PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Comparison of the effects of water deficiency and Cd stress on the photosynthetic apparatus of poplar. László Gáspár^*,1, Ferenc Láng¹, Ferenc Fodor¹, Edit Cseh¹, Éva Sárvári¹, ¹ Eötvös Loránd University, Budapest, Hungary

ABSTRACT- Cd and other heavy metals were shown to inhibit the development and functioning of the photosynthetic apparatus (Krupa, Baszynski, Acta Physiol. Plant. 17: 177, 1995). Disturbance of water balance in plants was considered as an early effect of heavy metal stress (Barceló, Poschenrieder, J. Plant Nutr. 13: 1, 1990). Here we compared the effects of strong water deficit and Cd stress to find out how much the changed development of the photosynthetic apparatus under Cd stress was connected to the Cd induced water deficiency. Poplar plants were grown hydroponically with 10M Fe-citrate or Fe-EDTA up to four to five-leaf stage and then treated with 10M Cd(NO₃)₂ up to seven-leaf stage. Polyethylene glycol (PEG) was added at 10% or 15% (w/v) concentration into the culture solution for seven days before harvesting. Light-induced ¹⁴CO₂ fixation was determined by liquid scintillation counting. Fluorescence induction and leaf stomatal conductance were measured with PAM fluorimeter and AP4 porometer, respectively. Chlorophyll (Chl)-proteins were solubilised by glucosidic detergents, and separated by Deriphat PAGE. The employed PEG treatments caused stronger increase in the dry weight percentage of leaves and retardation of growth than Cd did. Nevertheless, PEG treatment had much milder effect on the development of the photosynthetic apparatus of the emerging leaves. Though the whole-leaf Chl content moderately decreased due to the strong growth inhibition, the Chl content increased on a cm² leaf basis. The stability of Chl-proteins was obtained in the order of PSII>PSI>LHCII. The amount of PSII changed the least on a leaf basis. PSII was fully functional, what was shown by the unchanged fluorescence induction parameters. In contrast, the yield parameter decreased and the non-photochemical quenching increased in Cd treated plants. Therefore much stronger water deficit than the one observed under Cd treatment caused only slight effects on thylakoid development, and it cannot be the main factor in the Cd effect on the organization of thylakoids. However, CO₂ fixation was more influenced due to the partial closure of stomata in more developed leaves. This work was supported by grant T-043646 from OTKA

KEY WORDS: chlorophyll-protein, cadmium, polyethylene glycol, poplar