The Number and Sizes of Starch Granules in the Wheat Endosperm, and their Association with Grain Weight

The number and size of starch granules was measured in developingand mature endosperms of two wheat varieties, Chinese Springand Spica. Chromosomal effects on particular aspects of starchgranule size and number were detected in the analysis of disomicgenotypes derived from reciprocal monosomic hybrids betweenthe two parental varieties. Among these genotypes, a greaterweight per endosperm cell was associated with a greater volumeper A-type starch granule. It is suggested that the number percell and volume of these large starch granules are the majordeterminants of endosperm cell weight, and there exists separategenetic control of these parameters. It should therefore bepossible genetically to combine these attributes to achievedirected increases in mature grain weight. Triticum aestivum, grain weight, starch granules     

Changes in Nuclear DNA Content, Cell and Nuclear Size, and Frequency of Cell Division in the Cotyledons of Brassica napus L. during Embryogenesis

Cellular behaviour was examined during embryogenesis in Brassicanapus to test whether or not polyploidy occurs in the cotyledonsduring the phase of oil deposition. Nuclear DNA content, nuclearand cell size, and the mitotic index were measured in the cotyledonson various days post anthesis (dpa). In squashed monolayersfrom 15 dpa cotyledons, a polyploid (>5C) population wasdetected together with a substantial number of cells in G2 (4C).Nuclear volume was measured on sectioned tissues and, at 15dpa, the range of values from the cotyledons (40–500 *m³)contrasted with that in the vestigial suspensor and endosperm(50–> 600 µm³). At 15 dpa the nuclear volumedata suggest that whilst cells in the cotyledons were in Gland G2 many endosperm and suspensor cells were polyploid. Thus,polyploidy observed in the squashed monolayers was probablydue to contaminating endosperm/suspensor cells. At 25 and 35dpa, polyploidy was not detected; all cells were in Gl (2C)and cell area increased. The mitotic index peaked at 20 dpabefore declining and given the narrower distribution of nuclearvolumes at 25 and 35 dpa (50–300 µm³), these dataare consistent with cell arrest in Gl. Thus, polyploidy wasnot detected in the cotyledons of B. napus which differs fromwhat is known about cellular development in legume cotyledons. Key words: Brassica napus L., DNA, nuclear volume     

Seed Development in a Shrunken Endosperm Barley Mutant

Seg8 is one of eight barley (Hordeum vulgare L.) mutants whoseendosperm development is affected by the maternal plant genotype.This study was initiated to determine the nature and onset ofabnormal development to provide a basis for further studiesaimed at understanding the mechanism of genetic control. Seeddevelopment and synthesis and accumulation of reserve substanceswere compared between seg8 and its normal counterpart, cv. Klages.Light microscopic examination showed that the mutant phenotypeappeared as early as 4 d after anthesis (DAA), and seg8 graindry weight was significantly lower than cv. Klages by 8 DAA.Grain cell number was significantly lower in seg8 by 8 DAA,indicating an early termination of cell division. The mutanthad a lower starch concentration and higher sucrose concentration,also evident at 8 DAA. Rates of [¹⁴C]sucrose incorporation intostarch in excised half seeds were similar in both genotypesat 2 and 4 DAA, but at 8 and 12 DAA seg8 had a lower rate. Totalprotein concentration was not significantly different betweenthe two genotypes throughout endosperm development. These resultsindicate that the mutation affects cell division and starchaccumulation prior to 8 DAA. It is not known if the reductionin starch biosynthesis and accumulation results from a reducedcapacity for starch or a defect in starch biosynthesis. Hordeum vulgare L., barley, shrunken endosperm mutant, endosperm development, starch, protein, endosperm cell number     

The Structure of Mature Rye Endosperm

Endosperm tissue of mature kernels of rye (Secale cereale L.)cv. Dominant was examined by light and transmission electronmicroscopy. It was found that storage protein in sub-aleuronecells occupies up to 35 per cent of the cell volume and formsa continuous matrix in which starch grains and cytoplasmic remnantsare embedded. In the prismatic endosperm, the storage proteinis present as a fine network interspersed between the numeroustype A and B starch grains. Protein bodies are not found inthe prismatic endosperm; only a few, less than 1 µm indiameter, are observed in pockets of disorganized cytoplasmin the sub-aleurone tissue. Thick cell walls and intercellularmaterial may contribute to the high pentosan content of ryeendosperm. Secale cereale L., rye, endosperm, protein matrix, ultrastructure     

Storage-protein Deposition in the Developing Rice Caryopsis in Relation to the Transport Tissues

