Michael Moustakas

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.

Interaction of proline, sugars, and anthocyanins during photosynthetic acclimation of Arabidopsis thaliana to drought stress

The relationships among photosynthetic acclimation, proline (Pro), soluble sugar (SS), and anthocyanin (An) accumulation in Arabidopsis thaliana leaves to the onset of drought stress (OnDS), mild (MiDS) and moderate drought stress (MoDS), were evaluated. As leaf water content (LWC) decreased, metabolic concentrations (Pro, SS, and An) increased and were negatively and significantly correlated with LWC. Thus, these metabolites may have an important role in the acclimation process to drought stress (DS). No correlations among Pro, SS and An accumulation with the quantum efficiency of PSII photochemistry (Φ(PSII)) and the excitation pressure (1-q(P)) were observed under DS. This implies that, while metabolites increased in a drought-dependent way, PSII activity did not decrease in the same pattern. Our results indicated that, under MoDS, A. thaliana leaves were able to maintain oxidative compounds such as malondialdeyde, an end product of lipid peroxidation, within the range of control leaves, and to cope with oxidative damage, as was evident by the decreased excitation pressure (1-q(P)) and similar (ns difference) Φ(PSII) to that of control leaves. In addition, a statistically significant increased accumulation of Pro, SS and An was recorded only under MoDS compared to controls. The better PSII functioning of MoDS Arabidopsis leaves may reflect the greater capacity of these leaves to undertake key metabolic adjustments, including increased Pro, SS and An accumulation, to maintain a higher antioxidant protection and a better balance between light capture and energy use.

Spatio-temporal heterogeneity in Arabidopsis thaliana leaves under drought stress.

Using chlorophyll (chl) fluorescence imaging, we studied the effect of mild (MiDS), moderate (MoDS) and severe (SDS) drought stress on photosystem II (PSII) photochemistry of 4-week-old Arabidopsis thaliana. Spatio-temporal heterogeneity in all chl fluorescence parameters was maintained throughout water stress. After exposure to drought stress, maximum quantum yield of PSII photochemistry (F(v)/F(m)) and quantum efficiency of PSII photochemistry (Φ(PSΙΙ)) decreased less in the proximal (base) than in the distal (tip) leaf. The chl fluorescence parameter F(v) /F(m) decreased less after MoDS than MiDS. Under MoDS, the antioxidant mechanism of A. thaliana leaves seemed to be sufficient in scavenging reactive oxygen species, as evident by the decreased lipid peroxidation, the more excitation energy dissipated by non-photochemical quenching (NPQ) and decreased excitation pressure (1-q(p)). Arabidopsis leaves appear to function normally under MoDS, but do not seem to have particular metabolic tolerance mechanisms under MiDS and SDS, as revealed by the level of lipid peroxidation and decreased quantum yield for dissipation after down-regulation in PSII (Φ(NPQ)), indicating that energy dissipation by down-regulation did not function and electron transport (ETR) was depressed. The simultaneous increased quantum yield of non-regulated energy dissipation (Φ(NO)) indicated that both the photochemical energy conversion and protective regulatory mechanism were insufficient. The non-uniform photosynthetic pattern under drought stress may reflect different zones of leaf anatomy and mesophyll development. The data demonstrate that the effect of different degrees of drought stress on A. thaliana leaves show spatio-temporal heterogeneity, implying that common single time point or single point leaf analyses are inadequate.

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...

Effect of heavy metals on isoperoxidases of Wheat

The influence of increasing concentrations of copper, zinc, lead, nickel, chromium and cadmium on 14-day-old seedlings of wheat (Triticum aestivum L. cv. Vergina) was studied. Plants were grown in 1/10 strength Rorison’s nutrient solution with increasing concentrations of each of the metals added separately. The toxicity of metals depressed shoot growth but the most evident symptoms were on roots. The concentration of each metal which caused inhibition of root growth was chosen to study the influence of metals on isoperoxidases of wheat shoots. The concentrations employed did not alter the number of peroxidase bands but almost in all cases enhanced the intensities of bands of pH 4.0-4.2 and 5.0-5.4, while they decreased the intensities of bands of pH 4.2-4.6 and 5.4-6.5.The similar effects of the different heavy metals employed may suggest similarity in metal action on wheat isoperoxidases. The increased intensities of peroxidase bands may be considered as an indication of enhanced senescence caused by the heavy metal treatments.Generally, our results suggest that the heavy metals employed have caused complex changes on the multiple forms of peroxidases.

