Chlorophyll fluorescence in micropropagated Rhododendron ponticum subsp baeticum plants in response to different irradiances

The aim of this study was to investigate acclimation of micropropagated plants of Rhododendron ponticum subsp. baeticum to different irradiances and recovery after exposure to high irradiance. Plants grown under high (HL) or intermediate (IL) irradiances displayed higher values of maximum electron transport rate (ETR(max)) and light saturation coefficient (E(k)) than plants grown under low irradiance (LL). The capacity of tolerance to photoinhibition (as assessed by the response of photochemical quenching, q(p)) varied as follows: HL > IL > LL. Thermal energy dissipation (q(N)) was also affected by growth irradiance, with higher saturating values being observed in HL plants. Light-response curves suggested a gradual replacement of q(p) by q(N) with increasing irradiance. Following exposure to irradiance higher than 1500 mu mol m(-2) s(-1), a prolonged reduction of the maximal photochemical efficiency of PS 2 (F(v)/F(m)) was observed in LL plants, indicating the occurrence of chronic photoinhibition. In contrary, the decrease in F(v)/F(m) was quickly reverted in HL plants, pointing to a reversible photoinhibition