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     

Ultrastructural Changes of the Egg Apparatus Associated with Fertilization and Proembryo Development of Soybean, Glycine max (Fabaceae)

As part of a study involving pod retention in soybean, Glycinemax (L.) Merr., we investigated changes occurring in the eggapparatus of non-abscised flowers from the time immediatelypreceding fertilization through early embryogeny. Prior to theentry of the pollen tube into the embryo sac, one of the synergidsbegins to degenerate as evidenced by increased electron densityand a loss of volume. This cell serves as the site of entryfor the pollen tube. The cytoplasm of the second, or persistentsynergid, remains unaltered until after fertilization. Bothsynergids contain, in addition to a filiform apparatus, a singleunidentified inclusion of flocculent material located in thechalazal portion of each cell. The zygote can be distinguishedfrom the egg by its consistently narrow wall; and it dividesto form a proembryo, a mass of cells not yet differentiatedinto embryo proper and suspensor. The basal cells of the proembryoare more vacuolate than the apical ones, characteristic of thebasal vacuolation of both egg and zygote. Cells of the proembryoare connected to one another via plasmodesmata, and with theexception of the basal-most cell, are isolated symplasticallyfrom the surrounding endosperm. Wall ingrowths frequently occurin certain cells of the proembryo, notably those cells in contactwith the degenerate synergid and embryo sac wall. At a laterstage of ontogeny, by which time the globular embryo properhas become distinct from the suspensor, the wall ingrowths areconcentrated in the suspensor. Glycine max, soybean, embryogeny, synergids     

THE DEVELOPMENT OF THE SEED IN ANDROGRAPHIS SERPYLLIFOLIA

Mohan Ram , H. Y. (U. Delhi, India.) The development of the seed in Andrographis serpyllifolia. Amer. Jour. Bot. 47(3) : 215—219. Illus. 1960.–Andrographis serpyllifolia, a member of the Acanthaceae, has an embryo sac with a bifurcated chalazal part. At the time of fertilization both synergids and antipodal cells disintegrate. Early in its development the endosperm is composed of 3 distinct parts: (1) a binucleate densely cytoplasmic chalazal haustorium; (2) a large binucleate micropylar haustorium; and (3) a central chamber which develops into the endosperm proper. The divisions in the central endosperm chamber are ab initio cellular. A few of the endosperm cells elongate enormously, ramify into the integument and destroy the surrounding cells. These cells have been termed secondary haustoria. Due to the unequal destruction of the integument, the endosperm assumes a ruminate condition. The mature seed is nearly naked because the seed coat is almost completely digested. The embryo has a long suspensor. The micropylar cells of the suspensor are hypertrophied and multinucleate. Contrary to Mauritzon's (1934) belief, the course of endosperm development is markedly different from that observed in Thunbergia. So far, albuminous seeds have been reported only in the subfamily Nelsonioideae. The present investigation provides a case of its occurrence in the Acanthoideae also.     

Ultrastructural characteristics of « Diplotaxis erucoides (L.) DC. » suspensor

Abstract

The development and general morphology of Diplotaxis erucoides (L.) DC. suspensor is of the « Onagrad Type », « Alyssum Variation ». Maximum growth of the suspensor occurs from the globular to the early heart stage of embryo development. The suspensor starts then to degenerate disintegrating shortly after the torpedo stage of the embryo.

The wall ingrowths of the long, tapering, basal cell are especially abundant at the cell's micropilar pole which is closely surrounded by well developed wall ingrowths formed by the endosperm. Wall ingrowths and plasmodesmata are present on the suspensor cells cross walls with the exception of the cell closest to the embryo. No such structures in fact are present on the walls separating this last cell both from the embryo and from the rest of the suspensor. Wall ingrowths are generally associated with numerous, large, mitochondria.

The morphological data seem to indicate that absorption and transport of nutrients from the surrounding tissues is a main function of the suspensor. The possibility of an elaborative and secretory function of this structure is discussed.     

