Ovule Sterility Research Articles

Heat Stress in French Bean and Garden Pea : A Review

This review paper addresses the effect of high temperature on pea and similar legumes. The areas covered are field pea and its production, temperature stress effects on New Zealand agriculture, seed vigour which discusses hollow heart and conductivity, high temperature stress on seed germination, threshold temperature, high temperature effects on vegetative growth and reproductive development. This is followed by adaptation mechanisms for high temperature stress, and breeding strategies which cover conventional plant breeding. The quality traits refer to protein, sugars, and the effects of high temperature on the grain composition and quality. Because of various factors related to global climate change, ambient temperatures are expected to rise in the future. Heat stress, which is a serious danger to crop output in most nations, can emerge from these temperature rises. Legumes are well-known for their nutritional and health benefits, as well as their impact on agricultural sustainability. Heat stress is a problem for legume crops because it affects the morphology, physiology, and reproductive growth of the plants. As grain legume agriculture grows to warmer areas and temperature fluctuation increases owing to climate change, high-temperature stress during the reproductive stage is becoming a serious constraint for output. The reproductive stage is critical in the life cycle of all plants, and it is vulnerable to high-temperature stress because many metabolic processes are harmed at this time, resulting in lower crop yields. Flower abortion, pollen and ovule sterility, decreased fertilization, and reduced seed filling are all observed in food legumes exposed to high-temperature stress during reproduction, resulting in smaller seeds and poorer yields. Heat tolerance in major legumes can be improved through several breeding approaches to improve field performance. Understanding the processes of molecular responses to high-temperature stress necessitates the use of omics methods to uncover the pathways behind thermo-tolerance.

BELL1 interacts with CRABS CLAW and INNER NO OUTER to regulate ovule and seed development in pomegranate.

Pomegranate (Punica granatum) flowers are classified as bisexual flowers and functional male flowers. Functional male flowers have sterile pistils that show abnormal ovule development. In previous studies, we identified INNER NO OUTER (INO), CRABS CLAW (CRC) and BELL1 (BEL1), which were specifically expressed in bisexual and functional male flowers. However, the functions of ovule identity genes and the mechanism underlying ovule sterility in pomegranate remain unknown. Here, we found that the integument primordia formed and then ceased developing in the ovules of functional male flowers with a vertical diameter of 8.1-13.0 mm. Megaspore mother cells were observed in bisexual flowers when the vertical diameters of flowers were 10.1-13.0 mm, but not in functional male flowers. We analyzed the expression patterns of ovule-related genes in pomegranate ovule sterility and found that PgCRC mRNA was highly expressed at a critical stage of ovule development in bisexual flowers. Ectopic expression of PgCRC and PgINO was sufficient to increase seed number in transgenic lines. PgCRC partially complemented the Arabidopsis (Arabidopsis thaliana) crc mutant, and PgINO successfully rescued the seeds set in the Arabidopsis ino mutant. The results of Y2H assays, BiFC assays and genetic data analyses showed that PgCRC and PgINO directly interact with PgBEL1. Our results also showed that PgCRC and PgINO could not interact directly with MADS-box proteins and that PgBEL1 interacted with SEPALLATA (PgSEP) proteins. We report the function of PgCRC and PgINO in ovule and seed development and show that PgCRC and PgINO interact with PgBEL1. Thus, our results provide understanding of the genetic regulatory networks underlying ovule development in pomegranate.

ARF6s Identification and Function Analysis Provide Insights Into Flower Development of Punica granatum L.

