Data/hora: 04/06/2024 06:27:33

Biblioteca(s): | Embrapa Pantanal.
Data corrente: | 09/09/1996
Data da última atualização: | 08/09/2010
Autoria: | BIDDULPH, O.; WOODBRIDGE, C. G.
Título: | The uptake of phosphorus by bean plants with particular reference to the effects of iron.
Ano de publicação: | 1952
Fonte/Imprenta: | Plant Physiology, v.27, n.3, p.431-444, July, 1952.
Idioma: | Inglês
Conteúdo: | Absorption and translocation of phosphorus by bean plants was unimpaired at pH 4.0. A minimum in phosphorus accumulation occurs at or near pH 5.0 which reflects the slight solubility of basic ferric phosphate at or near this pH. It is conceivable that this minimum also reflects the minimal absorptions encountered at the isoelectric points of certain cellular constituents active in phosphorus absorption. As the pH of the nutrient solution was raised from 6.0 to 7.0, the concentration of phosphorus in the stems and petioles increased, whereas the concentration in the leaf blades decreased. This observations indicates a lodging of incoming phosphorus in the stem and petioles at high pH values, creating tissues rich in phosphorus through which ions being transported to the leaf blade must pass. As the phosphorus concentration of the nutrient medium is increased from low to higher values, the tissue cocentrations also increase, but at different rates. The general effect is a rapid rise, followed by lesser increases until a leveling off occurs. The phosphorus concentrations of the nutrient solutions at which the different plant organs level off in phosphorus concentrations are as follows: trifoliate leaves, 0.00005 M; cordate leves, 0.0005 M; stems, 0.005 M. Root concentrations begin leveling off at 0.005M. A concentration of approximately 6 mg. of P/gam. of dry matter in trifoliate leaves is attained from solutions at 0.00005 M P and this value is sufficient for continued growth of leaves. The corresponding combined stem and petiole concentration is approximately 2 mg. P/gm. dry matter when the leaves are adequately supplied. The stem and petioles will, however, build up to 4 mg. P/gm. dry matter as more phosphorus is made available. Cordate leaves correspondinggly rise from 3 to 7 mg. P/gm. dry matter. It is this additional accumulation of phosphorus, beyond the concentration which is adequate for leaf growth and stem extension, which causes disturbances in the metabolic use of other ions, particularly iron. The passage of such ions through tissues rich in phosphorus is interfered with and much of the iron is precipitated along thge conductive tissue. The principal effect of hugh phosphorus concentrations on the development of chloris is explained on this basis. In a nutrient solution containing both phosphorus and iron in nutrient quantities, a precipitate will form which will reduce the amount of available ions of both elements. The precipitate of iron and phosphorus forms both upon the container and upon the plant roots. The effect of the precipitation is twofold. First, it removes some of the materials from solution the effective concentration. Second, the presence of the precipitate upon absorbing surfaces furnishes a barrier to the rapid entrance of either species of ion, i.e., phosphate and iron. Under certain conditions, precipitation reactions may also occur in the conductive tissues of the stem and leaf and so constitute a block in the transfer of certain ions from the conductive tissue to the leaf mesophyll and growing points.
Palavras-Chave: | Bean plant; Efeito; Effect.
Thesagro: | Feijão; Ferro; Fósforo; Planta.
Thesaurus Nal: | iron; phosphorus.
Categoria do assunto: | --
Registro original: | Embrapa Pantanal (CPAP)
Exemplares: | CPAP - (32993-1) - ADD - SP - -- - SP3236 -  - 3236 - DIS