Showing papers on "Endosperm published in 1981"

Evidence for Independent Genetic Control of the Multiple Forms of Maize Endosperm Branching Enzymes and Starch Synthases

Abstract: Soluble starch synthase and starch-branching enzymes in extracts from kernels of four maize genotypes were compared. Extracts from normal (nonmutant) maize were found to contain two starch synthases and three branching enzyme fractions. The different fractions could be distinguished by chromatographic properties and kinetic properties under various assay conditions. Kernels homozygous for the recessive amylose-extender (ae) allele were missing branching enzyme IIb. In addition, the citrate-stimulated activity of starch synthase I was reduced. This activity could be regenerated by the addition of branching enzyme to this fraction. No other starch synthase fractions were different from normal enzymes. Extracts from kernels homozygous for the recessive dull (du) allele were found to contain lower branching enzyme IIa and starch synthase II activities. Other fractions were not different from the normal enzymes. Analysis of extracts from kernels of the double mutant ae du indicated that the two mutants act independently. Branching enzyme IIb was absent and the citrate-stimulated reaction of starch synthase I was reduced but could be regenerated by the addition of branching enzyme (ae properties) and both branching enzyme IIa and starch synthase II were greatly reduced (du properties). Starch from ae and du endosperms contains higher amylose (66 and 42%, respectively) than normal endosperm (26%). In addition, the amylopectin fraction of ae starch is less highly branched than amylopectin from normal or du starch. The above observations suggest that the alterations of the starch may be accounted for by changes in the soluble synthase and branching enzyme fractions.

New Endosperm Mutations Induced by Chemical Mutagens in Rice Oryza sativa L.

Abstract: Various kinds of mutations for endosperm or embryo character were induced in rice by treatment with three kinds of chemical mutagens, ethyl methanesulfonate (EMS), ethylene imine (EI) and N-methyl-N-nitrosourea (MNU). MNU induced few mutations in the treatment of dry seeds, but considerably more through the treatment of fertilized egg cells. The frequency of endosperm mutations was lower than that of chlorophyll mutations. The white core mutation was induced most frequently among mutations for endosperm or embryo character. Each of the mutants, except for floury mutant CM 2055, was controlled by a single recessive gene. Dull mutants were intermediate between waxy and non-waxy rice in the degrees of translucence and of staining by I-KI solution. The degrees of them were different among lines, although they were almost the same within a line. The phenotypic manifestations of white core and floury mutants were caused by the loose packing of round compound starch granules in their endosperm cells. From the analogy of grain features of rice with maize, the glassy and the floury types of wrinkled mutation were named as 'sugary' and 'shrunken', respectively. In addition to various endosperm mutations, a mutation for embryo character, 'giant embryo', was induced.

Isolation and Ultrastructure of Aleurone Cell Walls From Wheat and Barley

Abstract: Aleurone layers and cell walls from both wheat (Triticum aestivum L. cv. Insignia) and barley (Hordeum vulgare L. cv. Clipper) have been isoIated by differential centrifugation in benzene-carbon tetrachloride mixtures and by air classification. The isolated walls were obtained in sufficient quantities and purity for comprehensive chemical analysis. Morphological characteristics of the isolated aleurone layers and walls were examined by bright field, fluorescence and scanning electron microscopy and compared with their appearance in whole grains. Transmission electron microscopy of wall sections clearly showed their characteristic bilayered structure. Aniline blue-positive deposits were observed at the aleurone-starchy endosperm interfaces of both wheat and barley.

