Abortive Seeds Research Articles

Spatial and Temporal Expression of Cold-responsive DEAD-box RNA Helicases Reveals their Functional Roles During Embryogenesis in Arabidopsis thaliana

DEAD-box RNA helicases compose a large subfamily of RNA helicases found in all eukaryotes and prokaryotes. Functional DEAD-box RNA helicases are considered to be RNA chaperones that modify RNA secondary structure and perhaps three-dimensional structures during different cellular processes involving RNA metabolism. Although a relationship of DEAD-box RNA helicases to abiotic stress adaptation is known, few reports document the involvement of RNA helicases during plant growth and development. In this study, detailed analyses were performed for two cold-responsive DEAD-box RNA helicases, AtRH22 and AtRH52, on the transcript level during different developmental stages of Arabidopsis thaliana. Expression levels of AtRH22 and AtRH52 were up-regulated markedly in response to cold stress and were enriched in shoot apical meristems, floral buds, and siliques. The expression of AtRH22 and AtRH52 was spatiotemporally regulated during vegetative growth, floral transition and embryonic development. To investigate, the functional role of AtRH22 and AtRH52 in A. thaliana, we functionally characterized independent T-DNA insertion mutant lines for both genes. Genotypic analysis of self-fertilized heterozygous lines revealed only heterozygous (WT/T-DNA) and homozygous wild-type progeny for AtRH22 and AtRH52. Self-fertilized heterozygous mutants of AtRH22 and AtRH52 show normal vegetative phenotype, but produced normal-sized and abortive seeds. Collectively, these results demonstrate that the cold-responsive AtRH22 and AtRH52 genes are spatiotemporally regulated during plant development and are essential during Arabidopsis embryogenesis.

English

  Studies were conducted to assess the response of cowpea (Vigna unguiculata L. Walp) to some physical and chemical characteristics of soil in coastal region (Cameroon). The cowpea variety used in this trial was Tsacre, planted at a spacing of 80 cm × 80 cm. The experimental design was a randomized complete block comprising of five plots with three replicates. Productivity parameters (dry weight aerial parts, roots dry weight, abortion seeds rate, number of flowering per plant, flowering rate) and yield components (number of seeds per pod, number of pod per plant, grain yield, pod yield and weight of 1000 seeds) were determined. Soil samples were taken randomly from depths of 0 - 30 and 30 - 60 cm before seeds sowing. The results showed that the plot with the highest percentage of sand (71.80%), the lowest percentage of clay (21.00%) and silt (7.20%) and with the highest amount of organic matter (10.26%), exchange potassium (0.36 g Kg-1), calcium (0.49 g Kg-1) and magnesium (0.46 g Kg-1) increased significantly (P<0.05) the dry weight aerial parts from 4291 to 7051 mg, the roots dry weight from 293 to 454 mg, the number of flowering per plant from 8.10 to 28.82 and the flowering rate from 47.75 to 93.33%. Similar results were obtained with yield components where the number of pod per plant increased from 5.90 to 16.12, the grain yield from 729.70 to 2381 Kg ha-1, the pod yield from 1251.21 to 1679.21 Kg ha-1 and the weight of 1000 seeds from 81.70 to 145g. Results from this investigation showed that soil properties could influence cowpea growth, productivity and yield under Cameroon coastal growing conditions.   Key words: Cowpea, chemical composition, particle size distribution, productivity, yield

Seed and endocarp traits as markers of the biodiversity of regional sources of germplasm of tejocote ( Crataegus spp.) from Central and Southern Mexico

