Partitioning and flows of ions and nutrients in salt‐treated plants ofLeptochloa fuscaL. Kunth

Abstract

SUMMARYAn empirically based modelling technique, based on the relative immobility of Ca^+ in phloem, was used quantitatively to describe uptake, flow in xylem and phloem, and partitioning of K*, Na', Mg'^^, and Cr for a 13-d period at the end of vegetative growth of the main shoot in Leptochloa fusca (L.) Kunth grown in presence of 100 mM NaCl. The model incorporated data on net inerements of the ions in the root, the stem, individual leaf sheaths and laminae (blades), and tillers, secretion of salt by glandular hairs on sheaths and laminae, and the molar ion:Ca ratios in the xylem sap. Molar ratios of uptake of Na:Cl:K were 1-27:112:1, indicating an uptake selectiyity of 11-3 in favour of K+ against Na+. The flow pattern of K+ in the main shoot featured relatively low permanent deposition (22 % of the intake into the shoot in the stem axis and 10 % in leaves) but a high return flow via phloem to the root (67%) followed by cyelingof K'. In the whole plant a large share (72 "") of K* uptake was utilized for growth of tillers but K' cycling from shoot to root amounted to 96 "o of uptake. The flow pattern of Na'^ featured a somewhat smaller commitment (62 %) to deposition in tillers. In the main shoot 33 % of Na"' intake was deposited in the stem and 35 % in leaves. In these the sheaths incorporated by far the larger (2-8-fold) share compared with the laminae. Of the total Na' intake, 9% was excreted by salt glands (3-3-fold more by laminae than sheaths) and only 31 % was translocated to the root via phloem. Flows and partitioning of Cr were similar to those of Na"^, but phloem transport was larger (60% of intake into the main shoot) than that of Na+. The flow patterns are discussed in relation to changes in ion concentrations of leaves with leafage and in relation to snlmity tolerance. It is suggested that besides salt secretion a high efficiency in K* utilization contributes to the performance of this halophyte in presence of salt

Improved tolerance of maize plants to salt stress by arbuscular mycorrhiza is related to higher accumulation of soluble sugars in roots

“…Sodium is mainly accumulated in older leaves because of its poor translocation (Lazof and Laüchli 1991;Jeschke et al 1995). Accumulation of Na in plant cells decreases photosynthesis in old leaves and, thereby, transportation of carbohydrates from old leaves to young leaves and roots.…”

Transport and partitioning of phosphorus in wheat as affected by P withdrawal during flag-leaf expansion

“…The magnitude of the over-or underestimates was given by the relation of phloem to xylem transport of Ca 2+ . On the basis of data for Ricinus, for example, it was between 1.2% (young leaves) and 5% (old leaves) for other ions (Jeschke et al, 1995). Phloem flows, on the other hand, would be underestimated, no matter whether the organ in question is phloem-importing or -exporting.…”

“…In early studies, an empirically based modeling technique (Armstrong and Kirkby, 1979) has been used which allows the flows and utilization of different phloem-mobile elements within the plant to be depicted quantitatively. The partitioning and circulation are very different in different species, and these can change when plants grow under stressed conditions, such as for P under P-deficiency (castor bean: Jeschke et al, 1997); for K + under saline conditions (lupin: Jeschke et al, 1995;barley: Wolf and Jeschke, 1987) or sole NH + 4 -supply conditions (tobacco: Wang et al, 2003), and after decapitation (tobacco: Jiang et al, 2001); and for N under P deficiency (castor bean: Jeschke et al, 1997).…”

Cellular and whole-plant chloride dynamics in barley: insights into chloride?nitrogen interactions and salinity responses

“…The cytosolic exchange half-times were used to calculate fluxes to the shoot (see Materials and methods), which can be a significant component of total efflux from the cytosol of root cells (Hajibagheri et al 1988;Jeschke et al 1995). The underlying assumption that the cytosolic compartment of xylem-loading cells obeys similar exponential exchange kinetics as other root cells is supported by a study that showed that the half-time of 36 Cl ) labelling of the glandular exudate of Limonium vulgare leaf tissue was identical to the half-time of ''cytoplasmic'' 36 Cl ) efflux (Hill 1970; see also Cram 1968).…”