Based on the genome and small-RNA sequencing of pomegranate, miRNA167 and three target genes PgARF6 were identified in “Taishanhong” genome. Three PgARF6 genes and their corresponding protein sequences, expression patterns in pomegranate flower development and under exogenous hormones treatments were systematically analyzed in this paper. We found that PgARF6s are nuclear proteins with conserved structures. However, PgARF6s had different protein structures and expression profiles in pomegranate flower development. At the critical stages of pomegranate ovule sterility (8.1–14.0 mm), the expression levels of PgARF6s in bisexual flowers were lower than those in functional male flowers. Interestingly, PgARF6c expression level was significantly higher than PgARF6a and PgARF6b. Under the treatment of exogenous IBA and 6-BA, PgARF6s were down-regulated, and the expression of PgARF6c was significantly inhibited. PgmiR167a and PgmiR167d had the binding site on PgARF6 genes sequences, and PgARF6a has the directly targeted regulatory relationship with PgmiR167a in pomegranate. At the critical stage of ovule development (8.1–12.0 mm), exogenous IBA and 6-BA promoted the content of GA and ZR accumulation, inhibited BR accumulation. There was a strong correlation between the expression of PgARF6a and PgARF6b. Under exogenous hormone treatment, the content of ZR, BR, GA, and ABA were negatively correlated with the expressions of PgARF6 genes. However, JA was positively correlated with PgARF6a and PgARF6c under IBA treatment. Thus, our results provide new evidence for PgARF6 genes involving in ovule sterility in pomegranate flowers.

Mutagenic effectiveness and efficiency of gamma rays and ems on chilli (Capsicum annum L.)

The present investigation was carried out to find the efficiency and effectiveness of various mutagenic treatments of gamma rays and EMS on chilli var. Kashi Anmol. An experiment was conducted during winters of 2017-18 and 2018-19 at Vegetable Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, India. The experimental design was randomized block design. Treatments include one control, five doses of gamma rays (10 kR, 20 kR, 30 kR, 40 kR and 50 kR), five doses of EMS (10 mM, 20 mM, 30 mM, 40 mM and 50 mM) and their combinations (gamma rays 10 kR + 20 mM EMS, gamma rays 20 kR + 20 mM EMS, gamma rays 30 kR + 20 mM EMS, gamma rays 40 kR + 20 mM EMS and gamma rays 50 kR + 20 mM EMS). The observations revealed that plant lethality, pollen sterility and ovule sterility percentage increased with the increasing doses of gamma rays, EMS and their combinations. The gamma rays 10kR (0.072) was observed to be most effective, followed by EMS and combination treatments. The mutagenic efficiency calculated in M2 Population on the basis of lethality, sterility and injury with respect to induced morphological mutations revealed variations depending upon the criteria selected for its estimation. As the efficiency was analysed based on lethality per cent, the highest mutagenic efficiency was observed for 10 kR + 20 mM (0.192). When the efficiency was assessed with reference to pollen sterility percentage, the maximum mutagenic efficiency was observed for 30kR (0.118). The higher doses of both mutagen lead to lethal injury and sterility.

The utilities of Citrus tissue culture

Citrus is the third most important fruit crop in the world after apple and bananas, and the total area cultivated with the various Citrus cultivar covers over 7.2 million hectares, yielding total annual production of approximately 100 million metric tons of fruit. The genus Citrus possesses several undesirable characteristic including salt and cold sensitivity they are also susceptible to diseases caused by fungi, bacteria and viruses. Despit substantial genetic diversity and interspecific fertility, the genus Citrus includes some of the most difficult species to breeding. For example, most species are highly heterozygous and produce progeny that segregate widely for many characters when crosses are made. The juvenile periods are often very long, self- and cross-incompatibility and pollen and/or ovule sterility are relatively common, and the presence of adventitious somatic embryos in the nucellus of developing ovules of the most of Citrus greatly limits hybrid production. Genetic transformation is an alternative to overcome these difficulties. For successful transformation, regeneration of whole plants from the transformed cells is a prerequisite. On the other hand production of virus – free plants, development of new cultivars, and production of seedless fruit, production of flavonoid, micropropagation, germplasm conservation and cryopreservation are the other utilities of in vitro culture of Citrus.

Altered callose deposition during embryo sac formation of multi-pistil mutant (mp1) in Medicago sativa.