Genetic control of sucrose synthetase in maize endosperm

Abstract: Sucrose synthetase activity in endosperm extracts of seven shrunken(sh) mutants of spontaneous origin and three similar mutants due to the association of the controlling element Ds with the Sh locus is examined. A residual level of 3 to 5% as compared to the normal (Sh) endosperm is seen in all the mutants. The residual activity is similar to that of the Sh locus encoded endosperm sucrose synthetase by several criteria including an identical size of polypeptides and a similarity in antigenic properties. These two enzymes are, however, distinguishable by a slight difference in electrophoretic mobility in native gels and a difference in the relative abundance of enzyme molecules. The latter property is a reflection of a marked difference seen in the developmental profile of enzyme activity in the two genotypes. The earlier hypothesis (Chourey and Nelson 1976) that these two sucrose synthetases are encoded by two separate genes is strengthened by: (a) the presence of the residual enzyme in a sh deletion mutant and (b) an electrophoretic demonstration of two proteins, corresponding to the major and minor sucrose synthetase proteins, in the wild type (Sh) genotype. The two sucrose synthetase genes seem to provide a model system in plants for studying the molecular basis of temporal specificity of genes.

Fractionation of wheat gliadin and glutenin subunits by two-dimensional electrophoresis and the role of group 6 and group 2 chromosomes in gliadin synthesis.

Abstract: Subunits of wheat endosperm proteins have been fractionated by two-dimensional electrophoresis. To determine which subunits in the two-dimensional electrophoretic pattern belong to gliadin or glutenin the endosperm proteins have also been fractionated by a modified Osborne procedure and by gel filtration on Sephadex G-100 and Sepharose CL-4B prior to separation by two-dimensional electrophoresis.

Characterization of Starch from Maize Endosperm Mutants

Abstract: Some maize endosperm mutants have branched-chain starch components with long exterior chains which make the blue-value procedure for estimating amylose content questionable. Gel filtration was used to estimate starch composition of normal, high-amylose, waxy and other maize endosperm mutants. Loosely-branched polymers appeared responsible for the apparent amylose content. In some mutants high and intermediate loosely branched polysaccharides were found in addition to amylose. The sweet corn background of some endosperm genotypes influenced the types of polymers produced compared to the dent backgrounds used by previous researchers.

The Peptide pools of germinating barley grains: relation to hydrolysis and transport of storage proteins.

Abstract: A quantitative procedure for purifying small peptides from plant tissues, involving both ion-exchange and gel-exclusion chromatography, is described. Peptides were quantified and characterized by using the fluorescence reagents dansyl chloride and fluorescamine. Large pools of small peptides and amino acids have been identified in both the endosperm and embryo of germinating barley grains. The peptide pool of the endosperm increases during the first 3 days of germination, subsequently decreasing, an observation compatible with a role for peptides as intermediates in the breakdown of the storage proteins and their transfer to the embryo. The amino acid composition of these peptides indicates that all the major classes of storage protein contribute to the pool. The concentration of peptides produced in the endosperm during germination is sufficient for the efficient operation of the peptide transport system of the scutellar membrane characterized previously (Higgins and Payne, Planta 136: 71-76, 1977; Planta 138: 211-215 and 217-221, 1978). Data presented here indicate that peptides play at least as important a role as amino acids in the transfer of stored nitrogen from the endosperm to the embryo during germination.

Measurement of Metabolites Associated with Nonaqueously Isolated Starch Granules from Immature Zea mays L. Endosperm

Abstract: Starch granules with associated metabolites were isolated from immature Zea mays L. endosperm by a nonaqueous procedure using glycerol and 3-chloro-1,2-propanediol. The soluble extract of the granule preparation contained varying amounts of neutral sugars, inorganic phosphate, hexose and triose phosphates, organic acids, adenosine and uridine nucleotides, sugar nucleotides, and amino acids. Based on the metabolites present and on information about translocators in chloroplast membranes, which function in transferring metabolites from the chloroplast stroma into the cytoplasm, it is suggested that sucrose is degraded in the cytoplasm, via glycolysis, to triose phosphates which cross the amyloplast membrane by means of a phosphate translocator. It is further postulated that hexose phosphates and sugars are produced from the triose phosphates in the amyloplast stroma by gluconeogenesis with starch being formed from glucose 1-phosphate via pyrophosphorylase and starch synthase enzymes. The glucose 1-phosphate to inorganic phosphate ratio in the granule preparation was such that starch synthesis by phosphorylase is highly unlikely in maize endosperm.

