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     

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     

Rates of Cell Division in Developing Barley Endosperms

Counts of nuclei in enzyme digested endosperms of barley cultivarBomi show that the final number of cells, 170000, is reachedbetween 18 and 21d after anthesis. Based on the number of cellprofiles in transverse mid-grain sections, starchy endospermcells divide up to day 14. Thereafter, cell proliferation isrestricted to the aleurone layer. Hordeum vulgare, starchy endosperm, aleurone, mitotic activity, light microscopy     

Analysis of chromatin and DNA during chromosome endoreduplication in the endosperm ofTriticum durum Desf.

Summary Chromatin structure was studied in nuclei of the endosperm of durum wheat (Triticum durum Desf., cv. Creso), where a large number of cells undergo chromosome endoreduplication during caryopsis development. Optical density profiles of interphase nuclei at different ploidy levels after Feulgen staining were determined cytophotometrically. It was observed that, within each development stage, polyploid nuclei (6–12C and 12–24C) show more condensed chromatin than euploid nuclei (3–6C): this should indicate that endoreduplication is accompanied by some reduction of nuclear activity. Within the same ploidy level, 3–6C and 6–12C nuclei become increasingly condensed with development (except for the last stage), while 12-24C nuclei are identical at all stages. DNA methylation at different stages of caryopsis development was then analyzed in genomic DNA, highly repeated sequences and ribosomal DNA, by digestion with cytosine-methylation-sensitive restriction enzymes. We observed that (i), depending on the enzyme, DNA from caryopses may show higher mean length than DNA from shoot apices and variations occur during endosperm development; (ii) highly repeated DNA sequences also show some variation in base methylation between apices and endosperms and among endosperm development stages, even though to a lesser extent than genomic DNA; (iii) rDNA shows variations only between endosperm and apices while no variation was observed among endosperm development stages in relation to chromosome endoreduplication. Our data may be explained by assuming the occurrence, during endosperm development, of processes of chromatin condensation possibly involved in silencing the activity of extra copies of DNA resulting from chromosome endoreduplication. At least in part, DNA methylation is involved in the process of chromatin condensation. rDNA shows no variation during endosperm development: this suggests that rDNA copies are actively transcribed in both triploid and endoreduplicated nuclei.     

Structural Differentiation of the Nucellar Epidermis in the Caryopsis of Rice (Oryza sativa)

In the developing caryopsis of rice (Oryza sativa L.) the nucellarepidermis forms a uniseriate layer through which assimilatesare transported to the endosperm. An anatomical study demonstratedthat the nucellar epidermal cells are fusiform in shape andare hexagonally packed. The anticlinal walls of the nucellarepidermis are characterized by ribs of wall-thickening whichare orientated radially with respect to the caryopsis. The wall-thickeningsappear to be cellulosic primary walls, as indicated by theirstaining with Calcofluor and periodic acid-Schiff's reagent.It is proposed that the geometry of the nucellar cells and theribs of wall-thickening are structural adaptations to resistthe compressional force which is placed on the nucellar epidermisduring the latter stages of grain filling. Oryza sativa, rice, caryopsis, grain filling, nucellar epidermis, wall-thickening     

Apoplasmic assimilates and grain growth of contrasting rice cultivars differing in grain dry mass and size

