Georgia Ouzounidou

Responses of maize (Zea mays L.) plants to copper stress—I. Growth, mineral content and ultrastructure of roots

Changes in the morphology, physiology and ultrastructure of root systems of Zea mays cv. Aris under various Cu treatments were investigated. A progressive decrease of root length and biomass with increasing Cu in nutrient solution was observed. Mineral content and distribution were markedly affected by Cu. The roots accumulated significantly higher amounts of Cu than the above ground parts. Significant reduction of root calcium and iron contents as well as extensive damage to root epidermal cells occurred at the higher Cu concentration. In the remainder of the root, the effects of Cu (80 μM) varied within the same tissues. Thus, there were cortical or stelar cells with disintegrated cytoplasm, next to cells with well preserved plasmalemma, tonoplast and cytoplasm including cell organelles. Multi-lamellar bodies inside the vacuoles indicated an increased activity in digestion of the cytoplasmic components under Cu stress. Deposits of a less dense and less compact material were found behind the plasmalemma associated with the cell wall as well as an accumulation of dense material attached to the cell walls; cells with such deposits in their walls revealed extensive cytoplasmic damage. However, root ultrastructure was affected less than the morphology and physiology. The occurrence of well preserved cells indicates that Zea mays root cells do not respond uniformly to stressful conditions and suggests the development of a resistance strategy of maize roots to Cu-toxicity.

Copper-induced changes on growth, metal content and photosynthetic function of Alyssum montanum L. plants

Abstract The response of root systems of Alyssum montanum to increasing Cu levels was studied. Changes in chlorophyll and metal content and in photosynthetic function were also investigated. Low Cu concentrations in the nutrient solution did not affect root elongation, possibly due to the development of co-tolerance to Cu since the plants are tolerant to Zn and Pb. However, with higher Cu concentrations the extension of the root and the chlorophyll content declined sharply. Roots accumulated higher amounts of Cu than shoot-leaves at all Cu treatments. High Cu contents in plant tissues also negatively influenced uptake and translocation of Ca, Mg, Fe and K in roots and above-ground parts. In addition, excess Cu application was accompanied by a marked decline in the variable fluorescence and a retardation of the electron transfer in PSII, indicating an inhibitory site on the photooxidizing side of PSII. The decreased photochemistry activity of PSII suggests a decrease in the efficiency of the reduction of the primary electron acceptor and reflects damage to the donor and acceptor side of PSII. An absence of the intermediate transient at the slow part of the fluorescence induction kinetics and a dramatic decrease of the (F P -F S )/F S ratio were also observed under Cu treatments. The photosynthetic function of A. montanum seemed to be affected more than root growth and chlorophyll content under Cu stress.

Root growth and pigment composition in relationship to element uptake in Silene compacta plants treated with copper

Abstract The nature of copper (Cu) toxicity on the growth, and pigment, and element composition of a Cu‐tolerant ecotype of Silene compacta Fischer was investigated in nutrient solution. The most evident Cu effect was on root growth. Since for plants grown under lower Cu concentrations (4 and 8 μM), root elongation, and chlorophyll, and elemental [Cu, iron (Fe), calcium (Ca), and potassium (K)] contents were increased as compared to that of the control, the development of an adaptive mechanism by S. compacta to Cu is suggested. Higher Cu concentrations (80 and 160 μM) resulted in a significant reduction in root growth and an significant chlorophyll loss. Yet at the 160 μM Cu‐treatment, changes in elemental content of the plant tissues were observed. External Cu had a negative influence on the concentration of Ca, Fe, and K and a positive influence on the Cu concentration in the plant tissues. Our results demonstrate the existence of an adaptive mechanism of Silene compactoc at low Cu concentrations, but w...

