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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Increased Calcium Levels and Prolonged Shelf Life in Tomatoes Expressing Arabidopsis H⁺/Ca²⁺ Transporters¹

Vegetable and Fruit Improvement Center, Texas A&M University, College Station, Texas 77845 (S.P., K.S.Y., J.P., R.H.S., K.D.H.); and Plant Physiology Group, United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030 (N.H.C., J.K.P., K.D.H.)

Here we demonstrate that fruit from tomato (Lycopersicon esculentum) plants expressing Arabidopsis (Arabidopsis thaliana) H⁺/cation exchangers (CAX) have more calcium (Ca²⁺) and prolonged shelf life when compared to controls. Previously, using the prototypical CAX1, it has been demonstrated that, in yeast (Saccharomyces cerevisiae) cells, CAX transporters are activated when the N-terminal autoinhibitory region is deleted, to give an N-terminally truncated CAX (sCAX), or altered through specific manipulations. To continue to understand the diversity of CAX function, we used yeast assays to characterize the putative transport properties of CAX4 and N-terminal variants of CAX4. CAX4 variants can suppress the Ca²⁺ hypersensitive yeast phenotypes and also appear to be more specific Ca²⁺ transporters than sCAX1. We then compared the phenotypes of sCAX1- and CAX4-expressing tomato lines. The sCAX1-expressing tomato lines demonstrate increased vacuolar H⁺/Ca²⁺ transport, when measured in root tissue, elevated fruit Ca²⁺ level, and prolonged shelf life but have severe alterations in plant development and morphology, including increased incidence of blossom-end rot. The CAX4-expressing plants demonstrate more modest increases in Ca²⁺ levels and shelf life but no deleterious effects on plant growth. These findings suggest that CAX expression may fortify plants with Ca²⁺ and may serve as an alternative to the application of CaCl₂ used to extend the shelf life of numerous agriculturally important commodities. However, judicious regulation of CAX transport is required to assure optimal plant growth.

² Present address: Faculty of Life Sciences, University of Manchester, 3.614 Stopford Building, Oxford Road, Manchester M13 9PT, UK.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Sunghun Park (s-park4{at}tamu.edu).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.066266.

^* Corresponding author; e-mail s-park4{at}tamu.edu; fax 979–862–4522.

Received May 26, 2005; returned for revision August 11, 2005; accepted August 16, 2005.

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