Structure and Histochemistry of Embryo Envelope Tissues in the Mature Dry Seed and Early Germination of Phacelia tanacetifolia

The embryo envelope tissues in both mature dry seed and duringearly germination of Phacelia tanacetifolia were investigatedby bright-field and fluorescence light microscopy and scanningelectron microscopy. The ruminate seed had an irregularly reticulatesurface owing to the presence of polygonal areas, correspondingto the cells of the seed coat. The raised margins of these cellsjoined at the lobe tips, where radially arranged thickeningsoccurred. The unitegmic seed coat was made up of three distinctlayers: the frayed outer layer, the middle layer with portionsrising outwards to form the radial thickenings, and the innerlayer, the thickness of which was greatest in the micropylarzone. The endosperm tissue had two regions, the micropylar andthe lateral endosperm, which differed in polysaccharide composition,thickness and metachromasy intensity, and presence (in the lateralendosperm) or absence (in the micropylar endosperm) of birefringenceof the cell walls. Moreover, in the micropylar region, wherethe embryo suspensor remnant was found, Ca-oxalate crystalswere scarce or absent. The presence of a partially permeablecuticle covering the seed endosperm was observed. Incubationof seeds in Lucifer Yellow CH indicated that water was ableto penetrate quickly into the seed coat along the pathway formedby the radial thickenings, the raised margins of the polygonalcells and the middle layer. Afterwards, LY-CH readily infiltratedthe apical portions of the seed lobes and then the whole endosperm.Following imbibition, morphological changes were found in themicropylar endosperm, such as the initial digestion of proteinbodies. In addition, both in the seed coat and in the endosperm,a weaker fluorescence, probably due to leaching of polyphenolicsubstances, was observed. Once the seed coat was broken at themicropylar end of the seed, the endosperm cap surrounding theradicle tip had to be punctured by it so that complete germinationcould occur. Weakening and rupture of the micropylar endospermare briefly discussed. Copyright 2000 Annals of Botany Company Phacelia tanacetifolia, seed coat, micropylar endosperm, endosperm cap, early germination, structure, histochemistry     

Ricinosomes provide an early indicator of suspensor and endosperm cells destined to die during late seed development in quinoa (Chenopodium quinoa)

Background and Aims

In mature quinoa (Chenopodium quinoa) seeds, the lasting endosperm forms a micropylar cone covering the radicle. The suspensor cells lie within the centre of the cone. During the final stage of seed development, the cells of the lasting endosperm accumulate protein and lipids while the rest are crushed and disintegrated. Both the suspensor and endosperm die progressively from the innermost layers surrounding the embryo and extending towards the nucellar tissue. Ricinosomes are endoplasmic reticulum-derived organelles that accumulate both the pro-form and the mature form of cysteine endopeptidase (Cys-EP), first identified in castor bean (Ricinus communis) endosperm during germination. This study sought to identify associations between the presence of ricinosomes and programmed cell death (PCD) hallmarks in suspensor and endosperm cells predestined to die during quinoa seed development.

Methods

A structural study using light microscopy and transmission electron microscopy was performed. To detect the presence of Cys-EP, both western blot and in situ immunolocalization assays were carried out using anti-R. communis Cys-EP antibody. A TUNEL assay was used to determine DNA fragmentation.

Results and Conclusions

Except for the one or two cell layers that constitute the lasting endosperm in the mature seed, ricinosomes were found in suspensor and endosperm cells. These cells were also the site of morphological abnormalities, including misshapen and fragmented nuclei, vesiculation of the cytosol, vacuole collapse and cell wall disorganization. It is proposed that, in suspensor and endosperm cells, the early detection of Cys-EP in ricinosomes predicts the occurrence of PCD during late seed development.     