The genus Crateagus (Rosaceae: Maloideae), is distributed all around the world, but only in the Northern Hemisphere. In Mexico there is a considerable biodiversity with around 15 species, most of them authoctonous and it is called tejocote, a multi-purpose tree with economic importance. However the taxonomy of the Crategus species from Central and Southern Mexico still remains unclear. The gemplasm bank of tejocote of the Universidad Autónoma Chapingo (UACh) (State of Mexico) contains almost 100 accessions of Crataegus from Central and Southern Mexico. Based on previous studies that demonstrated that seeds and inner parts of the fruits are useful for germplasm characterization, the general objective was to investigate the usefulness of seeds and endocarps for the characterization of tejocote genetic pools, using 86 accessions from the tejocote germplasm bank of the UACh, with the specific objectives being: (i) to select from 37 morphological and morphometrical variables, the most informative for the assessment of the biodiversity; (ii) to contribute to the elucidation of the variability of the tejocote genetic pools from Central and Southern Mexico. The traits related with the size and shape of the endocarp, seed and seed cavity, plus the presence or absence of normal vs. abortive seeds, and the number of endocarps per fruit, were the characters that accounted for more variability and in conclusion the most adequate for the characterization of tejocote and some of them have been adopted for the official Crataegus descriptors. The present work confirms prior results with the same germplasm and other characters which postulated that the source from Chiapas is different from the rest of the sources and also that the sources from the State of Mexico and Puebla were not significantly different genetic pools. The accessions from the Chiapas source showed smaller endocarps and seed cavity, lower percentage of endocarps with normal seeds, higher percentage of endocarps without seed, and higher number of endocarps per fruit.

OsAP2-1, an AP2-like gene from Oryza sativa, is required for flower development and male fertility

Arabidopsis AP2 (AtAP2) is a member of AP2 subfamily of the AP2/EREBP class of transcriptional factors and plays crucial roles in regulating floral meristem determinacy, floral organ identity and ovule and seed development. In order to examine functional conservation and diversification of AP2 genes in monocots, here we analyze a rice AtAP2-like gene, OsAP2-1. This gene was expressed at high levels in both flowers and roots, and at faint levels in buds or leaves. Its transcript was also present in mature pollen grains. The OsAP2-1 down-regulated lines mediated by RNA interference showed obvious alternation in floral organs of innermost two whorls, including the reduced stamens, fused anther filaments and increased number of pistils. Abortive seeds were observed in the down-regulated lines. These results suggest that OsAP2-1 is required for flower and seed development, consistent with the roles of AtAP2 in Arabidopsis. Furthermore, our results demonstrated that the down-regulation of the endogenous transcripts led to decreased pollen viability and germination activity, suggesting that OsAP2-1 has roles in controlling pollen development.

Gamma-rays Induced Reciprocal Translocation in Black Cumin(Nigella sativa L.).

Gamma irradiations (5, 10, 20 kR) to Nigella sativa L. (black cumin) seeds (moisture content 7.5%) induced 5 translocation heterozygotes (P-14 and P-26 from 5 kR and P-32, P-36 and P-37 from 10 kR). P-14, P-32 and P-36 were viable translocations; while, P-26 and P-37 yielded only abortive seeds at R1 following selfing and on open or controlled pollination. The translocation heterozygotes exhibited the formation of either a ring or a chain of 4 chromosomes in 38.71% to 77.72% meiocytes. Predominance of rings occurred in all translocation heterozygotes excepting P-26 where rings and chains were nearly equal. P-14 and P-26 had more adjacent orientation of quadrivalents than alternate; while, P-32, P-36 and P-37 demonstrated random orientations. The quadrivalent behaviour was found to be persistent in all generations of P-14, P-32 and P-36. The rings showed preponderance of adjacent orientation and the chains demonstrated frequent alternate orientation. Though normal 6/6 separation of chromosomes at AI was observed in 85.8, 83.3, 69.4, 82.3 and 86.4% cells of P-14, P-26, P-32, P-36 and P-37 respectively, pollen fertility was reduced in the heterozygotes (8.2 to 37.5%). F1’s raised from intercrossing of P-14, P-32 and P-36 were meiotically assessed and the results indicated that same 2 non-homologous chromosomes were involved in translocation and the 2 longest chromosome pairs AA and BB (nucleolar pair) were suggested to be associated. P-14, P-32 and P-36 had marker phenotypic traits and characteristically P-36 possessed non-shattering capsule trait.

