Studies on Nucleic Acid and Protein Synthesis and D evelopment of Male Gametnphyte of Clivia nobilis Cultured in Vitro

A simple method for culture male gametophyte (MG) of Clivia nobilis in vitro was established and the process of their development was observed. After research on dynamic of nucleic acid and protein synthesis of MG in various developmental stages by using of inhibitors and autoradiography authors found that DNA synthesis fro mrelease of tetrad to sperm only takes place in nucleus of interphase. There is no 3H-tymidine incorporation into vegetative nucleus (Vn), generative nucleus (Gn) or nucleus of sperm in 96 hours before dehiscence of anthers (BDA). The dynamic of protein synthesis is similar to the same of RNA’s. Both of them have three peaks and two intermissions. The 1st peak is in 12–9 days BDA. The 2nd is in 7–5 days BDA and intermitted from 48 hours BDA. The 3rd begins from the 1st hour after culture (AC) decleases at 6th hour AC and stops before 20th hour AC. The kind of inhibitor, the time and quanlity of treatment are affected the morphogenesis, showing the relationship to synthesis among DNA, RNA and protein and to the same between biomacromolecular and morphological development of MG.     

Ultrastructure of Male Gametophyte in wheat I. The Formation of Generative and Vegetative Cells

The present study of the formation of the generative and vegetative cells in wheat has demonstrated some cytological details at the ultrastructural level. The phragmoplast formed in telophase of the first microsporic mitosis extended centrifugally until it connected with the intine of the pollen grain. A new cell wall was then formed to separate the generative and the vegetative cells. By unequal cytokinesis the former is small and the latter large. In early developmental stage of male gametophyte, the organelles in the cytoplasm of the generaVive cell and the vegetative cells are similar, including mitochondria, dictyosomes, rough endoplasmic retieulum, free and clustered ribosomes and plastids, but microtubules were observed only in the early cytokinesis stage. In the further developmental stage of the male gemetophyte, the generative cell gradually detached from the intine of pollen grain and grew inward to the cytoplasm of the vegetation cell. When the generative cell became round and free in the cytoplasm of the vegetative cell, the wall materials between plasma membranes of the cytoplasm of the generative and the vegetative cells disappeared completely, so that it was a naked cell with a double-layer membrane at this time. The heterogeneity between both cells was then very conspiceous. The organelles in the cytoplasm of the generative cell have hardly any changed besides the degeneration of plastids, but in vegetative cytoplasm the mitochondria and plastids increased dramatically both in number and size. The rapid deposition of starch in the plastids of the cytoplasm of the vegetative cell made the most conspicuous feature of the vegetative cell in mature pollen grain. The significance of the presence of a temporary cell wall in generative cell and heterogeneity between generative and vegetative cells are discussed.     

Association of the Generative Cell and Vegetative Nucleus in Pollen Tubes of Rhododendron

Mixed fluorescence/bright field microscopy of Rhododendron pollentubes in the first 72 h after germination reveals a lens-shapedgenerative cell which divides to give two associated spermswithin the original cell boundary. The generative cell is closelyassociated with the vegetative nucleus which precedes it in92 per cent of pollen tubes. Three-dimensional reconstruction from serial thin sections ofa pollen tube fixed 24 h after germination shows that the associationbetween the generative cell and vegetative nucleus is extremelycomplex. Elongated tails of the generative cell physically enfoldthe vegetative nucleus and penetrate into enclaves within it.The association has been clarified by use of the periodic acid-phosphotungsticacid-chromic acid technique to enhance electron contrast ofthe plasma membranes surrounding the generative cell. In thisbicellular system, the male germ unit association is apparentlyinitiated after pollen maturity but prior to generative celldivision. Pollen tube, generative cell, male germ unit, plasma membrane, vegetative nucleus, Rhododendron, Ericaceae     

Histochemical Observations on the Distribution of Adenosine Triphosphatase in Phloem and Motor Organs in Higher Plants

