Signal transmission during gravitropic curvature of primary roots of Zea mays

Primary roots of Zea mays cv. Ageotropic are nonresponsive to gravity and elongate approximately 0.80 mm h^?1. Applying mucilage-like material (K-Y Jelly) to the terminal 1.5 cm of these roots induces graviresponsiveness and slow elongation 28% (i.e. from 0.80 to 0.58mm h^?1). Applying mucilage-like material to one side of the terminal 1.5 cm of the root induces curvature toward the mucilage, irrespective of the root's orientation to gravity. Applying a 2-mm-wideband of mucilage-like material to a root's circumference 8 to 10 mm behind the root cap neither induces gravicurvature nor affects elongation significantly. Similarly, applying mucilage-like material to only the root cap does not significantly affect elongation or graviresponsiveness. Gravicurvature of mutant roots occurs only when mucilage-like material is applied to the root/root-cap junction. Reversing the caps of wild-type and mutant roots produces gravitropic responses characteristic of the root cap rather than the host root. These results are consistent with the suggestion that gravitropic effectors are growth inhibitors that move apoplastically through mucilage between the root cap and root.     

Impact of iron deficiency and iron re-supply during the early stages of vegetative development in maize (Zea mays L.)

The consequences of iron deficiency and iron re-supply were evaluated during the early stages of growth and development of young maize plantlets grown hydroponically in the absence of iron. Various parameters, such as fresh and dry weights, and the concentration of chlorophylls, iron, copper, manganese, calcium, magnesium and potassium in leaves, were measured at various times during the first 15 d of culture. Ten-day-old maize plantlets grown without iron displayed severe alterations, with a 50% decrease in iron and chlorophyll concentrations in leaves, and serious impairments in mitochondria and chloroplast ultrastructure. In contrast, neither leaf nor root growth, nor other mineral concentrations other than iron were significantly affected at this stage of development. In an attempt to characterize proteins potentially involved in iron nutrition or the adaptative response to iron starvation, comparative 2D-gel electrophoretic analysis of polypeptides was carried out on soluble and membrane fractions prepared from leaves and roots of iron-deficient and iron-sufficient 10-d-old maize plantlets. Two polypeptides (11 and 17 kDa, pI of about 6.8) from the microsomal fraction of leaves were found to be repressed under iron-deficient conditions. Some other polypeptides were found to he induced in microsomal fractions either from roots or leaves. Significant variations in the concentration of most of these polypeptides were observed from one experiment to another. It can be concluded from this study that, at this early stage of maize vegetative growth and development, molecular variations induced by iron deficiency do not affect major house-keeping proteins, but probably affect very specific events depending on low abundance proteins.     

Chilling stress and oxygen metabolizing enzymes in Zea mays and Zea diploperennis*

Abstract. The activities of five active-oxygen scavenging enzymes were compared for cold-lability and three were compared for chilling induction in two Zea genotypes of contrasting susceptibility to photoinhibition during chilling. Activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GTR, EC 1.6.4.2) in leaf extracts from plants grown without chilling stress were assayed at 19°C and 5°C. Enzymes from the chilling-susceptible Z. Mays cv. LG11 had lower specific activities at 5°C than did enzymes from the chilling-tolerant Z. diploperennis, except for MDHAR where no significant differences were observed. The activities of SOD and APX from Z. diploperennis were double those of Z. mays at both assay temperatures. Monodehydroa-scrobate reductase and glutathione reductase activities in both species were reduced by 63–78% at a 5°C assay temperature. The dehydroascorbate reductase (DHAR) showed the greatest low-temperature lability losing 96% (Z. diploperennis) and 100% (Z. mays) of its activity at 5°C. To examine possible chilling-induced changes in levels of enzyme activity, plants of both Zea genotypes were transferred to growth chambers at 10°C at moderate light intensities. Glutathione reductase activity was found to increase within 24h in Z. diploperennis, but it decreased slightly in Z. mays. MDHAR activity decreased by 50% in Z. diploperennis but showed only a transient increase in activity in Z. mays.     

Calcium-induced sperm fusion in Zea mays L.