Regeneration of zygotic-like microspore-derived embryos suggests an important role for the suspensor in early embryo patterning

The inaccessibility of the zygote and proembryos of angiospermswithin the surrounding maternal and filial tissues has hamperedstudies on early plant embryogenesis. Somatic and gametophyticembryo cultures are often used as alternative systems for molecularand biochemical studies on early embryogenesis, but are notwidely used in developmental studies due to differences in theearly cell division patterns with seed embryos. A new Brassicanapus microspore embryo culture system, wherein embryogenesishighly mimics zygotic embryo development, is reported here.In this new system, the donor microspore first divides transverselyto form a filamentous structure, from which the distal cellforms the embryo proper, while the lower part resembles thesuspensor. In conventional microspore embryogenesis, the microsporedivides randomly to form an embryonic mass that after a whileestablishes a protoderm and subsequently shows delayed histodifferentiation.In contrast, the embryo proper of filament-bearing microspore-derivedembryos undergoes the same ordered pattern of cell divisionand early histodifferentiation as in the zygotic embryo. Thisobservation suggests an important role for the suspensor inearly zygotic embryo patterning and histodifferentiation. Thisis the first in vitro system wherein single differentiated cellsin culture can efficiently regenerate embryos that are morphologicallycomparable to zygotic embryos. The system provides a powerfulin vitro tool for studying the diverse developmental processesthat take place during the early stages of plant embryogenesis. Key words: Brassica napus, microspore embryogenesis, pattern formation, polarity, suspensor, zygotic embryogenesis     

Are there symplastic connections between the endosperm and embryo in some angiosperms?—a lesson from the Crassulaceae family

It is believed that there is symplastic isolation between the embryo (new sporophyte) and the endosperm (maternal-parental origin tissue, which nourishes the embryo) in angiosperms. However, in embryological literature there are rare examples in which plasmodesmata between the embryo suspensor and endosperm cells have been recorded (three species from Fabaceae). This study was undertaken in order to test the hypothesis that plasmodesmata between the embryo suspensor and the endosperm are not so rare but also occur in other angiosperm families; in order to check this, we used the Crassulaceae family because embryogenesis in Crassulaceae has been studied extensively at an ultrastructure level recently and also we tread members of this family as model for suspensor physiology and function studies. These plasmodesmata even occurred between the basal cell of the two-celled proembryo and endosperm cells. The plasmodesmata were simple at this stage of development. During the development of the embryo proper and the suspensor, the structure of plasmodesmata changes. They were branched and connected with electron-dense material. Our results suggest that in Crassulaceae with plasmodesmata between the endosperm and suspensor, symplastic connectivity at this cell-cell boundary is still reduced or blocked at a very early stage of embryo development (before the globular stage). The occurrence of plasmodesmata between the embryo suspensor and endosperm cells suggests possible symplastic transport between these different organs, at least at a very early stage of embryo development. However, whether this transport actually occurs needs to be proven experimentally. A broader analysis of plants from various families would show whether the occurrence of plasmodesmata between the embryo suspensor and the endosperm are typical embryological characteristics and if this is useful in discussions about angiosperm systematic and evolution.     

Embryology ofCymbidium sinense:the Microtubule Organization of Early Embryos

InCymbidium sinense, the pattern of embryo development is unusualin that oblique cell divisions result in the formation of severalsuspensor cells prior to the development of the embryo proper.Characteristic changes in microtubular distribution can be foundwithin the zygote and the proembryo during their development.After fertilization, the ellipsoid-shaped zygote has randomlydistributed microtubules within its cytoplasm. As the zygotetakes on a more rounded appearance, microtubules organize intoa dense meshwork. Furthermore, microtubule bundles appear atthe chalazal region of the cell prior to the first mitotic divisionof the zygote. At the preprophase stage of mitosis, a preprophaseband of microtubules appears in the cytoplasm of the zygote.The zygote divides obliquely and unequally and gives rise toan apical cell and a slightly larger basal cell. Many randomly-alignedmicrotubules can be found in the cortex of the basal cell. Theincrease in the abundance of microtubules coincides with theisotropic expansion of the basal cell. The early division ofthe basal cell and subsequent division of the apical cell resultsin the formation of a four-celled embryo, of which three cellsnear the micropylar pole develop as suspensor cells. In thesuspensor cells, the microtubules tend to orient in the samedirection as the long axis of the cell. In addition, prominentmicrotubules can also be found near the adjoining cell wallsof the four-celled embryo. The terminal cell is highly cytoplasmicwith abundant microtubules within the cell. Subsequent divisionsof the terminal cell give rise to additional suspensor cellsand the embryo proper. In the mature embryo, five suspensorcells are usually present; one eventually grows through themicropyle of the inner integument and four grow towards thechalazal pole. The cortical microtubules of suspensor cellsredistribute from a longitudinal to a transverse direction asthey grow towards their respective poles.Copyright 1998 Annalsof Botany Company Embryogenesis, endosperm, microtubules, preprophase band, suspensor cells,Cymbidium sinense(Andr.) Willd.     

