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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The possibility of regulating productivity of potato plants by applying the promising analogues of auxin -compounds TA-12, TA-59, LN-14, LN-16 -has been proved experimentally. The compounds at optimal concentrations (TA-12 1.0, TA-59 0.5, LN-14 and LN-16 1.0 kg/ha) were found to activate the process of tuber formation, increasing the number of tubers and accumulation of assimilates in tubers. TA-12 is characterised by the highest activity: it increased the productivity of potato (~ 6.0 t/ha) as well as sugar-beet root yield (~3.0 t/ha) and sucrose content (~1.1). TA-12 is supposed to affect plant cell through the IAA receptory system.

A microscale bioassay based on 50% inhibition of K(+), Mg(2+)-ATPase activity in a microsomal fraction isolated from Nitellopsis obtusa cells was developed. Compared to that for a plasma membrane fraction purified in a sucrose gradient, the preparation procedure for a microsomal fraction is less time consuming and the yield is substantially higher. Characteristics of the microsomal preparation proved to be similar to those of the highly purified plasma membrane preparation (Manusadzianas et al., 2002), at least for heavy metals. Sensitivity to CuSO(4) of the frozen (-8 degrees C) microsomal fraction [49 +/- 17 (SD) microM; n = 8] did not significantly differ from that of the freshly isolated one (52 +/- 30, n = 8), at least for 40 days. Toxicity of leachate water from Kairiai (northern Lithuania) solid waste landfill was assessed by taking samples from various points including temporary reservoirs and analyzing them immediately after spillage (summer 2002) and after storage for almost 2 years at 4 degrees C-6 degrees C. Two tests with the macrophytic alga Nitellopsis obtusa (Charatox, 45-min EC(50) of resting potential depolarization, and ATPase assay, IC(50) of membrane ATPase activity) and one test with the crustacean Daphnia magna (Daphtoxkit F, 48-h 50% immobilization) tests were used. In general, all three tests showed successively decreasing values of landfill leachate toxicity with an increasing degree of dilution with surface waters. The possibility of employing preserved algal preparations on demand in test batteries seems to be promising, especially in emergencies.

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