Apical dominance in assimilate filling impacts grain growth in basal spikelets of rice panicle. In this study, organic materials of the pericarp, apoplasmic space and endosperm of the apical and basal caryopses, and photosynthesis of the flag leaf were measured during early part of grain development in three types of rice cultivars with similar phenology, but difference in grain weight and size in the dry and wet seasons of 2006 and 2007, respectively. Photosynthetic activity of the flag leaf was consistently low in small-seeded cultivars. Rates of grain filling and cell division of endosperm and concentration of assimilates, starch, proteins and chlorophylls of the caryopsis were lower, but spikelet ethylene production and peroxidase activity were higher in a small-seeded cultivar compared to a big-seeded cultivar. Similar disparities in grain filling and other attributes were noticed for the inferior basal spikelets of the panicle compared to the superior apical spikelets, except the assimilate concentration of the pericarp and endosperm. Temporal fluctuation in assimilate concentration of the organs were similar between the cultivars. Concentration of apoplasmic assimilates mostly exhibited negative correlation with that of pericarp and endosperm. Compared to the apical spikelets, correlation was more negative for the basal spikelets. Conversely, correlation was positive between the concentration of apoplasmic assimilates and endosperm cell number and grain weight of the cultivars. Ethylene released from the spikelets at anthesis affected growth and cell division rates of endosperm and enhanced protein and chlorophyll degradation and peroxidase activity of the caryopsis. It was concluded that variation in spikelet ethylene production may be responsible for differences in size or weight of grains among rice cultivars and spikelets at different locations of the panicle. The concentration of apoplasmic assimilates could be an indicator for grain filling capacity, and ethylene regulated the concentration by affecting pericarp activity for assimilate unloading.     

ULTRASTRUCTURE OF THE MATURE UNGERMINATED RICE (ORYZA SATIVA) CARYOPSIS. THE CARYOPSIS COAT AND THE ALEURONE CELLS

The results of a light and electron microscopic study of the caryopsis coat and aleurone cells in ungerminated, unimbibed rice (Oryza sativa) caryopses are presented. Surrounding the rice grain is the caryopsis coat composed of the pericarp, seed coat and nucellar layers. The outermost layer, the pericarp, consists of crushed cells and is about 10 μm thick. The seed coat, interior to the pericarp, is one cell thick and has a thick cuticle. Between the seed coat cuticle and endosperm are the remains of the nucellus. The nucellus is about 2.5 μm thick and has a thick cuticle adjacent to the seed coat cuticle. Interior to the caryopsis coat is the aleurone layer of the endosperm. The aleurone completely surrounds the rice grain and is composed of two cell types—aleurone cells that surround the starchy endosperm and modified aleurone cells that surround the germ. The aleurone cells of the starchy endosperm contain many aleurone grains and lipid bodies around a centrally located nucleus. The modified aleurone cells lack aleurone grains, have fewer lipid bodies than the other aleurone cells, and contain filament bundles (fibrils). Plastids of aleurone cells exhibit a unique morphology in which the outer membranes invaginate to form tubules and vesicles within the plastid. Transfer aleurone cells are not observed in the mature rice caryopsis.     

Endosperm and Embryo Development in Daucus carota L.

Maximum carrot seed dry weight and maximum endosperm volumewere reached about 35 d after anthesis, although at this timethe endosperm was still soft, the pericarp green and less than50% of the seeds were viable. Fully viable, ripe seeds werenot produced until 44 d later. Seventy per cent of the increasein endosperm volume was due to an increase in cell number, whichceased 35 d after anthesis. The increase in embryo volume wasslower and was due to an increase in both cell number and cellvolume which continued until 49 d after anthesis. At maturitythe embryo was the equivalent of between 2% and 3% of the endospermvolume. The relationship between embryo length and cell number per embryowas unaffected by seed crop plant density, seed crop harvestdate and position of the seed on the mother plant but it wasaffected by the year of seed production, possibly due to differencesin temperature during the period of seed growth. Key words: Endosperm, Embryo, Carrot, Development     

Studies on Endosperm Development and Deposition of Storage Reserves in Coix lacryma-jobi

The transition from free nuclear to cellular endosperm of Coix lacryma-jobi was eompleted 2 days after pollination. By 3 days after pollination the central cell was filled with endosperm cells. At first all cells of endosperm underwent division, later cell division was limited mainly in the peripheral region. 10 days after pollination the epidermal layer ceased its periclinal division and became the aleurone layer. Cell division persisted in the subepidermal 'cambium-like layers until the caryopsis nearly matured. Ceils of the inner region of endosperm became enlarged. Several layers of transfer cells were formed at the basal part of the endosperm. Starch grains appeared in endosperm cells on the 9th day after pollination. 10 days after pollination, lipid bodies occurred in the aleurone layer and the underlying layers. 13 and 15 days after pollination, the small vacuoles of aleurone cells contained protein and 20 days after pollenation they became aleurone grains. By 15 days after pollination pro tein bodies were formed in starch endosperm. Storage reserve deposition continued until the grain ripened. A correlation between endosperm and emoryo development was also observed.     