Il sospensore embrionale nelle Cruciferae. I. Morfologia e struttura

Abstract

Embryo suspensor in Cruciferae. I. Morphology and structure. — Embryo suspensors in seven species of Cruciferae (Alyssum argenteum All., Brassica nigra (L.) Koch, Capsella bursa-pastoris (L.) Medicus, Diplotaxis erucoides (L.) DC., Eruca sativa Miller, Lepidium graminifolium L., Matthiola tricuspidata (L.) R. Br.) were morphologically investigated. These species have significant differences in their seeds, so that probable differences could be found in the structure of their ovules and therefore of their suspensors. Results indicate that it is impossible to generalize on the suspensor morphology and structure even in the same family. In Eruca sativa and Brassica nigra polyploidy and polyteny were found, suggesting a probably important metabolic function of their suspensors. In the other species polyteny was not present; a various degree of polyploidy could probably be assumed, suggesting a less active function of suspensors, maybe absorption and transport of nutritive material from the integuments to the developing embryo. The development of the endosperm is almost the same in all species, so that seems to be improbable a negative correlation with the suspensor and endosperm function in the early embryogenesis.     

Activity of Some Hydrolytic Enzymes in Autolysis of the Embryo Suspensor in Tropaeolum majus L.

Assay of amino-peptidase, acid and alkaline phosphatase, esteraseand ß-glucosidase activity in the haustoria and suspensorof Tropaeolum majus embryos at different stages of developmentis made to evaluate the function of hydrolases in autolysisof the suspensor. Enzyme activities rise to a maximum sometimebetween heart-shaped and cotyledonary phases of embryo development. Tropaeolum majus L. nasturtium, embryology, suspensor, autolysis, hydrolytic enzymes     

Functional Anatomy of the Ovule in Broad Bean (Vicia faba L.): Ultrastructural Seed Development and Nutrient Pathways

Ovules of broad bean (Vicia faba L.) were studied to discloseultrastructural features, which can facilitate nutrient transportto the embryo sac from 10 d after pollination (DAP) to the matureseed. Fertilization occurs during the first 24 h after pollination.The endosperm is a coenocyte, which is eventually consumed bythe embryo. By 10 DAP the inner integument is degraded and theouter integument adjoins the embryo sac boundary. The heart-shapedembryo approaches the embryo sac boundary at two sites, whichhere are named contact zones. Small integument cells in theneighbourhood of the first formed contact zones become separatedby prominent intercellular spaces. A heterogenous scatteringmaterial, probably representing secretion products accumulatesin these spaces. By 14-16 DAP the integument exudate disappears,and the suspensor degenerates. As the contact zones increasein size, wall ingrowths form a bridging network in the narrowspace between the embryo sac boundary and the extra-embryonicpart of the endosperm wall. The epidermal cells of the embryoseparate adjacent to these zones, and develop conspicuous wallingrowths. At 20 DAP vacuoles showing various stages in formationof protein bodies appear in the cells of the embryo.Copyright1994, 1999 Academic Press Vicia faba, broad beans, ovule, seed, nutrient transport     

Studies in the Proteaceae: III. Embryology of Grevillea Banksii R. Br.

