Time Course of the Appearance of Cd Effects on Photosynthetically Competent Poplar Leaves
Cd effects on photosynthetic performance of the third leaf of hydroponically cultured poplar (Populus glauca var. Kopeczkii) plants were followed during a 2-week treatment with 10 μM Cd(NO3)2. Growth and chlorophyll concentration were reduced by about 20%. Chlorophyll a/b ratio was strongly lowered due to the stronger reduction in the amount of photosystem I than that of lightharvesting complex II. A delayed and fast decrease in the transcript levels of lhca1 and lhca2–4 genes, respectively, and a transient increase in those of lhca5 and lil1 were detected by quantitative RTPCR. Actual quantum efficiency of photosystem II did not change in spite of an early (after second day) decrease in stomatal conductance and CO2 fixation probably due to the increased photorespiration rate (elevated glycolate oxidase activity). Decline in ascorbate peroxidase activity resulted in a moderately higher malondialdehyde level in leaves. In conclusion, decreased stomatal conductance/CO2 fixation and thylakoid reorganization were the first detectable symptoms of Cd treatment in photosynthetically competent leaves.
KeywordsCadmium ELIP Lhca oxidative stress photosynthetic activity poplar
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