 In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS) or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 μm in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 μm. Staining of sperm nuclei with 4′, 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20–50 μm from the tip. The Sperms are found no closer than 90 μm to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid. Received: 12 August 1996 / Revision accepted: 6 December 1996     

Cellular differentiation in root caps of Zea mays that do not secrete mucilage

We quantified the structural changes accompanying cellular differentiation in root caps of Zea mays cv. Ageotropic to determine the developmental basis for the nongraviresponsiveness of their primary roots. Cells of the calyptrogen and columella of primary roots of the ageotropic mutant have structures indistinguishable from those of caps of primary roots of Z. mays cv. Kys the graviresponsive, wild-type parent of Z. mays cv. Ageotropic. However, the relative volumes of dictyosomes, dictyosome-derived vesicles and starch in the outermost peripheral cells of wild-type roots were significantly lower than were those in peripheral cells of mutant roots. This corresponds to a dramatic accumulation of starch and mucilage-filled vesicles in peripheral cells of mutant roots. Cellular differentiation in root caps of graviresponsive seminal roots of the Ageotropic mutant resembled that of primary and seminal roots of the wild-type cultivar, and differed significantly from that of primary roots of the mutant. We conclude that the mutation that blocks secretion of mucilage from peripheral cells of Ageotropic roots: (1) expresses itself late in cellular differentiation in root caps; (2) is expressed only in primary (but not seminal) roots of the Ageotropic mutant; and (3) is consistent with malfunctioning dictyosomes and dictyosome-derived vesicles being the cellular basis for agravitropism of primary roots of this mutant.     

Root-specific expression of a Zea mays gene encoding a novel glycine-rich protein,zmGRP3

The isolation and characterization of a cDNA clone from Zea mays coding for a novel glycine-rich protein (GRP) is described. The corresponding 1.4 kb mRNA accumulates exclusively in roots (primary, lateral seminal and crown roots) of young maize seedlings, following developmentally specific patterns. In agreement with previously described GRPs from other plant species the derived protein sequence exhibits a hydrophobic domain at the N-terminal region followed by repeated glycine-rich motifs. Genomic Southern analysis indicates that the zmGRP3 gene is present in the maize genome as one or two copies or at a low copy number.     

Environmental effects on the early stages of tassel morphogenesis in maize (Zea mays L.)

The effects of various environmental conditions on the initiation of tassel branches (NTB) and spikelet‐pairs (NSP) were examined in the stress‐sensitive maize inbred F53. Chilling induced the most important effect, with a dramatic decrease in both NTB and NSP, provided it was applied at the end of the vegetative phase and start of the floral transition phase. The primary cause of chilling‐induced abortion of the tassel branches could be oxidative stress in the leaves, since lowering light irradiance during chilling greatly reduced the effect of cold. The comparison of inbreds F53 and F2 revealed that both genotypes exhibited a similar period of cold sensitivity at the floral transition phase, although F2 was considered from field observations as a stress‐insensitive genotype (at least for tassel development). However, our results also showed a chilling acclimation response in inbred F2 but not in inbred F53. The similarities with the work by Lejeune & Bernier (1996 Plant, Cell and Environment 19, 217–224.) concerning the effect of chilling on ear initiation in the sensitive inbred, B22, are emphasized.     

Distribution of enzyme activities within the developing maize (Zea mays) kernel in relation to starch, oil and protein accumulation

The association of enzyme activities in developing kernels with specific storage product accumulation at maturity was analyzed in different parts of Zea mays inbred OH43 kernels. Maize kernels were harvested at 20 and 55 days post-pollination and dissected into basal region, pericarp, embryo, lower endosperm, middle endosperm and upper endosperm. Mature (55 days pos(-pollination) kernel parts were analyzed for starch, total protein, zein and oil content. Immature (20 days post-pollination) kernel parts were assayed for activities of 15 enzymes of sugar and amino acid metabolism. Statistical analyses of the data suggested that glucokinase (EC 2.7.1.2) fructokinase (EC 2.7.1.4) and phosphofructokinase (EC 2.7.1.1 11) activities were primarily associated with oil accumulation, whereas ADP'-glueose pyrophosphorylasc (EC 2.7.7.27) and sucrose synthase (EC 2.4.1.13) activities were associated with starch accumulation. The results suggest that oil biosynthesis utilizes inveitase-mediated sucrose degradation in a pathway not requiring pyrophosphatc. whereas starch biosynthesis utilizes a sucrose synthase-mediated pathway of sucrose degradation in a pathway requiring pyrophosphatc. Additional groups of enzyme activities were associated with each oilier but not with any specific storage product and appeared to be associated with general metabolic activity.     

