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.     

The occurrence of phenotypically complementary apomixis-recombinants in crosses between sexual and apomictic dandelions (<Emphasis Type="Italic">Taraxacum officinale</Emphasis>)

Apomictic seed development in dandelion ( Taraxacum officinale) involves (1) restitutional meiosis (diplospory), (2) egg cell parthenogenesis, and (3) autonomous endosperm development. The question is whether these elements of apomixis are controlled by one single gene or by several independent genes. Five triploid non-apomictic hybrids, obtained in diploid sexual × triploid apomict crosses were characterized using cyto-embryological and genetic methods. Nomarski-differential interference contrast microscopy and the transmission of microsatellite markers and ploidy levels indicated that the hybrids combined elements of the apomictic and the sexual developmental pathway. Hybrids form two complementary groups with respect to the presence or absence of parthenogenesis and autonomous endosperm development. The occurrence of complementary apomixis-recombinants suggests that parthenogenesis and autonomous endosperm development in Taraxacum are regulated independently by different genes. This study also indicates that early embryo development is independent of endosperm formation, but that endosperm is essential for later embryo growth.     

Investigations on Growth and Metabolism of Plant Cells: IV. Evidence on the Role of the Coconut-Milk Factor in Development

By the carrot-assay method it has been shown that the wateryendosperm of coconut contains the growth-promoting coconut-milkfactor at all stages of development. Some activity is shownby the parts of the immature embryo but not by the solid endosperm. Sources of analogous activity are in the endosperm of Zea maysin the milk stage, the gelatinous content of immature fruitsof Fuglans regia, and the young gametophyte of Ginkgo biloba.The data for other cases examined suggest that the materialdevelops best in nutritive tissues associated with delayed embryodevelopment.     

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     

Ageing in Triticum durum Seeds: Behaviour of Embryos and Endosperms from Aged Seeds as Revealed by the Embryo-transplantation Technique

The embryo-transplantation technique has been used to studythe behaviour of Triticum embryos and endosperm during the courseof ageing of 1-, 2-, 3-, 4-, and 5-year-old seeds. The resultsshow that the ageing process in Triticum seeds is a progressivephenomenon. It affects both embryo and endosperm as shown by(a) the behaviour of old embryos transplanted on young endosperms,and (b) the deleterious effects of aged endosperms on youngembryos.     

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     

Early Reproductive Ontogeny in Interspecific Crosses of Arachis hypogaea and Section Arachis Species

Wild Arachis species have been recognized as sources of resistanceto pests and pathogens that infect A. hypogaea L. and causesubstantial yield losses. However, utilization of these geneticresources for crop improvement has been difficult. This studywas conducted to (a) understand the processes of early embryogrowth and development in four Arachis species, two A. hypogaeacultivars and their hybrids and (b) identify parental compatibilitiesin reciprocal crosses of A. hypogaea. The results indicatedthat delayed fertilization beyond 24 h, coupled with slow proembryogrowth, leads to embryo abortion in many interspecific crosses.For example, in female A. cardenasii crosses, lack of or delayedfertilization leads to failure to obtain hybrids. When A. batizocoiwas used as a female parent, delayed fertilization and the inabilityof quiescent proembryos to resume growth after soil penetrationcaused abortion. Embryos of A. hypogaea x A. glandulifera crossesdeveloped normally during the first 21 d after fertilization,but then aborted at a later time. In this study, A. hypogaeawas always a better female parent than the wild Arachis species.Increasing the number of pollinations per cross, using the cultivatedspecies as the female parent, utilizing different A. hypogaeavarieties, and embryo rescue techniques are suggested to improvethe probability of obtaining interspecific hybrids in Arachis.Copyright1995, 1999 Academic Press Peanut, interspecific hybrids, Arachis, wild species, incompatibilities     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

The Initiation of Hybrid Vigour in Zea mays during the Germination Phase

The course of development during germination in the dark at21^{diaeresis} was followed for five hybrids of Zea mays andtheir immediate parents of flint or dent type by dissectingand weighing daily the endosperm, scutellum and embryo, whichincluded the radicle, plumule, coleoptile and coleorrhiza. Overall triplets there were detectable losses in scutellum weightby the third day from water imbibition, but already the embryoswere gaining weight, the rate being fastest for the hybrid suchthat by the sixth day the mean embryo of the hybrid was some40 per cent larger. The expansion of the radicle and the initial development ofthe root system was again greater in the hybrid where the advantagewas in the rate of cell division rather than the number of meristematiccells. Employing solution culture procedures and greenhouse conditionsthe effects of excising the endosperm on the second day werefollowed. By the ninth day the hybrid plants, irrespective ofendosperm removal, weighed more than those of their parents.By the time the shoot of the hybrid was becoming photosyntheticallyactive, differences in favour of the hybrid were much largerfor plants without endosperm. Treating the grains with varying concentrations of gibberellin(GA_s, kinetin, kaurene (a possible precursor for gibberellinsynthesis) and two inhibitors of gibberellin synthesis (CCCand AMO-1618) showed no consistent preferential effects on thegrowth of the embryo within a triplet. It is concluded that hybrid vigour is initiated by the greaterpotential of the hybrid for embryo development and a more effectiveutilization of reserve materials. Once the shoot emergesandbecomes photosynthetically active the better performance ofthe hybrid is primarily dependent on increases in the net assimilationrate or leaf area ratio.     

