薏苡种子胚芽鞘细胞的结构

观察了薏苡浸泡种子胚芽鞘的结构。胚芽 外,内表皮薄壁组织及２个侧位的维管束组成。在外表皮两处,观察到径向壁不边原细胞群,它们实际是合胞体。薄壁细胞含丰富的核糖体,内质网小泡和线粒体,说明代谢活动已经活跃。初生纹孔场内有胞间连丝,显示胞间已存在物质的共质运转。     

Histochemical and ultrastructural changes in the haustorium of date (Phoenix dactylifera L.)

Summary During imbibition ofPhoenix dactylifera embryos, all cotyledon cells show the same changes: protein and lipid bodies degrade, smooth endoplasmic reticulum (ER) increases in amount, and dictyosomes appear. At germination, the distal portion of the cotyledon expands to form the haustorium. At this time, epithelial cells have a dense cytoplasm with many extremely small vacuoles. Many ribosomes are present along with ER, dictyosomes, and mitochondria. The parenchyma cells have large vacuoles and a small amount of peripheral cytoplasm. Between 2 and 6 weeks after germination, epithelial cells still retain the dense cytoplasm and many organelles appear: glyoxysomes, large lipid bodies, amyloplasts, large osmiophilic bodies, and abundant rough and smooth ER which appear to merge into the plasmalemma. A thin electron-transparent inner wall layer with many small internal projections is added to the cell walls. Starch grains appear first in the subsurface and internal parenchyma and subsequently in the epithelium. Lipid bodies, glyoxysomes, protein, and osmiophilic bodies occur in the epithelial and subepithelial cell layers but not in the internal parenchyma. At 8 weeks after germination, the cytoplasm becomes electron transparent, vacuolation occurs, lipid bodies and osmiophilic bodies degrade, and the endomembranes disassemble. After 10 weeks, the cells are empty. These data support the hypothesis that the major functions of the haustorium are absorption and storage.     

Immunogold Localization of the L3 Protein of Maize Lipid Bodies during Germination and Seedling Growth

We have used antibodies directed against the 16.5 kilodalton protein L3, the most abundant integral protein of maize (Zea mays L. cv Mo 17) lipid bodies, to follow the fate of this protein in scutellar parenchyma cells of maize during germination and subsequent seedling growth. Using gel electrophoresis and immunoblotting as well as immunocytochemical electron microscopy, we found that the amount of L3 decreases gradually during the first 3 to 4 days of seedling growth and more rapidly over the course of the next several days. Immunogold localization of the protein on thin sections indicated that L3 is found exclusively in the surface phospholipid monolayer of lipid bodies. The density of L3 in the surface layer of individual lipid bodies does not change during seedling growth; therefore, the decrease in the amount of L3 can be attributed to a decrease in the number of lipid bodies rather than to selective removal of protein components from the surface of all lipid bodies. Thus, L3 is apparently degraded at the same time as the matrix lipid of each lipid body. Unlike lipase, L3 does not appear to be transferred to other cellular compartments such as vacuoles during late stages of seedling growth.     

ULTRASTRUCTURE OF NON-ARTICULATED LATICIFERS IN MATURE EMBRYOS AND SEEDLINGS OF ASCLEPIAS SYRIACA L. (ASCLEPIADACEAE)

The protoplast of the non-articulated branched laticifer in the embryo and seedling of Asclepias syriaca L. was studied at the ultrastructural level and was found to differ from that of adjacent cell types. Embryonal laticifers possess numerous vesicles with electron-dense contents, but lack a large organized central vacuole. Plastids have few lamellae, possess phytoferritin, and accumulate small amounts of starch. Other organelles and membrane systems are similar to those in other cells. After germination, laticifers develop numerous elongated vacuoles by dilation of endoplasmic reticulum. Nuclei in laticifers within the hypocotyl of seedlings are highly lobed and possess dilated perinuclear spaces. Plastids and other organelles are similar to those observed in the protoplast of laticifers in the embryo. The latex or rubber component of the laticifer is not apparent in mature embryos of 72-hr seedlings.     