玉米花粉特异的非编码RNA基因ZM401 cDNA全长的克隆及其发育表达模式

通过差异筛选法并结合冷噬菌斑筛选,从玉米(Zea mays L．)成熟花粉cDNA文库中克隆到一个玉米花粉特异表达的cDNA片段ZM401(663bp)。Northern杂交表明ZM401是一个玉米花粉特异表达的基因。本文采用5′RACE,3′RACE及重叠PCR技术获得了ZM401 cDNA的全长(1149bp)。采用生物学软件对ZM401 cDNA的序列和结构进行分析,结果表明,该基因缺乏明显的开放阅读框架,序列中最长的开放阅读框架仅有89个氨基酸,但具有poly(A)尾部结构,符合非编码RNA基因的特点。推断ZM401基因是一个非编码基因。RT-PCR及Northern blot分析表明ZM401基因从玉米花粉小孢子四分体时期、单核期、双核期、成熟花粉开始表达,而且表达量依次增强,证明ZM401可能与玉米花粉的晚期发育过程相关。同时,Northern杂交显示ZM401基因在玉米花粉发育中有两种转录本存在。     

Characterisation of Zea mays L. plastidial transglutaminase: interactions with thylakoid membrane proteins

Chloroplast transglutaminase (chlTGase) activity is considered to play a significant role in response to a light stimulus and photo‐adaptation of plants, but its precise function in the chloroplast is unclear. The characterisation, at the proteomic level, of the chlTGase interaction with thylakoid proteins and demonstration of its association with photosystem II (PSII) protein complexes was accomplished with experiments using maize thylakoid protein extracts. By means of a specific antibody designed against the C‐terminal sequence of the maize TGase gene product, different chlTGase forms were immunodetected in thylakoid membrane extracts from three different stages of maize chloroplast differentiation. These bands co‐localised with those of lhcb 1, 2 and 3 antenna proteins. The most significant, a 58 kDa form present in mature chloroplasts, was characterised using biochemical and proteomic approaches. Sequential fractionation of thylakoid proteins from light‐induced mature chloroplasts showed that the 58 kDa form was associated with the thylakoid membrane, behaving as a soluble or peripheral membrane protein. Two‐dimensional gel electrophoresis discriminated, for the first time, the 58‐kDa band in two different forms, probably corresponding to the two different TGase cDNAs previously cloned. Electrophoretic separation of thylakoid proteins in native gels, followed by LC‐MS mass spectrometry identification of protein complexes indicated that maize chlTGase forms part of a specific PSII protein complex, which includes LHCII, ATPase and pSbS proteins. The results are discussed in relation to the interaction between these proteins and the suggested role of the enzyme in thylakoid membrane organisation and photoprotection.     

云南产玉米须的化学成分研究

从玉米须60%乙醇提取液中分离得到了14个化合物,经波谱学方法分别鉴定为柯伊利素-7-O-β-D-葡萄糖苷(1)、柯伊利素-6-C-β-波伊文糖-7-O-β-葡萄糖苷(2)、柯伊利素-6-C-β-波伊文糖苷(3)、L-鼠李糖(4)、豆甾-4-烯-3β,6β-二醇(5)、7α-羟基谷甾醇(6)、7β-羟基谷甾醇(7)、胡萝卜苷棕榈酸酯(8)、大豆脑苷I(9)、7α-羟基谷甾醇-3-O-β-D-葡萄糖苷(10)、麦角甾-7,22-二烯-3β,5α,6β-三醇(11)、棕榈酸(12)、胡萝卜苷(13)和β-谷甾醇(14),其中化合物1、4和7～12为首次从玉米须中分离得到。     

Immunodetection and immunolocalization of globulin storage proteins during zygotic and somatic embryo development in Zea mays

Globulins (GLB) are storage proteins that accumulate to high levels during zygotic embryo development of Zea mays L. We visualized the distribution of GLB during zygotic embryo development by immunolabelling of polyethylene glycol sections with a GLB-specific antiserum and a fluorescent secondary antibody. In sections of embryos at 10 days after pollimation (DAP), GLB were detected in the scutellar node only. Sections of embryos of 17 DAP showed, besides the presence of GLB in the scutellar node, the presence of a low amount of GLB in the coleoptile and the leaf primordia. In 30-DAP embryos GLB were localized in the root, the coleorhiza, the leaf primordia, the coleoptile and in all cells of the scutellum with the exception of the epidermis and the pro-vascular tissues. The subcellular location of GLB was visualized by immunolabelling of ultrathin sections with anti-GLB and a gold-conjugated secondary antibody. Scutellum cells and root cortex cells of 30-DAP embryos were packed with protein storage vacuoles (PSV), which differed in electron density. GLB were either evenly distributed throughout the PSV or were localized in electron-dense inclusions within the PSV. SDS-PAGE and immunoblot analysis of total protein extracts indicated the presence of a low amount of the GLB1 processing intermediate proGLB1'in globular as well as mature somatic embryos. After maturation on an ABA-containing medium, somatic embryos showed the additional presence of the next GLB1 processing intermediate GLB1. By immuno-electron microscopy it was possible to localize GLB in globular deposits in PSV in scutellum cells of these somatic embryos.     

