição da MS (Fernandes et al, 2010), resultado da baixa mobilidade desses elementos nos tecidos (Raven, 1980;Malavolta, 2006 Ágata, exceto na fase inicial do ciclo, em que ela apresentou acúmulo radicular superior ao da cultivar Mondial, provavelmente, em função da menor MS radicular desta cultivar nesse período (Fernandes et al, 2010). Na fase final do ciclo, houve redução na quantidade de B, Cu, Fe, Mn e Zn acumulada nas raízes de todas as cultivares estudadas (Figuras 2b,3b,4b, 5b e 6b), o que em parte é resultado da diminuição da MS radicular nesse período (Fernandes et al, 2010).…”

Distribution of boron and its forms in young “Newhall” navel orange (Citrus sinensisOsb.) plants grafted on two rootstocks in response to deficient and excessive boron

“…In our results, citrange-grafted plants had lower free B content in B0 and B05, and higher free B at B50 than trifoliate orangegrafted plants (Table 3). These results could be explained by several reasons: (1) the critical level of free B in citrange was lower than in trifoliate orange (Goldbach et al 2000); (2) the ability of B transmembrane was stronger in citrange, resulting in relatively more B transported into the cytoplasm (Raven 1980); (3) xylem lording of B in citrange-grafted plants was easier in citrange-grafted plant than trifoliate orange-grafted plants under high B (Dannel et al 2002). Semi-bound B was relatively stable under B0 and B05 (Table 3), further implying that B in cytoplasm is not only as structural material, but also involved in metabolism.…”