Embryo Rescue and Induction of Somatic Embryogenesis as a Method to Overcome Seed Inviability in Zea mays ssp. mays × ; Zea mays ssp. parviglumis Crosses

Zea mays ssp. mays (2n=40) and Z. mays ssp. parviglumis (2n=20) were crossed to obtain hybrid plants by embryo rescue. Hybrid embryos were isolated and cultured on García et al. (1992) basic medium supplemented with 2,4-dichlorophenoxyacetic acid and/or kinetin in different concentrations. Caryopses harvested 23 d after pollination (DAP) were turgid, with 0.3 to 0.5 mm long embryos, while those harvested 30 DAP were shrunken, with 1 to 1.5 mm long embryos. Twenty days after plating, 100 % of the younger embryos gave rise to white, compact embryogenic calli. Subsequently, coleoptiles, leaf-like structures, shoots and roots originated from them and 35 hybrid plants were regenerated from 60 embryos. Embryogenic or organogenic calli frequencies did not differ among hormonal treatments, but they decreased, on average, from 90.5 to 44.3 %, comparing 50 and 120-d-old cultures. The older embryos regenerated plants only by germination, although they gave rise to organogenic callus with low frequencies. Regenerated plants showed a somatic chromosome number of 2n=30, pollen fertility of 40 to 80 % and 15 % viable naked caryopses.     

Root and shoot elongation as an assessment of heavy metal toxicity and ‘Zn Equivalent Value’ of edible crops

Seeds of thirteen edible plant species were tested for their response to heavy metals during their early development. It was found that a short-term root elongation test of six days could be used to evaluate the degree of toxicity of aqueous samples containing heavy metals. Shoot elongation was found to be less sensitive to metals than root elongation.The seeds were sown in pots containing freshwater sand to which known concentrations of metal solutions were added. The relative toxicity of the three metals, copper, nickel and zinc, followed the pattern of Ni > Cu > Zn.Results on the relative toxicity of Zn : Cu: Ni to various plant species indicated that the ratios were species-specific. The Zn equivalent concept of Zn : Cu : Ni = 1 : 2 : 8 could not be applied to all the plant species tested.The root growth of seeds of Brassica parachinensis (flowering Chinese cabbage) placed on filter papers in petri dishes to which metal solutions were added were tested. The sensitivity ranking of the metals tested was found to be as follows: Ni > Cd > Cu > Al > Fe > Zn > Pb > Mn > Ag. There was no significant difference (p > 0.05) in percentage reduction in root elongation among the four different repeated trials.     

Effect of nickel concentration and soil pH on metal accumulation and growth in tropical agromining ‘metal crops’

Plant and Soil - Phosphorus (P) deficiency is a major constraint for rice production in the tropics. Field-specific P management is key for resource-limited farmers to increase yields with minimal...     

Heterozygosity of Knob-Associated Tandem Repeats and Knob Instability in Mitotic Chromosomes of Zea （Zea mays L. and Z. diploperennis Iltis Doebley）

Knobs are blocks of heterochromatin present on chromosomes of maize （Zea mays L.） and its relatives that have effects on the frequency of genetic recombination, as well as on chromosome behavior. Knob heterozygosity and instability in six maize inbred lines and one Z. diploperennis Iltis Doebley line were investigated using the fluorescence in situ hybridization （FISH） technique with knob-associated tandem repeats （180 bp and 350 bp （TR- 1）） as probes. Signals of seven heterozygous knobs containing 180- bp repeats and of one heterozygous knob containing TR- 1 were captured in chromosomes of all materials tested according to the results of FISH, which demonstrates that the 180-bp repeat is the main contributor to knob heterozygosity compared with the TR- 1 element. In addition, one target cell with two TR- 1 signals on one homolog of chromosome 2L, which was different from the normal cells in the maize inbred line GB57, was observed, suggesting knob duplication and an instability phenomenon in the maize genome.     

Genetic control and racial variation of β-glucosidase isozymes in maize (Zea mays L.)