Effect of High Temperature Stress at Anthesis on Grain Yield and Biomass of Field-grown Crops of Wheat

Spring wheat (Triticum aestivumL., ‘Chablis’) wasgrown under field conditions from sowing until harvest maturity,except for a 12-d period [70–82 days after sowing (DAS)coinciding with anthesis] during which replicated crop areaswere exposed to a range of temperatures within two pairs ofpolyethylene-covered temperature gradient tunnels. At 82 DAS,an increase in mean temperature from 16 to 25 °C duringthis treatment period had no effect on above-ground biomass,but increased ear dry weight from 223 to 327 g m^-2and, at 83DAS, reduced root biomass from 141 to 63 g m^-2. Mean temperatureover the treatment period had no effect on either above-groundbiomass or grain yield at maturity. However, the number of grainsper ear at maturity declined with increasing maximum temperaturerecorded over the mid-anthesis period (76–79 DAS) and,more significantly, with maximum temperature 1 d after 50% anthesis(78 DAS). Grain yield and harvest index also declined sharplywith maximum temperature at 78 DAS. Grain yield declined by350 g m^-2at harvest maturity with a 10 °C increase in maximumtemperature at 78 DAS and was related to a 40% reduction inthe number of grains per ear. Grain yield was also negativelyrelated to thermal time accumulated above a base temperatureof 31 °C (over 8 d of the treatment from 5 d before to 2d after 50% anthesis). Thus, grain fertilization and grain setwas most sensitive to the maximum temperature at mid-anthesis.These results confirm that wheat yields would be reduced considerablyif, as modellers suggest, high temperature extremes become morefrequent as a result of increased variability in temperatureassociated with climate change.Copyright 1998 Annals of BotanyCompany Triticum aestivum, spring wheat, temperature, grain number, grain yield, root growth.     

Cytological Studies of the Double Fertilization in Rice

Detailed studies on the process of double fertilization in rice were conducted in the present work. The results are summarized as follows: 1. In the embryosac 30 minutes after anthesis, the pollen tube has already reached the micropyle in every specimen. In some cases, it has even entered further into the embryosac and discharged its contents, including the two male gametes. 2. 1½ hours after anthesis, the male gamete enters into the egg cell. As soon as it comes in contact with the egg nucleus, it increases in size. 2 hours after anthesis, the male nucleus is found inside the female one. A male nucleolus is now clearly discernible. 3. The male nucleolus is gradually growing until it reaches the size of the female one, and then the fusion of the two takes place. The fusion is generally completed and the zygote is formed 7 hours after anthesis. 4. The first mitotic division of the zygote occurs 9 hours after anthesis. 5. The fusion of the male gamete and the polar nucleus proceeds in a similar way as that of the male and female gametes, but it takes a much shorter time usually being completed within 3 hours after anthesis. 6. The male gamete enters into one of the polar nuclei and reveals its nucleolus which increases rapidly in size and then unites with that of the polar nucleus. As soon as the union is completed, the nuclear membrane between the closely contacted parts of the two polar nuclei disappears and the primary endosperm nucleus is formed. 7. The first mitotic division of the primary endosperm nucleus begins right after its formation. 8. With the fusion of the male and female gametes and the development of the zygote, the mitochondria in the cytoplasm surrounding the nucleus increase in size and number. However, in the central cytoplasm about the polar nuclei they show no notice- able change during the fertilization process. 9. Based on the facts that in the embryosac a secondary pollen tube is often seen in every stage of the fertilization process and that additional nucleoli are also observed sometimes in the egg nucleus, the authors believe that polyspermy most probably exists in rice plants, and that this may be one of the causes of polyploid plants often found in rice field as reported by several authors.     

