Journal of Agricultural Science; Vol. 6, No. 5; 2014 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 142 Effects of Drought Stress and Storage on the Metabolite and Hormone Contents of Potato Tubers Expressing the Yeast Trehalose-6-phosphate Synthase 1 Gene Zsófia Juhász 1 , Dirk Balmer 2 , Anita Sós-Hegedűs 1 , Armelle Vallat 3 , Brigitte Mauch-Mani 2 & Zsófia Bánfalvi 1 1 NARIC Agricultural Biotechnology Institute, Gödöllő, Hungary 2 Faculty of Sciences, University of Neuchâtel, Neuchâtel, Switzerland 3 Chemical Analytical Service of the University of Neuchâtel, Neuchâtel, Switzerland Correspondence: Zsófia Bánfalvi, NARIC Agricultural Biotechnology Institute, P.O. Box 411, Gödöllő, Hungary. Tel: 36-28-526-153. E-mail: banfalvi@abc.hu Received: February 8, 2014 Accepted: March 11, 2014 Online Published: April 15, 2014 doi:10.5539/jas.v6n5p142 URL: http://dx.doi.org/10.5539/jas.v6n5p142 Abstract Comparative studies on the tuber yield and quality of commercial potato cultivars were conducted. White Lady was the wild-type (WT) accession used, and transgenic lines in this background expressing the yeast trehalose-6-phosphate synthase 1 (TPS1) gene were analysed. The plants were grown in a greenhouse under well-watered and drought stress conditions, and the metabolite and hormone contents of freshly harvested and stored tubers were tested. Periodic drought resulted in an average 50% yield loss in WT and a 30% yield loss in TPS1 plants. However, the average tuber mass remained higher in WT than in TPS1 plants. Stress elevated the abscisic acid, proline, asparagine, and phenylalanine levels and significantly affected the levels of an additional 12 compounds in tubers. In contrast to abscisic acid, the salicylic acid levels in stressed tubers were reduced. In general, storage and stress had similar effects on the metabolite and hormone concentrations in both WT and TPS1 tubers. Interestingly, storage increased the mannose, phenylalanine, and abscisic acid concentrations and decreased the salicylic acid concentrations only in the tubers of well-watered plants. TPS1 tubers had a longer dormancy period than WT tubers and exhibited alterations in the concentrations of 13 metabolites. Keywords: drought stress, hormones, metabolic profiling, Solanum tuberosum L., sprouting, tuber Abbreviations: ABA: abscisic acid, CK: cytokinin, ET: ethylene, GA: gibberellic acid, GC-MS: gas chromatography-mass spectrometry, JA: jasmonic acid, JA-ILE: jasmonic acid-isoleucine, IAA: indole-3-acetic acid, TPP: trehalose-6-phosphate phosphatase, TPS1: trehalose-6-phosphate synthase 1, SA: salicylic acid, UHPLC-MS/MS: ultra-high-pressure liquid chromatography-tandem mass spectrometry, WT: wild-type 1. Introduction Drought is by far the most important environmental stress in agriculture, and improving crop yields under drought stress is a major goal of plant breeding. To date, various approaches have been used to produce drought-tolerant plants. One of the approaches is the engineering of transgenic cultivars expressing osmolyte biosynthesis genes (Cattivelli et al., 2008). Drought-tolerant transgenic rice lines showing tissue-specific or stress-inducible accumulation of the osmolyte trehalose, which has no negative effects, have been isolated previously (Garg et al., 2002). Based on this work, an attempt to improve the drought tolerance of the potato cv. White Lady was made by increasing the level of trehalose via transformation with the yeast trehalose-6-phosphate synthase 1 (TPS1) gene driven by the promoter of the drought-inducible potato gene, StDS2 (Dóczi et al., 2002). Using a marker-free transformation method, two independent TPS1 transgenic potato lines, T1 and T2, were isolated. In contrast to the expected drought-induced expression, only very low, constitutive TPS1 expression was detected in the transgenic lines, likely because of chromosomal position effects. This expression pattern, however, was sufficient to alter the plants' drought responses. Detached leaves of the T1 and T2 plants showed an eight-hour delay in wilting compared to the non-transformed wild-type (WT) control. Potted T1 and T2 plants retained water for six days longer than WT plants and maintained high stomatal conductance as well as a satisfactory rate of net photosynthesis. Under