The embryo-sac of Grevillea Banksii R. Br. develops accordingto the normal type. At the time of fertilization is has a veryirregular outline. The synergids show a well-marked filiformapparatus. The development of the embryo is similar to that in the twomembers of the family previously studied (Kausik, 1938, 1938a). The endosperm becomes cellular. The presence of the vermiformappendage of the endosperm described in Grevillea robusta (Kausik,1938), has been demonstrated here. Though similar in both, theendosperm of G. Banksii shows a narrow middle region with rowsof elongated cells which are absent in G. robusta. In conclusion, the writer has great pleasure in acknowledginghis indebtedness to Prof. M. A. Sampathkumaran, of the Universityof Mysore, for encouragement and kind help during the courseof this investigation. Thanks are also due to the Curator, GovernmentBotanic Gardens, Ootacamund, and Sim's Park, Coonoor, Nilgiris,South India, for permission to collect the material for thisstudy.     

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.     

Accumulation of Metabolites during Seed Development in Trifolium repens L.

Metabolite deposition during seed development was examined histochemicallyin Trifolium repens by light- and fluorescence microscopy. Allendosperm haustorium at the chalazal pole of the embryo sacand wall protrusions in cell walls of the suspensor and theembryo sac suggest that transfer of metabolites from maternalto offspring tissue takes place primarily at these sites. Thisis further supported by prominent cutinization of the interpolarregion of the embryo sac wall, accumulation of starch in integumentaltissue at the embryo sac poles, and breakdown of interpolarendothelial cells. Decomposition of osteosclereid starch isfollowed by accumulation in the cellular endosperm and subsequentlyin the embryo parallel to endosperm degradation. The starchaccumulates gradually inward from the subepidermal cells ofthe embryo to the stele. Protein bodies are formed in the vacuolesalong the tonoplast, later to be cut off in vesicles releasedinto the cytoplasm. At maturity the embryo is packed with proteinand starch, but without lipid reserves. Phytin is observed inthe protein bodies. The mature embryo is surrounded by a proteinand starch containing aleurone layer which originates from theendosperm.Copyright 1994, 1999 Academic Press White clover, protein, starch, cuticle, embryo sac wall     

ABNORMAL DEVELOPMENT OF THE SUSPENSOR IN AN EMBRYO-LETHAL MUTANT OF ARABIDOPSIS THALIANA

Developmental arrest of the embryo proper in aborted seeds from mutant 50B, a recessive embryo-lethal mutant of Arabidopsis thaliana, was shown to be followed by abnormal growth of the suspensor. Each of the 12 aborted seeds examined in sectioned material contained an abnormally large suspensor and an embryo proper arrested at a preglobular stage of development. Analysis of serial sections revealed that mutant suspensors contained 15–150 cells whereas wild-type suspensors were composed of only six to eight cells. Development of the mutant endosperm continued to a late nuclear or early cellular stage even in the absence of further development of the embryo proper. These results suggest that the missing gene product in mutant 50B is required for development of the embryo proper but not for continued growth of the suspensor or endosperm tissue. The pattern of abnormal development observed in this mutant provides further evidence that continued growth of the suspensor during normal development is inhibited by the developing embryo proper and that the full developmental potential of cells in the suspensor is expressed only when this inhibitory effect is removed through a mutation or experimental treatment that is lethal only to cells of the embryo proper.     

Capsella embryogenesis: The suspensor and the basal cell

Summary The suspensor and basal cell ofCapsella were examined with the electron microscope and analyzed by histochemical procedures. The suspensor cells are more vacuolate and contain more ER and dictyosomes, but fewer ribosomes and stain less intensely for protein and nucleic acids than the cells of the embryo. The end walls of the suspensor cells contain numerous plasmodesmata but there are no plasmodesmata in the walls separating the suspensor from the embryo sac. The lower suspensor cells fuse with the embryo sac wall and the lateral walls of the lower and middle suspensor cells produce finger-like projections into the endosperm. At the heart stage the suspensor cells begin to degenerate and gradually lose their ability to stain for protein and nucleic acids.The basal cell is highly vacuolate and enlarges to a size of 150 X 70. An extensive network of wall projections develops on the micropylar end wall and adjacent lateral wall. The nucleus becomes deeply lobed and suspended in a strand of cytoplasm traversing the large vacuole. The cytoplasmic matrix darkens at the late globular stage and histochemical staining for protein becomes very intense. The basal cell remains active after the suspensor cytoplasm has degenerated. It is proposed that the suspensor and basal cell function as an embryonic root in the absorption and translocation of nutriments from the integuments to the developing embryo.Research supported by NSF grant GB 3460 and NIH grant 5-RO 1-CA-03656-09.     