粒重差异显著的两种水稻颖果发育比较

为了探讨控制水稻(Oryza sativa L.)颖果发育的因素,选择了颖果干重有显著差异的Ootikara (大粒,36mg/粒)和Habataki (小粒,18 mg/粒)两个水稻品种,比较颖果重量、胚乳细胞数、果皮和胚乳的结构以及某些生理活性等变化。结果指出:与Habataki相比, Ootikara子房壁细胞和颖果的持续生长期长,最终颖果的胚乳细胞数目和每个细胞的平均干重大; Ootikara颖果的脱氢酶和H2O2酶活性、穗的呼吸速率、剑叶的绿色程度和光合速率等维持高水平的时间长;Ootikara子房背部维管束失去功能的时间也较迟。结果表明,大粒品种的库容大和生理活性期长是其颖果能显著增大的生理原因。     

薏苡胚乳发育及营养物质积累的研究

薏苡 ( Coix lacryma- jobi)授粉后 2 d,游离核胚乳已转变为细胞胚乳。授粉后 3d,中央细胞被胚乳细胞充满。起初 ,全部胚乳细胞均进行分裂 ,一定时期后 ,细胞分裂主要发生在胚乳周边区。授粉后 1 0 d,表皮停止平周分裂变为糊粉层 ,内方的数层形成层状细胞行平周分裂直到颖果接近成熟。胚乳内部生长则依赖于细胞体积扩大。胚乳基部 (颖果基部的胚乳 )形成了数层传递细胞。授粉后 9d,淀粉积累。授粉后 1 0 d,糊粉层及其内方数层细胞产生了脂体 ,后者的脂体以后又消失。授粉后 1 3、1 5 d,糊粉层细胞的液泡积累蛋白质。授粉后 2 0 d,液泡变为糊粉粒。授粉后 1 5 d淀粉胚乳细胞产生蛋白质体 ,营养物质积累持续到颖果成熟。还观察了胚和胚乳发育的对应关系。     

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     

大麦胚和胚乳发育的相关性及贮藏营养物质的积累

大麦(Hordeum vulgare L.)开花后1d,见合子及退化助细胞,游离核胚乳尚未形成;开花后2～3d,胚为5及10个细胞,胚乳为游离核期;开花后4及5、6d,胚为梨形及长梨形,胚乳达细胞化期;开花后8d,胚为胚芽鞘期,糊粉层原始细胞产生;开花后10d,胚具1叶,糊粉层1～2层;开花后13d胚为2叶胚,亚糊粉层发生;开花后17d,3叶胚形成,糊粉层多为3层并停止分裂,菱柱形及不规则胚乳细胞分化;开花后21～29d,胚为4叶胚,胚乳进一步分化;开花后33d,胚为5叶成熟胚,胚乳亦成熟。淀粉、蛋白质在胚中积累始于开花后13d。在盾片中由基向顶发生,在胚芽鞘及叶原基中,首先在顶端出现。成熟盾片顶端的淀粉消失。开花后6d,胚乳开始积累淀粉;开花后10d,糊粉层及胚乳细胞积累蛋白质。开花17d后胚乳的蛋白质体多聚集,29d后蛋白质体显著减少。开花后17d,在盾片及糊粉层细胞中检测到油脂。果长或果长与稃片长之比和盾片长可作为不同发育期胚和胚乳的形态指标。     

粒重差异显著的两种水稻颖果发育比较

为了探讨控制水稻(Oryza sativa L.)颖果发育的因素,选择了颖果干重有显著差异的Ootikara(大粒,36mg/粒)和Habataki(小粒,18 mg/粒)两个水稻品种,比较颖果重量、胚乳细胞数、果皮和胚乳的结构以及某些生理活性等变化.结果指出:与Habataki相比,Ootikara子房壁细胞和颖果的持续生长期长,最终颖果的胚乳细胞数目和每个细胞的平均干重大;Ootikara颖果的脱氢酶和H2O2酶活性、穗的呼吸速率、剑叶的绿色程度和光合速率等维持高水平的时间长;Ootikara子房背部维管束失去功能的时间也较迟.结果表明,大粒品种的库容大和生理活性期长是其颖果能显著增大的生理原因.     