Isolation and characterization of Azotobacter chroococcum from the roots of Zea mays

Abstract Bacteria showing rapid growth on a nitrogenfree medium and acetylene-reducing activity were isolated from maize roots collected from agricultural soils in Spain. The isolates were Gram-negative motile rods and were identified as Azotobacter chroococcum . Acetylene-reducing activity and microbial counts were determined on root segments from 7- and 30-day-old plants. Rates obtained were in the range of 0.0053–0.848 nmol C₂H₂· g⁻¹· h⁻¹. Root populations were 1.4–6.0 × 10⁴ micro-organisms · g⁻¹. These results showed that there was an association between A. chroococcum strains and roots of maize planted in some Spanish soils.     

一个与玉米基因表达沉默有关的cDNA片段的克隆及序列分析

利用cDNA-AFLP技术分离了一个与玉米基因表达沉默有关的cDNA片段,Northern杂交分析表明,该基因在Mo17的苗期和雄穗生长锥伸长期都表达,但在Mo17与其亲缘关系较近的另一亲本杂交的F1代中却表现沉默,即表现单亲沉默。同源性分析表明,该克隆片段与GenBank中玉米通用调控因子(GRF)部分区段有98．6％的同源性,与玉米通用调控因子编码的mRNA部分序列有83％的同源性。以上结果表明,基因沉默可能是亲本GRF在F     

Effect of environment on the early steps of ear initiation in maize (Zea mays L.)

The effects of environmental conditions on ear-shoot initiation have been investigated in three inbred genotypes of Zea mays L. which are used for seed production. Scanning electron microscopy (SEM) and binocular examination during the vegetative phase showed that axillary meristems are initiated at the same rate as the leaf primordia on the apical meristem, but with a delay of 5.6–7.0 plastochrons, depending on the genotype. Furthermore, the topmost axillary meristem is initiated on the same day as the tassel, whatever the genotype. One of the inbreds (B22) used in this study has been reported to exhibit, in field conditions, a reproductive failure affecting car initiation, causing the topmost car to be replaced at maturity by a sterile, leaf-like, structure. Scanning electron microscopic study of the formation of the abnormal axillary buds indicated that ear failure resulted from the early collapse of the axillary meristem followed by elongation of the prophyll or of the meristem itself. Using controlled environments, ear abortion was mimicked by a chilling treatment (10°C), given just before tassel initiation. Other factors, such as high irradiance and flooding, enhanced the abortive response. The critical stage for the main car was just before the initiation of the topmost axillary meristem which also corresponded to tassel initiation. Chilling the plants before or after tassel initiation either induced an acclimation response or had no effect. The three inbreds showed differential responses to the stress treatment, indicating that a genetic factor is implicated as well. It is suggested that chilling causes a perturbation of apical dominance which, in the responsive genotypes, represses axillary meristem development. The use of a stress-sensitive inbred such as B22 as a model system could yield some interesting clues to the mechanism of endogenous control of ear initiation in maize.     

Glutamine synthetase activity of the endosperm, embryo and pedicel-placento-chalazal regions of developing maize (Zea mays) kernels

Glutamine synthetase (GS, EC 6.3.1.2) activity in homogenates of the maize ( Zea mays L. hybrid A619 X W64A) kernel pedicel-placento-chalazal (PPCh), endosperm regions was characterized in order to optimize assay (hydroxylamine-dependent γ-glutamyl hydroxymate formation) conditions for quantitating maize kernel GS in crude extracts. The GS activities of all three tissue extracts exhibited optima at pH 7.0 with ATP:Mg²⁺ of 1:1.6. Assays of kernel tissue GS activity required relatively high concentrations of substrates to achieve saturation compared to GS from other plant tissue sources, a point which has not been considered in previous reports of maize kernel GS activity. When measured under optimal assay conditions. PPCh-GS increased to a peak of 51 nmol γ-glutamyl hydroxymate kernel⁻¹ min⁻¹ at 25 days after pollination and then declined throughout the remainder of kernel development. Embryo GS activity increased steadily throughout development to a maximum of 24 nmol γ-glutamyl hydroxymate embryo⁻¹ min⁻¹ by 50 days after pollination. In contrast, endosperm GS activity, which was 25 nmol γ-glutamyl hydroxymate endosperm⁻¹ min⁻¹ at 25 days after pollination, exhibited no discernable pattern of change during kernel development. These findings are discussed with respect to the possible roles PPCh, endosperm and embryo GS play in kernel development.