It is shown that aqueous extracts from bird cherry tree Padus avium L., aspen Populus tremula L., and celandine Chelidonium majus L., effectivily suppress the germination of Puccinia triticina Eriks uredospores. Fungitoxic activity of the extracts is supposed to be determined by high content of phenolic compounds and high peroxidase activity in the leaves of these plants. Fungitoxic activity of the extracts from the leaves, inflorescences, roots, and stems of siberian cowparsnip Heracleum sibiricum L., was also correlated with the content of phenolic compounds in these organs. Treatment of healthy wheat Triticum aestivum L., cv. Lyubava, with the extracts from common comfrey Symphytum officinale L., cowparsnip Heracleum sibiricum L., and giant knotweed Reynoutria sashalinensis (F. Schmitt) Nakai, stimulated the photosynthetic activity in treated leaves.
In the manganese-depleted photosystem II (PSII[-Mn]) preparations, oxidation of exogenous electron donors is carried out through the high-affinity (HA) and the low-affinity (LA) sites. This paper investigates the LA oxidation site in the PSII(-Mn) preparations where the HA, Mn-binding site was blocked with ferric cations [[11] B.K. Semin, M.L. Ghirardi, M. Seibert, Blocking of electron donation by Mn(II) to Y(Z)(*) following incubation of Mn-depleted photosystem II membranes with Fe(II) in the light, Biochemistry 41 (2002) 5854-5864.]. In blocked (PSII[-Mn,+Fe]) preparations electron donation by Mn(II) cations to Y(Z)(*) was not detected at Mn(II) concentration 10 microM (corresponds to K(m) for Mn(II) oxidation at the HA site), but detected at Mn concentration 100 microM (corresponds to K(m) for the LA site) by fluorescence measurements. Comparison of pH-dependencies of electron donation by Mn(II) through the HA and the LA sites revealed the similar pK(a) equal to 6.8. Comparison of K(m) for diphenylcarbazide (DPC) oxidation at the LA site and K(d) for A(T) thermoluminescence band suppression by DPC in PSII(-Mn,+Fe) samples suggests that there is relationship between the LA site and A(T) band formation. The role of D1-His190 as an oxidant of exogenous electron donors at the LA site is discussed. In contrast to electrogenic electron transfer from Mn(II) at the HA site to Y(Z)(*), photovoltage due to Mn(II) oxidation in iron-blocked PSII(-Mn) core particles was not detected.
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