Fernando C. Lidon

Comparison of resistance to drought of three bean cultivars

The aim of the present work was to evaluate oxidative stress and plant antioxidant system of three contrasting bean (Phaseolus vulgaris L.) genotypes in the response to drought. Drought was imposed 14 d after emergence, by withholding water, until leaf relative water content reached 65 %. Water stress increased lipid peroxidation (LPO), membrane injury index, H2O2 and OH⋅ production in leaves of stressed plants. Activities of the antioxidative enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APOX) increased significantly under water stress in all the studied cultivars, while catalase (CAT) increased in cvs. Plovdiv 10 and Prelom, but decreased in cv. Dobrudjanski ran. Furthermore cv. Plovdiv 10 which had the highest APOX and CAT activities also showed the lowest increase in H2O2 and OH⋅ production and LPO while cv. Dobrudjanski ran showed the lowest increases (and often the lowest values) in the antioxidant enzyme activities and the highest increases of H2O2 and OH⋅ production, and LPO. On the basis of the data obtained we could specify cv. Plovdiv 10 and cv. Prelom as drought tolerant and cv. Dobrudjanski ran as a drought sensitive.

Oxy radicals production and control in the chloroplast of Mn-treated rice.

The interactions between Mn accumulation and production and control of oxy radicals were investigated in rice (Oryza sati6a L. cv. Safari) chloroplasts. Rice plants were grown for 21 days in nutrient solutions containing 2.3‐582.5 mM Mn. The plant shoot and the photosynthetic membranes showed 18-fold increases over this range of treatments, but displayed different accumulation kinetics. Production of superoxide and hydroxyl radicals in the thylakoids decreased significantly up to the 36.4 m MM n treatment, but increased at higher concentrations. In the thylakoid lamellae the total activity of superoxide dismutase (SOD) showed a similar pattern. The enzyme activities of the peroxide system coupled to the photophosphorylation varied significantly with increasing Mn concentrations. Between the 2.3 and the 36.4 mM Mn treatments, the Vmax of ascorbate peroxidase decreased, but thereafter, until the 582.5 mM an opposite trend was found. The activity of dehydroascorbate reductase did not vary significantly with Mn concentration. Between the 2.3 and the 9.1 mM Mn treatments the Vmax of glutathione reductase decreased significantly. In cellular extracts, the Vmax of catalase decreased significantly until the 145.6 mM Mn treatment but in the highest Mn treatment this enzyme activity increased. It was concluded that rice shows a biphasic response to Mn concentrations in the chloroplast lamellae. Until the 36.4 mM, the increasing photosynthetic rates along with the decrease of free radicals production and of the maximum activities of ascorbate peroxidase and SOD indicates that an efficient adaptation of chloroplasts to increasing Mn concentrations occurs. Moreover, from the 36.4 mM onwards, as this process is reversed, the main conclusion is that Mn accumulation starts to be toxic, leading to oxidative stress.

Cadmium-Induced Changes in Chloroplast Lipids and Photosystem Activities in Barley Plants

Fatty acid content and composition of chloroplast membranes, ethylene production associated with thylakoid lipids degradation as well as photosynthetic electron transport involving photosystems 1 and 2 were used to determine the effects of increasing Cd concentrations in the growth medium [0, 14, 28, and 42 mg (Cd) kg−1(sand)] on the photosynthetic performance of barley plants (H. vulgare L., cv. CE9704). High concentrations of Cd triggered serious disturbances of the chloroplast membranes. Ethylene production increased whereas a drop of 18:3 fatty acid content occurred, indicating that Cd mediates lipid peroxidation in the thylakoids. The enhanced ethylene production could be used as an early indicator of Cd-induced membrane degradation, yet at very high concentration (42 mg kg−1) Cd decreased ethylene production.