Whether callose deposition is the cause or result of ovule sterility in Medicago sativa remains controversial, because it is unclear when and where changes in callose deposition and dissolution occur during fertile and sterile embryo sac formation. Here, alfalfa spontaneous multi-pistil mutant (mp1) and wild-type plants were used to compare the dynamics of callose deposition during embryo sac formation using microscopy. The results showed that both mutant and wild-type plants experienced megasporogenesis and megagametogenesis, and there was no significant difference during megasporogenesis. In contrast to the wild-type plants, in which the mature embryo sac was observed after three continuous cycles of mitosis, functional megaspores of mutant plants developed abnormally after the second round of mitosis, leading to degeneration of synergid, central, and antipodal cells. Callose deposition in both mutant and wild-type plants was first observed in the walls of megasporocytes, and then in the megaspore tetrad walls. After meiosis, the callose wall began to degrade as the functional megaspore underwent mitosis, and almost no callose was observed in the mature embryo sac in wild-type plants. However, callose deposition was observed in mp1 plants around the synergid, and increased with the development of the embryo sac, and was mainly deposited at the micropylar end. Our results indicate that synergid, central, and antipodal cells, which are surrounded by callose, may degrade owing to lack of nutrition. Callose accumulation around the synergid and at the micropylar end may hinder signals required for the pollen tube to enter the embryo sac, leading to abortion.

Chemo and Radio sensitivity to mutagens in Chilli (Capsicum annuumL.).

The effect of gamma rays, EMS mutagens and their combination on chilli genotypes Kashi anmol (KA-2) and VR-338 (Kashi Gaurav) were investigated in M1 generation to assess the radio and/or chemo sensitivity of different doses. Seeds were irradiated with different concentration of Gamma rays, EMS and combinations. With an increase in doses of Gamma rays, EMS and their combinations, substantial increase in pollen sterility and ovule sterility was reported. Gamma rays were more effective for germination percentage as compared to EMS and their combination in both varieties. Seedling height reduction was predominantly observed in EMS as compared to gamma rays and their combination.

Variation of DNA methylation and phenotypic traits following unilateral sexual polyploidization in Medicago

Sexual hybridization is an important generator of biodiversity and a powerful breeding tool. Hybridization can also overcome ploidy barriers when it involves 2n gametes, as in the case of unilateral sexual polyploidization (USP) that has been utilized in several crops, among which alfalfa. This research was aimed at gaining insights into the effects of USP on genome methylation and on phenotypic traits in alfalfa, an important forage species. The Methylation-Sensitive Amplified Polymorphism technique was used to estimate the cytosine methylation changes occurring in a tetraploid (2n = 4x = 32) USP progeny from crosses between a diploid Medicago sativa subsp. falcata genotype that produces 2n eggs and a cultivated tetraploid Medicago sativa subsp. sativa variety. De novo methylation or demethylation in the USP progeny were observed for 13% of the detected genomic sites, indicating that methylation changes can be relevant. USP plants showed larger surface area of the leaf epidermis cells than both parents, but this did not result in larger leaf size or higher plant biomass. They displayed significant higher ovule sterility than the tetraploid parent, but normal fertility was observed in crosses with unrelated male testers. We conclude that hybridization and sexual polyploidization resulted in novel variation in terms of remodeling of the methylation landscape as well as changes in phenotypic traits in alfalfa.

Hybridization between insular endemic and widespread species of Viola in non-disturbed environments assessed by nuclear ribosomal and cpDNA sequences