Clustering of genes for 20 kd zein subunits in the short arm of maize chromosome 7.

Abstract: Zein is the major storage protein of the endosperm of maize kernels. When this alcohol-soluble protein is subjected to SDS polyacrylamide gel electrophoresis, it is resolved into four fractions of different molecular weight: 10, 14, 20 and 22 kilodaltons (kd). Each fraction is heterogeneous with respect to isoelectric pH. For example, the 20 kd fraction contains at least seven subfractions as revealed by isoelectric focusing in polyacrylamide gels. In this report, we present evidence that the structural genes coding for the 20 kd proteins are clustered on the short arm of chromosome 7, a region that also bears loci regulating endosperm zein biosynthesis [opaque-2 (02) and defective endosperm-B30 (De*-B30)]. The organization of these zein genes suggests that the evolution of at least some of the maize genome has occurred as the result of repeated duplication and divergence of chromosome segments.

Endosperm Morphology and Protein Body Formation in Developing Wheat Grain

Abstract: The development of wheat grain from intact plants and from detached ears growing in culture has been studied by light and electron microscopy. Provided the sucrose concentration was at a level sufficient to maintain a normal rate of starch synthesis, the endosperm morphology of grain from cultured ears was essentially identical to that of endosperm from intact plants. If, however, sucrose concentration in the culture medium was very low (0.25%), some morphological abnormalities occurred in the endosperm near the crease and adjacent to the seed coat. The synthesis of storage protein in the endosperm is believed to occur largely on polyribosomes attached to endoplasmic reticulum even at the earliest stages of development. Protein bodies are always surrounded by a single membrane, the origin of which may vary. Some protein bodies arise by distention of the endoplasmic reticulum and clearly the membrane here represents the sac into which the protein is discharged after synthesis. In other cases the bounding membrane may be that of a true vacuole or it may be dictyosomal in origin. The methods by which it is suggested that protein bodies are formed in wheat endosperm have parallels in other seeds, although there are some significant differences.

Morphological Studies on Amaranthus cruentus

Abstract: The morphology of Amaranthus cruentus was studied using scanning election and light microscopy. The A. cruentus seed consists of a single layer of cells which is intimately associated with the perispeim. In the region of the embryo, the seed coat is attached to the endosperm remaining in the mature seed. The major portion of endosperm caps the root. Large, thick-walled endosperm cells contain spherical bodies embedded in a spongy matrix. The cells of the campylotropous embryo contain material which has properties typical of lipid and lipid complexes as demonstrated by hexane extraction and by staining with osmium tetroxide. Spherical cell bodies, embedded in the lipid-containing matrix are partially digested by trypsin, thus suggesting they are proteinaceous in nature. Perisperm in the center of the seed contains starch granules in the form of amylopectin, demonstrated by iodine-potassium iodide stain and α-amylase digestion.

Proteinases and enzyme stability in crude extracts of castor bean endosperm.

Abstract: The stability of catalase, fumarase, and isocitrate lyase from deliberately broken organelles in crude extracts from endosperm tissue of castor bean seedlings has been examined. These enzymes are relatively stable at 2 C in extracts from endosperm of 2-day seedlings, but rapid losses of activity occur in extracts from older seedlings. These losses are shown to be brought about by the thiol-proteinase present in the extracts. The inclusion of 35% glycerol prevented the loss of catalase, fumarase, and isocitrate lysase activity, and various inhibitors of proteinases afforded limited protection. The most striking protectant was leupeptin, an inhibitor of serine and thiol-proteinases. Leupeptin completely inhibited the loss of activity of the three enzymes in crude extracts and improved yields when included in the grinding medium.