-Glucosidase (-D-glucoside glucohydrolase, E.C. 3.2.1.21, -Glu) isozyme variants were studied in a large number of inbred lines, crosses, and races of maize (Zea mays L.). The pattern of Mendelian inheritance demonstrated for -GLU variants indicated that they are under nuclear gene control. Twenty-two allelic forms at a single locus were identified in the materials studied by starch gel electrophoresis. Genetic data indicate that -GLU in maize is functionally a dimer. Variation of -GLU isozymes in 51 racial collections of maize from Mexico showed little correlation with morphological or geographical data. In 39 collections from Central America, variation patterns appeared to have some association with altitude.This work was supported in part by NIH Research Grant GM 11546.Paper No. 5040 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina.     

Effects of Cadmium on Polar Lipid Composition and Unsaturation in Maize （Zea mays） in Hydroponic Culture

This study aimed to evaluate the effect of Cd exposure （100 μmol/L） on polar lipid composition, and to examine the level of fatty acid unsaturation in maize （Zea mays L.）. In roots, the level of 16：0 and monounsaturated fatty acids （16：1 ＋ 18：1） decreased in phosphatidylcholine （PC） and phosphatidylethanolamine （PE）. In contrast, the proportion of unsaturated 18-C fatty acid species showed an opposite response to Cd. The content, on the other hand, of PC, PE, digalactosyldiacylglycerol （DGDG）, and steryl lipids increased in roots （2.9-, 1.6-, 5.3-, and 1.7-fold increase, respectively）. These results suggest that a more unsaturated fatty acid composition than found in control plants with a concomitant increase in polar lipids may favor seedling growth during Cd exposure. However, the observed increase in the steryl lipid （SL） ： phospholipid （PL） ratio （twofold）, the decrease in monogalactosyldiacylglycerol （MGDG） ： DGDG ratio, as well as the induction of lipid peroxidation in roots may represent symptoms of membrane injury. In shoots, the unsaturation level was markedly decreased in PC and phosphatidylglycerol （PG） after Cd exposure, but showed a significant increase in sulfoquinovosyldiacylglycerol （SQDG）, MGDG and DGDG. The content of PG and MGDG was decreased by about 65%, while PC accumulated to higher levels （4.4-fold increase）. Taken together, these changes in the polar lipid unsaturation and composition are likely to be due to alterations in the glycerolipid pathway. These results also support the idea that the increase in overall unsaturation plays some role in enabling the plant to withstand the metal exposure.     

Location and Analysis of Introgressed Segments in the Parthenogenetic Progenies of Zea mays×Z.diploperennis by GISH

玉米×二倍体多年生类玉米孤雌后代渗入片段的GISH定位分析     

Interaction between NO 3 − and abscisic acid in the regulation of lateral root elongation in Zea mays L.

Lateral root (LR) elongation rate of 7–8-day maize seedlings depends on the availability of NO ₃ ^? , NO ₂ ^? , and abscisic acid (ABA) in an environment. Four-hour exposure to 0.01–1.5 mM NO ₂ ^? increases the relative LR elongation rate; in the case of NO ₂ ^? , the stimulation occurs only at an NO ₂ ^? concentration equal to 0.01 mM. Exogenous ABA (10^?6 M) inhibits the LR elongation process. In the case of a combined influence of NO ₃ ^? and ABA or NO ₂ ^? and ABA, the character of the response elongation reaction is different. The NO role in the regulation of LR elongation is discussed.     

Optimisation of DNA transfer and transientβ-glucuronidase expression in electroporated maize (Zea mays L.) microspores

Summary The ability to deliver free DNA into microspores of a highly androgenic hybrid of maize was assessed by electroporation, using a square wave pulse discharge apparatus. The electroporation medium was chosen according to its ability to maintain a high level of regeneration. Nuclease activities were analyzed and were inhibited by the addition of 100 mM KNO₃ and MgSO₄ in the electroporation medium. Seven expression vectors withUid A as the reporter gene under the control of cauliflower mosaic virus 35S, Lat 52-7, Zmg 13, Emu, Ubiq-1, Al, or Actl promoters were tested in relation to the level of ß-glucuronidase expression in maize microspores. The highest level of expression was obtained when theUid A gene was driven by the Actl promoter. Therefore, this vector was further used to define optimal conditions leading to highest levels of ß-glucuronidase expression. The parameters determined in this study could provide an ideal starting point for the obtention of transgenic maize plants from electroporated microspores.Abbreviations DH diplohaploid - PEG polyethylene glycol - GUS ß-glucuronidase - EDTA Ethylene-diaminetetra Acetic acid - CaMV Cauliflower mosaic virus     

Uptake and distribution of zinc,cadmium, lead and copper in Brassica napus var. oleífera and Helianthus annus grown in contaminated soils

Brassica napus var. oleifera and Helianthus annus were grown in artificially contaminated soils. Accumulation and translocation of the environmental pollutants zinc, cadmium, lead, and copper, was evaluated in different portions of the plants at two harvesting times. The distribution into the plants of these metal ions, as well as their capacity for contaminant phytoextraction and accumulation was assessed. For this purpose, an analytical method utilizing focused ultrasound employed for extraction and stripping voltammetry for measurement has been optimized and validated for the simultaneous measurement of Zn, Cd, Pb, and Cu in plant extracts.     

Partial purification of endo- and exo-β-D-glucanase enzymes from Zea mays L. seedlings and their involvement in cell-wall autohydrolysis

The proteins dissociated from isolated Zea seedling cell wall using high-ionic-strength salt solutions have been found to include a number of enzymes which appear to participate in autolytic reactions of the cell wall. These enzymes caused extensive degradation of enzymatically inactive cell wall, liberating as much as 100 g/mg dry weight over a 48-h period. Lithium chloride (3M) was shown to be most effective in yielding protein and wall-degrading activities.Molecular-sieve chromatography of the cell-wall protein resolved endo--D-glucanase and exo--1,3-glucanase (EC 3.2.1.58) activities when Avena glucan and laminarin, respectively, were employed as substrates. The exoenzyme (molecular weight around 60,000) was strongly inhibited by inorganic mercury at a concentration which suppressed the release of monosaccharide from autolytically active cell wall. The endo--D-glucanase (MW around 26,000), which showed a marked preference for substrates of mixed-linkage, exhibited features indicating that it initiates the autolytic solubilization of wall glucan.Cell-wall -D-glucan, recovered as a component of an alkali-soluble cell-wall fraction, served as a substrate for the purified glucanases. Their hydrolysis pattern, assessed using gel exclusion chromatography and product analysis, confirmed that they hydrolyze -D-glucan. The products generated by the endoglucanase were similar in molecular-size distribution to those liberated from autolytically active-wall. Exoglucanase activity was required for extensive hydrolysis of -D-glucan in vitro.During coleoptile development the autolytic activity of the cell wall increased dramatically. This increased activity, however, did not parallel the growth potential of the tissue, but more closely reflected an increase in cell-wall -D-glucan, the primary substrate for autolytic reactions.These results were presented, in part, as papers at the annual meeting of the American Society of Plant Physiologists. Ohio State University, Columbus, in August 1979     

Plastid targeting of E. coli β-glucuronidase and ADP-glucose pyrophosphorylase in maize (Zea mays L.) cells

Summary Dicot and monocot chloroplast targeting peptides (CTPs) were evaluated for their effect on targeting, processing, and expression of two reporter proteins in maize cells. When tested transiently in maize leaf protoplasts, the maize ribulose bisphosphate carboxylase small subunit CTP required the inclusion of the amino terminus of mature small subunit protein to target -glucuronidase (GUS) to the plastid. To remove this amino terminal extension from GUS after import and processing, a repeat of the native processing site was inserted between the native mature protein and the reporter protein. This repeat processing site was used with less efficiency than the native site. Parallel constructs using the Arabidopsis thaliana small subunit and maize granule-bound starch synthase CTPs also localized GUS, but varied in repeat site use and GUS expression levels. Data from the CTP fusions with GUS were generally confirmed with fusions to an allosteric variant of E. coli ADP-glucose pyrophosphorylase. Plastid targeting of this enzyme was required for starch enhancement of transgenic BMS cells.Abbreviations BMS maize Black Mexican Sweet suspension culture cells - CTP chloroplast targeting peptide - glgC16 an allosteric variant of E. coli ADP-glucose pyrophosphorylase - GUS -glucuronidase - LUX luciferase - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - SSU small subunit of ribulose bisphosphate carboxylase     

Characteristics and diversity of microbial communities in lead–zinc tailings under heavy metal stress in north-west China

High-throughput 16S rRNA and 18S rRNA sequencing were performed to study the changes of soil microbial diversity and community structure under different heavy metal pollution levels in Chengxian lead–zinc mining area, Gansu Province. In this study, we characterized the main physicochemical properties, multiple heavy metal pollution, and microbial community structure of the soil in the tailings. The results show that the soil near the tailings pond was alkaline, barren and the heavy metals were seriously polluted. The microbial diversity and richness of S1 and S2 sites were significantly lower than that of CK2 site (P < 0·05), indicating that the heavy metal pollution could change the physicochemical properties and microbial community structure in soil. Among 97 identified core operating taxa of fungal communities, Ascomycota, Teguta and Basidiomycota were dominant at the phylum level, while among 1523 identified core operating taxa of bacterial communities, Actinomycota was dominant at the phylum level. In addition, the redundancy analysis and Spearman correlation analysis showed that the physicochemical properties and the heavy metal concentration had significant effects on the composition and distribution of soil microbial community. The basic characteristics of soil physicochemical properties, multiple heavy metal pollution and microbial community structure in the tailings were revealed, hoping to provide a basis for ecological rehabilitation of tailings by revealing the variance rule of microbial community diversity in the future.     

Cytoplasmic free calcium in Riccia fluitans L. and Zea mays L.: Interaction of Ca2+ and pH?

In cells of Zea mays (root hairs, coleoptiles) and Riccia fluitans (rhizoids, thalli) intracellular Ca²⁺ and pH have been measured with double-barrelled microelectrodes. Free Ca²⁺ activities of 109–187 nM (Riccia rhizoids), 94–160 nM (Riccia thalli), 145–231 nM (Zea root hairs), 84–143 nM (Zea coleoptiles) were found, and therefore identified as cytoplasmic. In a few cases (Riccia rhizoids), free Ca²⁺ was in the lower millimolar range (2.3±0.8 mM). A change in external Ca²⁺ from 0.1 to 10 mM caused an initial and short transient increase in cytoplasmic free Ca²⁺ which finally levelled off at about 0.2 pCa unit below the control, whereas in the presence of cyanide the Ca²⁺ activity returned to the control level. It is suggested that this behaviour is indicative of active cellular Ca²⁺ regulation, and since it is energy-dependent, may involve a Ca²⁺-ATPase. Acidification of the cytoplasmic pH and alkalinization of the vacuolar pH lead to a simultaneous increase in cytoplasmic free Ca²⁺, while alkalinization of pH_c decreased the Ca²⁺ activity. Since this is true for such remote organisms as Riccia and Zea, it may be concluded that regulation of cytoplasmic pH and free Ca²⁺ are interrelated. It is further concluded that double-barrelled microelectrodes are useful tools for investigations of intracellular ion activities in plant cells.Symbols and abbreviations _m, _m membrane potential difference, changes thereof - PVC polyvinylchloride     

A direct solid‐phase assay specific for heavy‐metal toxicity. II. Assessment of heavy‐metal immobilization in soils and bioavailability to plants

We have used the solid‐phase MetPLA TE, an enzyme assay that is specific for heavy‐metal toxicity, to investigate metal toxicity of soils that have been amended with urban wastewater sludges or contaminated with dry deposition from metal‐plating industries. We have shown that soil toxicity, using MetPLA TE, ranged from 21 to 72.5% inhibition of enzyme activity. Evin soil, which displayed the highest toxicity, also had the highest concentrations of Pb and Zn. Metal uptake studies with ryegrass grown on Evin soil, showed Zn, Cd, and Pb accumulation in the plant that exceeds the standard levels reported for grasses

Solid‐phase MetPLA TE was also used as a tool to study the reduction of heavy‐metal toxicity following soil amendments to immobilize metals in soil and thus reduce their toxicity. It was found that the addition of 1% hydrated manganese oxide significantly reduced dissolved metals in soil, their accumulation by ryegrass, and soil toxicity as shown by MetPLA TE.     

Gas chromatographic-mass spectroscopic identification and quantification of cyclic guanosine-3′: 5′-monophosphate in maize seedlings (Zea mays)

Gas chromatographic-mass spectroscopic evidence is presented for the presence of guanosine-3′: 5′-monophosphate (cGMP) in maize seedlings. The amount of cGMP (35–72 pmol g^-1 fresh weight) was quantified as a tetra-silyl derivative using gas-chromatographic detection with reference to a silylated standard of authentic cGMP. Gas-chromatographic separation of tri-silyl adenosine-3′: 5′-monophosphate and tetra-silyl cGMP is demonstrated.