Seed abortion in Pongamia pinnata (Fabaceae)

Locations of seed abortion in response to defoliation differ with pollen source in a native perennial legume herb

PREMISE

In many flowering plants, flowers contain more ovules than fruits have seeds. What determines which ovules become seeds? When photosynthates are limited, as may happen when plants lose leaf area to herbivory, fewer fertilized ovules become seeds.

METHODS

Greenhouse-grown ramets of distinct individuals of a perennial herbaceous legume were manually defoliated to various levels determined in the field, then self- or cross-pollinated. For each seed produced, we recorded its position in the fruit and its mass. From a subset of seeds from different treatments and positions in the fruits, we grew seedlings and measured their dry mass.

RESULTS

Ovules were aborted more frequently in fruits from flowers that were self-pollinated and from those on plants with higher levels of defoliation. Ovules in the basal portion of the fruits were more likely to be aborted than those at the stigmatic end; this pattern was most pronounced for fruits after self-pollination with high levels of defoliation. Total number of seeds produced and seed mass per pod were greatest in cross-pollinated fruits after no or low levels of defoliation. Mean individual seed mass was greater for fruits with fewer seeds, indicating a trade-off between seed number and seed mass. Seedling dry mass (a measure of vigor) was greatest for seeds in the middle positions of fruit produced by cross-pollination after severe herbivory; no positional differences were seen for seeds from self-pollinated fruits.

CONCLUSIONS

Observed locations of seed abortion may have been selected not only by defoliation, but in part by propensity for dispersal, while positional differences in seedling vigor may be related to seed size and differential maternal allocation based on pollination treatment and leaf area lost.

Do Reproductive Traits of Invasive Populations of Scotch Broom, Cytisus scoparius (Fabaceae), Outperform Native Populations?

Reproductive traits are among the most important factors in determining the success of species establishment and invasion in a new area. Studies on transcontinental invasions have revealed that invasive species perform better in the invasive range than in their native ranges. We assumed that the same regularity exists in intracontinental invasions and thus investigated whether the reproductive traits of Scotch broom, Cytisus scoparius, perform better in the alien invasive range in Europe compared to its native range in the same continent. The aim of this research was to reveal the potential and realised fecundity of C. scoparius in its native and invasive ranges, as well as relationships with the size of pods, habitat type, and how these traits vary at the same site in different years. The results of this study were not able to unambiguously confirm our hypothesis that C. scoparius in the invasive range in Lithuania, specifically in the southern part of the Boreal biogeographical region, outperform plants in the native range with regard to the analysed reproductive traits. Potential fecundity of C. scoparius in the native range was significantly higher than in the invaded range; however, realised fecundity was not significantly different between the native and invasive ranges. The pod length was similar in both ranges, whereas the pod width was significantly greater in the invasive range than in the native range. The results suggest that the number of ovules per pod, number of matured seeds, and the size of pods are related with the type of habitat and local environmental conditions in the habitat. Although many studies on other species have confirmed higher fecundity and overall better performance of plants in the invasive range than in the native range on other continents, this rule probably cannot be applied for intracontinental invasive species occurring in relatively close geographical regions to their native ranges.

Abortion occurs during double fertilization and ovule development in Paeonia ludlowii

Paeonia ludlowii (Stern & Taylor) D.Y.Hong, an endangered species, is indigenous to Tibet, China and propagated only by seed under natural conditions. Its natural reproduction is constrained by low fecundity. Excess seed abortion is a key factor restricting its natural reproduction, cultivation, introduction, and protection. Understanding the specific origin and occurrence of aborted ovules is important for the protection of offspring. Using serial sectioning analysis, we studied the process of pollination and fertilization of P. ludlowii and examined the characteristics of aborted ovules, developmental differences after flowering of normal and aborted ovules, and their ratios at different positions in P. ludlowii ovaries. During pollination, fertilization, and seed development, ovule abortion was frequent, with a random abortion position. There were three types of abortion, namely, abnormal pistil, sterile ovules, and embryo and endosperm abortions. Of these, embryo and endosperm abortions could be divided into early abortion and middle abortion. The early aborted ovules stopped growing on day 12, the endoblast and endosperm in the embryo sac aborted gradually. Furthermore, the shape of the embryo sac cavity changed. The volume of aborted ovules was significantly different from that of fertile ovules. At ripening, the external morphology of different types of aborted seeds was significantly different. The possible reasons for the abortion of the ovules are also discussed.

