Enhanced Superoxide Radical Production in Roots of Zinc-Deficient Plants

The production of superoxide radical () was studied in roots of cotton (Gossypium hirsutum L. cv. Deltapine15/21), bean (Phaseolus vulgaris L. var. Pr?lude) and tomato(Lycopersicon esculentum L. cv. Super marmande) plants grownin nutrient solution with different Zn concentrations. UsingTiron as a spin-probe, electron spin resonance (ESR) was employedfor the measurements of levels. In the 48 000 g and 140 000 g supernatants of cotton root extracts theamplitude of the Tiron ESR signals reflecting production steeply increased with the appearance of visual Zndeficiency symptoms in the shoots. The changes in the amplitudeof the Tiron ESR signals were closely correlated with an NADPH-dependent generating oxidase activity with a high pH optimum. Increases in NADPH-dependent generation were also found in root extracts of Zn-deficientbean and tomato plants. In all experiments re-supply of Zn todeficient plants for 12 h or 24 h markedly decreased generation. Further, with advancing Zn deficiencyrates of NADPH oxidation increased and the activities of superoxidedismutase (SOD) and catalase decreased. The results suggest that cotton, bean and tomato roots possessan NADPH-dependent generating activity which is affected by the Zn nutritional status of the plants. UnderZn deficiency, enhanced generation and impaired detoxification of Of and H₂O₂ could lead to elevated levelsof and -derived oxidizing O₂ species and thus to increased peroxidation of membrane lipids. Key words: NADPH oxidase, superoxide radical, zinc deficiency     

Effect of Zinc Nutritional Status on Growth, Protein Metabolism and Levels of Indole-3-acetic Acid and other Phytohormones in Bean (Phaseolus vulgaris L.)

Bean (Phaseolus vulgaris L. var. Prelude) plants were grownfor 17 d under controlled environmental conditions with variedZn supply in the nutrient solution. The concentrations of aminoacids; indole-3-acetic acid, IAA; abscisic acid, ABA; isopentenyladenine, I-Ade; isopentenyl adenosine, I-Ado; zeatin, Z; andzeatin riboside, ZR were determined in various shoot fractions. The growth of plants, especially shoot growth, was severelydepressed under conditions of Zn deficiency. Simultaneously,concentrations of soluble protein and chlorophyll decreased,whereas amino acid concentrations increased several-fold. Inthe Zn-deficient plants, the level of IAA in the shoot tipsand young leaves decreased to about 50% of that in Zn-sufficientplants. A similar decrease occurred in the ABA levels of shoottips. In contrast, Zn deficiency was without effect on cytokininlevels in the leaves. Re-supply of Zn to the deficient plantsfor up to 96 h significantly increased shoot growth, solubleprotein, and IAA levels up to the values of Zn-sufficient plants.Simultaneously, the concentration of amino acids dropped tolow levels. The effect of Zn nutritional status on the tryptophanlevel was parallel to that of most of the other amino acids.The results confirm the role of Zn in protein synthesis anddemonstrate that the decrease in IAA level in Zn-deficient plantsis not brought about by impaired synthesis of tryptophan. Itis also unlikely that in Zn-deficient plants the conversionof tryptophan to IAA is specifically inhibited. Key words: Indole-3-acetic acid, tryptophan, zinc deficiency     

The fatty acid compositions of predator Piocoris luridus （Heteroptera： Lygaeidae） and its host Monosteria unicostata （Heteroptera： Tingidae） reared on almond

The changes in fatty acid compositions during nutritional interaction among almond Amygdalus communis Linnaeus （Rosales： Rosaceae） （host plant）, lacebug Monosteria unicostata （Mulsant and Rey） （Heteroptera： Tingidae） and its predator Piocoris luridus Fieber （Heteroptera： Lygaeidae） were determined by gas chromatography and gas chromatography-mass spectrometry analyses. The fatty acid profiles of phospholipids and triacylglycerols were substantially different. Unlike the general observations for virtually most terrestrial insects, arachidonic and eicosapentaenoic acids were detected in high proportions of phospholipid fractions in both insects, especially in P. luridus. Also the almond tissues provide very little oleic acid to the herbivore diet, yet both insect species developed high proportions of this component. Our data reveals instances of specific accumulation of fatty acid biosynthesis, elongation/desaturation, and not incorporating selected fatty acids into cellular lipids.     

Magnesium deficiency enhances resistance to paraquat toxicity in bean leaves

Effects of deficient (20mmol m^?3) and sufficient (1000 mmol m^?3) magnesium (Mg) supply and of varied light intensity (100 μmol m^?2 s^?1 to 580 μmol m^?2 s^?1) on paraquat-dependent chlorophyll destruction in bean (Phaseolus vulgaris) plants grown in nutrient solution were studied over a 12-d period using leaf discs or intact primary leaves. Treatment of leaf discs with 10mmol m ³ paraquat for 15h caused severe chlorophyll loss, especially with increasing light intensity. This chlorophyll destruction by paraquat was very much higher in Mg-sufficient than Mg-deficient leaves. The occurrence of paraquat resistance in Mg deficient leaves was already apparent after 6d growth in nutrient solution, i.e. before any decrease in chlorophyll or growth by Mg deficiency was evident. Also, following foliar application of paraquat (10–140 mmol m^?3) to intact plants, Mg-deficient plants were much more resistant to paraquat, even following longer exposure duration (72 h) and four to 14 times higher paraquat concentrations than those received by Mg sufficient plants. From experiments where exogenous scavengers of superoxide radical (O₂^.-), hydroxyl radical (OH^·) and singlet oxygen (¹O₂) were applied to leaf discs, it appears that O₂^.-, and partly, OH^· are the main O₂ species which contribute to chlorophyll destruction by paraquat. The results demonstrate that Mg-deficient bean plants become highly resistant to O₂^.--mediated and light-induced paraquat injury. The mode of this paraquat resistance is attributed to well-known stimulative effects of Mg deficiency on O₂^.- and H₂O₂ scavenging enzymes and antioxidants.     

