The responses of the freshwater macroalga Nitellopsis obtusa to heavy metal (HM) salts of Hg, Cd, Co, Cu, Cr, and Ni were assessed at different levels: whole-cell mortality (96-h LC(50)), in vivo cell membrane (45-min depolarization of resting potential, EC(50)), and enzyme in plasma membrane preparations (K+, Mg2+-specific H+-ATPase inhibition, IC(50)). To measure ATPase activity, a novel procedure for isolation of plasma membrane-enriched vesicles from charophyte cells was developed. The short-term ATPase inhibition assay (IC(50) from 6.0 x 10(-7) to 4.6 x 10(-4) M) was slightly more sensitive than the cell mortality test (LC(50) from 1.1 x 10(-6) to 2.6 x 10(-3) M), and the electrophysiological test with the end point of 45-min depolarization of resting potential was characterized by less sensitivity for HMs (EC(50) from 1.1 x 10(-4) to 2.2 x 10(-2) M). The variability of IC(50) values assessed for HMs in the ATPase assays was close to that of LC(50) values in the mortality tests (CVs from 33.5 to 83.5 and from 12.4% to 57.7%, respectively), whereas the EC(50) values in the electrophysiological tests were characterized by CVs generally below 30%. All three end points identified two separate HM groups according to their toxicity to N. obtusa: Co, Ni, and Cr comprised a group of less toxic metals, whereas Hg, Cu, and Cd comprised a group of more toxic metals. However, the adverse effects within each group were discriminated differently. For example, the maximum difference between the highest and lowest LC(50) for the group of less toxic metals in the long-term mortality test was approximately 60% of the response range, whereas the corresponding difference in IC(50) values in the ATPase assay was 30%. In contrast, the LC(50) values of the more toxic metals occupied only 10% of the response range, whereas the IC(50) values were spread over 70%. Further investigation should be done of the underlying mechanism or mechanisms responsible for the observed differences in the dynamic range of a particular end point of the groups of toxicants of varying strength.

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Ethephon and Aventrol were used as tools to provoke the processes taking part in the formation of rape seed yield and quality. Investigations on spring rape (Brassica napus L.) cultivars ‘Terra’ and ‘Landmark’ were carried out from 2008–2010. Ethephon (10 mM) and Aventrol (1 l/ha — pinolene 960 g/l) were used on different plant growth stages: BBCH-62–64 and BBCH-72–74, BBCH-80–82, respectively. Impact of ethephon manifested itself as activation of ethylene evocation by siliqua and a slight activation of growth of siliqua dehiscence zone. Siliqua cell plasmalemma and tonoplast H+-ATPases activation under the influence of ethephon occurred but did not lead to the destruction of transmembrane electrochemical potential. Extra seed yield and crude fat yield increased; tendency towards a lowering of the saturated/unsaturated fatty acid ratio was observed. Under the influence of Aventrol the dehiscence zone of siliqua was more closed when compared to the control and the ethephon treated variants, seed loss was significantly lowered and transmembrane cation transport was not damaged. The seed yield increased, and this was due to the accumulation of extra crude fat. Aventrol did not change the fatty acid content in rape seed oil. The positive impacts of ethephon and Aventrol for spring rape seed yield formation and possible mechanisms are discussed.

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