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Eric J. Biddinger, Chunming Liu, and K.G. Raghothama

We are interested in understanding the molecular changes that occur in response to phosphate starvation in the roots of tomato plants. Aeroponics offers a unique way to study the changes that occur in the roots of plants. Tomato plants were grown in an aeroponic system developed by L.A. Peterson at the Univ. of Wisconsin. Aeroponically grown tomato plants were treated with various concentrations of phosphate (Pi) ranging from 0 to 250 μm. Plants were harvested at different times after the initiation of Pi deficiency treatments for nutrient analysis and gene expression studies. Several changes in essential nutrient content were observed. A differential accumulation of magnesium between the root and shoot tissue of phosphorus-starved plants was noticed. The expression of a recently cloned phosphate starvation induced gene (TPSI1) increased with decreasing concentration of Pi in the growth media. There is a strong correlation between the concentration of the Pi in the growth media and expression of the gene. The effect of Pi starvation on the gene expression in different parts of the plant, including old and young leaves, will be discussed.

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Eric J. Biddinger, Chunming Liu, and K.G. Raghothama

Phosphate starvation in plants results in altered biochemical and physiological responses. We are interested in understanding the changes that occur in response to phosphate starvation in the roots of tomato plants. Plants were grown in an aeroponic system developed by L.A. Peterson at the Univ. of Wisconsin. Aeroponically grown tomato plants were treated with various concentrations of phosphate, ranging from to 250 mM. Phosphate-starved plants exhibited significantly higher root to shoot ratios and a 40% decrease in the chlorophyll content of the leaves. Several changes in essential nutrient content were also observed. The phosphate concentration of both root and shoot tissues decreased as the Pi content of the nutrient solution decreased. Whereas the ratio of phosphate content in roots compared to the shoots did not change significantly in response to Pi starvation. Phosphate-starved plants accumulated significantly higher amount of magnesium in stem tissues. Furthermore, it also resulted in an increased accumulation of potassium in roots. Interestingly, the total extractable RNA from phosphate-starved roots was 1/5th of that of control roots. There was also a noticeable decrease (50%) in the total extractable RNA content of leaves from phosphate-starved plants.

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Eric J. Biddinger, Chunming Liu, Robert J. Joly, and K.G. Raghothama

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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A.A. Watad, K.G. Raghothama, M. Kochba, A. Nissim, and V. Gaba

Explant growth and shoot multiplication of Spathiphyllum and Syngonium were compared on agar-solidified medium and interfacial membrane rafts floating on liquid medium. After 25 d of culture, greater shoot multiplication and fresh mass gain were achieved by plant material grown on rafts. Shoot multiplication of Spathiphyllum and Syngonium on membrane rafts reached a maximum at 25 d, whereas the fresh mass increased throughout the culture period (40 d). The number of shoots of Spathiphyllum and Syngonium material grown on membrane rafts remained constant between 25 and 40 d of culture. The plants grown on membrane rafts also developed more roots.