Viola jaubertiana Mares & Vigin. is a narrow endemic violet of the Balearic Islands, restricted to small, fragmented, and scattered populations living in inaccessible rocky places and calcareous overhangs. V. jaubertiana is entirely glabrous and morphologically very uniform. However, several authors have reported hairy individuals collected at the type locality, suggesting that these rupicolous, pubescent plants are putative hybrids with V. alba Bess. subsp. dehnhardtii (Ten.) W. Becker, a woodland violet growing in the area. Ribosomal ITS sequences of the putative hybrids analysed showed additive species-specific sites of V. alba subsp. dehnhardtii and V. jaubertiana, strongly supporting its hybrid origin from these progenitors. CpDNA sequences of all putative hybrids were uniform, and identical to those present in V. jaubertiana accessions. This suggests that the gene flow between V. alba subsp. dehnhardtii and V. jaubertiana is unidirectional and identifies the endemic V. jaubertiana as the unique ovule donor. The additivity of the ITS sequences, together with the pollen and ovule sterility, suggests that the sampled individuals are primary F1 hybrids, whereas no trace of introgressive hybridization or hybrid zone has been evidenced by the nuclear and plastid markers used. Judging from herbarium sheets, hybridization between V. alba subsp. dehnhardtii and V. jaubertiana is recurrent and dates back from the XIXth century. Hybrids between these species are not linked to disturbed environments. In fact, they have been always reported in rupicolous habitats, where the maternal species is restricted.

Parabolic effect in sodium azide mutagenesis in barley*

In order to study the influence of sodium azide concentration on its mutagenic effect, treatments with this chemical (0, 1X10-4 5X10-4 1X10-3 5X10-3 M, pH 6, 20 h.) were applied to seeds of the two-row barley variety Malteria Heda and its double-mutant MC 90. In both genotypes the highest mutagenic effect was observed in the intermediate azide concentrations. The plotted data described a second degree parabole in relation to the azide molarity. The parabolic effect was presented in both forms of recording (chlorophyll mutations/ M1 spikes, and chlorophyll mutants/ M2 seedlings), and it was also found in ovule sterility. On the other hand, the results in physiological vitality, chromosome damage and survival of M1 mature plants were similar to or slightly different from those of the untreated controls.

Expression of female sterility in alfalfa (Medicago sativa L.)

Female sterility associated with the presence of callose in the nucellus at anthesis was studied in an F1 progeny of two alfalfa plants displaying 5 and 81% ovule sterility. Transgressive segregation was observed and 100% sterile plants were obtained. Two of the sterile plants were used for cytological analyses on sectioned and stain-cleared whole ovules, in comparison to a 100% fertile full sib plant. The first sign of sterility was callose deposition in the nucellus cell walls surrounding the sporogenous cells of the young ovules. At the same stage, no trace of callose was present in ovule primordia of the fertile plant. Megaspore mother cells differentiated in both fertile and sterile ovules and meiosis was initiated, as indicated by chromatin patterning typical of a zygotene stage. However, meiosis was never completed in the sterile plants. In the control, callose was deposited around the meiocyte and as sects between the cells of the dyads and tetrads during meiosis, and disappeared after the completion of meiosis; an embryo sac developed and female fertility was normal. In the sterile ovules, some nucellus cells enlarged and callose accumulation continued forming thick deposits. At anthesis, the sterile ovules lacked an embryo sac and showed massive callose accumulation in the nucellus. Male fertility was normal in female-sterile plants, thus a female-specific arrest of sporogenesis appears to be the cause of sterility. Pistil development was aberrant in some sterile genotypes, even with arrested pistil growth in early flower buds.

Wide somatic hybrids of Citrus with its related genera and their potential in genetic improvement

Citrus wild relatives are an untapped germplasm reservoir, which possesses many elite resistance traits. Genetic introgression into Citrus by conventional methods has been greatly hindered by polyembryony, pollen / ovule sterility, sexual / graft incompatibility, long juvenility etc. Somatic hybridization via protoplast fusion may make it possible to transfer genes from wild relatives to Citrus. To date, more than sixty sexually compatible or incompatible intergeneric somatic hybrids between Citrus and its various related wild genera have been produced by PEG - orelectrically - induced fusion. These wide somatic hybrids were identified by morphology, cytology, isozyme, RAPD and RFLP analyses. Genetic variation or recombination was also revealed in some of them. Several sexually compatible combinations have flowered and set fruits. The agronomic performance of these wide somatic hybrids is diverse, and the current results are not conclusive. Somatic hybrids are being tested as rootstocks. The prospects of wide somatic hybridization of Citrus with its wild relatives are discussed.

