GeCl4 (Sigma) was carefully dissolved in 1 m HCl to give a final Ge concentration of 50 mm and subsequently converted to Ge(OH)4 by neutralization with 1 m KOH

GeCl4 (Sigma) was carefully dissolved in 1 m HCl to give a final Ge concentration of 50 mm and subsequently converted to Ge(OH)4 by neutralization with 1 m KOH. 2004). Very recently, Ma et al. made the finding of (and (Azam, 1974), oocytes injected with mRNA derived from the Furazolidone Furazolidone SIT1 clone of (Hildebrand et al., 1997) and in rat cells including mind (Mehard and Volcani, 1975; Taylor et al., 1992). Clear information as to the applicability of 68Ge like a tracer for Si in flower uptake, and its possible degree of discrimination, is still lacking. Earlier studies by Takahashi et al. (1976a, 1976b) showed that Ge seems to be taken up by flower origins similarly to Si, and in a recent study using wheat (= 4). = 4) sd. Table II. = 4) sd. Superscript characters denote significant variations between varieties at 0.05 relating to Duncan’s test. = 4) sd. = 4) sd. Open in a separate window Number 5. Effect of 2,4-DNP (A) and HgCl2 (B) on relative root-to-shoot translocation of 68Ge-labeled Si in rice, barley, cucumber, and tomato vegetation. In the control treatment (none of either 2,4-DNP or HgCl2), complete shoot amount of Si was denoted as 100%. Data are means (= 4). Conversation The use of radioactive isotopes provides a useful tool in the study of the uptake and transport of mineral elements either as ions or molecules in vegetation; however, their reliability as tracers must sometimes become cautiously verified. For instance, radioactive rubidium-86 with related chemical properties to that of K+, which has often been used like a tracer for K+, can give misleading results under certain conditions (Behl and Jeschke, 1982). In this study, both measurements of the radioactivity of 68Ge and chemical analysis of Si in flower cells were carried out to demonstrate that flower varieties with markedly different capacities for accumulating Si in their shoots are able to take up 68Ge without discriminating between these two elements (Table I; Fig. 1). The clearly shown tendency of all the flower species (rice, barley, cucumber, and tomato) to keep up a 68Ge:Si molar percentage in their cells similar to that in the supplied nutrient answer (Table I) is a key condition for the applicability of the tracer (Maas and Leggett, 1968). It has been proposed that uncharged Si(OH)4 is the only molecular species likely to mix the root plasma membrane at physiological pH (Raven, 2001). Consequently, taking into consideration the related physicochemical properties of Si(OH)4 and Ge(OH)4 such as their pKas of about 9.3 to 9.5 (Pokrovski and Schott, 1998; Tossell and Sahai, 2000), it would be expected the uncharged form of Ge(OH)4 should also be able to mix the plasma membrane passively (by diffusion) and/or actively via Si transporter(s). The results demonstrated in Number 1, A and B unequivocally support this assumption. The uptake of both Si(OH)4 and Ge(OH)4 identified through the radioactivity of 68Ge tracer showed saturable kinetics with related apparent residues in Si transporter(s) and/or poison-induced switch in the general metabolic status of vegetation (Maurel and Chrispeels, 2001; Tamai and Ma, 2003). It is of interest that this mercury-induced inhibition of Si uptake was not caused by the inhibition of water uptake (Tamai and Ma, 2003; Mitani and Ma, 2005), suggesting a difference between aquaporin-like Si transporter(s) and water channels. Furthermore, the gene, which is definitely constitutively expressed in the plasma membranes of both exodermal and endodermal root cells and hence controls xylem loading of Si in rice (manifestation of in Xenopus oocytes results in Si but not in water transport activity), is found to belong to the aquaporin family (Ma et al., 2006). Remarkably, in tomato, a Si-excluding varieties (see Table III; Helne et al., 2005), the application of both 2,4-DNP and HgCl2 actually caused an increase of uptake and root-to-shoot translocation of Si (Figs. 4D and 5, A and B). The application of 68Ge tracer for Si demonstrates the living of a system of metabolically active Si exclusion in tomato, not possible Furazolidone to be observed by the methods of dedication of Si in the root cell sap used in the previous studies of Furazolidone Mitani and Ma (2005). The nonaccumulators actually exclude Si(OH)4 using their origins, because they consist of less Si in the shoots than would be expected if there was nonselective passive influx with water (Liang et al., 2005, 2006). Metabolically active exclusion of Si against the concentration gradient in the root cortex might be responsible for lower uptake of Si by tomato at high concentration of Si in the external press (Figs. IFNB1 2D and ?and3).3). Consequently, it can be hypothesized that in the Furazolidone Si-excluding vegetation such as tomato, passive.