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The functional peculiarities and responses of the photosynthetic system in the flowering homoiochlorophyllous desiccation-tolerant (HDT) Haberlea rhodopensis and the non-desiccation-tolerant spinach were compared during desiccation and rehydration. Increasing rate of water loss clearly modifies the kinetic parameters of fluorescence induction, thermoluminescence emission, far-red induced P700 oxidation and oxygen evolution in the leaves of both species. The values of these parameters returned nearly to the control level after 24 h rehydration only of the leaves of HDT plant. PS II was converted in a non-functional state in desiccated spinach in accordance with the changes in membrane permeability, malondialdehyde, proline and H(2)O(2) contents. Moreover, our data showed a strong reduction of the total number of PS II centers in Haberlea without any changes in the energetics of the charge recombination. We consider this observation, together with the previously reported unusually high temperature of B-band (S(2)Q(B)-) emission of Haberlea to reflect some specific adaptive characteristics of the photosynthetic system. As far as we know this is the first time when such adaptive characteristics and mechanism of the photosynthetic system of a flowering HDT higher plant is described. These features of Haberlea can explain the fast recovery of its photosynthesis after desiccation, which enable this HDT plant to rapidly take advantage of frequent changes in water availability.

Indian mustard (Brassica juncea L. cv. Vitasso) plants exposed to 10, 30, 50 and 100 μM of Cd for 5 d in hydroponic culture were analysed with reference to the distribution of Cd 2+ , the accumulation of biomass and antioxidants and antioxidative enzymes in leaves. Cd induced a decrease in plant biomass. The maximum accumulation of Cd occurred in roots followed by stems and leaves. Cd induced a decrease in catalase (CAT) and guiacol peroxidase (GPX) activities but an increase in ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) activities. Enhancement in dehydroascorbate reductase (DHAR) activity was also at 10 μM Cd. Glutathione reductase (GR) activity showed pronounced stimulation after all treatments, but glutathione S-transferase (GST) and glutathione peroxidase (GPOX) activities decreased. The effectiveness of ascorbate-glutathione cycle (AGC) was determined by the ratio of ascorbate to H 2 O 2 . This ratio decreased in the Cd-treated leaves which indicated that the cycle was disordered.Additional key words: ascorbate-glutathione cycle, catalase, Indian mustard, guiacol peroxidase. ⎯⎯⎯⎯Contaminated soils with heavy metals pose a major environmental and human health problem, which may be solved by emerging phytoremediation methods. Plant properties important for metal phytoremediation are metal tolerance and accumulation. They are determined by metal uptake, root-shoot translocation, intracellular sequestration and chemical modification. Natural hyperaccumulators, such as Brassica juncea can accumulate exceptionally high concentrations of heavy metals in the roots (Reeves and Baker 2000, Simonova et al. 2007). They may be involved in phytoremediation directly as phytoremediation crops, or indirectly as sources of genes for improvement of other phytoremediation crops (Pollard et al. 2002). Brassica juncea L. cv. Vitasso possesses short vegetation period from 40 to 60 d, unpretentiousness to the soil type and forms high quantity of biomass. The plants accumulated heavy metals may be burned or processed.Cd like other heavy metals produces oxidative stress possibly by generating free radicals and active oxygen species (Hendry et al. 1992). Understanding the biochemical detoxification strategies that plants (predominantly hyperaccumulators) adopt against oxidative stress induced by accumulated metal ions is a key to manipulate its heavy metal tolerance.The aim of this study was to establish the possible antioxidative mechanism that could be operational in the leaves of Brassica juncea L. cv. Vitasso plants exposed for 5 d to environmentally relevant (10 μM) as well as to marginally acute (30, 50, 100 μM) of Cd in hydroponic culture.The experiments were conducted on 25 d-old plants grown in a Knop solution in a chamber with 16-h photoperiod (PAR 200 μmol m -2 s -1 , temperature 25 ± 1 °C, relative air humidity 50 -60 %). The nutrition solution was changed every two days and aerated every day. On the 20 th day Cd (as CdCl 2 . 2.5 H 2 O) was added into nutrient solution: 1) control -0 μM Cd; 2) 10...

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