Langstreckentransport von Natrium in Bohnenpflanzen

Abstract

Long distance transport of sodium in bean plants In 8–10 days old bean plants Na+ (22Na) has been applied to either a certain root zone, the stem, or the base and tip respectively of a primary leaf and the long distance transport of Na+ was studied in the following 12–48 h. The long distance transport of Na+ applied to the root zone 9–12 cm behind the tip was strongly restricted towards the shoot and hardly detectable towards the root tip (phloem transport). Presence of K+ in the surrounding solution strongly increased the Na+ efflux from the roots. After leaf application within 48 h 30–40% of the absorbed Na+ had been translocated out of the leaf in direction of the root where, from the basal root zones, intensive Na+ efflux took place. This Na+ efflux was hardly affected by presence of K+ in the external medium and was usually more than 10% of the Na+ taken up by the leaves. From the Na+ taken up by the hypocotyl within 12 h more than 25% had been released from the basal root zones into the nutrient solution. Less than 1% of the Na+ applied either to the leaf or the stem was translocated towards the shoot apex. Separation of the hypocotyl into cortex and stele at the end of the experiment demonstrated the high capacity of the stele for Na+ accumulation. Within the hypocotyl the transfer of Na+ from the stele to the cortex and the phloem seems to be a rapid process whereas the release of Na+ from the phloem into the stele is obviously very restricted. The long distance transport of Na+ within the phloem of the shoot is strictly basipetal and very efficient. Low Na+ contents of bean leaves are therefore the result of several regulating mechanisms: K+ stimulated Na+ efflux in the roots, restricted long distance transport in the xylem due to high Na+ accumulation in the stele, Na+ pumps at the phloem in stem and leaves for phloem loading of Na+, and finally strictly basipetal retranslocation of Na+ in the phloem into the roots and efflux into the solution from basal root zones.

Effects of NaCl and KC1 Salinity on Growth and Ionic Relations of Red Kidney Beans (Phaseolus vulgaris L.)

“…This may be achieved by a combination of the absence of metabolic Na fluxes in cortical root cells and selective metabolic Na absorption by some vascular tissue which results in phloem loading. Sodium thus returned to the apical region of the roots may be lost to the root medium by efflux (JACOBY andRATNER 1974, MARSCHNER andOssENBERG NEUHAUS 1976). Role of transfer cells in the process of xylem depletion and transfer of sodium to the phloem may also be considered important for this Na exclusion .…”

Transport de Na+ dans les feuilles et sensibilité des plantes à NaCl. I. Évaluation d'un effet piège au niveau des tiges

“…Seul le recyclage du Na+ ainsi prélevé vers le bas de la plante peut expliquer la stabilité du gradient longitudinal d'accumulation dans les tiges des plantes sensibles (fig 3). Effectivement, on sait que les plantes sensibles à NaCl sont capables de transporter Na+ dans la circulation descendante (Cooil et al, 1965;Lévi, 1968;Marschner et Ossenberg-Neuhaus, 1973;Jacoby, 1979). Cette aptitude au transport phloémien de Na+ parait typique des plantes sensibles, car elle n'apparaît pas chez les glycophytes tolérants (Lessani et Marschner, 1978), ni chez les halophytes (Flowers et Yeo, 1986).…”

Non-destructive methods for demonstrating chemical changes in the rhizosphere I. Description of methods

“…To demonstrate FelII reduction an agar technique was used (Marschner et al, 1982). Reduction of F e l I I is i n d i c a t e d by the f o r m a t i o n of a red c o m p l e x b e t w e e n F e l I and B P D S (bathophenanthroline-disulfonic acid).…”

“…Compared to the agar technique with MnlV (Gardner et al, 1982;Marschner et al, 1982) the filter p a p e r t e c h n i q u e (Uren, 1981) …”

“…Most methods are based on agar as a medium containing specific reagents and indicators. By colour reactions, it is possible to demonstrate the following processes in the r h i z o s p h e r e : pH c h a n g e s ( M a r s c h n e r and 1988;Armstrong et al, 1992); excretion of organic acids (Dinkelaker et al, 1989;Hoffland et al, 1989); reduction of FeIII (Gardner et al, 1982; Rt~mheld and M a r s c h n e r , 1986) and MnIV (Gardner et al, 1982;Marschner et al, 1982;Uren, 1981); solubilization of various inorganic p h o s p h a t e s ( G a r d n e r et al , 1982); and the activity of acid phosphatase (Dinkelaker and Marschner, 1992). In the f o l l o w i n g , s e v e r a l m e t h o d s are described for the detection and localization of reducing processes, the complexation of AI and the a c t i v i t y of acid p h o s p h a t a s e in the rhizosphere of soil-grown plants.…”