The response of the phosphate uptake system and the organic acid exudation system to phosphate starvation in Sesbania rostrata
Aono, T. (Tokyo Univ. (Japan)) | Kanada, N. | Ijima, A. | Oyaizu, H.
It is well known that the P sub(i) uptake system via the high-affinity P sub(i) transporter and the organic acid exudation system via PEPC are enhanced in the roots of P sub(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 micro M P sub(i) nutrient solution, the expression of both the high-affinity P sub(i) transporter and PEPC was enhanced within 2 d. The enhancement of the expression of the high-affinity P sub(i) transporter genes and the PEPC gene coordinated with the increases in the P sub(i) uptake rate and the PEPC activity, respectively. This suggests that the expression of the high-affinity P sub(i) transporters and PEPC is regulated in part at the transcript level. Furthermore, we examined which of the environmental or the endogenous P sub(i) level regulates the expression of these two systems. The P sub(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 micro M P sub(i) solution. At that time, the expression of the high-affinity P sub(i) transporters and PEPC was enhanced only in the 6-day-old plants. Moreover, the P sub(i) content in plants forming many nodules on their stems decreased. The expression of the high-affinity P sub(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 sub(i) content in the plants, not by the P sub(i) concentration in the soil.
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