The developing caryopsis of rice (Oryza sativa L.) was examinedhistologically at successive stages of grain-filling in orderto identify the factors which determine the distribution ofstorage protein in the endosperm, and which terminate the depositionof endosperm protein. The storage protein was deposited at theperiphery of the endosperm, and this distribution was apparentlycaused by the radial pattern of cell development in the endosperm,and by the proximity of the peripheral endosperm cells to thenucellar epidermis. The nucellar epidermis directly surroundsthe endosperm and functions as the pathway for amino acid transportto the endosperm. During the later stages of caryopsis developmentthe nucellar epidermis became compressed by being ‘sandwiched’between the expanding endosperm and the rigid hull (the tightlylocked palea and lemma) which encloses the caryopsis. It isproposed that this compression of the nucellar epidermis blocksthe supply of amino acids to the endosperm and thereby terminatesthe deposition of storage protein in the rice grain. Oryza sativa, rice, caryopsis (development), endosperm, grain filling, nucellar epidermis, storage protein     

Endosperm Development in Solanum nigrum L. Formation of the Zone of Separation and Secretion

Endosperm development in Solanum nigrum was ab initio cellular.During early seed development, a Zone of Separation and Secretion(ZSS) differentiated within the endosperm. There were threephases in the formation of the ZSS. Phase I—stainabilityof the cell walls and middle lamella increased followed by numeroussmall plasmalemma invaginations (blebs) which became filledwith a fibrillar material. Phase II—the plasmalemma withdrewfrom the cell wall as a fibrillar lipo-carbohydrate matrix accumulatedoutside the plasmalemma. The middle lamella was gradually removedfrom between the cells forming the central axis of the cone.Phase III—the lipo-carbohydrate matrix continued to accumulateoutside the plasmalemma and also within the developing intercellularspaces. Some axial cells were completely separated from theremaining ZSS cells and became embedded in the matrix. The formationof the ZSS did not entail the destruction of the endosperm cellsand cell divisions were frequent. The ZSS was initially cone-shaped,capping the globular embryo. As the embryo sac enlarged, theZSS continued to differentiate. This resulted in a narrow curvedcorridor through the peripheral region of the endosperm whichterminated above the vascular trace. The embryo grew throughthe centre of the ZSS and pushed aside the separated axial cells.The ZSS facilitated the growth of the embryo through the restof the endosperm.Copyright 1993, 1999 Academic Press Lipo-carbohydrate matrix, extracellular matrix, endosperm development, Solanum nigrum, Zone of Separation and Secretion     

Cell Production and DNA Accumulation in the Wheat Endosperm, and their Association with Grain Weight

Nuclear DNA content was measured in developing endosperm cellsof two wheat varieties, Chinese Spring and Spica. 3C, 6C, 12Cand 24C nuclei were detected, indicating that some form of endoreduplicationand/or endopolyploidization was occurring. The total amountof DNA in the endosperm continued to increase until 24 dayspost anthesis. This accumulation of DNA resulted both from productionof new nuclei and also from increases in the DNA content ofexisting nuclei. Estimates of endosperm cell numbers were made from the totalDNA content per endosperm and the mean DNA content per endospermnucleus for a range of genotypes differing in mature grain weight.Endosperm DNA content and cell number were both positively associatedwith mature grain weight among the genotypes examined. However,not all of the variation in grain weight could be attributedto variation in cell number because of differences in mean dryweight per endosperm cell. The large-grained variety, Spica, had a greater mean weightper endosperm cell than Chinese Spring and this difference aroseafter cell production in the endosperm had ceased. Triticum aestivum, grain weight, cell size, cell number, DNA content     

An Ultrastructural Study of The Embryo/Endosperm Interface in the Developing Seeds of Solanum nigrum L. Zygote to Mid Torpedo Stage

The early developmental sequences in the formation of the Zoneof Separation and Secretion in a hexaploid species of Solanumnigrum L. are described. Ultrastructural changes which occurredduring the development of the embryo/endosperm interface couldbe related to the different stages in the embryo's development.The first step was the completion of the cell wall around thechalazal end of the zygote; a thin wall was formed along theendosperm cell(s) abutting the zygote. From the mature zygotestage to the quadrant stage, minute plasmalemma invaginationsoccurred along the endosperm wall facing the zygote. These invaginationsenlarged, and from the mid-globular stage onwards became filledwith a fine fibrillar material; this material accumulated betweenthe endosperm cell wall and the plasmalemma before being releasedinto the developing periembryonic and intercellular spaces tobecome the extracellular matrix. Cell wall development in theendosperm cells abutting the embryo followed an unusual path.During the quadrant stage, whilst the outer embryo wall increasedin thickness due to vesicle fusion, the endosperm cell wallfacing the embryo showed a loosening of the wall fibrils aswell as partial separation of these same endosperm cells fromeach other. From the early-globular stage, the endosperm cellwalls opposite the embryo became electron-translucent, disappearinginto the extracellular matrix. Enzymic secretions by the embryomay account for the alteration in the abutting endosperm cellwalls. Enzymic activity may also explain the development ofa homogenous electron-opaque layer over the outer embryo wallas well as the differences in the width of the fibrillar layerwhich accumulated around the cotyledons as the embryo grew throughthe Zone of Separation and Secretion. The potential roles ofthe extracellular matrix are briefly discussed. Solanum nigrum L.; embryo/endosperm interface; Zone of Separation and Secretion; embryo development; cellular endosperm     

