Journal of Plant Physiology 164 (2007) 1527—1535 Localization of gamma-glutamyl transferase activity and protein in Zea mays organs and tissues Antonio Masi a , Tiziana Destro a , Loris Turetta a , Serena Varotto b , Giovanni Caporale c , Massimo Ferretti a,à a Department of AgriculturalBiotechnology, University of Padova, Viale dell’Universita` 16 – Agripolis, I-35020 Legnaro (PD), Italy b Department of Environmental Agronomy and Crop Production, University of Padova, Viale dell’Universita` 16 – Agripolis, I-35020 Legnaro (PD), Italy c Department of Experimental Veterinary Science, University of Padova, Viale dell’Universita` 16 – Agripolis, I-35020 Legnaro (PD), Italy Received 6 December 2005; accepted 24 July 2006 KEYWORDS Environmental sensing; Glutathione metabolism; Histochemical detection; Immunolocalization; Oxidative stress Summary Gamma-glutamyl transferase/transpeptidase (GGT, (5-L-glutamyl)-peptide:amino- acid 5-glutamyltransferase; EC 2.3.2.2.) is an ectoenzyme promoting the cleavage of the gamma-glutamyl moiety of glutathione (GSH) and gamma-glutamyl related compounds. In this work, we describe the localization of GGT by enzymehistochem- ical and immunohistochemical analysis in maize plants. Our results show that the tissue spatial distribution of GGT activity closely correlates with the localization of the GGT protein. We also demonstrate that GGT activity and protein are unevenly distributed in tissues, being higher in the epidermis and stomata, parenchyma of conductive elements and root meristem. These results can contribute to our understanding of GGT function and regulation as well as its role in glutathione metabolism. To date, these are largely unknown in plants. & 2006 Elsevier GmbH. All rights reserved. Introduction Glutathione, together with ascorbate, plays a key role in keeping the cell redox balance under control (Noctor and Foyer, 1998). Its level in tissues results from biosynthesis, degradation, conjugation with harmful xenobiotics and endogenous metabo- lites, as well as import and export processes. ARTICLE IN PRESS www.elsevier.de/jplph 0176-1617/$ - see front matter & 2006 Elsevier GmbH. All rights reserved. doi:10.1016/j.jplph.2006.07.016 Abbreviations: DON, 6-Diazo-5-oxo-L-norleucine; GGT, Gamma- glutamyl transferase/transpeptidase; GPNA, Gamma-glutamyl- paranitroanilide; GSH, Reduced glutathione à Corresponding author. Tel.: +39 049 827 29 13; fax: +39 049 827 29 29. E-mail address: massimo.ferretti@unipd.it (M. Ferretti).