The Response of the Phosphate Uptake System and the Organic Acid Exudation System to Phosphate Starvation in Sesbania rostrata

Abstract

It is well known that the P i uptake system via the highaffinity P i transporter and the organic acid exudation system via PEPC are enhanced in the roots of P i -starved plants. In this paper, we compared the expression of these two systems in Sesbania rostrata, a leguminous plant, on whose roots and stems it forms nodules. When S. rostrata plants were transferred to a 0 m m m mM P i nutrient solution, the expression of both the high-affinity P i transporter and PEPC was enhanced within 2 d. The enhancement of the expression of the high-affinity P i transporter genes and the PEPC gene coordinated with the increases in the P i uptake rate and the PEPC activity, respectively. This suggests that the expression of the high-affinity P i transporters and PEPC is regulated in part at the transcript level. Furthermore, we examined which of the environmental or the endogenous P i level regulates the expression of these two systems. The P i content in the 6-day-old plants decreased to a lower level than that in the 15-day-old plants when grown in a 30 m m m mM P i solution. At that time, the expression of the high-affinity P i transporters and PEPC was enhanced only in the 6-day-old plants. Moreover, the P i content in plants forming many nodules on their stems decreased. The expression of the high-affinity P i transporters and PEPC was then enhanced in the nodulated plants. These facts suggest that the expression of these two systems may be regulated by the P i content in the plants, not by the P i concentration in the soil.

Cloning of the plasma membrane H+-ATPase gene with suppressed expression under Pi-Deficient conditions inSesbania rostrata

“…The pH of the complete nutrient solution was adjusted to 6.0 and the solution contained 2.5 mM KN0 3 , 2 mM Ca(N0 3 )2' 0.5 mM NH 4 N0 3 , 1 mM KH 2 P0 4 , 1.0 mM MgS0 4 , 0. added per liter of solution. As described in the previous report (Aono et al 2001), the Pi concentration in the solution containing FeP0 4 was less than 1 IJ.M during the experiments. The volume of the nutrient solution was 400 mL per plant for 6-d-old plants, and 4 L per plant for l5-d-old plants.…”

“…The gene-specific probes for SrHA 1, SrHA4, and SrHA5 were obtained by PCR amplification of the 3' untranslated regions using the cDNA clones as templates, and with gene-specific primers (Table 1). The gene-specific probes for the Pi transporters (SrPTl and SrPT2) and PEPC (SrPEPC) were also obtained by PCR as described previously (Aono et al 2001).…”

“…In this study, attempts were made to isolate genes encoding such Pi-deficiencyresponsible isoforms from Sesbania rostrata, which is a leguminous plant forming nodules on stems as well as on roots. In a previous study (Aono et al 2001), we observed that the expression of the genes for high-affinity Pi-transporters and phosphoenolpyruvate carboxylase (PEPC) in the roots of S. rostrata was enhanced rapidly in response to Pi-deficiency, resulting in the increase of the Pi-uptake and exudation of organic acids from roots. Then, we compared the expression of the PM H+-ATPase gene to that of high-affinity Pi-transporters and PEPC.…”

Lon Protease of Azorhizobium caulinodans ORS571 Is Required for Suppression of reb Gene Expression

“…After germination, S. rostrata plants were transferred into a commercial horticultural soil (Kureha Chemical) and grown at 35°C under a 24-h light regimen at an intensity of 50,000 lx as described previously (57). Although this soil contained 0.4 g N/kg, stem nodule formation was not inhibited by the use of this soil because S. rostrata can form stem nodules even under 6.5 mM NO 3 Ϫ conditions (2). A. caulinodans cultures grown overnight were inoculated onto the stems at 2 weeks after transplantation.…”

Rhizobial Factors Required for Stem Nodule Maturation and Maintenance in Sesbania rostrata-Azorhizobium caulinodans ORS571 Symbiosis

“…The soil contained 0.4 g N/kg. As S. rostrata can form stem nodules even under 6.5 mM NO 3 Ϫ conditions (3), stem nodule formation was not inhibited by the use of this soil. The tubes containing the seedlings were placed on trays filled with tap water and grown for 2 weeks prior to bacterial inoculation at 35°C under a 24-h light regimen at an intensity of 50,000 lx.…”