Influence of light intensity on thylakoid development under Cd stress in poplar

Abstract

As fluorescence induction parameters pointed to an increased quenching of absorbed light energy in Cd treated leaves the effect of Cd at different light intensity was investigated in relation to the development of the photosynthetic apparatus. Poplar plants (Populus glauca var. Astria and Populus alba) grown hydroponically on 10mM Fe-citrate up to four-leaf stage were treated with 10µM Cd(NO3)2 at light intensities of 40, 90, and 140 mmol photons m-2 s-1 for two weeks, during which they developed another 4-5 leaves. Chlorophyll-protein patterns were obtained with Deriphat PAGE. The Chl a/b ratio, the relative amount of PSI and PSII increased, and that of LHCII decreased with the rising light intensity in control plants in agreement with literature data. The growth inhibition of leaves did not significantly varied as a function of light intensity under Cd treatment. However, while Cd treated plants showed more or less normal values of the photosynthetic parameters at low light intensity, a continuously stronger inhibition of chlorophyll accumulation, 14CO2 fixation, and the yield parameter were observed under higher light. Also the inhibition of accumulation of all chlorophyll-protein complexes was slight at the lowest light intensity. Increasing the light intensity first PSII, and then LHCII became the most stable components. Therefore, the higher the light intensity the stronger stress symptoms were observed on the photosynthetic apparatus. While the stability of PSII together with the rising Fo and non-photochemical quenching refer to a photoinhibitory acclimation of thylakoids, the persistence of LHCII shows the onset of senescence-like processes.