11 – Seed Storage Proteins: Characterization and Biosynthesis

Abstract: Publisher Summary This chapter discusses characterization and biosynthesis of seed storage protein. The storage proteins of seeds are an important group of plant proteins that provide nitrogen and amino acids in the germinating seedling, and constitute a major source of protein for human and livestock consumption. The large quantities of these proteins make the study of their synthesis particularly attractive as a model for the regulation of genetic expression. On the average, cereal seeds contain 10% protein, while legume seeds contain approximately 30% protein. The major storage proteins of most cereals are alcohol-soluble prolamines, but they are salt-soluble globulins in legumes. There are differences in protein structure and amino acid composition associated with the different solubility properties of these proteins. The prolamines of most cereals contain very little lysine and tryptophan, while the storage globulins of legumes contain two levels of methionine and cysteine. Storage proteins in cereals occur in the endosperm and are found in deposits sequestered within the endoplasmic reticulum.

Amino Acid Transport in Germinating Castor Bean Seedlings

Abstract: During germination and early growth of the castor bean (Ricinus communis) nitrogenous constituents from the endosperm are transferred via the cotyledons to the growing embryo. Exudate collected from the cut hypocotyl of 4-day seedlings contained 120 millimolar soluble amino nitrogen and glutamine was the predominant amino acid present, comprising 35 to 40% of the total amino nitrogen. To determine the nature of nitrogen transfer, the endosperm and hypocotyl were removed and glutamine uptake by the excised cotyledons was investigated. Uptake was linear for at least 2 hours and the cotyledons actively accumulated glutamine against a concentration gradient. The uptake was sensitive to respiratory inhibitors and uncouplers and efflux of glutamine from the excised cotyledons was negligible. Transport was specific for the l-isomer. Other neutral amino acids were transported at similar rates to glutamine. Except for histidine, the acidic and basic amino acids were transported at lower rates than the neutral amino acids. For glutamine transport, the Km was 11 to 12 millimolar and the Vmax was 60 to 70 micromoles per gram fresh weight per hour. Glutamine uptake was diminished in the presence of other amino acids and the extent of inhibition was greatest for those amino acids which were themselves rapidly transported into the cotyledons. The transport of amino acids, on a per seedling basis, was greatest for cotyledons from 4-to 6-day seedlings, when transfer of nitrogen from the endosperm is also maximal. It is concluded that the castor bean cotyledons are highly active absorptive organs transporting both sucrose and amino acids from the surrounding endosperm at high rates.

Isoenzymes of Sugar Phosphate Metabolism in Endosperm of Germinating Castor Beans

Abstract: Two isoenzymes each of phosphoglucomutase, hexose phosphate isomerase, aldolase, fructose diphosphatase, phosphofructokinase, and 6-phosphogluconate dehydrogenase have been separated by DEAE-cellulose column chromatography of extracts from endosperm of germinating castor beans (Ricinus communis cv. Hale). One of each of the enzymes is localized in the cytosol and the other is confined to plastids. Developmental studies of these isoenzymes were carried out to clarify their roles in the endosperm. In extracts from ungerminated seeds the activities of marker enzymes of mitochondria (fumarase), plastids (ribulose bisphosphate carboxylase), and glyoxysomes (catalase) were low, but phosphoglucomutase, hexose phosphate isomerase, aldolase, and 6-phosphogluconate dehydrogenase were present in relatively high activity. The total amounts of these enzymes increased 3- to 4-fold during the first 5 days of growth. The activities of isoenzymes in the plastids rose in parallel with that of ribulose bisphosphate carboxylase to reach a maximum at day 4, and like the carboxylase they declined sharply thereafter. The activities of the cytosolic isoenzymes peaked at day 5. These changes are consistent with the roles previously proposed for the sequences present in plastid and cytosol.

Early Development of the Macadamia Ovary

Abstract: Macadamia integrifolia ovaries were sampled for light microscopy from anthesis to 8 weeks after flowering. Both ovules increased in size following anthesis but only one was normally fertilized. Fertilization of one ovule appeared to inhibit fertilization of the other. The unfertilized ovule was eventually crushed by the fertilized ovule which developed a globular embryo with a short suspensor. Division of the endosperm preceded division of the embryo, and cell formation in the initially free nuclear endosperm progressed by the development of cell walls inwards from the embryo sac wall at the micropylar end of the embryo sac only. Thickenings developed on the walls of the embryo sac, persistent synergid and embryo and a hypostase developed at the base of the nucellus between the cavity occupied by the embryo sac and the integument. Both specializations are suggested to be important in the nutrition of the developing embryo. Ovaries which abscissed 4-5 weeks after anthesis had a similar anatomy to ovaries retained on the tree. Some embryos showed signs of degeneration but this was not considered to be the cause of abscission.

Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds 10. IN VIVO AND IN VITRO SYNTHESIS OF α-AMYLASE IN RICE SEED SCUTELLUM

Abstract: Scutellar tissues were dissected from germinating rice seeds and the incorporation of [35S]methionine into the α-amylase molecule was examined by in vivo and in vitro assay systems. Immunoprecipitation with monospecific anti-α-amylase immunoglobulin G raised against the purified enzyme preparation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography were used to identify α-amylase and its possible precursor molecule. Using freshly prepared scutellar tissues, it was demonstrated that α-amylase is synthesized de novo in the scutellar epithelium and secreted into endosperm. The synthesis of α-amylase directed by the polyadenylic acid-containing ribonucleic acid isolated from the scutellar tissues was also established using the translation system of either wheat germ extract or reticulocyte lysate. The immunoprecipitable product obtained in the in vitro translation system was smaller in molecular weight than that synthesized in vivo on the basis of mobilities in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results are discussed in relation to the processing of the nascent polypeptide precursor of the enzyme molecule and the introduction of the oligosaccharide chain to the cleaved polypeptide to make up the mature form of α-amylase.

Red-Light-Induced Endosperm Preparation for Radicle Protrusion of Lettuce Embryos

Abstract: Light microscopic examination of red-light-treated Lactuca sativa achenes at various stages of imbibition revealed that, prior to visible germination (radicle protrusion), the endosperm cells of the micropylar end undergo rapid characteristic structural changes. The cytoplasm becomes highly vacuolated, and reserve materials are mobilized. Generally, these cells swell, while the cell walls remain PAS positive. In dark-, far-red, and red + far-red-light-treated achenes, however, the endosperm remains unchanged. The structural changes may be a prerequisite for endosperm rupture and radicle protrusion.

Synthesis of SP II albumin, β-amylase and chymotrypsin inhibitor CI-1 on polysomes from the endoplasmic reticulum of barley endosperm

Abstract: Free and initially membrane bound polysomes were isolated from 20 day old endosperms of Bomi and Hiproly barley and used as templates in an in vitro protein synthesizing system based on wheat germ extract. Three35S-labelled translation products were identified as SP II albumin, β-amylase and chymotrypsin inhibitor CI-1 among the polypeptides synthesized by the polysomes of the endoplasmic reticulum. Identification employed immunoaffinity isolation. Protein Z was not detectable among the in vitro translation products of either initially membrane bound or free endosperm polysomes. Compared to Bomi barley the Hiproly endosperm is enriched for translatable mRNA coding for SP II albumin, β-amylase and chymotrypsin inhibitor CI-1. In vitro and in vivo synthesized β-amylases have identical molecular weights. Only one form of SP II albumin is produced in vitro, confirming that the lower molecular weight SP II B albumin is a proteolytic cleavage product of the SP II A albumin.

Proteinase activities in resting and germinating seeds of Scots pine, Pinus sylvestris

