被子植物核型胚乳的细胞化

文章介绍被子植物胚乳多核体的产生及其意义、初始垂周壁和初始平周壁的产生以及微管在初始垂周壁和初始平周壁产生中的作用、胚乳发育及胚乳核细胞化的分子机制以及胚乳细胞壁的物质来源和组成的研究进展。     

Embryo and Endosperm Metabolism of Barley Seeds during Early Germination

Embryos detached from germinating barley seeds were immersedin tritiated water or solutions containing ¹⁴C-labelled compounds.Amino acids rapidly became radioactive and later acids of theKrebs cycle. Labelled alanine did not give rise to radioactivesucrose.     

The Methylation Cycle and its Possible Functions in Barley Endosperm Development

Barley endosperm development can be subdivided into the pre-storage, intermediate, storage and desiccation phase. Nothing is known about DNA methylation events involved in different endosperm-specific developmental programmes. A complete set of methylation cycle enzyme genes was identified and investigated by mRNA expression analysis. During the pre-storage phase, methionine synthase and S-adenosylmethionine (AdoMet) synthase genes are expressed at high levels, mainly to produce AdoMet, which might be used for methylation processes as indicated by high expression of methyltransferases HvMET1, HvCMT1 and HvDnmt3-1 as well as AdoHcy hydrolase genes. The methyltransferases, core histones and DNA-unwinding ATPases are co-expressed at the mRNA level. On the contrary, storage protein (prolamin) gene expression is repressed due to CpG methylation. Expression of genes responsible for starch biosynthesis is also developmentally regulated but not methylation-dependent. Thus, during pre-storage phase, activity of HvMET1 and HvCMT1 possibly maintains DNA replication and suppresses specific pathways of maturation. Besides, HvDnmt3-1 might be responsible for differentiation-specific de novo methylation. Expression of methyltransferases HvDnmt3-2 and HvCMT2 peaks during the onset of massive starch accumulation. The enzymes are likely responsible for DNA methylation involved in determining plastid division and amyloplast differentiation as concluded from the patterns of co-expressed genes. Levels of AdoMet decarboxylase mRNA, but not methyltransferase- and AdoHcy mRNA, increase at the beginning of desiccation together with methionine synthase and AdoMet synthase levels. This increase may be indicative for utilization of AdoMet in polyamine production protecting aleuron and embryo cell membranes during desiccation.     

The Induction of Endosperm Plantlets and Their Ploidy of Barley in Vitro

The endosperm callus has been induced from immature endosperm of barley (Hordeum vulgare L.) on the MS medium supplemented with auxin. When the callus was transferred to the medium supplemented with lower concentration of auxin, the differentiation of shoots began to occur. The regenerated plantlets can be green, albino and whitegreen stripe. The chromosome number in the cells from same root tip of endosperm plantlet is very unstable. They can be euploid (2n=7, 14, 21, 28) or aneuploid (2n = 8, 9, 10, 13).     

The Fine Structure of the Developing Euphorbia dulcis Endosperm

Euphorbia dulcis has a nuclear type of endosperm which laterbecomes cellular. During the coenocytic period, the Golgi apparatusconsists of moderately proliferating dictyosomes. The endoplasmicreticulum is large, rough and manifests as long cisternal profileswhich are scattered singly or packed in parallel multiple arrays.The mitochondria exhibit different numbers of small cristaeand frequent outline constrictions suggesting approaching binaryfission. The plastids have only slightly structured stromataand contain little or no starch; like the mitochondria, manyof them have indented profiles. Wall formation is seen as chain-like aggregates of coalescingdictyosome vesicles with much associated endoplasmic reticulum.The latter is discussed in terms of cisternal shape, generalthree-dimensional form and probable involvement in trappingGolgi derivatives. The newly constituted cells are highly vacuolateelements having large populations of free ribosomes, many immatureplastids and relatively more numerous mitochondria. Opaque (lipid)bodies are found in the neighbourhood of the plasmalemma. Theendoplasmic reticulum is granular. The presence of a micropylar network of labyrinthine ingrowthsstudding the boundary wall of the coenocytic endosperm is alsodescribed. Euphorbia dulcis, endosperm, ultrastructure, wall ingrowths     

