posted on 2015-09-03, 00:00authored byRon Simkovitch, Dan Huppert
Steady-state
and time-resolved fluorescence techniques were employed
to study the photophysics and photochemistry of trans-resveratrol. trans-Resveratrol is found in large
quantities in fungi-infected grapevine-leaf tissue and plays a direct
role in the resistance to plant disease. We found that trans-resveratrol in liquid solution undergoes a trans–cis isomerization
process in the excited state at a rate that depends partially on the
solvent viscosity, as was found in previous studies on trans-stilbene. The hydroxyl groups of the phenol moieties in resveratrol
are weak photoacids. In water and methanol solutions containing weak
bases such as acetate, a proton is transferred to the base within
the lifetime of the excited state. When resveratrol is adsorbed on
cellulose (also a component of the plant’s cell wall), the
cis–trans process is slow and the lifetime of the excited state
increases from several tens of picoseconds in ethanol to about 1.5
ns. Excited-state proton transfer occurs when resveratrol is adsorbed
on cellulose and acetate ions are in close proximity to the phenol
moieties. We propose that proton transfer from excited resveratrol
to the fungus acid-sensing chemoreceptor is one of the plant’s
resistance mechanisms to fungal infection.