Cytological and genical differentiation between cytotypes ofEcheandia nana(Anthericaceae)

The analysis of 9 populations of Echeandia nana showed all to be dip- loid, with 2n = 16, n - 8 (x = 8). The analyzed populations displayed two cyto- types. Cytotype A — 10m+6sm, having two pairs of chromosomes with a satellite, was observed in four populations from the eastern flanks of the Pachuca mountain range. The five remaining populations from the western flank of the Pachuca and Sierra Nevada mountain ranges (Mexico) showed cytotype B = 6m+8sm+2st, having one pair of chromosomes with a satellite. The analysis of meiosis revealed heterozygotic exchanges. Analysis of MI showed three heteromorphic bivalents in cytotypes A and B. Analysis of AI showed sub-chromatid aberrations, (side arm bridges = SAB), which were more frequent in cytotype B (39.88-44.84%) than in cytotype A (2.86- 31-53%). Cells with two bridges (SAB aberrations) were observed in cytotype B. The intraspecific cytological and genical differentiation of cytotypes A and B is probably the result of geographical isolation between populations of E. nana. This suggests that this species is undergoing through a major process of genomic differentiation involving heterozygotic chromosomal rearrangements; which favors a process of speciation between both cytotypes without the occurrence of significant morphological changes. This cytological and genical differentiation between cytotypes A and B was evident in the significant differences of the low number of fruits and viable seeds produced after cross-pollination among cytotypes (AxB: 0-16 fruits; 0-448 abortive seeds), relative to the larger values recorded after cross- pollination within cytotypes (AxA: 4-48; 152-1824) (BxB: 3-89; 14-3382).

Embryo Rescue Techniques to Generate Variation in Citrus Crops

Although no longer as glamorous as it was a few decades past, the routine application of embryo rescue techniques, leading to plant recovery, is a valuable tool for citrus cultivar improvement. Embryo rescue approaches can be used to generate useful variation or to capture various kinds of spontaneous genetic variation. Embryo rescue, by in vitro culture of undeveloped, and presumably unfertilized, ovules in colchicine-supplemented media is a practical method of producing tetraploid clones, which are used then in crosses with diploids to produce seedless triploid hybrids. This same approach, i.e., in vitro culture of undeveloped ovules, is also used to recover plants from chimeric sectored fruit exhibiting economically important mutations for fruit characteristics, and for producing potentially variant somaclones. Seedlessness is an important objective for fresh citrus fruit cultivar improvement, and triploidy following 2x × 4x hybridizations is one approach being exploited for this objective. When monoembryonic diploid seed parents are crossed with tetraploid pollen parents, however, normal seed development is not usually possible. Embryos must be excised from abortive seeds fairly early in development and cultured appropriately to ensure the recovery of sufficient numbers of 3x offspring from these crosses, to increase the likelihood of identifying superior seedless hybrids. These applications will be described in some detail, and progress toward breeding objectives are highlighted.

Somatic hybridization between Lycopersicon esculentum and non-tuberous Solanum species of the Etuberosa series

Intergeneric somatic hybrid plants have been obtained by protoplast fusion between leaf mesophyll protoplasts from two cultivars of tomato (cv. Tamina and plastome mutant Pl-alb I) and mesophyll protoplasts from two representatives of the Etuberosa series of the genus Solanum (wild species S. etuberosim and sexual interspecific hybrid S. brevidens × S. etuberosum). A hybrid selection scheme was based on the faster growth of hybrid microcalli in comparison with parental calli and on the morphological characteristics of hybrid calli and hybrid regenerants. Hybridity was confirmed by morphological and cytological characteristics, esterase and peroxidase isozyme analyses. Somatic hybrids were also characterised by Southern hybridization of the 5,3 kb probe of the tomato meiotic gene mL-I. Twelve out of sixty hybrids produced fruits after selfing; however, their fruits had abortive seeds. Three progeny plants were obtained via embryo culture after selfpollination of intergeneric somatic hybrids.

