A phosphoenol pyruvate phosphatase transcript is induced in the root nodule cortex of Phaseolus vulgaris under conditions of phosphorus deficiency

Abstract

Although previous studies on N2-fixing legumes have demonstrated the contribution of acid phosphatases to their phosphorus (P) use efficiency under P-deficient growth conditions, localization of these enzymes in bean nodules has not been demonstrated. In this study, phosphoenol pyruvate phosphatase (PEPase) gene transcripts were localized within the nodule tissues of two recombinant inbred lines, RIL115 (P-deficiency tolerant) and RIL147 (P-deficiency sensitive), of Phaseolus vulgaris. Nodules were induced by Rhizobium tropici CIAT899 under hydroaeroponic conditions with a sufficient versus a deficient P supply. The results indicated that PEPase transcripts were particularly abundant in the nodule infected zone and cortex of both RILs. Analysis of fluorescence intensity indicated that nodule PEPase was induced under conditions of P deficiency to a significantly higher extent in RIL147 than in RIL115, and more in the inner cortex (91%) than in the outer cortex (71%) or the infected zone (79%). In addition, a significant increase (39%) in PEPase enzyme activity in the P-deficient RIL147 correlated with an increase (58%) in the efficiency of use in rhizobial symbiosis. It was concluded that nodule PEPase is upregulated under conditions of P deficiency in the P-deficiency-sensitive RIL147, and that this gene may contribute to adaptation of rhizobial symbiosis to low-P environments.

Fig. 1.

In situ localization of PEPase transcripts (green spots) in nodules of common bean RIL115 and RIL147 (as indicated) inoculated with R. tropici CIAT899 and grown under a sufficient (250 P) versus a deficient (75 P) P supply. (A, A') Negative controls without reverse transcriptase; (B, D) P-sufficient RIL115; (C, E) P-deficient RIL115; (F, H) P-sufficient RIL147; (G, I) P-deficient RIL147. InC, infected cell; IC, inner cortex; IZ, infected zone; OC, outer cortex; UC, uninfected cell; VT, vascular trace parenchyma. Bars, 500 µm (A, A', B, C, F, G); 200 µm (D, E, H, I). (This figure is available in colour at JXB online.)

Fig. 2.

PEPase transcript signal (pixel number of the green spots) in (A) total nodule sections, (B) infected zone, (C) inner cortex, (D) outer cortex, and (E) vascular traces of common bean RIL115 and RIL147 inoculated with R. tropici CIAT899 and grown under a sufficient (open columns) versus a deficient (filled columns) P supply. Data are means ±SD of ten images of nodules harvested at 42 DAT. Mean values labelled with the same letter were not significantly different at P <0.01.

Fig. 3.

PEPase (A) and APase (B) activities in nodules of common bean RIL115 and RIL147 inoculated with R. tropici CIAT899 and grown under a sufficient (open columns) versus deficient (filled columns) P supply. Data are means ±SD of six replicates harvested at 42 DAT. nfw, Nodule fresh weight. Mean values labelled with the same letter were not significantly different at P <0.01.

Fig. 4.

Nodule (A, B) and shoot (C) P content of common bean RIL115 and RIL147 inoculated with R. tropici CIAT899 and grown under a sufficient (open columns) versus deficient (filled columns) P supply. Data are means ±SD of six replicates harvested at 42 DAT. Mean values labelled with the same letter were not significantly different at P <0.01.

Fig. 5.

Nodule (A) and shoot (B) N contents of common bean RIL115 and RIL147 inoculated with R. tropici CIAT899 and grown under a sufficient (open columns) versus a deficient (filled columns) P supply. Data are means ±SD of six replicates harvested at 42 DAT. Mean values labelled with the same letter were not significantly different at P <0.01.

Fig. 6.

Efficiency of use of rhizobial symbiosis of common bean RIL115 and RIL147 inoculated with R. tropici CIAT899 and grown under a sufficient (open circles) versus a deficient (filled circles) P supply. Data represent individual values of 14 replicates harvested at 42 DAT. Ndw, Nodule dry weight.