Distribution and changes of reserve materials in cotyledon cells of Panax ginseng related to direct somatic embryogenesis and germination

Cotyledon explants from zygotic embryos of Panax ginseng produced somatic embryos on Murashige and Skoog basal medium without growth regulators. Somatic embryos developed directly from epidermal cells at the cotyledon base. Somatic embryos were always formed from the side of the cotyledon opposite to the one attached to the medium surface regardless of cotyledon orientation. The frequency of somatic embryo formation from the abaxial epidermis (66%) was much higher than that from the adaxial epidermis (12%). Differences in embryogenic response were likely related to cell structure. Abaxial epidermal cells were filled with reserve materials (lipid bodies), while adaxial epidermal cells were devoid of any prominent reserves. During germination, the reserve materials in the cells of the cotyledons disappeared rapidly. At the same time, the competency of somatic embryo formation from cotyledon explants declined rapidly to zero. Upon culture of the cotyledon explants (for somatic embryo induction), lipid bodies slowly disappeared, but starch grains accumulated prominently. Reserve materials disappeared after commencement of embryogenic cell division. During germination, lipid bodies rapidly disappeared, and chloroplasts developed instead of starch grains. Received: 29 January 1997 / Revised version received: 16 April 1997 / Accepted: 9 May 1997     

Dry mass of Fusarium roseum spores before and after germination

The total dry mass of Fusarium roseum spores and contained lipid bodies were determined before and after spores germinated using quantitative interference microscopy. The mean for spore dry mass before germination was about 57 pg. Lipid bodies accounted for about 61% of that. Areas of lipid bodies in spores before and after germination were about 23 % but the contents of the lipid bodies accounted for only 10% of the spore dry mass after germination. The total dry mass of the spore and germ tube(s) greatly exceeded that of the spore before germination. We infer that nutrients for germ tube growth are derived from within the germinating spore and from the medium which must contain nutrients leached from non-germinating spores.     

Changes in cell-wall polysaccharides in relation to seedling development and the mobilisation of reserves in the cotyledons of Lupinus angustifolius cv. Unicrop

Some 22% of the dry weight of the cotyledons of resting seeds of Lupinus angustifolius cv. Unicrop has been shown to be non-starch polysaccharide material comprising the massively thickened walls of the storage mesophyll cells. On hydrolysis this material released galactose (76%), arabinose (13%), xylose (4%), uronic acid (7%): only traces of glucose were detected indicating the virtual absence of cellulose from the walls. Changes in the amount and composition of this material following germination have been studied in relation to parameters of seedling development and the mobilisation of protein, lipid and oligosaccharide reserves. Starch, which was not present in the resting seed, appeared transitorily following germination: under conditions of continuous darkness starch levels were reduced. During the period of bulk-reserve mobilisation, 92% of the non-starch polysaccharide material disappeared from the cotyledons. The residual cell-wall material released galactose (14%), arabinose (19%), xylose (24%) and uronic acid (43%). The galactose and arabinose residues of the cotyledonary cell walls clearly constitute a major storage material, quantitatively as important as protein. The overall role of the wall polysaccharides in seedling development is discussed.     

Radicle ofEchinocactus platyacanthus (Cactaceae)

Radicle of matureEchinocactus platyacanthus embryo is approximately 320 m long and represents less then 1/7 of the embryonal axis length. The radicle-hypocotyl boundary can be distinguished according to the striking difference in the size and shape of cells in protoderm and procambium, as well as discontinuity and different number of the cell files in the ground meristem. The root cap is small, consists of 4 layers of cells covering the apex of the radicle. The upper limit of the root cap is approximately 100 m closer towards the radicle tip than the radicle-hypocotyl boundary. Ultrastructure of radicle cells showed numerous lipid bodies as is typical for other oily seeds. Protein bodies of variable structure were also present together with other cell structures. Striking differences in protein body structure were found when protoderm and ground meristem were compared. Several small globoid crystals were present in each protein body of the protoderm, while protein bodies in the radicle ground meristem mostly contained one large globoid crystal. X-ray microanalysis revealed presence of P, K and Mg in all analyzed globoid crystals. Fe, Ca and Zn were detected in some of them.Abbreviations EDX microanalysis energy-dispersive X-ray microanalysis - GC(s) globoid crystals - ICP spectroscopy ion-coupled plasma spectroscopy - LM light microscopy - PB(s) protein bodies - SEM scanning electron microscopy - TEM transmission electron microscopy     

