Seasonal and tissue-specific transgene expression and resveratrol-3-glucoside (piceid) accumulation in genetically modified white poplars carrying the grapevine StSy gene

Unexpected responses may occur in trees at specific stages after extensive cultivation time or they may be induced by specific environmental signals. The present work reports on a greenhouse trial carried out with transgenic white poplars (Populus alba L. cv. ‘Villafranca') expressing the StSy gene from Vitis vinifera L., responsible for resveratrol biosynthesis. Notwithstanding the presence of the constitutive 35SCaMV promoter, significant fluctuations in the amount of the StSy transcript were observed in relation to season, tissue/organ type and position. High-Performance Liquid Chromatography with Diode-Array Detection revealed that the trans-isomer of resveratrol-3-glucoside (trans-piceid) accumulated in highly variable concentrations in leaves while reaching more stable values in stems and roots. Substantial amounts were observed in leaves (up to 717 mg kg⁻¹ fresh weight), stems (up to 226 mg kg⁻¹ fresh weight) and roots (up to 330 mg kg⁻¹ fresh weight) while the cis-isomer was present only in leaves (up to 321 mg kg⁻¹ fresh weight).