Effect of Zinc Deficiency on Proton Fluxes in Plasma Membrane-Enriched Vesicles Isolated from Bean Roots

Plasma membrane-enriched vesicles were isolated by density gradientcentrifugation from roots of zinc-sufficient and zinc-deficientbean (Phaseolus vulgaris L. cv. Prélude) plants. Thetwo populations of vesicles had similar activities of specificmembrane marker enzymes and ATP hydrolysis and were competentfor proton transport. However, vesicles from zinc-deficientroots showed lower rates of ATP-dependent intravesicular acidificationand increases in passive permeability to protons as well asin the rate, of dissipation of a non-metabolic transmembranepH gradient. The decrease of the rate of proton accumulationin isolated vesicles closely paralleled the increase in potassiumleakage from intact roots and the appearance of visual zincdeficiency symptoms in the shoots. Re-supply of zinc to deficientplants for 24 h promoted shoot growth, reduced potassium leakagefrom roots and led to partial recovery of the proton accumulationcapacity and to a decrease in passive permeability to protonsin isolated vesicles. The results obtained with isolated vesiclesconfirm the previously observed ‘in vivo’ effectsof zinc deficiency and are consistent with the idea that analteration of plasma membrane lipids leads to an increase inpermeability and an impairment in trans-plasma membrane protongradient. Key words: Plasma membrane, H⁺ fluxes, ATPase, zinc deficiency     

Differences in Zinc Efficiency among and within Diploid, Tetraploid and Hexaploid Wheats

Greenhouse experiments were carried out with six diploid, ninetetraploid and seven hexaploid wheats, including wild and primitivegenotypes, to study the influence of varied zinc (Zn) supplyon the severity of Zn deficiency symptoms, shoot dry matterproduction and shoot Zn concentrations. In addition to wildand primitive genotypes, one modern tetraploid cultivar withhigh sensitivity to Zn deficiency and two modern hexaploid cultivars,one highly sensitive to and one resistant to Zn deficiency,were included for comparison. Plants were grown for 44 d ina severely Zn-deficient calcareous soil, with (+Zn; 5 mg Znkg^-1soil) and without (-Zn) Zn fertilization. Visible Zn deficiencysymptoms, including whitish-brown necrotic patches on leaf blades,appeared very rapidly and severely in all tetraploid wheat genotypes.Compared with tetraploid wheats, diploid and hexaploid wheatswere less sensitive to Zn deficiency. With additional Zn, shootdry matter production was higher in tetraploid than diploidand hexaploid wheats. However, under Zn-deficient conditionstetraploid wheats had the lowest shoot dry matter production,indicating the very high sensitivity of tetraploid wheats toZn deficiency. Consequently, Zn efficiency expressed as theratio of shoot dry matter produced under Zn deficiency to Znfertilization, was much lower in tetraploid wheats than in diploidand hexaploid wheats. On average, Zn efficiency ratios were36% for tetraploid, 60% for diploid and 64% for hexaploid wheats.Differences in Zn efficiency among and within diploid, tetraploidand hexaploid wheats were positively related to the amount ofZn per shoot of the genotypes, but not to the amount of Zn perunit dry weight of shoots or seeds used in the experiments.The seeds of the accessions of tetraploid wild wheats containedup to 120 mg Zn kg^-1, but the resulting plants showed very highsensitivity to Zn deficiency. By contrast, hexaploid wheatsand primitive diploid wheats with much lower Zn concentrationsin seeds had higher Zn efficiencies. It is suggested that notonly enhanced Zn uptake capacity but also enhanced internalZn utilization capacity of genotypes play important roles indifferential expression of Zn efficiency. The results of thisstudy also suggest the importance of the A and D genomes asthe possible source of genes determining Zn efficiency in wheat.Copyright 1999 Annals of Botany Company Seeds, Triticum aestivum, Triticum monococcum, Triticum turgidum, zinc concentrations, zinc deficiency, zinc efficiency.     

Activities of Hydrogen Peroxide-Scavenging Enzymes in Germinating Wheat Seeds

During imbibition and germination of wheat (Triticum aestivum)in the dark over 72 h, activities of the enzymes of the ascorbate(AsA)-dependent H₂O₂-scavenging pathway, AsA peroxidase, monodehydroascorbate(MDAsA) reductase, dehydroascorbate (DHAsA) reductase and glutathione(GSSG) reductase as well as superoxide dismutase (SOD), catalaseand guaiacol peroxidase were determined both in whole grainsand in isolated embryos and endosperm. With the exception of DHAsA reductase, activities of the otherenzymes assayed increased in germinating seeds, especially duringradicle emergence (between 24–48 h of imbibition). Theseincreases, particularly for AsA peroxidase, were much higherin the embryo than in the endosperm. Within 72 h of imbibition,activities per seed increased 116-fold for AsA peroxidase, 19-foldfor guaiacol peroxidase, 5-fold for catalase and only 1·4-foldfor SOD. In contrast to the decreases in DHAsA reductase, theother AsA recycling enzyme, MDAsA reductase, increased 5-foldwithin 72 h. The results indicate that, in wheat seeds, imbibition and germinationis associated with enhanced cellular capacity to detoxify H₂O₂.For this detoxification the operation of AsA peroxidase togetherwith the AsA-regenerating enzymes appears to be of particularimportance. Key words: Ascorbate peroxidase, germination, hydrogen peroxide detoxification, inhibition, wheat