DIFFERENTIAL ACTIVITIES OF ACID PHOSPHATASE FROM ADAXIAL AND ABAXIAL REGIONS OF LUPINUS LUTEUS (FABACEAE) COTYLEDONS

Acid phosphatases of abaxial and adaxial regions in the cotyledons of the Lupinus luteus which possess structurally distinct protein bodies were examined. Acid phosphatase activity was investigated by enzyme assays and by gel electrophoresis and was localized by cytochemical methods in the cotyledons of Lupinus luteus L. during germination and seedling development. Acid phosphatase activity was significantly higher in the adaxial (heterogeneous protein body) region as compared to the abaxial (homogeneous protein body) region of the cotyledon. The pH optimum of acid phosphatase from the abaxial region and from the adaxial region was 4.5 and 5.0, respectively. There were significant differences in substrate specificity and isoenzymic composition of the enzyme between the two regions. Isoenzymic composition changed during the course of germination and seedling development. Acid phosphatase was localized in the matrix of the homogeneous protein bodies and in the globoids of the heterogeneous protein bodies at imbibition. After germination (d 3, d 4, d 7) acid phosphatase was localized primarily in the inner cell walls and intercellular spaces of both regions. These results show that different isoenzymes of acid phosphatase show differential localization and the rate of acid phosphatase activation or synthesis differs in cells from the two regions of the cotyledon.     

Molecular characterization of proteins in protein-body membrane that disappear most rapidly during transformation of protein bodies into vacuoles

During the post-germination growth of seeds, protein bodies fuse with one another and are converted to a central vacuole. To investigate this transition, protein-body membranes from dry seeds of pumpkin (Cucurbita sp.) were prepared and their protein components characterized. Five major proteins (designated MP23, MP27, MP28, MP32 and MP73) were detected in the protein-body membranes. A cDNA clone encoding both MP27 and MP32 has been isolated. The deduced precursor polypeptide was composed of a hydrophobic signal sequence, MP27 and MP32, in that order. A putative site of cleavage between MP27 and MP32 was located on the COOH-terminal side of asparagine 278, an indication that the post-translational cleavage may occur by the action of a vacuolar processing enzyme that converts proprotein precursors of seed proteins into the mature forms. Immunoelectron microscopic analysis showed that MP27 and MP32 were associated with protein-body membrane of dry pumpkin seeds. Among the five membrane proteins, MP27 and MP32 disappeared most rapidly during seedling growth. The degradation of MP27 and MP32 starts just after seed germination and proceeds in parallel with the transformation of the protein bodies into a vacuole.     

ULTRASTRUCTURE OF THE MATURE UNGERMINATED RICE (ORYZA SATIVA) CARYOPSIS. THE GERM

An in-depth transmission electron microscope study of the ungerminated, unimbibed rice germ was conducted. All tissues in the germ were examined. Plastids were similar in all cells; many contained osmiophilic globules and phytoferritin, some displayed a limited thylakoid system, and all contained cytoplasmic tubular and vesicular inclusions formed by invaginations of the outer plastid membranes. Filament bundles were found in cells of the coleoptile, plumule, mesocotyl, radicle, and epiblast. Three general categories of cells could be identified in the germ based on protein body characteristics and on lipid body distribution: 1) Cells having inclusions in protein bodies and having numerous lipid bodies scattered throughout the cytoplasm; 2) Cells having or lacking protein body inclusions and possessing peripheral lipid bodies and/or having electron-dense deposits in the lipid bodies; and 3) Cells lacking protein bodies and having peripheral lipid bodies.     