Uncovering Trait Associations Resulting in Maximal Seed Yield in Winter and Spring Oilseed Rape

Seed yield is a complex trait for many crop species including oilseed rape (OSR) (Brassica napus), the second most important oilseed crop worldwide. Studies have focused on the contribution of distinct factors in seed yield such as environmental cues, agronomical practices, growth conditions, or specific phenotypic traits at the whole plant level, such as number of pods in a plant. However, how female reproductive traits contribute to whole plant level traits, and hence to seed yield, has been largely ignored. Here, we describe the combined contribution of 33 phenotypic traits within a B. napus diversity set population and their trade-offs at the whole plant and organ level, along with their interaction with plant level traits. Our results revealed that both Winter OSR (WOSR) and Spring OSR (SOSR); the two more economically important OSR groups in terms of oil production; share a common dominant reproductive strategy for seed yield. In this strategy, the main inflorescence is the principal source of seed yield, producing a good number of ovules, a large number of long pods with a concomitantly high number of seeds per pod. Moreover, we observed that WOSR opted for additional reproductive strategies than SOSR, presenting more plasticity to maximise seed yield. Overall, we conclude that OSR adopts a key strategy to ensure maximal seed yield and propose an ideal ideotype highlighting crucial phenotypic traits that could be potential targets for breeding.

Short-term cell death in tissues of Pulsatilla vernalis seeds from natural and ex situ conserved populations

Pulsatilla vernalis is a IUCN listed species that occurs in mountain and lowland habitats. The seeds collected from different populations are remarkably diverse in their viability depending on locality or year of collection. We aim to analyse seed viability, among others, by investigation of the percentage of alive, dying, and dead cells in embryos and endosperm when comparing the seeds from a wild lowland population and ex situ cultivation of plants of lowland and Alpine origin. The cell death was detected by staining with two fluorescence probes, one penetrating only the changed nuclear membranes, the other penetrating also the unchanged cells. 54.5% of Alpine origin seeds were presumably capable of germination if they were sown after collection, however, four months later only 36.4% had healthy embryos. In the case of lowland wild plants it was 31.8% and 18.2%, and from ex situ, 27.3% and 13.6%, respectively. 27.3% of Alpine origin seeds had embryo in torpedo stage (9.1% in the case of lowland seeds). Mean weight of the former was 2.9 mg (2.0 mg in lowland ones). Our results confirm the significance of seed origin and seed weight on viability, and that Pulsatilla seeds have a short ‘germination time window’.

Comprehensive transcriptome profiling to identify genes involved in pistil abortion of Japanese apricot

Flower development exists as a key period in the angiosperms life cycle and the proper development is considered with its reproductive success. Pistil abortion is one of the widely distributed aspects of berry plants and its basic mechanism in Japanese apricot is quite unclear and needs thorough investigation. The present study was carried out to get a deep insight into the pistil abortion mechanism in Japanese apricot using a transcriptomic approach. A large number of DEGs were identified from different development stages of normal and abortive pistils. Pair-wise comparison analysis was performed as LY1 vs DQD1, LY2 vs DQD2, and LY3 vs DQD3 and produced 3590, 2085, and 2286 transcripts, respectively. The Gene Ontology (GO) showed that different metabolic processes, plant hormones, developmental processes, and photosystem-related genes were involved in pistil abortion. The pathway analysis revealed significant enrichment of plant hormone's signal transduction and circadian rhythm pathways. Furthermore, transcription factors such as MYB, MADS-box, and NAC family showed lower expression in abortive pistils. The current study presents a new strategy for advanced research and understanding of the pistil abortion process in Japanese apricot and provides a possible reference for other deciduous fruit trees.

Delayed pollination and low availability of assimilates are major factors causing maize kernel abortion

Selective seed abortion is a survival strategy adopted by many species that sacrifices some seeds to allow the remaining ones to set. While in evolutionary terms this is a successful approach, it causes huge losses to crop yields. A pollination time gap (PTG) has been suggested to be associated with position-related grain abortion. To test this hypothesis, we developed a novel approach to alter the natural pattern of maize (Zea mays L.) pollination and to examine the impact of PTGs on kernel growth and the underlying physiological basis. When apical and basal kernels were synchronously pollinated, the basal kernels set and matured but the apical kernels were aborted at an early stage. Delaying pollination to the basal ovaries suppressed their development and reduced invertase activity and sugar levels, which allowed the apical kernels to set and grow normally. In situ localization revealed normal cell wall invertase activity in apical and basal kernels under synchronous pollination but reduced activity in the delayed-pollinated kernels independent of their position. Starch, which was abundant in basal kernel areas, was absent in the apical kernel regions under synchronous pollination but apparent with delayed pollination. Our analyses identified PTG-related sink strength and a low level of local assimilates as the main causes of grain abortion.

Proteomic Identification of Differentially Expressed Proteins during Alfalfa (Medicago sativa L.) Flower Development