The use of photoacoustic spectroscopy in assessing leaf photosynthesis under copper stress: correlation of energy storage to photosystem II fluorescence parameters and redox change of P700

The effects of Cu-ions on an in vivo Cu-treated leaf system of Thlaspi ochroleucum have been identified by using photoacoustic, modulated fluorescence methods and leaf absorbance. The deficiency in light harvesting capacity of PSII caused by the Cu-induced chlorophyll loss may result in the energy distribution of the two photosystems being out of balance. Copper decreased maximal fluorescence (Fm, Fm′) and changes at the variable fluorescence were also observed. The reduction state of the primary electron acceptor (QA) of PSII in leaves resulted in changes due to the imbalance between the rate of QA reduction by PSII activity and the rate of QA− reoxidation by PSI activity. Copper treatment also resulted in a dramatic decrease of Rfd (vitality index), a moderate decrease in PES (energy storage) and a marginal decrease in Fv′Fm′ values. High Cu concentrations inhibit O2 evolution and the enhanced heat emission may be due to an inhibition of electron transfer and consequently of photochemistry. Thlaspi leaves maintained an increased capacity for PSI-driven energy storing electron flow, since measurements of 820 nm absorbance changes in saturating far-red light indicated less pronounced changes in the reaction center of PSI (P700) activity after Cu exposure compared with that of PSII.

Aluminum effects on photosynthesis and elemental uptake in an aluminum-tolerant and non-tolerant wheat cultivar

Abstract The effects of aluminum (Al) on photosynthesis and elemental uptake were studied in two wheat cultivars (Triticum aestivum L. cvs Yecora E, Nestos) differing in their tolerance to Al. Concentrations of calcium (Ca), magnesium (Mg), potassium (K), and iron (Fe) in the plant tissues of both cultivars grown in nutrient solutions (pH 4.5) decreased at all Al levels (0, 37.1, 74.1, and 148 μM). The tolerant cultivar Yecora E retained larger concentrations of all elements measured in roots and above ground parts compared with the non tolerant cultivar Nestos. Concentrations of Ca and Mg in leaves of the cultivar Nestos under high Al treatment were within the deficiency range. Changes in the shape of the chlorophyll fluorescence induction curves showed that Al‐stress altered thylakoid photofunctioning even in the more tolerant cultivar. Aluminum stress resulted in partial inhibition of photosynthetic electron transport at photosystem II and closure of photosystem II reaction centers. Chloroplast element...

Field study of the effects of excess copper on wheat photosynthesis and productivity

Abstract Copper concentration in wheat plants growing in a Cu-contaminated area, was 3.5-times higher than that of the control, while the total chlorophyll (a + b) content of plants growing in an ore site was significantly reduced. The significant decline of the chlorophyll concentration in the Cu-stressed wheat plants in relation to the decrease in the chlorophyll a/b ratio was an indication of the poor condition of those plants and the lack of adaptive adjustment in pigment concentrations to high Cu levels. Plants grown in ore soils displayed a significantly smaller height and length of ear and produced significantly fewer seeds and spikelets per ear, while grain filling and development were negatively affected. The relative decrease in the assimilation rate for stressed plants was 90%. Increased Cu levels in the soil led to a decrease of the stomatal conductance (43%) and of the transpiration rate (10%). The water use efficiency (i.e. the ratio between leaf photosynthesis and transpiration) of the stre...

Amelioration of copper toxicity by iron on Spinach physiology

Abstract The effect of excess copper (Cu) on young spinach (Spinacia oleraced) as well as the role of iron (Fe) for amelioration of toxicity on growth and photosynthesis in Cu‐treated plants was evaluated. Plants treated with 160 μM Cu showed symptoms of heavy metal toxicity, while addition of Fe (40 μM) ameliorates to a certain extent toxic effects of Cu, due to antagonistic action between Cu and Fe. Root length and biomass revealed a lower decrease under Cu+Fe than under Cu treatment. Copper accumulation in plant tissues increased, while Fe, sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) declined under Cu treatment. The significant increase in chlorophyll fluorescence (Fo) under 160 μM Cu, possibly reflects the more severe damages suffered at the membrane level with respect to Cu+Fe treatment. Copper decreased the efficiency of excitation energy capture by PSH reaction centers and negatively affected the effective antenna size of PSH. Changes in the rate of carbon dioxide (CO2) assimilatio...