Introgressive hybridization of tomatoes by ‘gamma-fusion’ of Lycopersicon esculentum Mill. and Lycopersicon peruvianum var. dentatum Dun. protoplasts

Leaf mesophyll protoplasts of chlorophyll-deficient Lycopersicon esculentum Mill. (plastome mutant Pl-alb 1) were fused in a fusion-inducing solution (PEG + Ca 2+ + high pH) with mesophyll protoplasts of wild-type Lycopersicon peruvianum var. dentatum Dun. (lines 3767 and 3772) and interspecific nuclear and/or cytoplasmic hybrid plants were regenerated under selective conditions. The selection of hybrid clones was based on the inability of the L.peruvianum protoplasts to divide after gamma pre-irradiation and white colouration of minicalli from protoplasts of the other parent in contrast to that of the hybrid calli. The hybrids were identified on the bases of esterase isozymes spectra, plastid and mitochondrial DNA, mitosis and meiosis, and also leaf, flower and fruit morphology. Field testing of hybrid plants in the course of one vegetation period demonstrated their high viability. All hybrid clones abundantly blossomed and set fruits with abortive seeds.

Use of an interspecific hybrid in identifying a new allelic specificity generated at the self-incompatibility locus after inbreeding in Lycopersicon peruvianum

An interspecific hybrid between Lycopersicon esculentum (♀) and L. peruvianum has been raised by embryo rescue in vitro and used to confirm the presence of a new S-allelic specificity in its inbred L. peruvianum parent, a plant derived by enforced bud self-pollination of a self-incompatible clone with the genotype S 1 S 2. The inbred plant showed breeding behavior characteristic of both S 2 and a second specificity which was not S 1, S 2, S 3 or S f. Two-dimensional gel electrophoresis of stylar proteins, however, showed only a single typical S-associated component with the Mr and pI characteristic of S2. The alteration in specificity, therefore, was not associated with a detectable change in an S-associated protein. The F1 interspecific hybrid showed intermediacy of vegetative and reproductive characters, relatively high fertility and full self-incompatibility. Backcrossing to L. esculentum produced only abortive seeds requiring embryo culture. Backcrosses to L. peruvianum produced a very low proportion of filled germinable seeds. Pollen of the hybrid showed superior viability and tube growth rate compared with pollen of the two parent plants.

SEEDLING GROWTH AND ROOT CONTRACTION IN THE SOAP PLANT, CHLOROGALUM POMERIDIANUM (LILIACEAE)

Radicles and adventitious roots of the soap plant are contractile and through their activity, mature bulbs of this species are buried to depths of 20–30 cm. Experiments were performed to determine rates of contraction and displacement of the shoot apex resulting from activity of the contractile radicle and the first several adventitious roots. The average displacement was 23.2 mm over a 10‐wk period and 63.8 mm over 29 weeks. Small glass beads and abortive seeds served as controls and showed no displacement through the soil column. Measurements from longitudinal and transverse sections of contracted and uncontracted portions of radicles revealed average increases of 26–64% in radial dimensions and 40–56% decreases in longitudinal dimensions of inner and middle cortical cells (excluding the endodermis) following contraction. Cells of the outermost cortex (excluding the exodermis) decreased in average longitudinal dimensions by 18–26% before becoming distorted and collapsed as contraction was completed. Average volumes of innermost cortical cells decreased by 15–54%, while two or three cell layers of the middle cortex, adjacent to collapsed outer cortical cells, increased in volume up to 75%. These middle cortical cells are identified as the “active” cells which, by their growth, are responsible for the shortening of the root. Throughout the process of contraction, the stele remains straight and undistorted, although the closer spacing of tracheary element secondary wall thickenings following contraction suggests longitudinal compression of the stele. The average number of cortical cells per transverse section does not differ in contracted and uncontracted roots and no evidence is found to support the “interdigitation” hypothesis of root contraction. However, reorientation of middle cortical cell expansion may be the mechanism of root contraction in Chlorogalum pomeridianum.

