Characterizing the Physiological Response of Tomato to Phosphorus Deficiency and Recovery Jonathan Frantz1, Scott Heckathorn2, Sasmita Mishra2, Deanna Bobak3, Anju Giri2 1USDA-ARS, Greenhouse Production Research Group, Toledo, OH 2Department of Environmental Science, The University of Toledo, Toledo, OH 3Department of Curriculum and Instruction, The University of Toledo, Toledo, OH INTRODUCTION Expt. 2. Expt. 3. The plant response to phosphorus (P) deficiency is well defined: plants tend to shift growth to roots in order to explore the soil for more P, root-zone pH declines as the rhizosphere adjust to increasing availability of P (Taylor et al., 2010), and high-affinity P transporters are up-regulated (Raghothama, 1999). If P deficient for prolonged periods, P is reallocated from older to younger leading to marginal, and eventually total, leaf necrosis (Gibson et al., 2007). At what point a plant can recover from P deficiency is less well understood, and the physiological adjustments to P replenishment have not been characterized. Figure 2. Nitrate reductase (NR), high affinity P transporter (Pht1) and glutamate dehydrogenase (GDH) protein in tomato roots. Phosphate uptake and N metabolism change shortly after P stress begins; P uptake responds more slowly to P recovery than N metabolism Figure 1. Tomato grown hydroponically with complete (left) or –P nutrient solutions (right) for 12 days. P deficiency symptoms can be seen by overall smaller size, lower leaf chlorosis, or purpling of leaf margins. Figure 3. Single leaf photosynthesis, normalized to control rates. After 4 d of P deficiency, Pn is significantly lower than control values and does not recover until 4 d after P re-supply. Both of those time points are earlier than visible symptoms appear. MATERIALS AND METHODS Expt. 4. Expt. 1: Tomato plants were grown hydroponically for 31 days. After 7 days, P was withheld from some tubs; every 4 days (4 days after treatment, DAT), a subset of those plants were returned to P-sufficient conditions. Half the plants were harvested 12 DAT and the remaining plants were harvested 24 DAT. Leaf, root, and stem dry weight were recorded, and tissue was analyzed for P concentration with ICP. Expt. 2: Tomato plants were grown hydroponically for 12 days. After 7 days, P was withheld from some tubs; 1 DAT, half the plants were harvested. At 4 DAT, plants were resupplied with P and 5 DAT (1 day after P recovery), remaining plants were harvested. Tissue was analyzed for the high-affinity P transporter (Pht1), nitrate reductase (NR), and glutamate dehydrogenase (GDH). Expt. 3: Tomato plants were grown hydroponically for 31 days. After 7 days, P was withheld. 12 DAT, plants were returned to P sufficient conditions. Plants were harvested on 0, 1, 2, 4, 6, 12, 13, 14, 16, 18, and 24 DAT. Plants were analyzed for tissue dry weight (old and new leaf, stem, root), P concentration, and enzymes from Expt. 2. Expt. 4: Similar to Expt. 3 except leaf photosynthesis was analyzed on old and new leaves on the same days that Expt. 3 was harvested. Figure 5. Leaf P concentration decreased rapidly under P deficiency and increased even more rapidly during recovery, even surpassing concentrations found in control plants. Figure 4. Leaf and root dry weights of tomato (left) and root fraction (right) during P deficiency and recovery. Dry weights were not significantly different until 12 days of P deficiency, but root fraction was higher in P treated plants from 6 d of deficiency until 6 d after recovery. CONCLUSIONS RESULTS P deficiency and recovery is complex and appears to influence both P and N uptake / metabolism. Plants need at least 2 weeks to fully recover from P deficiency after visible symptoms appear. Due to more roots and more / high affinity P transporters, plants can hyperaccumulate P upon recovery. Expt. 1. P def/ P rec days Leaf g / plant Stem g / plant Root g / plant Root % [P] g kg-1 [N] g kg-1 Table 1. Tomato harvested 24 days after treatments began, each with different amounts of P deficiency and recovery. The more deficiency, the smaller the plant, the greater the root fraction, and in short-term recovery, P is higher than control plants. Even after 4 d of deficiency and 20 d recovery, plants are significantly smaller than controls. Data are averages of 4 replicate plants. ACKNOWLEDGEMENTS control 14.8 a 11.9 ab 11.4 ab 8.6 bc 5.4 c 4.1 c 6.6 a 7.2 a 6.1 ab 3.8 bc 3.1 c 2.0 c 2.4 a 2.3 ab 2.2 ab 1.6 abc 1.3 bc 1.0 c 10.0 b 10.8 b 11.2 b 13.5 a 14.4 a 8.6 b 9.5 b 8.5 b 8.9 b 9.4 b 13.6 a 68.3 a 69.5 a 70.4 a 71.1 a 68.2 a 66.5 a We thank Doug Sturtz, Russ Friedrich, Sujin Kim, and Alycia Pittenger for assistance with plant and protein analysis 4/20 REFERENCES 8/16 Gibson, J.L., D.S. Pitchay, A.L. Williams-Rhodes, B.E. Whipker, P.V. Nelson, and J.M. Dole. 2007. Nutrient deficiencies in bedding plants: a pictorial guide for identification and correction. Ball Publishing, Batavia, IL. Raghothama, K.G. 1999. Phosphate acquisition. An. Rev. Plant Physiol. Plan Mol. Biol. 50:665-693. Taylor, M.D., P.V. Nelson, J.M. Frantz, and T.W. Rufty. 2010. Phosphorus deficiency in Pelargonium: effects on nitrate and ammonium uptake and acidity generation. J. Plant Nut. 33:701-712. 12/12 16/8 20/4