No abstract

The toxic effects of Cu on growth, element uptake, chlorophyll content, cellular ultrastructure, and morphometry of a Zn-and Pb-tolerant ecotype of Thlaspi ochroleucum have been investigated in hydroponic cultures. Increasing Cu concentrations in nutrient solutions caused a reduction of root growth, a decrease in total chlorophyll content in the leaves, an increased uptake of Cu, and a decreased uptake of nutrient elements such as Ca, Mg, K, and Fe. Gross anatomy and intercellular spaces of leaves of plants treated with Cu did not differ significantly from the controls. However, cells contained fewer and smaller chloroplasts that lacked starch grains and contained a number of large plastoglobuli. The volume fraction of the internal membrane system was reduced, but ultrastructurally it was similar to the control. These findings, in combination with the reduced quantity of chlorophyll, indicate that the existence of a well-organized internal membrane system does not necessarily imply the presence of high amounts of chlorophyll. Other leaf cell components, such as mitochondria, microbodies, and nuclei, displayed little ultrastructural malformation. In roots, however, all cell types were so disorganized by treatment with Cu that cell organelles could hardly be identified. Our results indicate that toxic effects of Cu appear to be manifested primarily in roots and secondarily on aerial plant parts. Key words: chlorophyll content, copper, element uptake, morphometric cytology, ultrastructure, Thlaspi ochroleucum.

No abstract

The effect of excess Ni (1 mM Ni) on wheat plants as well as the role of Ca (1 mM Ni+5000 microM Ca) for amelioration of toxicity and recovery of growth and photosynthesis in Ni-stressed wheat was evaluated. Growth, nutrient status (Ca, Mg, Fe, K, Na), and photosynthesis showed a distinct decrease strictly related to the period of treatment. Calcium ameliorated to a certain extent toxic symptoms of Ni, due to antagonistic action between Ni and Ca ions. Since chlorophyll content and variable fluorescence (Fv) decreased significantly, but Fo did not particularly change, the decrease of t1/2 with increasing duration of Ni exposure indicates negative changes on the acceptor side of PSII, which also may result from diminution of Calvin cycle. The maximum quantum yield for energy trapping was also suppressed. Plant transfer to Hoagland solution+5000 microM Ca caused recovery to plant morphology and physiology. Even in control plants, during recovery period an increased Ca concentration in plant tissues with concomitant increased rates of growth and morphology was observed. Ni concentration in plants exposed to 1 mM Ni+5000 microM Ca was lower than in plants exposed to 1 mM Ni. In all treatments a certain increase of plant nutrients was observed during recovery.

Some elemental levels, morphological and photosynthetic characteristics and cellular metabolites of wheat plants (Triticum aestivum L. cv. Vergina) growing in the field on an ore body (Cu concentration in the soil 3050 ug g−1) were compared to control plants growing in the same environment where the Cu concentration in the soil was 140 μg g1. The concentrations of Cu, K, Pb, Zn, Mg and Fe were higher in the ore plants but Ca was lower. Growth of the ore plants was inhibited, with decreased height (25%), weight (5%), leaf area (7%) and leaf dry weight (5%) compared to the control plants. Leaf protein concentration of the ore plants was 16. 2 mg cm2 leaf area, 63% of that of the control plants. The ore plants were chlorotic and chlorophyll concentration was 3. 8 μg cm−2 leaf area, 6. 4 times lower than that in the control plants. Ribulose 1. 5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4. 1. 1. 39) activity was 13. 4 μmol CO2 fixed (mg dry weight)−1 min−1, 164% of the activity in control plants. Therefore, growth inhibition did not appear to result from inhibition of the dark reactions of photosynthesis. High Rubisco activity appears to be maintained to permit maximal CO2 fixation rates whenever energy is available. Parameters of chlorophyll fluorescence Fm, Fv, I1/2 and Fv/Fm were lower in the ore‐grown plants than in control plants; Fm was higher. These values indicate that there is a decrease in the pool size of the electron acceptors on the reducing side of photosystem II (PSII), a destruction of PSII centres and interference in the photochemistry of PSII. The nitrogen content, soluble sugars, starch and lipid content were lower in ore‐grown plants. Lower carbohydrate levels appear to result from low photosynthetic activity. The fatty acid composition of lipids was similar in both groups. A lower proportion of polyunsaturated fatty acids was found in the ore‐grown plants. Stress caused by high Cu concentration in the soil appears to affect the light reactions of photosynthesis leading to growth inhibition.