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.

Molecular identification of Greek olive (Olea europaea) cultivars based on microsatellite loci

Olea europaea is one of the oldest species of domesticated trees. We used microsatellite markers for fingerprinting and for evaluation of genetic similarity and structure of 26 Greek olive cultivars, which cover most of the olive cultivation regions of Greece, including previously undescribed denominations from northern Greece. Eighty-one alleles were revealed with six SSR loci that were selected as most informative of 10 SSR primers that were initially investigated. The number of alleles per locus varied from 7 to 20 (mean, 13.5). Heterozygosity ranged from 0.240 at locus DCA-3 to 0.826 at locus UDO99-9, with a mean value of 0.600. Analysis of 104 trees representing 26 denominations (four trees per denomination) revealed 26 distinct SSR profiles, indicating 26 olive cultivars; no intracultivar variability was observed. Genetic and geographic distances were not significantly correlated, based on the Mantel test. These SSR loci allowed unequivocal identification of all the cultivars and will be useful for future breeding and olive germplasm management efforts.

Protein Phosphorylation-Dephosphorylation in Alfalfa Seeds Germinating under Salt Stress

Summary When seeds of alfalfa (Medicago sativa L. cv. Luzerne Euver) were germinated under iso-osmotic solutions of NaCl (0.10M solution equivalent to conductivity 8.0 dSm-1) and mannitol (0.19m) or an increased level of NaCl (0.15M solution equivalent to conductivity 11.6dSm-1) seedling growth indicated a continuous decrease in plant height and dry weight in subsequent days of germination. In contrast, the extractable proteins of NaCl and mannitol stressed seedlings were more comparable to controls. Protein kinase (EC 2.7.1.37) and protein phosphatase (EC 3.1.3.16) specific activities were determined in crude extracts of alfalfa seedlings. At both concentrations of NaCl protein kinase specific activities towards endogenous substrates were higher than the control or mannitol except at day 7 under 11.6 dSm-1 NaCl. Unlike protein kinase specific activities, the protein phosphatase specific activities against 32P-labeled bovine casein were inhibited in the presence of NaCl at all days of germination, except at day 5, when 8.0 dSm-1 NaCl enhanced them. The presence of mannitol (0.19 m) also inhibited protein phosphatase specific activites. These observations suggest that some specific ionic effect of salt was responsible for the behaviour of the enzymes. SDS-electrophoresis followed by autoradiography revealed three major groups of in vitro phosphorylated proteins (in the presence of Ca2+ or Mn2+) in ungerminated seeds: a low molecular group (Mrs ca. 10–20,000), a medium molecular group (Mrs ca. 35–50,000) and a high molecular group (Mrs ca. 50-86,000). The latter was absent from the seedlings in all treatments. An increase in salinity (11.6dS m-1 NaCl) retarded the disappearance of medium molecular group protein bands in contrast to control or mannitol where these almost disappeared from the first day of germination. A condition of normal alfalfa seedling growth may be regulated by dephosphorylation of medium molecular group protein bands.

Aluminum toxicity effects on durum wheat cultivars

Abstract The effects of aluminum on biomass, nutrients and kinases were studied in two durum wheat cultivare (Triticum durum Desf. cvs Sapfo, Capeiti 82) grown in nutrient solutions (pH 4.5) at seven Al levels (0, 9.3, 18.5, 37.1, 74.1, 148, and 297 μM). The most evident Al toxicity symptom was a reduction in root growth. Sapfo showed greater Al tolerance than Capeiti 82. However, both cultivare must be characterized as Al‐sensitives. Aluminum in the nutrient solution above 74.1 μM significantly (P<0.05) reduced root growth of both durum wheat cultivare. The concentration of 74.1 μM Al can be suggested for screening of durum wheats on the basis of tolerance to Al. The concentrations of the nutrients Ca, Mg, K, and Fe in the plant tissues of both cultivare decreased even at low Al levels. The decrease of Ca+2 content in leaves and roots of the two durum wheat cultivare was almost the same while the less sensitive cultivar Sapfo retained larger amounts of Mg+2 in roots and leaves compared with the more sens...