Unpollinated Flowers Research Articles

Animal pollination contributes to more than half of citrus production

Animal pollination is crucial for the reproduction and economic viability of a wide range of crops. Despite the existing data, the extent to which citrus crops depend on pollinators to guarantee fruit production still needs to be determined. Here, we described the composition of potential pollinators in citrus (Citrus spp.) from the main growing areas of Argentina; moreover, we combined Bayesian models and empirical simulations to assess the contribution of animal pollination on fruit set and yield ha−1 in different species and cultivars of lemons, grapefruits, mandarins, and oranges. Honeybee (A. mellifera L.) was the most commonly observed potential pollinator, followed by a diverse group of insects, mainly native bees. Regardless of citrus species and cultivars, the probability of flowers setting fruit in pollinated flowers was 2.4 times higher than unpollinated flowers. Furthermore, our simulations showed that about 60% of the citrus yield ha−1 can be attributable to animal pollination across all species and cultivars. Therefore, it is crucial to maintain environments that support pollinator diversity and increase consumer and to producer awareness and demand in order to ensure the significant benefits of animal pollination in citrus production.

Just add water: Rainfall‐induced anther closure and color change in Ripariosida hermaphrodita (Malvaceae)

AbstractAnther opening has commonly been thought of as unidirectional, but reports of anthers closing in response to rainfall show this is not the case. In some species, anther closure can protect pollen from degrading or washing away, thus possibly enhancing male fitness. Similarly, although floral color is often presumed to be static, numerous floral parts may change color during blooming. These color changes primarily occur in response to pollination or aging, thus potentially increasing pollination efficiency by directing floral visitors to recently opened, unpollinated flowers. Daily observations of 364 Ripariosida hermaphrodita flowers from seven individuals showed that anthers that were purple, open, and shedding pollen became beige colored and tightly closed after rainfall. These findings were further supported by observations of plants exposed to simulated rainfall in a greenhouse and time‐lapse photography of flowers misted with water. To our knowledge, our work represents the first report of anther closure in response to rain in Malvaceae and the first report of floral color change induced by rainfall.

Does pollination alter the cannabinoid composition and yield of extracts from hemp (Cannabis sativa L. cv. Finola) flowers?

This study was undertaken to compare cannabinoid levels and yields in floral extracts from unpollinated and artificially pollinated industrial hemp (Cannabis sativa L. cv. Finola) flowers grown under identical growth chamber conditions. Of the 16 cannabinoids analyzed using high performance liquid chromatography (HPLC), the levels of 10, cannabichromene (CBC), cannabichromenic acid (CBCA), cannabidivarin (CBDV), cannabigerol (CBG), cannabicyclol (CBL), cannabinol (CBN) cannabinolic acid (CBNA), ∆8-tetrahydrocannabinol (∆8-THC), tetrahydrocannabivarin (THCV) and tetrahydrocannabivarinic acid (THCVA) were near or below the limit of quantification. Total ∆9-tetrahydrocannabinol (THC), was present at concentrations below the legal limit of 0.3% (w/w). The level of cannabidiol (CBD) in extracts from pollinated flowers was the same as that from unpollinated flowers, but cannabidiolic acid (CBDA) and cannabidivarinic acid (CBDVA) levels were not. This suggested that, although pollination changes the pool sizes of the precursors in the metabolic pathway leading to CBD production, cannabinoid levels in floral extracts from the Finola cultivar, were reduced but not eliminated, by pollination of hemp flowers compared with levels in floral extracts from unpollinated flowers.

