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Teryl R. Roper and John S. Klueh

The source of photosynthate for developing cranberry (Vaccinium macrocarpon Ait.) fruit can be partitioned spatially among new growth acropetal to fruit, 1-year-old leaves basipetal to fruit, and adjacent uprights along the same runner. Cranberry uprights were labeled with 14CO2 in an open system with constant activity during flowering or fruit development. When new growth acropetal to fruit was labeled, substantial activity was found in flowers or fruit. Little activity was found in basipetal tissues. When 1-year-old basipetal leaves were labeled, most of the activity remained in the labeled leaves, with some activity in flowers or fruit. Almost no labeled C moved into acropetal tissues. When new growth of adjacent nonfruiting uprights on the same runner were labeled, almost no activity moved into the fruiting upright. These data confirm that new growth acropetal to developing flowers and fruit is the primary source of photosynthate for fruit development. Furthermore, they show that during the short time studied in our experiment, almost no C moved from one upright to another.

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Michelle DaCosta and Bingru Huang

Rachmilevitch for assisting in the radioactive labeling work. Partial funding for this study was provided by the Rutgers University Center for Turfgrass Science.

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Camilo Canel, Julia N. Bailey-Serres, and Mikeal L. Roose

The acidless phenotype of the pummelo 2240 [Citrus maxima [Burro.] Merrill] is caused by a mutation affecting a key element of the citric acid accumulation pathway. To test the functionality of the tonoplast citrate transport mechanism, we obtained a tonoplast-enriched membrane fraction from juice tissues of acidless fruit by centrifugation through a discontinuous Ficoll gradient. The isolated tonoplast vesicles incorporated radioactively labeled citrate at a higher rate than vesicles from similarly fractionated high-acid fruit juice. Uptake of [14C]citrate occurred against a concentration gradient was stimulated by nitrate-sensitive ATP hydrolysis, but not by hydrolysis of PPi, and was not affected by the ionophore nigericin. Uptake was not inhibited by malate and only slightly by isocitrate. We did not find evidence of a defective citrate transport mechanism at the tonoplast of juice cells of acidless fruit. We propose that citric acid accumulation in the fruit of citrus is mediated by a carrier that uses energy produced during hydrolysis of ATP to transport citrate into the vacuole actively and specifically.

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Michael S. Reid and George L. Staby

reaction that results in the substrate or inhibitor “tag” being covalently attached to the enzyme protein at a location close to the actual binding domain. If the ligand is radioactively labeled, one can thereby radioactively label the binding site protein

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Matthew A. Escobar, Andrew Shilling, Pine Higgins, Sandra L. Uratsu, and Abhaya M. Dandekar

using a TA Cloning Kit (Invitrogen, Carlsbad, CA). The PPO fragment was subsequently excised from the vector by restriction digestion, gel-purified (Geneclean Kit; MP Biomedicals, Solon, OH), and radioactively labeled using a Boehringer Mannheim Random

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Antal Szőke, Erzsébet Kiss, László Heszky, Ildikó Kerepesi, and Ottó Toldi

FBPase (key enzyme of sucrose synthesis) causing a two- to threefold increase in the amount of sucrose in plants expressing bisphosphatase (F406 and F407; Fig. 2A ). Experiments with radioactively labeled 14 CO 2 feeding in transgenic Arabidopsis and

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Lamia Krichen, Joao M.S. Martins, Patrick Lambert, Abderrazzak Daaloul, Neila Trifi-Farah, Mohamed Marrakchi, and Jean-Marc Audergon

concentrations (reduction by 1/4 of the volumes used). Eco RI primers were radioactively labeled using [γ- 33 P]ATP. PCR products were run on denaturing polyacrylamide gel (5%) and exposed to X-ray films for 2 d. After development, the autoradiographs were

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Jinpeng Xing, Yan Xu, Jiang Tian, Thomas Gianfagna, and Bingru Huang

coding region of ipt gene was radioactively labeled with α- 32 P-dCTP by using the random primer labeling system (Promega, Madison, WI) and was purified by MicroSpin™ G-50 Columns (GE Healthcare). Prehybridization and hybridization were carried out in