Comparative Responses of a Copper-tolerant and a Copper-sensitive Population of Minuartia hirsuta to Copper Toxicity

Summary The response of two populations of Minuartia hirsuta with different copper tolerance to an excess of copper was studied. The population originatin from copper contaminated sites showed a distinct tolerance to copper. A more vigorous growth of copper tolerant plants under increasing copper concentrations was found, since their root-length growth and chlorophyll content were higher than the control, as well as their unchanged percentage survival. In contrast, copper treatments caused progressive reduction in the above mentioned parameters in copper-sensitive plants. The total uptake of copper and its distribution between roots and shoots differ significantly between the two populations. At all external copper concentrations the sensitive plants took up more copper, and a higher percentage of the total copper concentration was allocated to the shoot, compared with the tolerant plants. A distinct population differentiation was observed with respect to the distribution of calcium, magnesium, iron and potassium in roots and shoot-leaves. Under copper treatments the sensitive population showed a direct relation to the calcium concentration both in roots and shoot-leaves, while the tolerant population revealed an inverse relation to calcium concentration in plant tissues. The magnesium concentration decreased in the presence of increasing copper levels both in tolerant and, especially, sensitive populations. The total iron concentration seems to be unaffected under an excess of copper in tolerant plants, while an inverse relation of iron concentration to external copper supply in the sensitive population was observed. The concentration of potassium dropped more in sensitive plants. It seems likely that a constitutive copper tolerance mechanism also operates both in shoot and root and that this also contributes to the increased copper requirements of tolerant plants.

Photoacoustic measurements of photosynthetic activities in intact leaves under copper stress

Abstract Photoacoustic spectroscopy was used to monitor Cu damage to photosynthesis by measuring photochemical energy storage (PES) at high frequency of 600 Hz and yield of O 2 evolution (Aox/Apt) at low frequency of 19 Hz in intact leaves of a Cu-tolerant ( Silene compacta ) and a non-Cu-tolerant ( Alyssum montanum ) species. The results indicated that Cu affected root growth (RRG), more severely than photoacoustic parameters in both species. Plants of S. compacta grown in lower Cu concentration revealed an enhancement phenomenon on RRG, PES and Aox/Apt, in contrast, plants of A. montanum revealed a slight decrease in the above mentioned parameters. A remarkable decline of PES and Aox/Apt for both species, was observed, at higher Cu concentrations, a fact considered to reflect inhibition of the photsynthetic e − flow in thylakoids. PES was less affected by Cu stress than O 2 evolution showing a differential sensitivity of two photosystems in Cu. Photosystem II (PSII) seemed to be more sensitive because of degradation and leakage of chloroplasts membranes, inducing a decline in yield of O 2 evolution. On the other hand, PES was appreciable because of cyclic e − transfer around the intact or less inhibited photosystem I (PSI).

Short-term effects of aluminium at alkaline pH on the structure and function of the photosynthetic apparatus

A 24 h exposure of the salt-tolerant grass Thinopyrum bessarabicum (Savul. and Rayss) A. Love seedlings to 1 mM aluminium (Al) in nutrient solution at pH of 9.0 resulted in a significant reduction of the biomass. In control samples the mesophyll chloroplasts exhibited the usual lens shape with most grana arranged in straight or slightly curving lines, and only 6.5 % of the grana were out of order. In Al-treated plants the mesophyll chloroplasts displayed a slightly distorted shape and distended size with most grana arranged in bow-like lines, while in the central region of the organelle as many as 26.7 % of the grana were independent and out of order in relation to the long axis. The morphological changes in the chloroplast shape and grana arrangement were probably due to swelling and distension of the chloroplasts in consequence to the altered membrane permeability. The initial in vivo chlorophyll (Chl) fluorescence FO, as well as the intermediate FI and peak fluorescence FP were increased under the Al stress: this indicated a destruction of photosystem (PS) 2 reaction centres and increased reduction of QA. The (FI-FO)/(FP-FO) ratio exhibited a significant increase indicating higher proportion of PS2 centres unable to reduce QB. Changes in the chloroplast ultrastructure seemed to be the reason of photosynthetic electron transport inhibition. Yet all these changes in the photosynthetic performance and chloroplast ultrastructure were considered as indirect effects of Al treatment since Al concentration in the leaves was undetectable. Disturbances in the chloroplast ultrastructure could be caused by a reduced uptake and/or transport of other nutrients.