Abstract: Resting seeds of Scots pine contained a moderate amount of acid proteinase activity, about 90% of which was inhibited by pepstatin A and about 10% by p-hydroxymer-curibenzoate. In gel chromatography on Sephacryl S-200 the proteinase activity showed a complex elution pattern with poorly separated peaks at positions corresponding to mol. wts. 100,000 and 30,000 and several shoulders. The results suggested that pine proteinases I and II, which are the main proteinases in the endosperms of germinating seeds (Salmia 1981: Physiol. Plant. 51: 253–258), were not present in the resting seeds.—Seedling extracts showed a low level of acid proteinase activity, which separated into several peaks in chromatography on Sephacryl S-200. As none of the peaks had the catalytic properties of proteinase I or II, it seems that these endospermal enzymes are also lacking in the seedling tissues.—In the endosperms of germinating seeds the activity of the pepstatin-sensitive acid proteinase(s) remained at a constant level throughout the period of reserve protein mobilization (lasting up to the stage when the length of dark-grown seedlings was 60 mm). Proteinases I and II were absent from resting seeds, showed a small increase up to the 20-mm stage, and then increased rapidly up to the 60-mm stage.—Resting embryos contained relatively higher acid proteinase activity than resting endosperms, and again about 90% of it was inhibited by pepstatin A and about 10% by p-hy-droxymercuribenzoate. During germination the former activity decreased, the latter activity remained at approximately the same level, and the activity of the other acid proteinases increased continuously with the growth of the seedling.—It is concluded that the pepstatin-sensitive proteinase(s), which is not affected by endogenous proteinase inhibitors, plays a central role in the initiation of reserve protein mobilization in both the embryo and the endosperm. Proteinases I and II, on the other hand, seem to account for the greater part of reserve protein breakdown in the main protein storage tissue, the endosperm.

Endosperm cell number in barley

Abstract: Grain weight is one of the major components of grain yield and it has been suggested that in wheat, final grain weight may be a function of endosperm cell number1. If grain weight is to be increased by increasing the rate and/or duration of endosperm cell division, it is important to establish the stage of development at which maximum endosperm cell number is attained. Evers2 reported that no cell division occurred in the endosperm of wheat later than 16 days after anthesis and other workers3,4 have come to a similar conclusion using cell counts. However, biochemical analyses5 have shown that the maximum DNA content of wheat endosperm is not reached until 25 days after anthesis and both Donovan6 and Radley7 have suggested that endosperm cell division may continue until about 30 days after anthesis. We have estimated the number of endosperm nuclei in developing caryopses of barley and have examined transverse sections of endosperms of different ages. We report here that cell division in barley endosperm continues until 28–30 days after anthesis.

Genetic variation in wheat endosperm proteins: an analysis by two-dimensional electrophoresis using intervarietal chromosomal substitution lines.

Abstract: The major endosperm proteins in a range of genotypes of hexaploid wheat have been fractionated by two-dimensional electrophoresis. The genotypes included nine varieties and forty four intervarietal substitution lines in which chromosomes 1A, 1B, 1D, 6A, 6B or 6D from eight of the varieties have been introduced one at a time into a common genetic background. The appearance of different protein subunits was often correlated with a chromosome substitution. This showed that many of the genes for the high molecular weight protein subunits (molecular weight range 55,000 to 140,000 determined by SDS polyacrylamide gel electrophoresis) are specified by chromosomes 1A, 1B and 1D while many of the lower molecular weight subunits (molecular weight range 30,000 to 45,000) are specified by chromosomes 6A, 6B and 6D. The different protein subunits correlated with chromosome substitution could not always be recognised in the varietal source of the substituted chromosome. The different subunits specified by homologous chromosomes in different wheat varieties may differ in isoelectric point and/or molecular weight.

THE DEVELOPMENT OF β‐GLUCAN SOLUBILASE DURING BARLEY GERMINATION

Abstract: β-Glucan solubilase in either germinating barley or in endosperm slices treated with gibberellic acid is synthesized before endo-β-glucanase, α-amylase and protease. In common with these enzymes, β-glucan solubilase is synthesized much sooner in endosperm slices than in whole grain. Gibberellic acid stimulates β-glucan solubilase synthesis in endosperm slices and most of the activity is rapidly released into the surounding medium, irrespective of whether the hormone is present. Inhibitors of RNA and protein synthesis block the formation of β-glucan solubilase. Unlike β-glucanase, α-amylase and protease, β-glucan solubilase is present in significant quantity in untreated barley where it is concentrated in the embryo-containing half of the grain. The only β-glucan solubilase activity in barley is due to an acidic carboxypeptidase. Malt contains a small amount of a second solubilizing enzyme which appears to be an endo-β1, 3-glucanase.