Quantitative ovule sterility in Medicago sativa

Ovule sterility was found to be associated with callose deposition in B17, a plant with low fertility from the alfalfa cv Blazer XL. The site of callose deposition, which began during embryo-sac development and affected 81% of the ovules in mature florets, at random positions in the ovary, appeared to be the embryo-sac wall or the integumentary tapetum. The fertile ovules of B17 transmitted the ovule-sterility trait to the progenies, thereby demonstrating a sporophytic genetic control. B17 was crossed with P13, a Peruvian plant with 5% callosized ovules, to generate reciprocal F1 populations, and an F1 plant (91% callosized ovules) was used to obtain the backcross populations. B17 was also crossed to unrelated, highly fertile, plants. S1 progenies from B17 and P13 were also studied. All the progeny populations displayed continuous variation for the percentage of sterile ovules, supporting a polygenic control. Narrow-sense heritability estimated by offspring-midparent regression was 0.85. Reduced transmission of the sterility trait through the pollen is hypothesized to explain the difference between reciprocal crosses. Six progeny plants showing 100% callosized ovules proved to be female-sterile. Ovule sterility could be an important component of the generally observed low realized seed potential in alfalfa.

Maximising seed production potential in white clover: factors influencing seed set per floret

The causes of low seed set per floret in white clover (Trifolium repens L.) are reviewed. Three stages of flower head development are distinguished as important for a high level of seed set: a pre-fertilisation stage, a stage of anthesis leading to pollination, and a postfertilisation stage in which seed provisioning occurs. In sunny conditions the percentage seed set is limited at the pre-fertilisation stage by up to 20-30% ovule sterility. Relatively low light intensities during the postfertilisation stage can lead to abortion of a high proportion of fertilised ovules and developing seeds. Experimental results suggest that seed yields under optimal growing conditions can be limited solely by the level of pre-fertilisation ovule sterility and probably cannot be bettered, but further understanding of the seed-provisioning requirements for photosynthate could lead to improved management practices for seed production under conditions of lower light intensities. Keywords: abortion, light intensity, ovule, seed provisioning, sterility, white clover

Causes of low seed set in white clover (Trifolium repens L.)

AbstractA field experiment was conducted to clarify the factors responsible for poor seed set in four white clover (Trifolium repens L.) cultivars. Although the mean number of ovules per floret was 5·18–5·29, the average number of seeds per floret was found to be only 1·23‐1·82. A stainclearing technique was used to examine the cytoplasmic state of the embryo sac in intact, unfertilized, mature ovules and it was found that 28–33% of ovules per carpel were sterile. The abortion rate of fertilized ovules and immature seeds (7 days after pollination) ranged between 32 and 34%. Beyond this period, it was observed that only a very small proportion of the total seeds were lost. The observation of high pollen fertility and a high pollen load strongly suggests that poor pollination does not account for the reduced number of seeds per floret. A ‘nutrient competition’ hypothesis was proposed for high ovule sterility and post‐fertilization abortion of developing seeds.

Effect of canopystructure and light intensity on seed production in white clover

A field experiment was structure and light intensity on seed production A field experiment conducted during the summer of 1989-90 to determine to what extentand under what growing conditions the seed yield of white clover flower heads is influenced by canopy density and overcast weather conditions in plants of 'Grasslands Pitau'. Overcast weather was simulated by artificially shading the plants. The flower heads developed in a dense canopy produced 37% fewer seeds per head than those formed in an open canopy. Seed yield per flower head was also strongly affected by artificial shading. When plants were shaded only before pollination there was a 3 1% reduction in seed number per head; when shade was given only after pollination there was a reduction of 25%. It is argued that a major advantage of the practice of defoliation at the time of closing for seed production is enhancement of flower fertility; and that decreased seed set in duller, wetter summers is probably, at least in part; attributable to increased ovule sterility in the dense canopies formed under those conditions, Keywords: white clover, canopy, light intensity, seed yield

