Phosphorus is one of the essential but limiting nutrients in nature. In this study, we link the physiological changes occurring under phosphate (Pi) starvation to gene expression. Roots of aeroponically grown tomato (Lycopersicon esculentum L.) plants were sprayed intermittently with nutrient solutions containing varying concentrations of P. Decreasing the concentration of Pi in the nutrient solution resulted in reduced biomass production and altered the tissue concentration of nutrients in roots and shoots. Phosphorus starvation increased the root:shoot biomass ratio and decreased net CO2 assimilation and stomatal conductance. Phosphorus concentrations in roots and shoots decreased with decreasing concentration of Pi in the nutrient solution. Pi-deficient plants had a higher concentration of Ca in roots and Mg in shoots. Expression of the Pi starvation-induced gene, TPSI1, persisted even after 3 weeks of Pi starvation. The transcript accumulation in leaves was found to be a specific response to Pi starvation and not to the indirect effects of altered N, K, Fe, Mg, or Ca status. Accumulation of transcripts was also observed in stem and petioles, suggesting a global role for TPSI1 during Pi starvation response of tomatoes.
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