Histological and anatomical characteristics of parthenocarpic and normal pear fruits

The external and internal development of normal and parthenocarpic ‘Bonne Louise’ and ‘Conference’ pear fruits was studied. The diameter of the normal fruits and their locules increased almost linearly between mid-April (bloom) and the end of June. Thereafter, the fruits continued to grow, while locule expansion virtually stopped. Parthenocarpic fruits grew at nearly the same rate as normal ones, although the length/diameter ratio was consistently larger. The mean width of their locules had already begun to decrease from about mid-May because undifferentiated tissue started to grow inside, in due course partly or entirely filling the locules. In ‘Conference’, this led to the disappearance of locules and core in many fruits; in ‘Bonne Louise’, the locules remained visible. In addition, the pith tissue surrounding the carpels appeared to exert pressure on the locules, with the result that they became partly or entirely flattened in ‘Bonne Louise’ and ‘Conference’ fruits, respectively. In the normal fruits, locules with normal seeds were much larger than locules with only abortive seeds. The parthenocarpic fruits had a much smaller core than the normal fruits with abortive seeds, the core of the latter being smaller than in fruits with normal seeds. Fruit diameter decreased with core diameter; on this account parthenocarpic pear fruits were more slender than normal fruits.

4倍体ナツダイダイ花粉の受粉による無種子のヒューガナツおよびハッサク果実の生産

1. The present paper deals with the preliminary efforts to produce seedless fruits in Hyuganatsu and Hassaku using crosses of 2X×4X, a procedure which results in the formation of abortive seeds in many cases.2. Two hundred flowers of Hyuganatsu (Citrus tamurana Hort. ex TANAKA) were emasculated and pollinated with pollen grains of the 4X Natsudaidai (Citrus natsudaidai HAYATA). The fruits thus obtained were normal in size, weight and skin color, but almost all the seeds degenerated into rudiments and traces at an early stage of development. They were virtually seedless.3. The soluble solid and titrable acid contents in the juice of the ripe seedless fruits showed no difference from the control. The edible portion of these fruits increased by 15% as compared with the control.4. The seedless fruits did not differ from the controls by date of dropping early or late. Also they displayed similar pattern of development of dry juice sacs after freezing in the winter. The fruits after harvest were stored in a carton box under room condition for about two months. They did not display any particular change in the contents of the soluble solids and titrable acids in the juice during storage. The seedless fruits seemed to soften a little faster than that of the control fruits.5. The flowers of the Hassaku (Citrus hassaku HAYATA) were pollinated with pollen grains of the 4X Natsudaidai. The fruits thus obtained were virtually seedless and did not differ from the control in fruit growth and size or in other qualities. The results coincided with those for the Hyuganatsu×4X Natsudaidai cross.6. Further investigations are under way for the purpose of finding the proper proportion of the 4X Natsudaidai tree to be planted as a pollinizer for Hyuganatsu.

Cytogenetical Studies on Ecological Races of <i>Mecardonia dianthera</i> (SW) Pennel