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.     

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     

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     

GROWTH, DEVELOPMENT AND RESPIRATION IN THE OVULES OF ZEPHYRANTHES LANCASTERI AT DIFFERENT STAGES OF MATURATION

Changes in the rate of respiration and activity of succinicdehydrogenase in the ovules, embryo and endosperm have beeninvestigated at different stages of seed development in Z. lancasteri.An attempt has been made to find any possible relation betweenphysiological changes and the growth pattern of ovule. The fertilizedovules mature into seeds in 16–19 days from the time ofpollination. The respiratory course and the growth of ovulesfollow identical trends. The curve for oxygen uptake is characterizedby at least two peaks; the first on the sixth or seventh dayis related to the laying down of walls in the coenocytic micropylarchamber of the endosperm and the second on the 11th day precedesthe elongation of cotyledon. In excised endosperm the activityof succinic dehydrogenase is highest during its transformationfrom freenuclear to cellular state, while in the embryo it isso after the attainment of mature size. ¹Present address: AEC Plant Research Laboratory, Michigan StateUniversity, East Lansing, Mich., U.S.A.     

Ontogeny, Structure and Breakdown of Protein Bodies in Linum usitatissimum Linn.

In Linum usitatissimum protein bodies are observed in the cellsof endosperm and embryo. They originate in vacuoles. Proteinbodies have both crystalloid and globoid inclusions. The breakdownoccurs by vacuolization and fragmentation. Linum usitatissimum, seed, embryo, endosperm, protein bodies     

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     

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.     

A Flower and Pod Staging System for Soybean

Flower and pod abscission limit soybean yield. A system forquantifying flower and pod development based on the morphologicalappearance of the flower prior to and following anthesis hasbeen developed to aid in studies of pod abscission. Changesin the appearance of the corolla, primarily the banner petal,are used to distinguish the different stages of the system.External pistil dimensions have been correlated with internalfeatures for each stage of development. From anthesis to podset, pistil length and weight increase almost two- and fivefold,respectively, and ovule development progresses from unfertilizedegg cells to embryos surrounded by cellular endosperm. Pod determinedare correlated with ovule length and width and embryo cell number.Flower and pod stages can be determined in situ, thus permittingnon-destructive observation and experimental manipulation offlowers or pods without necessarily impeding their development.Stages have been identified that indicate precisely when podset occurs and when young pods cease growing and ultimatelyabscise. This system of flower and pod staging is useful instudies designed to assess effects of abiotic or biotic stressand genetic factors on pod set and abortion. Abscission, anthesis, Glycine max (L.) Merr, embryo development, pod set     

Development of the Almond Nut (Prunus dulcis (Mill.) D. A. Webb). Anatomy and Chemical Composition of Fruit Parts from Anthesis to Maturity

The growth of the fruit of two varieties of almond (Prunus dulcis(Mill.) D. A. Webb) was studid from anthesis (week 0) to maturity(week 32). The dimensions, fresh weight, moisture content, anatomyand chemical composition of the pericarp, testa, embryo, endospermand nucellus are recorded diagrarnmatically, graphically andby micrographs for one variety. Of the two ovules present atflowering only one normally developed further. By 12 weeks afterflowering the whole fruit had reached full size. The space encloscdby the pericarp was filled by nuallus until weck 10, with subsequentenlargement of both endosperm and embryo. From week 16 to week20 the embryo increased to full size with a concumnt decreasein the size of the endosperm. Sixteen weeks after flowering,the embryo began to accumulate protein and lipid, little ofwhich originated from either the nucellus or endosperm. Theembryo contained no starch or reducing sugar but up to 3% sucrosein the early stags which dtcreascd as lipid and protein increased.Starch and sucrose levels were high in the testa at week 16but subsbquently dropped, starch more rapidly than sucrose.The role of the testa in transport of metabolites to the embryois discussed. Prunus dulcis, almond, fruit development, anatomy, embryo, endosperm     

Comparative cyto-embryological investigations of sexual and apomictic dandelions (Taraxacum) and their apomictic hybrids

. In the autonomous apomictic Taraxacum officinale (common dandelion), parthenogenetic egg cells develop into embryos and central cells into endosperm without prior fertilisation. Unreduced (2n) megaspores are formed via meiotic diplospory, a nonreductional type of meiosis. In this paper, we describe the normal developmental pathways of sexual and apomictic reproduction and compare these with the development observed in the apomictic hybrids. In sexual diploids, a standard type of megasporogenesis and embryo sac development is synchronised between florets in individual capitula. In contrast, we observed that megasporogenesis and gametogenesis proceeded asynchronously between florets within a single capitulum of natural triploid apomicts. In addition, autonomous endosperm and embryo development initiated independently within individual florets. Parthenogenetic initiation of embryo development in outdoor apomicts was found to be temperature-dependent. Egg cells produced in natural apomicts were not fertilised after pollination with haploid pollen grains although pollen tubes were observed to grow into their embryo sacs. Both reductional and diplosporous megasporogenesis were observed in individual inflorescences of triploid apomictic hybrids. Embryo and endosperm development initiated independently in natural and hybrid apomicts.