ORIGINAL ARTICLE Transglutaminases and their substrates in kinetin-stimulated etioplast-to-chloroplast transformation in cucumber cotyledons Ewa Sobieszczuk-Nowicka & Magdalena Krzeslowska & Jolanta Legocka Received: 30 November 2007 / Accepted: 19 February 2008 / Published online: 19 June 2008 # Springer-Verlag 2008 Abstract In the light of our previous work, we know that there is a relationship between bound polyamines and the chloroplast differentiation process. This relationship may represent an important component of the process and be part of the mechanism of kinetin action, which stimulates chloroplast differentiation. To clarify the nature of the binding of polyamines to chloroplast structures, the possible involvement of transglutaminases in kinetin-stimulated chlo- roplast photodevelopment was investigated. Immunodetec- tion of transglutaminases revealed bands at 77, 50 and 30 kDa both in etioplasts and chloroplasts. The data indicated a positive correlation between enzyme level and activity. It also demonstrated the regulation of transglutami- nase protein expression by kinetin. The suborganellar location of transglutaminases by electron microscopy showed that the enzyme is peculiarly localised, mainly in pro-thylakoids and appressed grana thylakoids. The data corroborated that spermidine post-translational modification of certain plastid proteins of 58, 29, 26 and 12 kDa occurred. The results we obtained suggest that transglutaminases take part in the formation of the chloroplast structure via a mechanism whereby polyamines bind to their protein substrates. These findings about the effect of kinetin on conjugation provide a new contribution to the understanding of the mechanism of kinetin action on etioplast-to chloroplast transformation. Keywords Cucumber cotyledon . Kinetin . Plastid transformation . Polyamines . Transglutaminases Abbreviations LHCPII light-harvesting chlorophyll a/b complex protein PA polyamine PSII photosystem II Put putrescine Spd spermidine Spm spermine TGases transglutaminases DMC, N’ N’-dimethylcasein Introduction The light-dependent development of etioplasts into chloro- plasts is one of the most interesting differentiation processes that occurs in plants. The chloroplast is an organelle of great metabolic complexity and its biogenesis is critical in determining the photosynthetic capacity of plants. One of the metabolic activities is the biosynthesis and catabolism of polyamines (PAs) and their conjugation to chloroplast structures (Kotzabasis et al. 1993, 1999; Del Duca et al. 1994, 2000; Dondini et al. 2003). PAs are synthesised and oxidised in chloroplasts (Kotzabasis 1995; Andreadakis and Kotzabasis 1996; Bernet et al. 1999), and a correlation has been observed between PA levels, chlorophyll biosynthesis and the Protoplasma (2008) 233:187–194 DOI 10.1007/s00709-008-0002-y E. Sobieszczuk-Nowicka (*) : J. Legocka Department of Plant Physiology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland e-mail: evaanna@rose.man.poznan.pl M. Krzesłowska Department of Botany, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland