Characterization and Fine Mapping of a Necrotic Leaf Mutant in Maize (Zea mays L.)

Maize (Zea mays L.) is a commercially important crop. Its yield can be reduced by mutations in biosynthetic and degradative pathways that cause death. In this paper, we describe the necrotic leaf (nec-t) mutant, which was obtained from an inbred line, 81647. The nec-t mutant plants had yellow leaves with necrotic spots, reduced chlorophyll content, and the etiolated seedlings died under normal growth conditions. Transmission electron microscopy revealed scattered thylakoids, and reduced numbers of grana lamellae and chloroplasts per cell. Histochemical staining suggested that spot formation of nec-t leaves might be due to cell death. Genetic analysis showed that necrosis was caused by the mutation of a recessive locus. Using simple sequence repeat markers, the Nec-t gene was mapped between mmc0111 and bnlg2277 on the short arm of chromosome 2. A total of 1287 individuals with the mutant phenotype from a F₂ population were used for physical mapping. The Nec-t gene was located between markers T31 and H8 within a physical region of 131.7 kb.     

Control of Nitrate Uptake by Phloem-Translocated Glutamine in Zea mays L. Seedlings

Abstract: The putative role of glutamine, exported from leaves to roots, as a negative feedback signal for nitrate uptake was investigated in Zea mays L. seedlings. Glutamine (Gln) was supplied by immersion of the tip-cut leaves in a concentrated solution. Nitrate (NO₃⁻) uptake was measured by its depletion in amino acid-free medium. The treatment with Gln resulted in a strong inhibition of nitrate uptake rate, accompanied by a significant enrichment of amino compounds in root tissue. The effect of N-availability on NO₃⁻ uptake was determined in split-root cultures. The plants were subjected to complete or localized N supply. Inducible NO₃⁻ uptake systems were also induced in N-deprived roots when the opposite side of the root system was supplied with KNO₃. The inhibitory effect of Gln was unaffected by localized N supply on one side of the split-root. The potential role of Gln in the shoot-to-root control of NO₃⁻ uptake is discussed.     

Fertility of Deep-frozen Maize (Zea mays L.) Pollen

On average, 50 per cent of maize pollen grains can be kept viableand almost 30 per cent remain fertile for up to a year whenthe water content on a fresh weight basis is reduced to about30 per cent of the original and the pollen is stored at –76or –196 °C. Over this period no significant differencewas found between storage at either temperature. Zea mays L., maize, pollen, fertility, viability     

Endopolyploidy in Diploid and Tetraploid Maize (Zea mays L.)

Nuclei from different tissues such as stem, mesocotyl, nodalroot and root tip of diploid and tetraploid maize were isolated,stained with propidium iodide and passed through an EPICS-751flow-cytometer cell sorter. Variations in flow histograms wereobserved in different tissues. Stem tissues of both the diploidand tetraploid had two peaks representing G1 and G2 somaticnuclei. The remaining tissues in both the diploids and tetraploidsexhibited three peaks. The first peak observed in these tissuesrepresents G1 somatic nuclei of the lowest ploidy level. Thesecond peak represent G2 somatic nuclei of the lowest ploidylevel+G1 somatic nuclei of the next ploidy level. The thirdpeak represents G2 of the higher ploidy level+G1 somatic nucleiof the next higher ploidy level. Statistically significant differenceswere observed between the diploid and tetraploid maize tissueswith respect to nuclei distribution in the higher ploidy levelpeaks implying variation in the degree of endopolyploidy inthe diploid and tetraploid maize. The results of this studysuggest that the amount of endopolyploid observed in maize genotypeshas an effect on their overall agronomic performance under thefield conditions.Copyright 1993, 1999 Academic Press Zea mays L., maize, endopolyploidy, diploid, tetraploid, flow cytometry     

Electrotropism of Maize (Zea mays L.) Roots (Facts and Artifacts)

Intact and decapped primary roots of maize (Zea mays L.) were exposed to DC electric fields of 0.5 to 8.0 V/cm in low-salinity media to resolve conflicting results about the direction of electrotropism. In DC fields of 0.5 V/cm or 1.0 V/cm, intact roots always curved toward the cathode. In a field of 8.0 V/cm, intact roots curved toward the anode and stopped growth. Decapped roots also curved toward the anode both in weak and strong fields. The results indicate that growth toward the cathode is the true response of healthy roots.     

Growth Substance Interactions during Uptake by Mesocotyl Segments of Zea mays L.

The effects of various growth substances on the ‘metabolic’uptake of indol-3yl-acetic acid (IAA) by Zea mesocotyl segmentswas investigated using methods of fluorescence spectroscopyand radioactivity assay. 2, 4-Dichlorophenoxyacetic acid (2,4-D) and -(I-naphthylmethylthio)propionic acid (NMSP) exertedno discernible effects on IAA uptake, whereas N-I-naphthylphthalmicacid (NPA) stimulated uptake to some degree. Low concentrationsof 2,3,5-tri-iodobenzoic acid (TIBA) promoted the uptake oflow IAA concentrations, while higher concentrations were decidedlyinhibitory. 2,4-Dinitrophenol (DNP), ioxynil, and bromoxynilalso induced marked inhibition presumably by preventing oxidativephosphorylation. The uptake interactions between these compoundswere examined in relation to concentration and time. In no casewas there evidence of competitive interaction. The inhibitoryeffects of TIBA on IAA uptake were considerably greater thanthose of DNP. SH-enzyme protectors such as BAL and cysteinedid not relieve these inhibitions. The absorption of TIBA-¹³¹Iwas completely unaffected by any concentration of IAA tested.Chromatographic and radio-autographic analysis revealed no detectableproducts of IAA-I-¹⁴C metabolism or degradation in maize mesocotyltissue during the 6-h experimental period and this was not alteredby TIBA treatment. Respiratory decarboxylation of IAA-I-¹⁴Cwas found to be negligible and unaffected by TIBA.     

Chlorophyll Synthesis from Protochlorophyll(ide) in Chill-Stressed Maize (Zea mays L.)

Illumination of aetiolated maize at temperatures lower than20 °C results in negligible accumulation of chlorophyll.Illumination of leaf tissue, previously incubated in 10 molm^–3 ALA in darkness, shows only a slight conversion ofprotochlorophyll(ide) to chlorophyll a and b at temperaturesless than 20 °C. A refined procedure for measuring photosynthesisby photo-acoustic spectroscopy in leaves that differ in chlorophyllcontent is presented. Studies of photosynthesis in aetiolatedseedlings illuminated at different temperatures by photo-acousticspectroscopy suggests that impairment of the chlorophyll pathwayis paralleled by an aberrant development of the thylakoid membrane. Key words: Protochlorophyll(ide), temperature, photo-acoustic spectroscopy, membrane biogenesis     

Cyanide-resistant Respiration and Cold Resistance in Seedlings of Maize (Zea mays L.

Respiratory activity of mitochondria isolated from seedlingsof two cold-resistant and two cold-susceptible maize cultivarswas examined. The greater potential for cyanide-resistant respirationfound in the cold-resistant seedlings raises the possibilityof a role for the alternative respiratory pathway in cold-resistance. alternative respiration, cold-resistance, cyanide-resistant respiration, maize, mitochondria, Zea mays     

Solubilization of a Proline Dehydrogenase from Maize (Zea mays L.) Mitochondria

L-Proline is oxidized to pyrroline-5-carboxylic acid in intact plant mitochondria by a proline dehydrogenase (EC 1.4.3) that is bound to the matrix side of the inner mitochondrial membrane (TE Elthon, CR Stewart [1981] Plant Physiol 67: 780-784). This investigation reports the first solubilization of the L-proline dehydrogenase (PDH) from plant mitochondria. The supernatant from NP-40-treated etiolated shoot mitochondria of maize, Zea mays L., reduced iodonitrotetrazolium violet in a proline dependent manner. The pH optimum for this activity was 8. The apparent K_m for proline was 6.6 millimolar. When supplied with proline, this solubilized PDH activity also synthesized pyrroline-5-carboxylic acid. The PDH activity was inhibited in vitro by 300 millimolar potassium chloride but not by 300 millimolar potassium acetate. The PDH activity had a molecular mass that was greater than 150 kilodaltons. Mitochondria were prepared from etiolated shoots grown in 100% water-saturated vermiculite (control) and 16% water-saturated vermiculite (stress). The specific activity of solubilized PDH from the stress treatment was 11% of the same activity from the control treatment. Oxygen uptake in the presence of proline and ADP (state 3 proline oxidation) by mitochondria from the stress treatment was 25% of the same rate by mitochondria from the control treatment. Mitochondria were also prepared 16 hours after rewatering the seedlings growing in the stress treatment. Both the solubilized PDH specific activity and state 3 proline oxidation returned to the control levels. The specific activities of the NAD⁺-dependent pyrroline-5-carboxylic acid dehydrogenase and cytochrome c oxidase in the solubilized preparations were unaffected by these stress and recovery treatments. Oxygen uptake rates by intact mitochondria in the presence of ADP and NADH, succinate or malate-pyruvate were also unaffected by these treatments.     

玉米mir1基因在玉米和薏苡中的比较物理定位

玉米基因mir1编码一种抗秋季黏虫的半胱氨酸蛋白酶。利用RFLP作图mir1基因被定位在玉米第 6号染色体短臂上 ,但它在第 6号染色体短臂上的物理位置还不知道。实验以mir1和 4 5SrDNA为探针 ,通过双色荧光原位杂交技术确定了mir1基因在玉米细胞分裂中期和粗线期第 6号染色体上的物理位置。Southern杂交结果表明 ,在薏苡基因组中存在mir1基因的同源序列 ,进一步利用荧光原位杂交的方法确定mir1基因的同源序列定位于薏苡第 7号染色体长臂的近末端 ,其信号与着丝粒的百分距离为 73 33± 0 15。     

Effects of Moniliformin on Mitosis in Maize (Zea mays L.)

Maize (Zea mays L. ‘Norfolk White’) roots were treatedwith solutions of moniliformin (a metabolite of Fusarium moniliformeSheldon) at 0.0001 M and 0.001 M for 8, 24, and 48 h. Only aslight inhibition of division was noted in root tips treatedwith the lower concentration. The higher concentration causeda disruption of the spindle apparatus and consequent C-mitosis,and metaphase accumulation. (Received February 14, 1984; Accepted May 18, 1984)     

Development of Endopeptidase Activities in Maize (Zea mays L.) Endosperms

An activity stain was used after native polyacrylamide gel electrophoresis, and at least 17 different endopeptidase activities were detected in maize (Zea mays L.) endosperm extracts prepared during the first 6 d after imbibition. The enzymes detected were classified into four groups based on their time of appearance and on their mobility in polyacrylamide gels. The first group, which included two enzymes present in dry endosperms, disappeared soon after imbibition. The second group, comprising five activity bands, appeared during the first 2 to 3 d after imbibition and then disappeared. The third set of enzymes increased continuously throughout the experimental period. The fourth group appeared after d 3 and remained at a constant level after that time. The endopeptidase activities were characterized by the effect of specific inhibitors on their activities. The two enzymes of the first group are metalloendopeptidases based on their sensitivity to ethylenediaminetetracetate (EDTA). Enzymes of the second, third, and fourth groups are sulfhydryl-endopeptidases as judged by their sensitivity to antipain, chymostatin, leupeptin, and E-64 and by their requirement for 2-mercaptoethanol. Pepstatin, phenylmethylsulfonyl fluoride, or EDTA had no effect on these enzymes. Many of the second, third, and fourth group enzymes cleaved [alpha]-zein-rich proteins as well as such easily obtained proteins as gelatin (used in our standard assay) and hemoglobin. The second group had a high affinity for [gamma]-zein, whereas none of the bands in the fourth group of enzymes cleaved this type of zein. The two metalloenzymes of the first group cleaved neither [alpha]- nor [gamma]-zeins.     

Mechanistic studies of perfluorooctane sulfonate, perfluorooctanoic acid uptake by maize (Zea mays L. cv. TY2)

Aims

There is a need to predict trace metal concentration in plant organs at given development stages. The aim of this work was to describe the Cd hyperaccumulation kinetics in the different plant organs, throughout the complete cultivation cycle, independently of a possible soil effect.

Methods

Plants of Noccaea caerulescens were exposed in aeroponics to three constantly low Cd concentrations and harvested at 6 to 11 dates, until siliquae formation.

Results

Dry matter allocation between roots and shoots was constant over time and exposure concentrations, as well as Cd allocation. However 86 % of the Cd taken up was allocated to the shoots. Senescent rosette leaves showed similar Cd concentrations to the living ones, suggesting no redistribution from old to young organs. The Cd root influx was proportional to the exposure concentration and constant over time, indicating that plant development had no effect on this. The bio-concentration factor (BCF), i.e. [Cd]_plant/[Cd²⁺]_solution for the whole plant, roots or shoots was independent of the exposure concentration and of the plant stage.

Conclusions

Cadmium uptake in a given plant part could therefore be predicted at any plant stage by multiplying the plant part dry matter by the corresponding BCF and the Cd²⁺ concentration in the exposure solution.     

Acetolactate Synthase Activity in Developing Maize (Zea mays L.) Kernels

Acetolactate synthase (EC 4.1.3.18) activity was examined in maize (Zea mays L.) endosperm and embryos as a function of kernel development. When assayed using unpurified homogenates, embryo acetolactate synthase activity appeared less sensitive to inhibition by leucine + valine and by the imidazolinone herbicide imazapyr than endosperm acetolactate synthase activity. Evidence is presented to show that pyruvate decarboxylase contributes to apparent acetolactate synthase activity in crude embryo extracts and a modification of the acetolactate synthase assay is proposed to correct for the presence of pyruvate decarboxylase in unpurified plant homogenates. Endosperm acetolactate synthase activity increased rapidly during early kernel development, reaching a maximum of 3 micromoles acetoin per hour per endosperm at 25 days after pollination. In contrast, embryo activity was low in young kernels and steadily increased throughout development to a maximum activity of 0.24 micromole per hour per embryo by 45 days after pollination. The sensitivity of both endosperm and embryo acetolactate synthase activities to feedback inhibition by leucine + valine did not change during kernel development. The results are compared to those found for other enzymes of nitrogen metabolism and discussed with respect to the potential roles of the embryo and endosperm in providing amino acids for storage protein synthesis.     

In Vitro Gibberellin A(1) Binding in Zea mays L

The first and second leaf sheaths of Zea mays L. cv Golden Jubilee were extracted and the extract centrifuged at 100,000g to yield a supernatant or cytosol fraction. Binding of [³H]gibberellin A₁ (GA₁) to a soluble macromolecular component present in the cytosol was demonstrated at 4°C by Sephadex G-200 chromatography. The binding component was of high molecular weight (HMW) and greater than 500 kilodaltons. The HMW component was shown to be a protein and the ³H-activity bound to this protein was largely [³H]GA₁ and not a metabolite. Binding was pH sensitive but only a small percentage (20%) appeared to be exchangeable on addition of unlabeled GA₁. Both biologically active and inactive GAs and non-GAs were able to inhibit GA₁ binding. [³H]GA₁ binding to an intermediate molecular weight (IMW) fraction (40-100 kilodaltons) was also detected, provided cytosol was first desalted using Sephadex G-200 chromatography. Gel filtration studies suggest that the HMW binding component is an aggregate derived from the IMW fraction. The HMW binding fraction can be separated into two components using anion exchange chromatography.     

Further Studies on Mosaic Disease of Maize (Zea mays L.)

Schizaphis graminum (Rondani) is proved to be an additional vector of maize mosaic virus (MMV). The pH range for the infectivity of the virus in extracted juice is found to be from 4.4 to 9.0, the optimum being 5.6 to 7.2. Effect of certain chemicals on the virusin vitro has also been studied. Cross protection between MMV and Sugar-cane mosaic virus (SMV) indicated positive results. It has been concluded on the basis of similar physical properties, tolerance towards certain chemicals, host range, symptomatology, aphid vectors and positive immunological tests, that MMV and SMV are related viruses.     

不同基因型玉米间作的群体质量

采用大田试验,研究了不同基因型玉米间作的群体质量特征.结果表明,HF9‖XD20间作,植株中部叶片平均叶龄延长,而对下部和上部叶片影响不大;ZD958‖LD981间作,ZD958植株下部叶片平均叶龄延长,而中、上部叶片则缩短,LD981植株下、中、上部叶片平均叶龄均有所延长.吐丝前,群体叶面积指数(LAI)单间作无明显差异,吐丝后,HF9和LD981的LAI分别大于和显著大于单作群体,而ZD958和XD20则分别小于和显著小于单作群体.紧凑型品种和半紧凑型品种间作增加了群体透光率,吐丝后10d,4个品种棒三叶叶色值(SPADR)均有所增加,并且除ZD958外,其余3个品种棒三叶净光合速率均有所增加,其中LD981增加显著.间作对吐丝以前的群体干物质积累量影响不大,吐丝后,半紧凑型品种(HF9和LD981)的干物质积累量增加,其中LD981增加显著,而紧凑型品种(XD20和ZD958)的干物质积累量减少,其中ZD958显著减少;间作还提高了收获指数,并且两种间作群体的土地当量比(LER)均大于1.结果提示,紧凑型与半紧凑型玉米品种的间作可以提高群体质量,延长叶片功能期,提高光合效率,增加籽粒产量.     

Heat Shock Protein Synthesis Induced by Methomyl in Maize (Zea mays L.) Seedlings

Exposure of plumules of intact maize seedlings (Zea mays L.) to S-methyl-N-[(methylcarbamoyl)-oxy]thioacetimidate (methomyl) represses synthesis of several polypeptides normally made under control conditions and induces synthesis of polypeptides similar to maize heat shock polypeptides (HSPs). Three of the methomyl-induced polypeptides (18 kilodaltons) are recognized by antibodies raised against 18 kilodalton maize heat shock polypeptides.