THE EFFECT OF THE INTEGRATION OF THE RAT GLUCOCORTICOIDGR RECEPTOR ON THE RESPONSE OF NICOTIANA TO ABIOTIC STRESS

The rat glucocorticoid receptor (GR) is a member of the animal steroid hormone receptor (SR) family (Eick & Thornton, 2011), that is capable to activate transcription from glucocorticoid response elements (GRE elements) in response to steroid (glucocorticoids) hormones. In animals GR receptor acts as a steroid-dependent transcription factor, regulating the expression of several glucocorticoid responsive genes that control development, organ physiology, cell differentiation and homeostasis or are switched on during stress response (Mangelsdorf et al. 1995). In plants GR receptor has been used as a glucocorticoid inducible expression system (Aoyama and Chua 1997) and in many plants the transformation with the GR hormone-binding domain (HBD) leads to severe growth defects (Kang et al., 1999; Andersen et al. 2003, Amirsadeghi et al., 2007). Recently our data on the transformation of two Nicotiana species, N. glauca and N. langsdorffii with a binary vector bearing the GR HBD showed modifications on in vitro morphogenetic patterns and in the endogenous phytohormone content suggesting the interaction of GR with the plant hormonal signaling system, leading to changed physiological balances (Giannarelli et al., 2010). In this work N. langsdorffii transgenic GR plants and isogenic wild type genotypes have been treated with different stress agents. Cell dedifferentiation and differentiation capacity along with hormonal patterns analysis, were monitored and compared. Electrolyte leakage, an effective tool of measuring cell membrane stability was used as an indicator of stress injury. Results showed higher value in the content of S-ABA and IAA phytohormones and a different morphogenetic behaviour in transgenic plants. Data obtained could suggest that the response to stress, due to a modified hormonal balance, may derive from the interaction between the GR receptor and phytosteroids, or may be due to the binding of the receptor with endogenous chaperones HSP90 proteins, respectively known to play a key role in plant development and responsiveness to external stimuli.