In a previous communication (Kuo 1964), it was shown by histochemical means that the phloem of cucurbit, as compared with the ground parenchyma, is particularly rich in adenosine triphosphatase (ATPase). A concurrent research by Yen et al. (1965) has succeeded in actually extracting from the vascular bundle of tobacco a crude protein fraction which not only possesses high ATPase activity, but also exhibits viscosity changes on addition of ATP or AMP. Such properties have been known to be characteristic of the contractile proteins constituting the muscle in animals. Although little is known about the actual role played in food transport by the living tissues in phloem, evidence has been accumulating that the active participation of the protoplasm in the phloem is necessary to facilitate sap movement. All these results have tempted us to think that higher plants, just like animals, also derive the energy required for performing mechanical work directly from ATP through the mediation of the contractile protein which is the ATPase itself. Accordingly, the present investigation is engaged in further histochemical observations to locate more precisely ATPase in the sieve element and to map out the distribution of the enzyme in various motor organs of higher plants, with the purpose in mind to see whether the map of enzyme distribution in the tissue has anything to do with its peculiar way of movement. 1. Presence of ATPase in the slime body of the functioning sieve element. In the functioning sieve element, high ATPase activity is displayed at the slime body and the connecting strands traversing the pores of the sieve plate (Plate Ⅰ, figs. 2, 3 & 4). However, as the pores of the sieve plate are partially blocked by the callose, the enzyme reaction becomes lessened. If the plate is completely covered by the callose pad, none could be detected. Since the slime body has been claimed by many workers to be pro- teinaceous in nature (cf. Esau 1950), there should be no surprise that it also possesses enzyme activity and contractile action. This seems to indicate that the slime body and the connecting strands are not mere hindrance to the sap flow but may actively participate in propelling the translocation stream. The fact that the intense ATPase reaction is given in the companion cell (Plate I, figs. 1 & 3) is in conformity with the common notion that the cell is actively involved in the normal functioning of phloem. 2. Enzyme distribution in various motor organs of different sensitivity. The ATPase content in the various motor organs (pulvinus, stamen, tendril, etc.) of different sensitivity has been compared histochemically, ranging from. 1) the highly sensitive organs; e.g. the pulvinus of Mimosa pudica (Plate Ⅱ, fig. 5) and of Oxalis piota (Plate Ⅱ, fig. 6), the stamen of Berberis Watsonae (Plate Ⅲ, fig. 10), the young tendril of Cucurbita maxima Duchesne and Vitis vinifera (Plate Ⅲ, figs. 11 & 12); 2) the moderately sensitive organs; e.g. the pulvinus of Sesbania cannabina (Plate Ⅱ, fig. 8); 3) the feebly sensitive or insensitive organs, e.g. the pulvinus of Robinia pseudoacacia (Plate Ⅱ, fig. 7), the stamen of Brassica campestris var. oleifera (Plate Ⅲ, fig. 9). From the results, it can be seen that the higher the sensitivity of the organ, the greater its enzyme activity. In addition to the morphological assymetry which is typical of plant motor organs, there also exists a physiological gradient, as evidenced by the uneven distribution of ATPase, usually being more intense on the more irritable side. The claim made recently by Aimi (1963) and others that the sudden collapse of the pulvinus of Mimosa on stimulation is not a direct result of the loss of turgidity as is generally assumed, but an immediate manifestation of the active vacuolar contraction in the motor cells is supported by the high ATPase content in the motor cells in our investigation.     

Ultrastructure of Male Gametophyte in Wheat II. Formation and Development of Sperm Cell