Effects of Parental Embryo and Endosperm Mitotic Cycle Times on Development of Hybrids Between Barley and Rye

Seven different barley/rye crosses were made using genotypeshaving close (predicted compatible) or dissimilar (predictedincompatible) mean cell doubling times. The relative successof the crosses was determined by a cytological study of earlyhybrid seed development and by the yield of 16-day-old hybridembryos. The results support the hypothesis that parental developmentalrates must be similar for successful hybridization. The degenerationof the hybrid endosperm occurred earlier in the predicted incompatiblecrosses than in the more compatible ones. Fewer hybrid embryoswere harvested at day 16 from predicted incompatible crossesthan from compatible crosses. We conclude that development ofhybrid embryos depends on the early stages of endosperm developmentand that mitotic rates in parental endosperms are more importantthan in embryos. Hordeum vulgare L., Secale cereale L., barley, rye, hybrid, mean cell doubling time, embryo, endosperm     

Changes in Nuclear DNA Content of Endosperm Cells During Grain Development in Rice (Oryza sativa)

Morphological, cytological and quantitative DNA changes associatedwith endosperm development in rice caryopsis were investigated.Following a brief free-nuclear phase, the endosperm became cellularby the 4th d after anthesis. While the mean length and breadthof grain attained maximum values at about 10, d after anthesis,f. wt of the whole grain, and of the endosperm separately, continuedto increase until about 16 d after anthesis. Cell divisionsin the endosperm continued until 10 d and following stabilizationof the cell number, the nuclei attained irregular shapes. Thesize of the nuclei and nuclei and the amount of nuclear DNAvaried considerably during endosperm development. The endospermnuclei did not retain the expected 3C–6C DNA level afterthe first few rounds of division and nuclei having more than30C DNA were frequent 8 d past anthesis. The highest C valuerecorded was 74C in a 16-d-old endosperm cell. Oryza sativa, rice, caryopsis, endosperm, cell number, nuclear area, nuclear DNA content, endoreduplication     

Some Responses of Avena Coleoptiles to Ethylene

Ethylene pretreatment of intact Avena seedlings or of excisedcoleoptile sections results in an increased response of thecells to auxin. It is suggested that ethylene brings about theacceleration of hydrolytic reactions controlling the physicalproperties of cell walls and hence increases their capacityfor growth. Coleoptile elongation of intact seedlings is inhibitedby ethylene; this inhibition is concurrent with a lateral expansionof the entire coleoptile. It is suggested that under a givenset of conditions coleoptile cells are capable of attaininga finite volume and that the preferential lateral expansioninduced by ethylene is accomplished at the expense of longitudinalextension. Experiments with intact and deseeded plants indicatethat lateral expansion depends on the supply of some factorfrom the endosperm.     

An Ultrastructural Investigation of Protein and Lipid Reserves in the Endosperm of Pinus pinea L.

Proteins and lipids are the two main storage substances in theendosperm of Pinus pinea L. In imbibed seeds, lipid and proteinbodies almost completely fill the cell volume and only a fewpoorly structured organelles can be detected. During germinationthe storage substances are reabsorbed whilst plastids, roughendoplasmic reticulum, ribosomes and polysomes, microbodies(glyoxysomes, most likely) become evident. Starch is also formed.When the cotyledons emerge completely from the endosperm envelopethe latter shows highly vacuolate cells but still rich in cytoplasmicorganelles, lipids, protein bodies and starch grains. Different patterns of protein body degradation are discussed. Pinus pinea, endosperm, ultrastructure, protein, lipid, stored reserves     