Mecardonia dianthera, a Scrophulariaceous weed of Tropical America comprises of two edaphic ecotypes viz. erect and repent. While the former is a facultative calcicole, the latter is an obligate calcifuge. The present paper gives an account of plant performance and cytological behaviour of colchicine induced tetraploids that were produced by treating the inbred lines of these plants with 0.3% colchicine for 12 hours. Majority of the surviving plants were tetraploids exhibiting a slower growth delayed phenological events, deep green thick green rough foliage, increased dry matter production, enlarged epidermal and mesophyll cells, chloroplast, stomatal apparatus and frequency, pollen grains and a reduced seed viability than that of the diploids. While repent ecotype tetraploids had increased flower number per plant than that of the diploids, reverse was observed in the erect ecotype tetraploids.At metaphase I, uni, bi, tri, tetra and hexa-valents in a varying frequency were observed in the colchiploids and the total number of multivalent associations and univalents per PMC on an average was equal in the tetraploids of each ecotype. This indicates a competition for pairing between homologous chromosomes which is supported by the fact that a significant positive correlation between chiasma frequency and multivalent formation was also observed. However, the colchiploids of the erect ecotype possessed greater number of multivalents and univalents than those of the repent ecotype colchiploids. Further stages of meiosis in the colchi-ploids were abnormal and resembled the typical autoploid meiois. Multiple spindles, complement fractionation and secondary association were also observed. The contribution of univalents and multivalents in inducing pollen sterility in the tetraploid material is significant. Attempts to cross these colchiploids with diploids produced non-viable abortive seeds. Artificial crossings amongst these colchiploids resulted in an early degeneration of the ovary and a failure of the seed formation. Natural self pollination yielded 5-9% of seeds that died after an extrusion of radicle when germinated.The study indicated that the two edaphic ecological races (ecotypes) exhibit a differential susceptibility to colchicine in relation to frequency of induced polyploids, morphological and reproductive features, number and frequrncy of chromosomal associations and univalents, pollen and seed fertility. However, a general agreement in having a morphological gigas, slowed growth rate, delayed phenological events and reduced reproductive capacity occurs in the tetraploids in comparison to the diploid progenitors, of both the ecotypes. A tendency to change the plant form (repent erect), which is governed by a single gene, was not observed, indicating thereby that the gene remains uneffected by the drug, in both the ecological races of M. dianthera.

Intergeneric Hybridization Involving Species of Solanum and Lycopersicon

1. Twenty accessions, comprising fifteen species in the section Tuberarium of the genus Solanum, were cross-pollinated with species of the genus Lycopersicon. Other than S. lycopersicoides and S. pennellii, which were known to hybridize with L. esculentum, S. ochranthum and S. etuberosum were the only Solanum accessions to show any indication of cross-compatibility with the Lycopersicon species. The primary reasons for cross-incompatibility in the unresponsive crosses appeared to be failure of the foreign pollen to germinate when placed on a given stigma. 2. S. ochranthum showed a slight degree of cross-compatibility in that it set fruit when pollinated with either L. chilense or L. peruvianum pollen, but no evidence was found that fertilization had occurred. 3. The pollen of S. etuberosum stimulated ovary development on L. esculentum, but the fruits contained only small abortive seeds. Microscopic studies of the reproductive processes following the cross-pollinations revealed that only a few of the S. etuberosum pollen grains had germinated, and still fewer reached the vicinity of the receptive ovules. At 120 hours after pollination a limited amount of hybrid endosperm development was observed, indicating that fertilizaton had occurred. The hybrid endosperm was delayed, had smaller cells than normal, and was accompanied by abnormal growth and proliferation of the endothelial cells. Beyond this point there was no further development of the hybrid tissue. It appeared that the endothelial cells replaced the endosperm and resulted in abortion. The embryos, if ever formed, failed to undergo any development following cross-fertilization between L. esculentum and S. etuberosum and were, therefore, not accessible for embryo culture. 4. These studies suggest, with respect to the phylogenetic relationships between the genus Lycopersicon and certain of the Solanum species, that the two genera are linked by continuous relationships rather than being separated into discontinuous entities