Ultrastructural events in wheat sperm cell development were examined from the division of generative cell stage to the maturation of sperm cell in pollen grains. The results are smnmarized as follows: 1. The generative cell in forming microspore by mitosis goes through a series of changes including tile displacement and transformation. It finally becomes a spindle-shaped cell getting ready for another mitosis. The generative cell at this stage is naked. it is only surrounded by both membranes of its own and vegetative cell Most part of the generative cell is occupied by the conspicuous elliptical nucleus with highly condensed chromatin. With the exception of ribosomes, the organelles in the thin layer of generativc cell cytoplasm are obviously fewer and smaller than those in the vegetative cytoplasm. The mierotubules may also be seen in the cytoplasm of spindle-shaped generative cell parallel to the long axis of the cell. There is no amyloplast in generative cell. 2. When the generative cell has moved to the position close to the vegetative nucleus again, it begins to divide. The formation of sperm cells as the result of mitosis of generative cell, and the development of sperm cell involves the following main changes. The shape of the sperm cell tranforms from spherical to elliptical, finally it forms an elongated cell with a tail-like structure. At the sametime, the distribution of cytoplasm gradually concentrated at one end of the sperm cell to form the cytoplasmic extension, so that the so called "tail" of the sperm cell is formed. There are more organelles, especially the mitochondria, assembling in this part. The sperm cell just formed after mitosis is naked and the enclosed plasma membrane is discontinuous. The sperm cell membrane is enclosed by vegetative cell membrane, and the double membranes may be completed at a later stage. It is considered that the period which follows is very short, the deposition of wall material, the callose, occurs to fill up continuously the space between two membranes, but soon after this period the cell wall becomes discontinuous and the wall material is obviously decreased. The significance of the position of the generative cell before its mitosis and the morphological changes during the development of the sperm cell are discussed in this paper.     

The Comportment of the Vegetative Nucleus and Generative Cell in the Pollen and Pollen Tubes of Helleborus foetidus L

It has been reported that in species of Plumbaginaceae, Chenopodiaceae,Cruciferae and Amaryllidaceae a ‘male germ unit’is formed in which the two male gametes remain inter-connected,with one of the pair linked intimately to the vegetative nucleus.In two species the unit has been shown to remain intact in thepollen tube, and some accounts imply that it is polarized inits movement, the vegetative nucleus leading in the tube. Evidence given in this paper indicates that such a unit is unlikelyto be present in Helleborus foetidus L. (Ranunculaceae). Applicationof an optical sectioning technique has shown that at no timeis there a persistent linkage between the generative cell andthe vegetative nucleus in unhydrated, hydrated and germinatingpollen, nor is one present in the early pollen tube. Furthermore,no inter-connections between the two entities were seen in protoplastsfrom living, hydrated and incipiently germinating grains isolatedmechanically in an osmotically balancing medium. Following germination,the vegetative nucleus leaves the grain in advance of the generativecell in most instances, but in the samples examined the generativecell led in about 30 per cent of the tubes. Assembling a polarisedmale germ unit in these circumstances would require (a) theformation of an inter-connection between the vegetative nucleusand the generative cell or one of the gametes derived from itduring passage through the tube, and (b) where the generativecell initially leads in the tube, an exchange in relative positions.It is considered improbable that these conditions could consistentlybe met. Mature, incipiently germinating pollen of H. foetidus releasesa fibrillar component when extruded into suitable media. Websor clusters of fibrils are commonly seen to be associated withboth the vegetative nucleus and the generative cell. The possibilitythat the fibrils are composed of aggregates of microfilamentsis considered. Helleborus foetidus L., pollen germination, generative cell, vegetative nucleus, male germ unit     

Cytochemical Observations on Proteins,Alkaline and Acid Phosphatases,Adenosine Triphosphatase,and 5′-Nucleotidase in Chick Liver Cell Cultures Infected with Trichomonas vaginalis*, †