A Comparison of Leek (Allium porrum) and Onion (Allium cepa) Seed Development

Leek and onion seed dry weight increased exponentially for thefirst 31 days after flowering (DAF) but thereafter the increasein dry weight was slower. Before maximum seed dry weight wasreached at 45 DAF in onion and 59 to 66 DAF in leek, seed moisturecontent, seed oxygen uptake and conductivity of the seed steepwater fell from initially high levels. Although some seeds germinated31 DAF in both species, full germination in both was not reacheduntil 66–80 DAF. Tolerance of the seed to artificial dryingimmediately after harvesting occurred 45 DAF in onion and 74DAF in leek. Free nuclear division continued in the endospermuntil 17–22 DAF in onion and until 31–35 DAF inleek but it was not until 45 DAF in onion and 66 DAF in leekthat the embryo and endosperm filled the cavity formed by thepericarp. After formation of cell walls in the endosperm thepattern of change in cell number in both species was similar.The shrunken appearance of the seed coat in leek, which occurredearly in seed development, was associated with the period offree nuclear division in the endosperm and, in addition, thepericarp was thinner than in onion. There was no evidence thatthe shrunken seed coat early in development was associated withself as opposed to open-pollination. Allium porrum, Allium cepa, seed development, endosperm, embryo, cell number, germination, respiration, seed leachates     

A Comparative Study of Early Seed Development in Genotypes of Barley and Rye

Early seed development was studied in 17 genotypes of barley,Hordeum vulgare L., and 11 genotypes of rye, Secale cerealeL. The numbers of cells and nuclei in the embryos and endospermsof developing seeds were scored daily for 5 days after selfpollination. For embryos, the mean cell doubling times variedfrom 9.2–12.9 h for barley and 15.7–22.7 h for rye.Endosperm mitotic cycle times of both species were shortestover the first 24 h after pollination but then became longer.A non-linear correlation was found between the number of embryocells and the number of endosperm nuclei in barely and rye andis similar to that for other members of the Triticeae. Hordeum vulgare L., Secale cereale L., barley, rye, embryo, endosperm, mean cell doubling time     

Changes in Cell Number and Cell Division Activity during Endosperm Development in Allohexaploid Wheat, Triticum aestivum L.

Nuclear or cell number, and the mitotic index, were recordedin endosperms of Triticum aestivum cv. Mardler to test if aparticular stage of endosperm development was critical in determiningthe final grain weight. The basal four florets of emasculatedspikelets (controls), and the third and fourth florets of spikeletswhere the two basal ovaries were removed (ovary-removed), weresampled at various times up to 360 h after hand-pollination.The coenocytic phase in endosperms ended about 84 h after pollinationregardless of both grain position and the treatment. The onsetof the cellular stage was characterized by the final large fluctuationsin the mitotic index reflecting the culmination of the synchronousnuclear division of the coenocytic stage. Thereafter, the mitoticindex fluctuated with smaller amplitudes and, by 216 h afterpollination, was < 1%. Neither floret position in the spikeletnor the treatment affected the pattern of alteration to themitotic index. However, ovary removal from first and secondflorets resulted in significantly heavier grains and higherendosperm cell number in the 3rd and 4th florets compared withthe controls. In all florets, mean endosperm cell number peakedat 280 h but decreased by 360 h after pollination. At this time,the mean cell numbers in endosperms of the 3rd and 4th floretsof ovary-removed spikelets were significantly higher than inthe corresponding endosperms in the controls. Thus, a key contributoryfactor in determining the final endosperm cell number may bethe number of cells which are lost during the late period ofthe cellular stage of endosperm development. Key words: Endosperm cell number, florets, grain weight, mitotic index, Triticum aestivum     

An Analysis of Seed Development in Pisum sativum L.

Growth analysis has been performed on developing seeds and seedcomponents of six contrasting genotypes of Pisum sativum. Seeddevelopment has been divided into three phases of high growthrate separated by two ‘lag’ phases, or phases oflow growth rate. It is suggested that the timing of these growthphases may not be determined by the developing seed, since thereappeared to be no consistent correlation with particular physiologicalstages of seed development. The relationship between the absolutegrowth rate of the embryo sac and of the embryo as determinedfrom changes in volume is reflected in the accumulation andabsorption of the endosperm. The relative growth rate of theembryo volume was invariably higher than that of the embryosac although the difference between these two relative ratesvaried with genotype and may account in part for the differencein seed phenotype. It is suggested that the testa and embryo are sinks which bothcompete for the endosperm which may act as a common source,and that this relationship accounts for variation in endospermvolume. It is concluded that seed development is dependent on threelevels of plant organization, the maternal parent, interactionsbetween the components of the seed and the genetic constitutionof the embryo. Pisum sativum L., garden pea, seed development, growth analysis     

Structure and In Vitro Growth of Zygotic Embryos of Taro (Colocasia esculenta var. antiquorum)