Studies on the Fertilization and the Seed Formation of the Tea Plant

Double fertilization : The pollen tubes entered into the embryosac and the mail gametes were situated close to the egg cell or the pollar nuclei in about 2-5 days after pollination. The male nucleus came into contact with the egg cell and on the other hand, the triple fusion was comleted in about 5-8 days. The male and egg nuclei were situated confronting each other within the egg cell, and the first division of the primary endosperm nucleus took place in about 8-13 days. The male nucleus in the egg cell grew as large as the egg nucleus and four endosperm nuclei were formed by the second division in about 13 days. The male nucleus in the egg cell was seen as the fused nucleus, and nuclear division was repeated more than three times in about 20 days. It was 35 days after pollination that, the first mitosis occurred in the fertilized egg cell.The maximum percentage of fertilization was seen in 8 days after pollination, and the percentage of normal ovules amounted to 50-60% in each reciprocal crossing of Yabukita and Sayamamidori. The process of collapse of auxiliary cells varied according to individuals, so, to know the success of fertilization it was thought to be desirable to judge it from the conditions of egg cell and pollar nuclei.Formation of seeds in-the fruit : One ovary involved about 12 ovules, but the average numder of seeds in one fruit was three in common varieties. This was due both to the low fertilization percentage and to the occurrence of many abortive seeds which was seen 13 days after pollination. The definite causes that the number of seeds in a fruit varied among varieties were thought to be either the failure of fertilization or the degeneration of fertilized ovules.Fruit drop : The fertilization percentage was very high in every variety, so the cause of fruit drop was thought to be scarcely due to fertilization' failure. The fruit drop rate till March was comparatively low. Early stage of fruit growth in April and May corresponded just to the first growth period of tea shoots, and fruit drop in this period fairly increased in every variety. But after this time, the percentage of fruit drop was very different among varieties. In common varieties, the fruit drop continued up to the autumn, but in well seed setting varieties it seldom occurred when the flowers were open pollinated; the fruit drop habit was observed to be similar to that of non-pollinated fruits, so it was considered that the low percentage of fruit setting in open pollinated plant was largely due to the fertilization failure.

Morphological and Physiological Studies on Occurrence of Abortive Seeds in Leguminous Forage Crops : V. Formation of one-seeded pod in kidney vetch

The pod of kidney vetch (Anthyllis vulneraria L.), when matured, contains usually only one seed. But the ovary at its young stage involves several ovules, ranging 2-4. In this experiment, some embryological observations were carried out, using two-ovuled ovaries, to know the causes concerned about formation of one-seeded pod. The results obtained are summarised as follows : 1) When classified by the ovule number in ovary, 81.5% of 363 ovaries examined were two-ovuled ovaries as shown in Fig. 1. 2) When the ovaries are classified by numbers of fertilized ovules involved, 17.4% of them contained only one fertilized ovule as shown in Fig. 2. Out of them, 8.7% contained one normal but non-fertilized ovule, the remained 8.7% contained one abnormal ovule in which the embryosac was not normally formed. Those ovaries should grow into one-seeded pods. 3) Meanwhile, 77.3% were the ovaries containing two fertilized ovules. In this case, however, the two fertilized ovules never develop evenly, but one of them was arrested in its growth and degenerated without exception. The degeneration of fertilized ovule began from about 4th day after pollination, and one-seeded pods were confirmed on about 7 th day. 4) As to the position of normal seeds in the pods, so far as this experiment is concerned, the seed-setting was found more highly at the apical (stylar) position of the ovary than at the basal as shown in Fig. 3. 5) As to the one-seeded pod formation in 3- and 4- ovuled ovaries, the main cause was the degeneration of fertilized ovules as in the case of two-ovuled ovaries.

Morphblogical and Physiological Studies on Occurrence of Abortive Seeds in Leguminous Forage Crops : IV. Occurrence of abortive seeds and their position in pod of common vetch

This paper deals with the results of studies on occurrence of abortive seeds and their position in pod of common vetch, Vicia sativa L. When classified with respect to the ovule number in pod, 85.5 percent of 380 pods examined were 7-and 8-ovuled pods as shown in Fig. 1. In this experiment, therefore, 7- and 8-ovuled pods were used as materials. The results obtained are sumrnarized as follows. 1) The occurrence of abortive seeds was least frequent at the medium position in a pod and increased toward both the basal and the apical ends, with a more marked tendency to abort toward the basal one as shown in Fig.2 and 3. 2) By examination of the dry weight of each 1081 abortive seeds which were taken out from 380 pods of 10 plants at the matured stage, in comparison with the average dry weight of the normally growing ovules collected on every 5th day after flowering, it was presumed that the majority of abortive seeds would occur within 10 days after flowering as shown in Table.1 and Fig.4. 3) The state of fertilization was observed, using 7-ovuled ovaries at 2nd day after flowering. 97.7 percent of the ovules observed were normally functional. A few non-fertilized ovules were found out, but they were of rather less importance in occurrence of abortive seeds, because the frequency of them was merely less than 3 percent as shown in Table 2. Thus, it was confirmed that the majority of abortive seeds occurred as a result of collapse of fertilized ovules. 4) When observed the embryonal development of undeveloped fertilized ovules, in comparison with normally developing ones, it was confirmed that in the majority of them their normal embryonal development were arrested before 10th day after flowering as shown in Fig.5. 5) It appears that the difference in occurrence of abortive seeds found out between at both basal and apical positions and at medium one may be caused by their competition on absorbing water and nutrients.