SYNOPSIS. By means of the ninhydrin-Schiff method for proteins a diffuse reaction as well as one localized in granular inclusions can be shown in the cytoplasm of fibroblasts, epithelial cells, and macrophages in trypsin-dispersed chick liver cell cultures. Nuclei and nucleoli also take the specific stain. A progressive loss of cytoplasmic and nuclear staining occurs in the fibroblasts in cultures infected with a relatively pathogenic strain of T. vaginalis. A loss occurs in epithelial cells in advanced stages of degeneration, but in less damaged cells, while the diffuse reaction disappears, the number and staining intensity of the cytoplasmic inclusions remain unchanged or possibly may increase somewhat. The intensity of the diffuse reaction and the number and size of the characteristic inclusions increase in the active, parasite-free, experimental macrophages, but phagocytes with trichomonads closely applied to their external surfaces and those containing the flagellates within their cytoplasm typically retain only a few weak-staining inclusions. Similar distribution of alkaline and acid phosphatases occurs in preparations treated according to Gomori's and Burstone's methods, except that no nuclear staining is obtained with the latter. Activity of both enzymes is localized primarily in inclusions which are dispersed thruout the cytoplasm of fibroblasts and epithelial cells and tend to accumulate along the cell membranes and around the nuclei. In the course of infection with T. vaginalis there is a progressive loss of alkaline phosphatase from both cell types; however, the acid phosphatase activity increases. In the control macrophages both enzymes are localized in mostly rather large, rounded cytoplasmic inclusions. The number of such inclusions increases in the parasite-free experimental macrophages, but only a few weak-staining granules remainin phagocytes with engulfed trichomonads and in those whose external surfaces are in direct contact with the parasites. The loss of the inclusions is less apparent in macrophages containing degenerated flagellates than in the ones with healthy trichomonads, but regardless of the condition of the parasites, the highest enzymatic activity is found around them. ATPase and 5′-nucleotidase are localized in small granules dispersed thruout the cytoplasm of fibroblasts and epithelial cells. The granules tend to accumulate along the periphery of the cells and around the nuclei. A diffuse cytoplasmic reaction is present in preparations processed for 5′-nucleotidase. Nuclei and nucleoli give positive reactions for both enzymes. In the course of infection with trichomonads, activity of the 2 enzymes declines in both culture cell types. Control macrophages have diffuse cytoplasmic reaction for ATPase and 5′-nucleotidase and these enzymes are localized also in rounded cytoplasmic inclusions. Activity of both enzymes increases in the parasite-free experimental phagocytes, but little if any diffuse staining and only a few characteristic inclusions are left in macrophages with engulfed healthy trichomonads and in those whose external surfaces are invested with the flagellates. The ninhydrin-Schiff-positive inclusions found in the macrophages appear to be the same as some of those which have acid phosphatase activity and may well be identical with the glycolipoprotein bodies noted by us previously. On the grounds of their chemical constitution and behavior it seems likely that the inclusions are lysosomes.     

A Cytochemical Study of DNA, RNA, and Protein in the Developing Maize Anther: II. Observations

Changes in acetic-alcohol fixable DNA, RNA, and protein werefollowed in the tapetum, sporogenous tissue, and spores of thedeveloping maize anther using standard cytochemical methodsand microdensitometry. In the tapetum, early nuclear divisionsoccur without prior DNA synthesis, giving a population of IC nuclei. Subsequent synthesis produces the equivalent of 34,000C amounts per pollen sac, 20 times more than is present in thespores before pollen mitosis. The main tapetal RNA synthesisis during the meiotic prophase, with a further period of accumulationin the interval, tetrad to young spores. In the meiocytes, theprincipal accumulation is in the early prophase, with no synthesisduring the meiotic divisions or through the tetrad period. Proteinaccumulation occurs in the tapetum up to mid-meiotic prophase;after this there is a pause, followed by further synthesis frommeiotic metaphase I to the final dissolution of the tissue.In the meiocytes, protein is accumulated through the early prophase;there is no synthesis during the meiotic mitoses or in the tetradperiod, but active accumula-tion occurs in the developing spores. The implications of these observations are discussed in relationto the function of the tapetum.     

羽衣甘蓝花粉母细胞减数分裂及雄配子体发育观察

采用常规压片法对羽衣甘蓝花粉母细胞减数分裂及雄配子体发育进行了细胞学观察,结果显示:羽衣甘蓝减数分裂类似甘蓝种,细胞质分裂为同时型,四分体以正四面体型或十字交叉型为主;终变期有9个二价体,此时可进行染色体计数;中期Ⅰ和Ⅱ少数细胞中可见赤道板外染色体,后期Ⅰ和Ⅱ存在落后染色体,四分体时期可观察到少量含微核的异常四分体;单核靠边期时花蕾长度约为2.0~2.2 mm,小孢子经过发育最终成为3-细胞型花粉并具3个萌发孔,成熟花粉中败育花粉比率为1.3%.     

