Foliar application of nitrate or ammonium as sole nitrogen supply in Ricinus communis. II. The flows of cations, chloride and abscisic acid

Abstract

Following a precultivation with pedospheric nitrogen nutrition, Ricinus plants were supplied with nitrogen solely by spraying nitrate or ammonium solution onto the leaves during the experimental period. The chemical composition of tissues, xylem and phloem exudates was determined and on the basis of the previously determined nitrogen flows (Peuke et al., New Phytologist (1998), 138, 657–687) the flows of potassium, sodium, magnesium, calcium, chloride and ABA were modelled. These data, which permit quantification of net‐uptake, transport in xylem and phloem, and utilization in shoot and root, were compared with results obtained in plants with pedospherically‐supplied nitrate or ammonium and data in the literature. Although the overall effects on the chemical composition of supplying ammonium to the leaves were not as pronounced as in pedospherically supplied plants, there were some typical responses of plants fed with ammonium (ammonium syndrome). In particular, in ammonium‐sprayed plants uptake and transport of magnesium decreased and chloride uptake was increased compared with nitrate‐sprayed plants. Furthermore, acropetal ABA transport in the xylem in ammonium‐sprayed Ricinus was threefold higher than in nitrate‐sprayed plants. Additionally, concentrations of anions were more or less increased in tissues, particularly in the roots, and transport fluids. The overall signal from ammonium‐sprayed leaves without a direct effect of ammonium ions on uptake and transport systems in the root is discussed.

Cytosolic potassium homeostasis revisited: 42 K-tracer analysis in Hordeum vulgare L. reveals set-point variations in [K + ]

“…Seedlings were then transferred from growth solutions to 42 K + labelling solutions for 60 min (see . This time period was long enough to substantially enrich the cytosolic compartments of root cells with radioisotope, but too short to label potentially interfering back-fluxes from the vacuole (Behl and Jeschke 1982;Jeschke 1982;Memon et al 1985) and the phloem, the latter of which are known to be sizeable (White 1997;Peuke et al 1998;Engels and Kirkby 2001). Labelled roots were attached to efflux funnels with clamped rubber spouts .…”

Flows of elements, ions and abscisic acid in Ricinus communis and site of nitrate reduction under potassium limitation

“…On the contrary, there seemed to be the tendency to compensate the charge balance of a missing ion by the enhanced uptake of others. This was chloride in the case of imposing low or no nitrate pedospherically (N-deficiency: Peuke et al, 1994a, ammonium nutrition: Peuke andPeuke et al, 1998). Under the present K q -limitation, the uptake of Ca 2q and Mg 2q were about 120% and that of Na q 244% of the control.…”

“…The nutritional conditions included the type of nitrogen source (Peuke and Jeschke, 1993), salt stress (Peuke and Jeschke, 1995;Peuke et al, 1996), foliar application of nitrogen (Peuke et al, 1998) as well as the limitation or deficiency of nitrogen (Peuke et al, 1994a) or phosphorus (Jeschke et al, , 1997a. However, the influence of potassium, the third most important nutrient, has not yet been investigated in the long-distance transport of solute and stress signals.…”

“…Whereas the mobility and long-distance transport of potassium in the xylem and phloem has been studied intensively in the past (in xylem sap, wheat: Barneix and Breteler, 1985;bean: Cakmak et al, 1994a, b;Ricinus: Peuke andJeschke, 1993, 1995;Peuke et al, 1994aPeuke et al, , 1998; rye: White, 1997;Lupinus: Jeschke et al, 1985; in phloem sap, Lupinus and Spartium: Pate et al, 1974;Jeschke et al, 1985;Ricinus: Peuke and Jeschke, 1995), few data have been published about the effects of potassium supply on the transport of solutes, assimilates and hormonal stress signals, such as ABA.…”

Influência do nitrato e do amônio sobre a fotossíntese e a concentração de compostos nitrogenados em mandioca

“…Depois do desbaste, o substrato passou a ser fertilizado com soluções nutritivas, modificadas a partir da solução utilizada por CRUZ (2001 + podem reduzir a condutividade hidráulica das raízes, diminuindo, assim, o transporte de água para atender a demanda da parte aérea (ADLER et al, 1996). Adicionalmente, a elevação dos níveis de ácido abscísico, como conseqüência da fertilização amoniacal, também pode ter concorrido para o observado fechamento estomático (PEUKE et al, 1998 , mas a atividade da redutase do nitrato é relativamente baixa (PEREIRA & SPLITTSTOESSER, 1986;CRUZ et al, 2004), o que não explica essa menor concentração de nitrato das folhas em relação à concentração das raízes. Assim, a baixa concentração foliar de nitrato pode ser conseqüência da capacidade reduzida de seu transporte das raízes para a parte aérea, e não de sua redução pelas folhas, à semelhança do resultado obtido para soja por RADIN (1978).…”