DNA endoreduplication in maize endosperm cells: the effect of exposure to short-term high temperature

DNA endoreduplication in Zea mays L. (cv. A619 × W64A) endosperm peaks between 16 and 18 d after pollination (DAP). The physiological function of DNA endoreduplication is not known but it is believed to be important in maize kernel development. In the present study, we investigated how 2, 4 or 6 d of high temperature (35 °C) affected DNA endoreduplication and maize kernel development in comparison with control kernels grown at 25 °C. Data were collected on fresh weight (FW), nuclei number, mitotic index, and DNA endoreduplication. Maize endosperm FW and nuclei number were reduced by exposure to 4 or 6 d of high temperature. At 18 DAP, the 2 d high temperature treatment (HTT) caused a reduction in FW and nuclei number, but had no effect on DNA endoreduplication and average DNA content per endosperm. However, when the exposure to high temperature was increased to 4 or 6 d, FW, nuclei number and the magnitude of DNA endoreduplication were progressively reduced, and the peak mitotic index was delayed compared with the control endosperm. At 18 DAP, the 4 d treatment showed 54·7% of the cells were 3 or 6 C, whereas only 41·2% were 12 C or higher. Six days of high temperature also resulted in a reduction in endosperm FW, nuclei number and a delay in the peak of mitotic index. DNA endoreduplication occurred in the kernels exposed to this treatment, although the magnitude was severely reduced compared with the control kernels. Nuclear DNA content was highly correlated (r = 0·93) with kernel FW, suggesting an important role of DNA endoreduplication in determining endosperm FW. The data suggest that high temperature during endosperm cell division exerted negative effects on DNA endoreduplication by dramatically reducing the nuclei number, leaving fewer nuclei available for DNA endoreduplication. However, the data also suggest that prolonged exposure to high temperature restricts entry of mitotic cells into the endoreduplication phase of the cell cycle.     

Transport of assimilates in the developing caryopsis of rice (Oryza sativa L.)

The movement of water in the dorsal region of the developing rice caryopsis was studied using solutions of the heavy metals lanthanum and uranium. In the electron microscope electron-opaque deposits were confined to the cell walls of the pigment strand indicating that this is the main route for the water which enters and leaves the caryopsis during grain filling. The pathway of assimilates into the developing caryopsis was examined using isolated caryopses which had taken up solutions of fluorescent dyes and also by autoradiography of caryopses which had transported ¹⁴C-labelled assimilates in vivo. The results show that assimilates unloaded from the phloem move through the pigment strand and circumferentially via cells of the nucellus before entering the endosperm. A scheme is presented for the interrelations of water and assimilate transport during grain filling     

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     

Protein Body Inclusions in Developing Wheat Endosperm

Endosperm tissue of two wheat cultivars, Maris Freeman and Mardlerwas examined by light and electron microscopy from early stagesof development until maturity. Spherical electron-dense inclusionswere first seen embedded in the periphery of endosperm proteinbodies of both cultivars 11 days after anthesis. The inclusions,which gave a positive histochemical reaction for both proteinand lipid, persisted throughout endosperm development and werepresent in the protein matrix of mature grain. Two types ofmembranous inclusions were found. In Maris Freeman and Mardler,vesicles and myelin whorls were associated with the surfaceof the protein mass during development and maturation. In MarisFreeman, membrane lattices of branched tubules with a basiccubic repeat unit of 44.8 nm were found in close contact withthe protein mass, but these were not present in mature grain. Triticum aestivum L., wheat, endosperm, protein body inclusions, ultrastructure