Biochemical and molecular characterization of the antioxidative system of Coffea sp. under cold conditions in genotypes with contrasting tolerance

Low positive temperature (chilling) is frequently linked to the promotion of oxidative stress conditions, and is of particular importance in the coffee plant due to its severe impact on growth, development, photosynthesis and production. Nevertheless, some acclimation ability has been reported within the Coffea genus, and is possibly related to oxidative stress control. Using an integrated biochemical and molecular approach, the characterization of the antioxidative system of genotypes with different cold acclimation abilities was performed. Experiments were carried out using 1.5-year-old coffee seedlings of Coffea canephora cv. Apoatã, C. arabica cv. Catuaí, C. dewevrei and 2 hybrids, Icatu (C. arabicaxC. canephora) and Piatã (C. dewevreixC. arabica) subjected to a gradual cold treatment and a recovery period. Icatu showed the greatest ability to control oxidative stress, as reflected by the enhancement of several antioxidative components (Cu,Zn-SOD and APX activities; ascorbate, alpha-tocopherol and chlorogenic acids (CGAs) contents) and lower reactive oxygen species contents (H(2)O(2) and OH). Gene expression studies show that GRed, DHAR and class III and IV chitinases might also be involved in the cold acclimation ability of Icatu. Catuaí showed intermediate acclimation ability through the reinforcement of some antioxidative molecules, usually to a lesser extent than that observed in Icatu. On the other hand, C. dewevrei showed the poorest response in terms of antioxidant accumulation, and also showed the greatest increase in OH values. The difference in the triggering of antioxidative traits supports the hypothesis of its importance to cold (and photoinhibition) tolerance in Coffea sp. and could provide a useful probe to identify tolerant genotypes.

Rice tolerance to excess Mn: Implications in the chloroplast lamellae and synthesis of a novel Mn protein

Rice (Oryza sativa L. cv. Safari) plants were grown over a 21-d period in nutrient solutions containing Mn concentrations varying between 0.125 and 32 mg·L -1 . The plant shoots and the thylakoid membranes showed similar overall Mn increases for this range of treatments, but different accumulation kinetics. It was found that the highest Mn treatment were associated to the synthesis of a new thylakoid protein with an average molecular mass of 36.5 kDa and a Mn:protein ratio of about 1. This protein exhibited superoxide dismutase activity, as well as a high content of Gln, Asp, Glu, Leu and Gly. Its EPR spectrum is characteristic of high-spin Mn(II), in a S=5/2 ground state. A comparative study of SDS polyacrylamide gel profiles of thylakoid polypeptides from the various treatments disclosed quantitative changes, as well as a new 37/36-kDa polypeptide band in the two highest Mn treatments. The photosynthetic electron transport rates coupled to PSII and PSI showed a significant increase until the 8-mg·L -1 Mn treatment. The related superoxide production of thylakoids (monitored by EPR spectroscopy) showed minimum values from the 0.5-mg·L -1 Mn treatment onwards, which, as shown by the thiobarbituric acid reaction was coupled to a non-significant variation of the acyl lipid peroxidation. It was concluded that Oryza sativa L. cv. safari has a high internal tolerance to Mn as it synthesises a new manganese protein that mimics superoxide dismutase functioning.

Effects of copper toxicity on growth and the uptake and translocation of metals in rice plants

Abstract Copper (Cu) contamination in the lower reaches of the Sado River in the Alcacer do Sal region of Portugal (a major rice producing area) has became a major pollution problem. In an attempt to study the changes in rice growth (Oryza sativa L.), the effect of excess Cu on the plasma membrane activity (as measured throughout proton extrusion) and membrane permeability as well as on the zinc (Zn), nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), boron (B), molybdenum (Mo), and aluminum (Al) net uptake and translocation was studied. Long‐term studies (30 days) were conducted with rice subjected to increasing Cu concentrations (ranging from 0.002 to 6.25 mg/L) showed a concentration increase of Cu in root and shoot tissues. Root proton extrusion increased 7.4‐fold between the 0.01 and the 1.25 mg/L Cu treatments, whereas its membrane permeability (as measured throughout the electrolytic conductance) revealed a marked increase after the 1.25 mg/L Cu treatment. Zinc ...

Effects of aluminum toxicity on nutrient accumulation in maize shoots: Implications on photosynthesis

Abstract The physiological characterization of aluminum (Al) toxicity in C4 plants prompted this study, having maize (Zea mays cv. XL‐72.3) used as a test system. Two weeks after germination, maize plants were submitted to increasing Al concentrations (from 0 up to 81 mg L‐1) for 20 days in a growth medium with low ionic strength, after which several analyses were carried out. In root tissues, Al concentrations significantly increased between the 0 and the 81 mg L‐1 Al treatment. In the shoots nitrogen (N), phosphorus (P), and iron (Fe) significantly decreased with increasing Al concentrations, but at different rates. Magnesium (Mg) showed a tendency to decrease for Al treatments higher than 9 mg L‐1, the opposite occurring with manganese (Mn) contents. Chlorophyll a fluorescence parameters Fo and Fv/Fm showed non‐significant changes, while photosynthetic capacity, electron transport rate associated with photosystem I and cytochromes (cyt) f and b563 contents decreased above the 9 mg L‐1 Al treatment. Alu...