The Nucellus, Embryo Sac, Endosperm, and Embryo of Aesculus and their Interdependence during Growth

Immature fruits of Aesculus yield powerful stimuli to growthand cell division. Therefore, the developing fruit of Aesculuswoerlitzensis Koehne has been investigated from pollinationto maturity. The fluid, or liquid endosperm, which containsthe growth-promoting substances is produced in a large vesiclewhich forms at the chalazal tip of the embryo sac. As the vesiclegrows, it encroaches upon the nucellus and, when the embryodevelops, one of its cotyledons penetrates into the vesicleof the embryo sac where it grows and absorbs the contents. Theembryo, which has only a vestigial suspensor, reaches the vesicleby growing along the neck of the long curved embryo sac. Thecotyledon which first penetrates the vesicle grows into a massivestructure; the other remains small. The tip of the cotyledonseems to function as an absorbing surface, for the endospermwith which it comes into contact disorganizes. Fertilizationand the presence of a viable embryo at the micropylar end ofthe embryo sac therefore sets in train a number of other events.These are the extensive development of the nucellus at the chalazalend of the embryo sac, the swelling of the vesicle and the formationof a free nuclear and some cellular endosperm, and the disorganizationof the nucellus as it is encroached upon by the vesiculate embryosac. Attention is directed to the organization of the nucellusin the vicinity of the embryo sac. Files or richly protoplasmicnucellar cells(hypostase) which converge upon the chalazal tipof the embryo sac suggest a principal route by which the vesiclemay be nourished. Special attention is drawn to the very differentsizes of cells, their nuclei and nucleoli, in the differentparts of the nucellus. The growth and development of the embryohas also been traced from the zygote to the mature seed. Thenutritive role of the veaiculate embryo sac, and the supplyof growthstimulating substances, through the function of a cotyledonas an absorbing organ, are now seen as important features ofthe development of the Aesulus embryo in the ovule. Many outstandingproblems still remain. The sequential events that follow fertilizationin the different interdependent regions (nucellus, embryo sac,cotyledon, &c.) are here described, but not casually explained.     

The Relationship between Embryo and Endosperm in Interspecific Hybrids in PennisetumL. Rich

In the interspecific cross [diploid Pennisetum typhoides X hexaploid(P. typhoides X P. purpureum)] X diploid P. typhoides, embryosand endosperms in the same ovule may respond differently totreatment with the growth substance gibberellic acid, as maydo different genotypes. Size of embryo and size of its endospermare positively correlated in some genotypes but not in others.Large fully developed normal embryos may be associated withnormal, retarded, degenerate or even no endosperm at all. Conversely,large normal endosperms, even in mature seeds, may contain large,small, or no embryos. Fully developed embryos may be viableregardless of whether they had been associated with normal,retarded or degenerate endosperm, or even no endosperm at all. It is concluded that the embryo is not always dependent on theendosperm during its early development and that a degeneratingendosperm need not have a detrimental effect on the developmentof its embryo or on the viability of the latter.     

Alcuni Aspetti Citologici Dell'Endosperma di Phaseolus Coccineus L.

Abstract

Some cytological aspects of Phaseolus coccineus L. endosperm. — Cytological observations were made on the endosperm of Phaseolus coccineus, in a limited stage of development of the seed, using different dyes and labelling with ³H-thymidine and ³H-uridine. The results seem to indicate that, contrary to suspensor cells, in the endosperm of Phaseolus, at least in the considered stage, extra DNA synthesis is not present. Chromosomes in these nuclei, however, undergo several endoreduplication cycles. Nucleoli may be either one or more in a cell, and show a characteristic structure. They are often eccentric in the nucleus and extrusions of nucleolar content in the nucleoplasm or cytoplasm are seen. An apparent alternate activity of RNA synthesis in the nucleoli of the suspensor and in those of endosperm cells is discussed.