Morphological and Physiological Studies on Occurrence of Abortive Seeds in Leguminous Forage Crops : II. Formation of one-seeded pod in red clover

The pod of red clover, when it matures, contains usually only one seed. But the ovary involves two ovules at its young stage. Experiments were undertaken to know of the causes concerned in formation of one-seeded pods from two-ovuled ovaries. Using plants of the variety Mammoth as materials, all their flowers were artificially cross-pollinated and examined through the paraffin method. The results obtained from three years' studies were as follows : I. At the time of flowering, (1) 30∼50 % of ovaries contained one normal and one abnormal ovules each, in the latter the embryo-sac being not normally formed ; (2) 6∼10 % contained two abnormal ovules in each ; and (3) the rest 40∼60 % contained two normal ovules. The ovaries of the case (1) should develop into one-seeded pods provided that the normal one of the ovules are fertilized. II. Even if the ovaries involve two normal ovules, as in the case (3), they might produce one-seeded pods when one of the two is not fertilized. By observation made at 48 hours after pollination, it was confirmed that (4) 20.8 % of them corresponded to above-mentioned case of one seeded pod formation. (5) The remaining 18.3 % were the ovaries consisting of two ovules both of which were non-fertilized ; while (6) 60.8 % were the ovaries containing two fertilized ovules. III. In the case (6), however, when observed on the tenth day after pollination, the two fertilized ovules never developed evenly, but one of them was arrested in its growth and degenerated without exception, so far as this experiment was concerned, and thus the ovaries grew into one-seeded pods. The degeneration was found to begin within five days after pollination.

Morphological and Physiological Studies on Occurrence of Abortive Seeds in Leguminous Forage Crops : III. Formation of one-seeded pod in sweet clover

Usually the pod of sweet clover, when matured, contains only one seed, while the ovary at its young stage involves several ovules, ranging 2-5. In this experiment, some embryological observations were carried out, using four-ovuled ovaries, on the process of above-mentioned one seed formation and abortion, and the results obtained were summarized as follows : (1) The abortion of ovules is partially due to fertilization failure. Namely, 27.0 % of ovules observed were not fertilized. Out of them ; 22.0 % were abnormal ovules in which the embryo-sac was not normally formed, and the remained 5.0 % were normal but non-fertilized ovules. Therefore, the main cause for non-fertilization is owing to embryo-sac failure. (2) When the ovaries are classified by numbers of fertilized ovules involved, 12.0 % of them contained only one fertilized ovule and these ovaries should grow into one-seeded pods. The remained 88.0 % were the ovaries consisting of more than two fertilized ovules, especially, 38.0 % were the ovaries in which all ovules were fertilized. Nevertheless, when observed on the 10th day after pollination, 97.4 % were the ovaries in which more than two fertilized ovules never developed evenly and all but one were arrested their growth, and consequently they grew into one-seeded pods. (3) The degeneration of fertilized ovules began from about 5th day after pollination, and one-seeded pods were confirmed on about 7th day. (4) As to the position of normal seeds in the pods, there was a marked tendency that the seed-setting increased from the stylar (apical) end toward the basal end of the ovary. So far as this experiment is concerned, 85.7 % were the pods in which either basal or subsequent ovule developed into normal seed.