Zygotic embryos of taro, Colocasia esculenta var. antiquorumwere examined using both light and scanning electron microscopyand cultured on Linsmaier-Skoog (LS) medium without the additionof growth regulators. Embryos present within mature seed consistof a hypocotyl-root axis and an undeveloped cotyledon and aresurrounded by two major types of endosperm cells, aleurone andstarchy endosperm. Embryos cultured on LS medium developed intomature plants only in the presence of endosperm tissue. Excisedembryos turned green after 2–4 d in culture and reacheda rapid growth period between days 4 and 6. Culture of taroembryos leading to viable plantlet development depends upon(1) removal of the outer and inner integument, and (2) the presenceof endosperm tissue (including an intact aleurone layer). Colocasia esculenta var. antiquorum, Araceae, taro, embryo culture, integument, endosperm     

Embryo and Endosperm Function and Failure inSolanumSpecies and Hybrids

Although the importance of the endosperm as a food store inmany angiosperm seeds is well known, its significance duringearly embryogenesis has been neglected. In many interspecifichybrids, and in some other situations, embryos do not developfully and abort. It has often been stated that this is causedby the endosperm failing to conduct sufficient nutrients tothe embryo, but seldom has it been suggested that the endospermactively controls most of the early stages of morphogenesisof the embryo. Information gleaned from a broad survey of theliterature, combined with additional evidence presented here,obtained fromSolanum incanumand interspecific hybrids, indicatethat the endosperm is dynamic and very active in regulatingearly embryo development. This requires highly integrated geneticcontrol of rapidly changing metabolism in the endosperm. Ininterspecific hybrids, lack of coordination may cause unbalancedproduction of growth regulating substances by the endospermand hence abortion of the embryo, or even unregulated productionof nucleases and proteases resulting firstly in autolysis ofthe endosperm and then digestion of the embryo. The endospermmay thus serve to detect inappropriate hybridization of speciesor ploidy levels and so prevent waste of resources by producingseeds that would result in sterile hybrids or unthrifty subsequentgenerations. This discriminatory function of the endosperm hasdiminished during evolution and domestication of the crop plantSolanummelongenaL.Copyright 1998 Annals of Botany Company Solanum, embryo morphogenesis, endosperm, hybrid, seed development.     

Embryology of Early Abortion Due to Limited Maternal Resources in Pisum sativum L.

In most flowering plants, many embryos are aborted early intheir development due to limited maternal resources. The kin-conflictinterpretation of plant embryology predicts these abortionsshould be under maternal control. In a study of the abortionprocess in Pisum sativum, we found the first visible indicationof abortion was formation of a weak hypostase. Callose was locallydeposited around the chalazal endosperm haustorium, and ligninalong the outer cell walls of the remnant nucellar tissue. Thenucellus was compressed by proliferating adjacent inner integumentalcells. The endosperm haustorium's cytoplasm was forced backinto the embryo sac cavity. With suppression of haustorial activitythe endosperm nuclei gradually enlarged followed by enlargementof the embryo and suspensor nuclei. Finally, nuclei and cytoplasm throughout the endosperm and embryolost stainability and broke down. Four successive stages wererecognized in seed abortion. In seeds developing to maturity,no hypostase was developed and the haustorium continued to digestboth the remnant nucellus and the proliferated inner integumentalcells. These observations are consistent with the kin-conflicthypothesis. Pisum sativum, garden pea, ovule abortion, histology, hypostase, kin-conflict hypothesis     

Effect of Post-anthesis Drought on Cell Division and Starch Accumulation in Developing Wheat Grains

Wheat plants (Triticum aestivum L., cv. Warigal) were subjectedto 20 d of water deficit during the period of endosperm celldivision. Drought accentuated the differences in final grainweight between spikelets and between grains within spikelets.The distal grains of top spikelets were most affected by drought.The maximum number of endosperm cells was, respectively, 30and 40 per cent lower in basal grains and distal grains of draughtedplants. In basal grains of middle spikelets, the number of largestarch granules per cell was unaffected but the number of smallstarch granules per cell was 45 per cent lower in grains ofdraughted plants. The initiation of small starch granules wasmore affected than cell division because severe water deficitoccurred earlier during the former process than the latter.Final dry weight appeared to correlate well with the maximumnumber of endosperm cells, but depended also on the number ofstarch granules per cell. Consequently, the amount of dry matterper cell was not constant in both treatments. The concentration of sucrose per endosperm cell was lower onlyin the droughted distal grains of top spikelets. The supplyof sucrose to endosperm cells did not regulate the initiationof small starch granules. Triticum aestivum L., wheat, drought, grain growth, cell division, starch