Flower development, pollination, and fertilization are important stages in the sexual reproduction process of plants; they are also critical steps in the control of seed formation and development. During alfalfa (Medicago sativa L.) seed production, some distinct phenomena such as a low seed setting ratio, serious flower falling, and seed abortion commonly occur. However, the causes of these phenomena are complicated and largely unknown. An understanding of the mechanisms that regulate alfalfa flowering is important in order to increase seed yield. Hence, proteomic technology was used to analyze changes in protein expression during the stages of alfalfa flower development. Flower samples were collected at pre-pollination (S1), pollination (S2), and the post-pollination senescence period (S3). Twenty-four differentially expressed proteins were successfully identified, including 17 down-regulated in pollinated flowers, one up-regulated in pollinated and senesced flowers, and six up-regulated in senesced flowers. The largest proportions of the identified proteins were involved in metabolism, signal transduction, defense response, oxidation reduction, cell death, and programmed cell death (PCD). Their expression profiles demonstrated that energy metabolism, carbohydrate metabolism, and amino acid metabolism provided the nutrient foundation for pollination in alfalfa. Furthermore, there were three proteins involved in multiple metabolic pathways: dual specificity kinase splA-like protein (kinase splALs), carbonic anhydrase, and NADPH: quinone oxidoreductase-like protein. Expression patterns of these proteins indicated that MAPK cascades regulated multiple processes, such as signal transduction, stress response, and cell death. PCD also played an important role in the alfalfa flower developmental process, and regulated both pollination and flower senescence. The current study sheds some light on protein expression profiles during alfalfa flower development and contributes to the understanding of the basic molecular mechanisms during the alfalfa flowering process. These results may offer insight into potential strategies for improving seed yield, quality, and stress tolerance in alfalfa.

Comparative proteomic analysis of pistil abortion in Japanese apricot (Prunus mume Sieb. et Zucc)

The phenomenon of pistil abortion widely occurs in Japanese apricot and has seriously affected the yield in production. We used a combination of two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time of flight/time of flight (MALDI-TOF/TOF) approaches to identify the differentially expressed proteome between perfect and imperfect flower buds in Japanese apricot. More than 400 highly reproducible protein spots (P<0.05) were detected and 27 protein spots showed a greater than two-fold difference in their expression values. The proteins identified were classified into eight functional classifications and ten process categories, according to the Gene Ontology (GO). Acetyl-CoA produced by ATP citrate lyase (ACL) as a structural substance during formation of the cell wall could regulate pistil abortion in Japanese apricot. S-adenosylmethionine (SAM), xyloglucan endotransglucosylase/hydrolases (XTHs) and caffeoyl-CoA-O-methyl transferase (CCoAOMT) could promote cell wall formation in perfect flower buds of Japanese apricot, greatly contributing to pistil development. Spermidine hydroxycinnamoyl transferase (SHT) may be involved in the O-methylation of spermidine conjugates and could contribute to abnormal floral development. The identification of such differentially expressed proteins provides new targets for future studies that will assess their physiological roles and significance in pistil abortion.

Selective embryo abortion in a perennial tree-legume: a case for maternal advantage of reduced seed number per fruit

In this study, I analyzed time-course of embryo abortion, positional bias in seed maturation and maternal costs of seed packaging in Cercis canadensis. While basal embryos experience similar rates of abortion as those in other positions during the first week of development, abortion rates peak during the second week. Head start in resource sequestration by stigmatic embryos may explain high rates of basal embryo abortion. Similar seed packaging costs and seed mass for single and multi-seeded pods suggests that maternal parent regulates pod size in accordance with seed numbers per pod investing equally in the surviving offspring. Competition during early developmental period results in the abortion of less competitive embryos allowing for optimal resource investment.

Comparative proteomic analysis of longan (Dimocarpus longan Lour.) seed abortion

Two-dimensional gel electrophoresis (2-DE), coupled with mass spectroscopy, was used to study seed abortion in Dimocarpus longan Lour. (cv. Minjiao 64-1) by comparing normal and aborted seeds at three developmental stages. More than 1,000 protein spots were reproducibly detected in 2-DE gels, with 43 protein spots being significantly altered in their intensity between normal and aborted seeds at least at one stage. Thirty-five proteins were identified by matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry (MALDI-TOF-MS/MS) analysis and protein database searching. Most of the identified proteins were associated with a variety of functions, including energy and metabolism (30%), programed cell death (9%), antioxidative processes (14%), chaperonin (23%), cell division, amino acid metabolism, secondary metabolism, and other functional classes. Furthermore, the expression patterns of HSP70 and cytosolic ascorbate peroxidase (cAPX) were validated by immunoblotting analysis. This study provides a novel, global insight into proteomic differences between normal and aborted seeds in longan. We anticipate that identification of the differentially expressed proteins may lead to a better understanding of the molecular basis for seed abortion in longan.

Effect of ovule position on patterns of seed maturation and abortion in Robinia pseudoacacia (Fabaceae)

I examined the effect of ovule position on patterns of ovule development within the linear pods of black locust, Robinia pseudoacacia L. Fruits were sampled from three sites in southwestern Ontario, Canada. Approximately two-thirds of all ovules failed to show visible signs of fertilization or development. Patterns of seed maturation and abortion within fruits were nonrandom and depended on ovule position. The probability of seed maturation within individual fruits decreased significantly from the distal to basal ends, suggesting the existence of a fertilization gradient. Seeds at the basal ends of fruits were also lighter than more distally located seeds. While seed mass did not influence the likelihood of germination, seed mass was positively correlated with seedling size. Hence, ovule position exerts an influence on offspring vigour and has the potential, ultimately, to affect plant fitness.