Some Observations on the Characteristics and Distribution of Adenosine Triphosphatases in Young Roots of Pisum sativum, Cultivar Alaska

A study has been made of some characteristics of ATPases fromyoung pea roots and these enzymes have been shown to differfrom ß glycerophosphatases in several respects. DEAEchromotography and gel electrophoresis have confirmed the existenceof a number of different phosphatases with differing affinitiesfor ATP and sodium ß glycerophosphate. At least twoATP-specific phosphatases have been detected and these accountfor about 57 per cent of the total ATPase activity in pea roots. The distribution of ATPase activity along the axis of the roothas been determined by biochemical assay of serial sectionsand by histochemical methods. It is shown that ATPase activityhas a quite different distribution from ß glycero-phosphataseactivity, thus confirming the separate identity of the two enzymesystems. The distribution of ATPases is discussed in relation to theirpossible role in ion transport.     

Observations on the Fine Structure of Plant Cell Walls II. The Microfibrillar Framework of the Parenchymatous Cell Wall in Cucurbita

The microfibrillar framework of parenchymatous walls in Cucurbitawas observed in petioles treated so as to remove various non-cellulosiccell wall components. Such extraction typically results in separationof the microfibrillar components into concentric lamellae. Thenumber and thickness of these lamellae vary according to theage and type of cell wall. The microfibrils appear to be orientatedwithin the plane of their lamellae but the orientation may varyin successive lamellae, and in many walls the crossed polylamellatecondition was detected. The collenchyma—and the outerepidermal cell walls show an alternation of lamellae with almostvertical microfibrils with those with a practically transverseorientation. In ordinary parenchymatous walls the alternationis not so extreme and is revealed only by the occasional presenceof the ‘herring bone pattern’ in non-radial sections.As a rule the lamellae are continuous around the circumferenceof a cell though individual lamellae may vary in thickness andsometimes appear to ‘fade out’. The present observationssuggest that growth of the primary wall occurs by depositionof microfibrils in successive lamellae thus confirming the basicpremise of the multinet theory of growth.     

Induced Resistance to 6-Methylpurine and Cycloheximide in Tetrahymena. II. Variation within Vegetative Cultures of Micronucleate T. THERMOPHILA and Amicronucleate T. PYRIFORMIS

Resistance to 6-methylpurine and cycloheximide has been induced in both the micronucleate species Tetrahymena thermophila and the amicronucleate species T. pyriformis. Resistance follows only after mutagen treatment and vegetative growth. The frequencies with which resistant variants are induced and the independence of mutagenesis and selection are demonstrated. All evidence is consistent with the hypothesis that macronuclear subunits are assorting in both species during vegetative growth to produce new phenotypes among subclones.     

Some Observations on the Taxonomy of the Genus Microbacterium. II. Cell Wall Analysis, Gel Electrophoresis and Serology

S ummary . The chemical composition of the cell wall mucopeptide, the esterases and catalases of the cell free extracts, and the serology of the 25 species of microbacteria whose morphological and cultural characteristics had been investigated previously, were examined. Suggestions are made about the relationships of the species within the genus Microbacterium and with other genera.     

Growth and Differentiation of Plant Tissue Cultures: II. Synchronous Cell Divisions in Developing Callus Cultures

Explants isolated from Jerusalem Artichoke tubers are stimulatedto divide when placed in contact with a nutrient medium containingsucrose, mineral salts, coconut milk, and 2: 4-dichlorophenoxyaceticacid. The first two or three cell divisions, which only occurin the outer layers of the explant, do not occur uniformly withtime but are, at least, partially synchronous. This synchrony,which decreases with successive divisions, is inherent. DNAsynthesis, which is an essential prerequisite for division inthese cells, is also partially synchronous. These conclusions,while being of some significance in relation to the interpretationof the early development of the callus, are also of some interestin relation to the possible exploitation of this system forthe study of cell division.     

Polyamines and Flower Development in the Male Sterile Stamenless-2 Mutant of Tomato (Lycopersicon esculentum Mill.) : II. Effects of Polyamines and Their Biosynthetic Inhibitors on the Development of Normal and Mutant Floral Buds Cultured in Vitro