The Developing Endosperm of Wheat -- A Stereological Analysis

A stereological analysis of light and electron micrographs ofwheat endosperm during grain formation and development providesinformation on a range of parameters of cell structure. Thecell volume increases approximately ten-fold; mitochondrialnumber per cell increases but the individual mitochondrial volumedecreases, the overall volume fraction of the cell occupiedby mitochondria remaining fairly constant. Amyloplast divisionstops before cell division, resulting in the distribution ofpreviously-formed plastids; there are differences in starchgranule growth rate in different cell layers of the endosperm.The rough endoplasmic reticulum increases four-fold in areaper cell and its surface-to-volume ratio increases just priorto protein deposition. Triticum aestivum, L., wheat, endosperm, seed development, starch, stereology     

Dynamics of Nuclear DNA Quantities during Zygote Development in Barley

Quantities of DNA were estimated in the nuclei of mechanically isolated egg and zygote protoplasts in two cultivars of barley using 4[prime],6-diamidino-2-phenylindole staining and microfluorometry. Unlike many previous studies on DNA amounts within the sex cells of flowering plants, we obtained consistent and unambiguous results indicating that the egg and sperm nuclei are at the 1C DNA level (basic haploid amount) at the time of karyogamy. Karyogamy was initiated within 60 min postpollination, and the male chromatin became completely integrated into the egg nucleus within 6 to 7 hr postpollination (hpp). Zygotic nuclear DNA levels began to increase at ~9 to 12 hpp in cultivar Alexis and at 12 to 15 hpp in cultivar Igri. The 4C DNA complement was reached in most zygotes by 22 to 26 hpp in cultivar Alexis and by 23 to 29 hpp in cultivar Igri. These data are fundamental to a better understanding of fertilization and zygote maturation in flowering plants. They are also relevant to studies in which the timing of zygotic DNA replication is of interest, such as ongoing investigations on genetic transformations in barley using the microinjection technique.     

The Extraction and Separation of Barley Glutelins and their Relationship to Other Endosperm Proteins

Procedures are described for the extraction of unmodified andalkylated barley glutelin fractions and their subsequent separationby sodium dodecyl sulphate-polyacrylamide gel electrophoresis.The resulting separations are considerably clearer and sharperthan those previously published. One major polypeptide is presentin the salt-soluble and glutelin fractions in varying proportionsdepending on whether or not the salt-soluble fraction is extractedin the presence of a reducing agent. There is also variationin the amount of contaminating hordein polypeptides in the glutelinsand this appears to depend not only on the conditions used toextract hordein but also those used to extract the salt-solublefraction. Finally, variation in the glutelin pattern also occurswhen different denaturing agents or reducing agents are used. ¹ Visiting Scientist, permanent address: U.S. Department ofAgriculture, Science and Education Administration, AgriculturalResearch, Dept. of Agronomy Univ. of illinois, 1102 S. GoodwinAve., Urbana, IL 61801, USA.     

Arabidopsis RAN 1 Mediates Seed Development through Its Parental .Ratio by Affecting the Onset of Endosperm Cellularization

Although previous studies have demonstrated that endosperm development is influenced by its parental genome constitution, the genetic basis and molecular mechanisms that control parent-of-origin effects require further elucidation. Here we show that the Ras-related nuclear protein 1 （RAN1） regulates endosperm development in Arabidopsis thaliana. Reciprocal crosses between wild-type （WT） and transgenic lines misexpressing RAN1 （msRAN1） gave rise to small F1 seeds when RAN1 down-regulated/up-regulated individuals were used as a male/female parent; in contrast, F1 seeds were aborted when RAN1 down-regulated/up-regulated plants were used as a female/male parent, suggesting that seed development is affected by the parental genome ratio of RAN1. Whereas RAN1 expression in wild-type plants is reduced before the onset of endosperm cellularization, F1 seeds from reciprocal crosses between WT and msRAN1 showed abnormal endosperm cellularization and ectopic expression of RAN1. The expression of MINISEED3 （MINI3）-a gene that also controls endosperm cellularization-was also affected in these reciprocal crosses, and the misregulation of MINI3 activity rescued F1 seeds when msRAN1 plants were used in reciprocal crosses. Taken together, our results suggest that the parental ratio of RAN1 regulates the onset of endosperm cellularization through its genetic interaction with MINI3.     