The protective effect of hypoxia and dithiothreitol on X-ray induced genetic damage in Arabidopsis

A study was made on the protective effect of hypoxia and dithiothreitol (DDTT) on X-ray-induced ovule sterility and embryonic lethality in Arabidopsis. Both hypoxia and DTT gave on pronounced and additive reduction of radiation-induced genetic damage. The reduction was significantly higher for ovule sterility than for embryonic lethals. It is suggested that non-fertilized ovules contain ratio of strand breaks/other damage than embryonic lethals do, for hypoxia and DTT are shown specifically to give a reduction of strand breaks.

Transmission of primary trisomics in pearl millet

Transmission rates of extra chromosomes found in the full set of trisomics of pearl millet (Pennisetum americanum) (2n = 14) were estimated by examining the progeny of selfed trisomics and the progeny of trisomics crossed to disomics. When the trisomics were selfed, 'dark green' and 'tiny' had the highest transmission rate (23.8% and 23.3%, respectively) and 'pseudonormal' the lowest (13.8%). Other trisomics had an intermediate rate of transmission. When the trisomics were used as females in crosses with disomics, both 'dark green' and 'tiny' again had the highest transmission rate and 'pseudonormal' the lowest. When the trisomics were used as males in crosses to disomics, no trisomic was transmitted to the progeny except for 'spindle', and this occurred with a very low frequency (2.0%). A variation in transmission rate was observed from plant to plant and season to season for the same trisomic type. A study of the transmission rate of the extra chromosomes indicated that the following factors were probably contributing to the lower rate of transmission: small- or light-weight seeds tended to have a higher proportion of trisomics than heavier seeds; lighter seeds had a lower percentage germination; a positive and significant correlation was noticed between trivalent frequency and transmission rate. Plants with reduced vigour produced a higher frequency of trisomics. Though trisomics involving longer extra chromosomes showed a high degree of pollen and ovule sterility, they were highly transmissible. This has resulted in a close relationship between gametic sterility and transmission rate of extra chromosome.

A tertiary trisomic interchange heterozygote in pea (Pisum sativum L.)

In M2 generation of an interchange heterozygote, one off-type plant was isolated which was characterized by the presence of weak and slender stems, with profuse semi-spreading branching, narrow and yellow-green foliage, small and weak pods, and 10 days late-flowering and-maturing as compared to wildtype. The mutant had high pollen and ovule sterility (76–80%) and showed 5II+2II (heteromorphic)+1I (small chromosome) in 85% of the cells. The mutant appeared to be a tertiary trisomic interchange heterozygote. The possible mechanism of the formation of heteromorphic bivalents and a small chromosome are discussed.

Studies on induced tetraploid in four diverse cultivars of pea (Pisum sativum L.).

Tetraploids were induced through colchicine treatment of 1.5-2.0 cm long seedlings in four pea cultivars, namely, T 163 (indigenous), 68 C (W. Germany), 5064-S (Sweden) and P. I. 280064 (Canada). Four hours treatment with 0.025% colchicine produced 10-15% tetraploids. Large seeded cultivars, T 163 and 68 C gave more tetraploids than small seeded ones. Tetraploids showed siginficant varietal differences and were characterised by large stomata, flowers, seeds and pod width and delayed flowering and maturity by 10-15 days while stomata frequency and pod length showed reduction. Both bivalents and quadrivalents were prominent in tetraploid. Chromosome abnormalities were more in T 163 tetraploid (55 per cent cell); laggards were frequent. Pollen and ovule sterility were parallel and ranged from 33 to 85 and 24 to 80 per cent in tetraploid as compared to 0.7 to 5.0 and 0.5 to 3.2 per cent in diploid, respectively. Colchicine treated diploids also showed high pollen and ovule sterility ranging from 16 to 56 and 7 to 56 per cent, respectively but had no chromosome abnormality. The possible role of colchicine and chromosomal abnormalities in reducing fertility were discussed.