The floral organs of the male sterile stamenless-2 (sl-2/sl-2) mutant of tomato (Lycopersicon esculentum Mill.) contain significantly higher level of polyamines than those of the normal (R Rastogi, VK Sawhney [1990] Plant Physiol 93: 439-445). The effects of putrescine, spermidine and spermine, and three different inhibitors of polyamine biosynthesis on the in vitro development of floral buds of the normal and sl-2/sl-2 mutant were studied. The polyamines were inhibitory to the in vitro growth and development of both the normal and mutant floral buds and they induced abnormal stamen development in normal flowers. The inhibitors of polyamine biosynthesis also inhibited the growth and development of floral organs of the two genotypes, but the normal flowers showed greater sensitivity than the mutant. The inhibitors also promoted the formation of normal-looking pollen in stamens of some mutant flowers. The effect of the inhibitors on polyamine levels was not determined. The polyamine-induced abnormal stamen development in the normal, and the inhibitor-induced production of normal-looking pollen in mutant flowers support the suggestion that the elevated polyamine levels contribute to abnormal stamen development in the sl-2/sl-2 mutant of tomato.     

Circannual Variation of Cell Proliferation in Lymphoid Organs and Bone Marrow of Dbf1 Male Mice on Three Lighting Regimens

The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artifical light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.     

The Biology of Gregarina fernandoi n. sp. in the Cockroach Pysnoscelus surinamensis with Observations on its Development and Cytochemical Nature

SYNOPSIS. Gregarina fernandoi n. sp. is a eugregarine. Its structure, development and life history in the gut of the cockroach Pycnoscelus surinamensis are described. It is named as a new species on the basis of its size, nuclear structure, structure and form of the gametocyst and oocyst. Observations were made on the different stages of the parasite and related to the pH of the gut. In the ceca, pH 4.5–5, the parasite was in its early stages of development, in the midgut, pH 6.5–7, it was in syzygy and in the rectum, pH 7.5–8, gametocysts were found.     

Interactions between the Nucleus and Cytoplasmic Organelles during the Cell Cycle of Euglena gracilis in Synchronized Cultures: II. Associations between the Nucleus and Chloroplasts at an Early Stage of the Cell Cycle under Photoautotrophic Conditions

Chloroplast-nucleus interactions were examined in cells of Euglenagracilis Z synchronized under photoautotrophic conditions. Thechloroplasts were localized near the cell periphery. At an earlystage of the cell cycle, however, some chloroplasts were transientlylocated in the inner space close to the nucleus. Electron microscopyusing serial cell sections revealed that the chloroplast formedprotrusions at several sites, which became associated with thenucleus. The outer membrane of the chloroplast envelope wasin contact, or at least continuous in part, with the outer membraneof the nuclear envelope at the sites of association, and densematerial was present in the chloroplast membrane. A chromosomewas close to each site of the association between these twoorganelles. Most of the chloroplasts including those in associationwith the nucleus were connected by fine bridges. The 4',6-diamidino-2-phenylindole-stainednucleoids in the chloroplast associated with the nucleus appearedto have a thread-like shape. There was another type of chloroplast-nucleusconnection, in which an intervening membranous body was in contactwith the outer part of the nuclear envelope on one side andwith the chloroplast envelope on the other side. ¹ This work was reported at the 48th Annual Meeting of the BotanicalSociety of Japan, Kyoto, October, 1983. (Received June 5, 1984; Accepted November 20, 1984)     

Genetic Linkage in the Horse. II. Distribution of Male Recombination Estimates and the Influence of Age, Breed and Sex on Recombination Frequency

In the present study an extensive amount of data, comprising more than 30,000 offspring in total, was analyzed to evaluate the influence of age and sex on the recombination frequency in the K-PGD segment of the equine linkage group (LG) I and the influence of age, breed and sex on recombination in the Al-Es segment of LG II. A highly significant sex difference is reported for both segments. Male and female recombination values in the K-PGD segment were estimated at 25.8 ± 0.8 and 33.3 ± 2.5%, respectively. Similarly, recombination was less frequent in the male (36.6 ± 0.7%) than in the female (46.6 ± 1.2%) in the Al-Es segment. Comparison of data from two Swedish horse breeds revealed no significant breed differences in either sex for recombination in the Al-Es segment. No evidence of an age effect was found in any segment or sex. The distribution of individual male recombination estimates was also investigated, and a significant heterogeneity among stallions was revealed in the K-PGD segment. The results are discussed in relation to previous studies on factors affecting recombination in mammals.