Observation on the Characteristic Features of Cell Wall Formation in Free-Nuclear Endosperm During the Early Stages of Cellularization in Triticum aestivum

Triticum aestivum cv. “Yang Mai # 1” was used to study the celI wall formation in free-nuclear endosperm with electronmicroscopy and fluorescence microscopy. During the initiation of cellularization the peg-like wall ingrowths developed, and the freely growing walls gradually cleaved the cytoplasm into small compartments in both regions (ventral and dorsal) of the 'endosperm sac, but in ventral region the anastomose of freely growing wall often occured. The striking resemblance and close connection betwteen nucellar debris and freely growing walls showed the possibility that the disintegrated nucellus played an important role in supporting the wall formation of endosperm during the early stages of cellularization.     

Studies on the Non-starchy Polysaccharides of the Endosperm of Naked Barley

The F-1 β-glucan from naked barley endosperm, a main component of water soluble β-glucan, has been subjected to degradation with the laminarinase from Bacillus circulans. This enzyme converts the F-1 β-glucan to a trisaccharide, 3-O-β-cellobiosyl-d-glucose*, and a tetrasaccharide, 3-O-β-cellotriosyl-d-glucose*, as the main products. These products, which constitute 74% of the polymer, have been identified by chemical methods. As the minor or trace components, laminaribiose, cellobiose, cellotriose** and two unidentified tetrasaccharides are detected. Overall data show that F-1 β-glucan mainly consists of two types of structural sequences; one is trimeric unit in which a single β-(1→3) linkage alternates with two consecutive β-(1→4) linkage, and the other, a tetrameric unit in which a single β-(1→3) linkage alternates with three consecutive β-(1→4) linkages.

It is shown that this laminarinase from B. circulans hydrolyses the glucoside bond of the reducing side of 1,3-linked β-d-glucopyranose residues.     

Studies on the Non-Starchy Polysaccharides of the Endosperm of Naked Barley

Two β-glucans were prepared from the aqueous extract of the endosperm of naked barley. The extraction was carried out under conditions which obviated enzyme action and eliminated the contamination of starch fraction. The precipitate obtained with 20% concentration of ammonium sulfate of the extract was adsorbed on DEAE-cellulose (borate form) column and fractionated into two fractions by the elutions with H₂O and 0.5 N NaOH, respectively. From 5 kg. of the endosperm the yield of the former was 13.3 g. (0.27% of the endosperm), the latter was 2.0 g. (0.04%). Both showed only one peak ultracentrifugally, were slightly levorotatory, not degraded with α-amylase, and consisted of only d-glucose. These data suggest that they are both β-glucans.

β-Glucan consumed in periodate oxidation 0.74 mole periodate per 1 mole of anhydro- glucose. Hydrolysate of the methylated β-glucan gave 2, 3,6-tri-O-methyl-d-glucose and 2, 4, 6-tri-O-methyl-d-glucose, and methanolysate of the methylated β-glucan gave methyl 2, 3, 6-tri-O-methyl-β-d-glucopyranoside and methyl 2, 4, 6-tri-O-methyl-β-d-glucopyranoside, although α-anomers were not separated. From sedimentation and diffusion coefficients the molecular weight of the β-glucan was calculated as 220,000.

These results indicated that the β-glucan was consisted of β-1, 4 and β-1, 3 linked glucopyranose residues with proportions of 2.5 : 1 to 3:1 (β-1, 4 linkage to be predominant) and that the β-glucan had a linear structure.     

Studies on the Non-Starchy Polysaccharides of the Endosperm of Naked Barley

The structure of F-4 β-glucan, a minor component of water soluble non-starchy polysaccharides from the endosperm of naked barley, was elucidated. Hydrolysate of the methylated F-4 β-glucan gave 2,3,6-tri-O-methyl-d-glucose and 2,4,6-tri-O-methyl-d-glucose as main components with small amounts of 2,3,4,6-tetra-O-methyl-d-glucose and unidentified di-O-methyl-d-glucose. This result indicated that the main chain of F-4 β-glucan consisted of 1,4- and 1,3-linked β-d-glucopyranose residues with proportions of approximately 2:1 (β-1,4 linkage to be predominant) with some branching.