| Summary: | In northern Sweden, Empetrum hermaphroditum Hagerup dominates the ground layer vegetation in post fire successions by suppressing other plant species. Previous studies suggest that this negative effect by E. hermaphroditum may be explained, at least in part, by the release of phenolic compounds, particularly batatasin-III, from foliage to soil. In this pilot study, we evaluated the effect of batatasin-III on photosynthesis by applying the compound (0.1, 1.0, or 2.8 mM) directly to the transpiration stream of intact Spinacia oleracea L. (spinach) and Betula pendula L. (birch) leaves. Within the concentration range used, batatasin-III had a small, but significant, effect on photosynthesis. The strongest effect was found on CO2 assimilation, but there were also significant effects on respiration and on maximum quantum yield of chlorophyll fluorescence (Fv / Fm). In spinach leaves treated with 2.8 mM of batatasin-III, a 14 % decrease in Fv / Fm-685 coincided with a 30 % inhibition of CO2 assimilation rates. It is possible, that the inhibition of photosynthesis by batatasin-III was caused by direct effects on chloroplast membrane energization processes and subsequent control on the primary photochemistry of PSII. The variable fluorescence kinetics indicated that maximum quantum yield of variable fluorescence of PSII was depressed while continued upstream transported allowed oxidation of the primary electron acceptor.
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