Synthesis and Posttranslational Segregation of Glyoxysomal Isocitrate Lyase from Castor bean Endosperm

Abstract: Total Polyadenylated RNA isolated from 3-day-old germinating caster bean endosperm was translated in the rabbit reticulocyte lysate cell-free protein-synthesizing system in either the presence or absence of canine pancreatic microsomal vesicles. Isocitrate lyase synthesized in vivo had the same apparent molecular weight as the authentic glyoxysomal enzyme irrespective of whether synthesis occurred in the presence or absence of microsomes. Furthermore, in contrast to several protein encoded by mRNA isolated from maturing seed endosperm tissue, isocitrate lyase was not contranslationally segregated into the lumen of the microsomal vesicles. Intact 3-day-old endosperm tissue was labeled in vivo by adding [35S]methionine and at various times the tissue was homogenized and the cellular organelles fractionated. Separated fractions were assayed for newly synthesized isocitrate lyase. Immunoreactive product was initially detected in the cytosolic fraction and subsequently began to accumulate in glyoxysomes. The results indicate that glyoxysomal isocitrate lyase is synthesized on free polysomes and released into the cytosol. Transfer to the matrix of the glyoxysome involves a posttranslational membrane translocation step which is not accompanied by proteolytic cleavage of the polypeptide chain.

Levels of glucose-6-phosphate and 6-phosphogluconate dehydrogenases in the embryos and endosperms of some dormant and nondormant lines of Avena fatua during germination

Abstract: To investigate the possible role of the pentose phosphate pathway in dormancy and germination of seeds of Avena fatua L., levels of glucose-6-phosphate and 6-phosphogluconate dehydrogenases were analyzed in genetically dormant and nondormant pure lines. Embryos and endosperms of dry mature seeds of each line exhibited high activity for both enzymes. Dehydrogenase levels in the embryos isolated from dormant lines remained constant during the first 48 h of incubation in water, but in nondormant lines there was a sharp increase after 24 h of incubation, well after the onset of germination. Similarly, when seeds of a dormant line were incubated with gibberellin A3 (GA3), there was no increase in dehydrogenase levels in embryos prior to the onset of germination. Thus, in Avena fatua the levels of pentose phosphate pathway dehydrogenases are not involved in the regulation of seed dormancy.In endosperm tissue the pentose phosphate pathway dehydrogenase activity declined rapidly after germination (GA3-induced in ...

Endosperm—Its Morphology, infrastructure, and Histochemistry

Abstract: Publisher Summary This chapter discusses the morphology, ultrastructure and histochemistry of endosperm. Endosperm is formed by the repeated divisions of the primary endosperm nucleus. It is the main source of food for the embryo in angiosperms. The central cell is a highly active cell that performs several important functions in the embryo sac. The fusion of the secondary nucleus or the polar nuclei with the sperm nucleus gives rise to the primary endosperm nucleus, which is generally triploid. The primary endosperm nucleus is associated with aggregates of dense material in the perinuclear cytoplasm. The primary endosperm nucleus divides rapidly to form the endosperm tissue. The endosperm nuclei increase in size as the development proceeds. In angiosperms there are three types of endosperm development— namely, nuclear, cellular, and helobial. The mature endosperm in some plants shows rumination that is caused by the seed coat activity or by the endosperm itself. The endosperm haustoria are of widespread occurrence in angiosperms. The haustorial cells undergo enlargement and aggressive growth during development that results in the destruction of ovular tissues adjacent to the invading haustoria. When endosperm cells are actively dividing, the haustoria become involved in the nutrition of the endosperm cells. The cytoplasm of the aleurone cell is characterized by many small to large electron-transparent osmiophilic lipid bodies/droplets, also known as, spherosomes. The reserve materials of endosperm tissue undergo autolysis to yield simpler components that are used up during the growth and germination of embryo.