The effects of abscisic acid on the maturation ofBrassica napus somatic embryos

Summary A comparison of embryos, cultured for increasing periods of time with and without abscisic acid (ABA), was undertaken to investigate, at the ultrastructural level, the influence of this growth regulator on the maturation of rapeseed (Brassica napus) somatic embryos. In the absence of ABA, the embryos germinated precociously while lipid bodies (LB), which were not numerous, soon degraded, as revealed by a depletion process associated with the appearance of morphologically mature glyoxysomes and an increase in the number of mitochondria. Moreover, a lack of protein bodies indicated that storage protein accumulation was not initiated under these conditions. On the contrary, the addition of ABA (10 M) induced marked modification of embryo metabolism. Indeed, ABA completely prevented precocious embryo germination and inhibited lipid reserve catabolism. Moreover, the formation of small vacuoles and proliferation of rough endoplasmic reticulum in their vicinity suggested the onset of storage protein accumulation. After 15 days in the presence of ABA, the embryos contained abundant lipid and protein bodies. Nevertheless, these somatic embryos were not exactly the same as their mature zygotic counterparts since differences were found in chloroplasts, amyloplasts, and nuclear structures. These observations suggest that additional factors might be required to obtain fully mature somatic embryos.Abbreviations ABA abscisic acid - ABM ABA medium - BM basal medium - LB lipid bodies - MS Murashige and Skoog (1962) - PB protein bodies - RER rough endoplasmic reticulum     

Seed of Cercis siliquastrum L (Leguminosae,Caesalpinioideae): Reserves and their Utilization after Germination

An ultrastructural study on the reserves stored in cotyledons and endosperm and on their utilization after germination has been carried out in Cercis siliquastrum seeds. The observations have shown that all the cotyledonal reserves of proteins and lipids are used during seedling growth. However, inside the endosperm cells only the protein reserves are depleted, and large quantities of lipids remain undigested. In both cell walls and intercellular spaces of the endosperm cells huge masses of polysaccharide reserves are stored. However, only the polysaccharides inserted in the cell walls are dismantled, while those located in the intercellular spaces are not attacked by the lytic enzymes. Some hypotheses regarding the possible roles of those endospermic non-nutritional materials in the strategies of seed germination and seedling growth are suggested.     

Storage reserves and cellular water in mature seeds of Araucaria angustifolia

Seed tissues of Araucaria angustifolia (Bertol.) Kuntze were investigated using histochemistry, transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. Moisture content and water status in tissues were also evaluated. In the embryo, TEM studies revealed the presence of one to several central vacuoles and a peripheral layer of cytoplasm in cells from different tissues of the cotyledons and axis. In the cytoplasm, lipid bodies, starch grains, mitochondria and a nucleus are evident. In most tissues, vacuoles contain proteins, indicating that the storage proteins are highly hydrated. In cells of the root cap, proteins are stored in discrete protein bodies. Both protein storage vacuoles and discrete protein bodies have inclusions of crystal globoids. EDX analysis of globoids revealed the presence of P, K and Mg as the main constituents and traces of S, Ca and Fe. In the root and shoot meristems, deposits of phytoferritin are present in the stroma of proplastids. The gametophyte consists of cells characterized by relatively thin cell walls and one to several nuclei per cell. Protein and lipid bodies are present, although starch is the most conspicuous reserve. Immediately after shedding, moisture content is approximately 145% (dry weight) for the embryo and 95% (dry weight) for the gametophyte. Calorimetric studies reveal that axes and cotyledons have a very high content of freezable water, corresponding to types 5 and 4, i.e. dilute and concentrated (or capillary) solution, respectively. The results are discussed in relation to the behaviour of the species, which has been categorized as recalcitrant.  © 2002 The Linnean Society of London . Botanical Journal of the Linnean Society , 2002, 140 , 273−281.     

The fine structural localization of p-Nitrophenyl phosphatase activity in the storage cells of pea (Pisum sativum L.) cotyledons

Summary p-Nitrophenyl phosphatase activity was cytochemically demonstrated within protein bodies, cell walls and the cell-wall cytoplasmic interface in storage cells of germinating pea seeds. The activity associated with the cell wall increased over the initial period of germination and seedling growth. All enzymatically active components at_pH 5.0 were found to represent acid phosphatase, since they were inhibited by sodium fluoride and survived treatment with 1-p-bromotetramisole and ouabain. The relevance of these observations to biochemical data is discussed.     