Copper Toxicity In Rice: Diagnostic Criteria And Effect On Tissue Mn And Fe

Long-term experiments (30 days) were carried out with rice in solution culture containing varying concentrations of Cu in an attempt to examine the threshold toxic concentration of this metal and its effects on Mn and Fe concentration in plant tissues. Cu concentration by rice roots (Oryza sativa L.) consisted of two distinct accumulation phases: a slow phase, in solution containing up to 0.01 mg/L, and a rapid phase above this concentration. In both phases the net absorption rate, as measured by Cu concentration in the roots, increased with metal concentration in the culture solution, but the increase was much faster in the second phase. Total Cu tissue concentration showed little variation between normal tissue and that clearly showing initial symptoms of the metal toxicity. Cu toxicity, as expressed by reduced root length, appeared to be a direct result of the accumulation of excess Cu in total tissues, the average concentration being 35.1 μg/g (dw) Cu at threshold toxicity. With respect to the effects of excess Cu on Mn and Fe concentrations, it was observed that while Mn and Fe concentrations in the shoot decreased at solutions of Cu concentrations above 0.05 mg/L, in the root these metals showed different patterns, with Fe concentration decreasing above 0.05 mg/L Cu and Mn concentration showing no defined trend. It is suggested that Cu affects Mn and Fe net translocation by different mechanisms, having the X coefficient for Mn and Fe values of 0.995 and 0.581, respectively.

Drought effects on membrane lipids and photosynthetic activity in different peanut cultivars

The effects of drought on thylakoid acyl lipid composition, photosynthetic capacity (Pmax), and electrolyte lekage were evaluated in two-months-old peanut cultivars (57-422, 73-30, GC 8-35) growing in a glasshouse. For lipid studies, plants were submitted to three treatments by withholding irrigation: control (C), mild water stress (S1), and severe water stress (S2). Concerning membrane and photosynthetic capacity stability, drought was imposed by polyethylene glycol (PEG 600). In the cv. 73-30 a sharp decrease in the content of thylakoid acyl lipids was observed, already under S1 conditions, whereas cv. 57-422 was strongly affected only under S2. Cv. GC 8-35 had the lowest content of acyl lipids under control conditions, a significant increase under S1 conditions, and only under S2 a decrease occurred. Thus concerning lipid stability, cv. 73-30 was the most sensitive. Among lipid classes, phospholipids and galactolipids were similarly affected, as was MGDG relatively to DGDG. Water deficit imposed by PEG induced a higher increase in electrolyte leakage in cv. 73-30 than in the other cvs. A positive relationship between acyl lipid concentration and membrane integrity was found in all studied cvs. A positive association between acyl lipid concentration, membrane integrity, and Pmax was found in the cvs. 57-422 and 73-30.

Photosynthetic performance and content of some nutrients in cadmium- and copper-treated barley plants

ABSTRACT Barley (Hordeum vulgare L. cv. CE9704) plants grown in sand culture were exposed to increasing cadmium (Cd) (0, 14, 28, and 42 mg Cd kg−1 sand) or copper (Cu) (0, 5, 10, and 15 mg Cu kg−1 sand) concentrations for a duration of 10 days. The effect of excess Cd or Cu on plant growth, selected mineral elements content, leaf gas exchanges, and chlorophyll content were studied. The excess of Cd or Cu inhibited relative growth rate (RGR) of barley plants mainly through net assimilation rate (NAR) retardation, but leaf area ratio (LAR) was barely affected or unaffected. After 10 days of exposure, the shoot content of Cd and Cu was about 1/10 (Cu) to 1/20 (Cd) that of roots. Cadmium- and Cu-treated plants with equal RGR inhibition had some differences in photosynthesis response and in the content of some nutrients, which were not distinctive enough. Stomatal limitation to photosynthesis in Cd-treated plants was well expressed, but in Cu-treated plants factors limiting photosynthesis were more related with mesophyll constraints. Cadmium and Cu treatment reduced the chlorophyll content, relative to untreated plants more probably through degradation of photosynthetic components. In conclusion, among observed physiological disturbances in Cd and Cu-treated barley plants with relatively equal growth inhibition, the similarities prevailed over the differences.