I. Mistríková

Short-and long-term effects of cadmium on transmembrane electric potential (E m) in maize roots

In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (Em) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 µM to 1 mM) for several hours to one week were studied. The Em values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization was concentration-dependent reaching the value of diffusion potential (ED) when the Cd concentration exceeded 100 µM. The values of ED ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of Em was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 µM) or complete repolarization (Cd < 100 µM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly after the maximum repolarization of Em a continuous concentration-dependent decrease of Em followed at all Cd concentrations. Depolarization of Em was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 µM to 1 mM Cd, with the exception of root cells treated with 1 and 10 µM Cd for 24 and 48 h. Time course analysis of Cd impact on root respiration revealed that at higher Cd concentrations (> 50 µM) the respiration gradually declined (∼ 6 h) and then remained at this lowest level for up to 24 h.All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher than 100 µM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible changes in the electrogenic plasma membrane H+ ATPase because fusicoccin, an H+ ATPase activator diminished the depolarizing effect of Cd on the Em. The depolarization of Em in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability, and activity of H+ ATPase.

Morphology and anatomy of Echinacea purpurea, E. angustifolia, E. pallida and Parthenium integrifolium

The Echinacea species are native to the Atlantic drainage area of the United States of America and Canada. They have been introduced as cultivated medicinal plants in Europe. Echinacea purpurea, E. angustifolia and E. pallida are the species most often used medicinally due to their immune-stimulating properties. This review is focused on morphological and anatomical characteristics of E. purpurea, E. angustifolia, E. pallida, because various species are often misidentified and specimens are often confused in the medicinal plant market.

Patterns of long-distance movement of water in roots

Determining the relationship between xylem anatomy and water flow is essential to our understanding of its development and function in the plant. Studies on the conducting capacity of xylem vascular tissues enables us to examine the potential ability of water flow in the plants. For a complete description of long distance water flow it is important to identify the functional vessels. The pattern of vasculature has been analyzed mostly in shoots of arborescent monocotyledons (Zimmermann, 1983; Zimmermann and Tomlinson, 1968), dicotyledons (Chaney and Kozlowski, 1977; Newbanks et al., 1983; Zimmermann, 1978) and conifers (Ewers, 1985; Petty, 1970). Very few investigations of patterns of water movement in conducting elements of roots of herbaceous plants have been carried out.

Impact of fusaproliferin on primary roots of maize cultivars differing in their susceptibility to Fusarium

Effects of fusaproliferin (FUS) on membrane potential (EM), electrolyte leakage, enzymes activity and respiration of roots, were studied in two maize cultivars (Zea mays L.), differing in their susceptibility to this toxin. In short-term experiments (≤ 6 h), EM has been rapidly and significantly depolarized by FUS. The rapidity of EM depolarization in tolerant cv. Lucia was more expressive in comparison with susceptible cv. Pavla, but the extent of EM depolarization was higher in cv. Pavla. In both maize cultivars, higher depolarization of EM was registered in cells of root zone I. In long-term experiments after the first EM depolarization, which occurred during the first 6 h of FUS treatment, gradual depolarization continued up to 24 h and was represented not only by the active component (EP) but also by the passive component (ED) of EM. The decrease in EM and ED was followed by a loss of K+ ions from FUS treated roots of both cultivars. The leak of K+ ions from the root cells of both root zones as well as both maize cultivars increased with the time of FUS treatment and was significantly higher in susceptible cv. Pavla than in tolerant cv. Lucia. FUS treatment of maize roots resulted in a significant decrease of root respiration which was higher in susceptible cv. Pavla than in tolerant cv. Lucia.The analysis of enzyme activities revealed that FUS significantly stimulated POD activity in both maize cultivars. SOD activity was significantly increased only in susceptible cv. Pavla, while APX activity was not affected by the presence of FUS. GST activity was specifically induced by FUS only in tolerant cv. Lucia.Due to the observed correlation between the extent of depolarization and the sensitivity of the studied maize cultivars to fusaproliferin, the EM parameters should be used for rapid screening of FUS-resistant cultivars for agricultural practice.