Fine structure of germinatingPenicillium megasporum conidia

Summary Penicillium megasporum conidia have spore walls consisting of several layers. There is no visible change in the outer wall layers during spore germination, but the inner layers increases in thickness on only one side of the spore, resulting in a rupture of the outer wall layers and subsequently in germ tube formation. Invaginations in the plasma membrane disappear as the germ tube forms and emerges, and the nucleus migrates into the developing germ tube. Mitochondria gather at the base of the germ tube during its formation. During germination, the amount of lipid in the spore decreases and portions migrate into the germ tube. Membrane-bound, electron dense bodies are present in resting spores. These bodies decrease in size as germination proceeds, and the cytoplasm in the developing germ tube appears much more electron dense than the cytoplasm within the spore.     

Subcellular Localization Studies Indicate That Lipoxygenases 1 to 6 Are Not Involved in Lipid Mobilization during Soybean Germination

Soybean (Glycine max) lipoxygenase (LOX) has been proposed to be involved in reserve lipid mobilization during germination. Here, subcellular fractionation studies show that LOX1, -2, -3, -4, -5, and -6 isozymes were associated with the soluble fraction but not with purified oil bodies. The purified oil bodies contained small amounts of LOX1 (<0.01% total activity), which apparently is an artifact of the purification process. Immunogold labeling indicated that, in cotyledon parenchyma cells of LOX wild-type seeds that had soaked and germinated for 4 d, the majority of LOX protein was present in the cytoplasm. In 4-d-germinated cotyledons of a LOX1/2/3 triple null mutant (L0), a small amount of label was found in the cytoplasm. In epidermal cells, LOX appeared in vacuoles of both wild-type and L0 germinated seeds. No LOXs cross-reacting with seed LOX antibodies were found to be associated with the cell wall, plasma membrane, oil bodies, or mitochondria. Lipid analysis showed that degradation rates of total lipids and triacylglycerols between the wild type and L0 were not significantly different. These results suggest that LOX1, -2, -3, -4, -5, and -6 are not directly involved in reserve lipid mobilization during soybean germination.     

Histochemical Studies of Scutellum During Germination of Oat Seed by Light Microscopy and Immunofluorescent Localization of Oat Globulin

The protein, phytin, lipid and starch contents of the scutellum of oats showed marked changes during the first three days after seed germination. Protein and phytin disappeared almost completely during the first two days after seed germination. The degradation at lipid was much slower. In the scutellum of the ungerminated seed very few starch granules were seen. At days-1 and -2 after germination the starch contents increased, but at day-3 the starch contents decreased. Immunofluorescent localization of oat globulin indicated that the oat globulin was sequestered mostly, if not exclusively, in the protein bodies. The degradation of the oat globulin inside the protein bodies was very rapid. At day-3 after seed germination it disappeared almost completely. When excited by the ultraviolet light the walls of both the epithelial and parenchyma cells of the scutellum autofluoresced intensely. As germination progressed further, the autofluorescence in the walls of the epithelial cells gradually faded away, whereas the autofluorescence in the walls of the parenchyma cells did not.     

Seed ageing-induced inhibition of germination and post-germination root growth is related to lower activity of plasma membrane H(+)-ATPase in maize roots

Seeds of most crops can be severely damaged and lose vigor when stored under conditions of high humidity and temperature. The aged seeds are characterized by delayed germination and slow post-germination growth. To date, little is known about the physiological mechanisms responsible for slow root growth of seedlings derived from aged seeds. Plasma membrane H(+)-ATPase is a universal H(+) pump in plant cells and is involved in various physiological processes including the elongation growth of plant cells. In the present study, we investigated the effect of a mild seed ageing treatment on plasma membrane H(+)-ATPase activity of seedling roots. Maize (Zea mays L.) seeds with 17% water content were aged at 45 degrees C for 30h. The aged seeds showed a 20% reduction in germination. Seedlings from aged seeds grew slowly during an experimental period of 120h after imbibition. Plasma membranes of maize seedling roots were isolated for investigation in vitro. Plasma membrane H(+)-ATPase (EC 3.6.3.6) activity was 14% lower for seedling roots developed from aged seeds as compared to control seeds. Protein gel immunoblotting analysis demonstrated that the reduced activity of plasma membrane H(+)-ATPase was attributed to a decrease in steady-state protein concentration of this enzyme. In conclusion, seed ageing causes a lower steady-state enzyme concentration of the H(+)-ATPase in the plasma membrane, which is related to slow germination and post-germination growth of seedling roots.