Pollinators of Lavandula angustifolia Mill., an important factor for optimal production of lavender essential oil

Lavender essential oil is widely used in pharmacy, perfumery and the food industry. It is one of the key essential oils in aromatherapy due to its valuable pharmacological properties. The producers of lavender essential oil are well aware that the greatest quantity of oil is obtained near the end of the inflorescence anthesis and that oil quantity is correlated with the pollination as unpollinated flowers drop down. In addition, it has been demonstrated that oil quality is also highest at the end of the flowering period, related to the gradual increase of monoterpenes (particularly the valuable linalool) and the decrease of sesquiterpenes during flower ontogenesis. The aim of this preliminary study was to measure the occurrence of spontaneous self-pollination in Lavandula angustifolia Mill. and to identify external pollinators. The field experiments were performed in a lavender plantation near Gorna Lipnitza Village, north Bulgaria and in the ex-situ lavender collection in the experimental plot of the Botanical Garden of Sofia University. It was revealed that spontaneous self-pollination did not occur in flowers from which external pollinators had been excluded. Exposed flowers were pollinated by polylectic insects, such as honeybees, several species of bumblebees and butterflies. Wild pollinators (particularly bumblebees) dominated over honeybees at both study sites. Our observations showed that all pollinators actively collected nectar. The pollen baskets of most bees were full, indicating the active consolidation of pollen adhering to the pollinators’ bodies. Although lavender growers tend to place beehives in the fields for optimal essential oil production, it is also crucial to conserve wild pollinators.

Spatiotemporal Distribution of Homogalacturonans and Hemicelluloses in the Placentas, Ovules and Female Gametophytes of Utricularia nelumbifolia during Pollination.

Utricularia nelumbifolia is a large carnivorous plant that is endemic to Brazil. It forms an extra-ovular female gametophyte, which surpasses the entire micropylar canal and extends beyond the limit of the integument and invades the placenta tissues. Due to the atypical behavior of the female gametophyte, it is interesting to determine the interaction between the gametophyte and sporophytic tissue. Therefore, the aim of this study was to evaluate the role of the placenta, the ovular tissues, the hypertrophied central cell and the integument in guiding the pollen tube in Utricularia nelumbifolia Gardner by studying the distribution of homogalacturonans and hemicelluloses. It was also determined whether the distribution of the homogalacturonans (HG) and hemicelluloses in Utricularia are dependent on pollination. The antibodies directed against the wall components (anti-pectin: JIM5, JIM7, LM19, LM20 and the anti-hemicelluloses: LM25, LM11, LM15, LM20, LM21) were used. Because both low- and high-esterified HG and xyloglucan were observed in the placenta, ovule (integument, chalaza) and female gametophyte of both pollinated and unpollinated flowers, the occurrence of these cell-wall components was not dependent on pollination. After fertilization, low methyl-esterified HGs were still observed in the cell walls of somatic cells and female gametophyte. However, in the case of high-esterified HG, the signal was weak and occurred only in the cell walls of the somatic cells. Because xyloglucans were observed in the cell walls of the synergids and egg cells, this suggests that they play a role in sexual reproduction. Utricularia nelumbifolia with an extra ovule-female gametophyte is presented as an attractive model for studying the male-female dialogue in plants.

Embryo-gynogenic induction of Indonesia shallot (Allium cepa L. Aggregatum group) cultivars using three different protocol unpollinated flower cultures

Embryo-gynogenic induction was an important step in haploid induction. The research was determined the best method of unpollinated flower culture of Indonesia shallot varieties. Three methods were used including method 1 with two-step cultures using BDS as basic medium supplemented with polyamines 2 mM putrescine on the first step and spermidine 0,1 mM at the second step, method 2 using BDS as basic medium supplemented with 2,4-D 2 mgL−1 and BA 2 mgL−1 on the first step and NAA 1 mgL−1 and 2iP 2 mgL−1 on the second step and method 3 using B5 medium supplemented with 2,4-D 2 mgL−1 and BA 2 mgL−1. Six shallot cultivars used as flower donor were Katumi, Bima Brebes, Tajuk, Trisula, Superphilip, and Bauji. Flower umbel was collected and pretreated using Yoshida liquid medium then placed on incubator at four °C for overnight. The results showed that all flowers cultured could anthesis properly in the first week of cultured. The embryos could emerge from ovaries from week 7th of cultured in all methods. However, the highest percentage of embryos gynogenic developed to seedlings was achieved using method 3 in Superphilip (6.98%) followed by method 2 in Tajuk (4.44%).

Spatio-Temporal Distribution of Cell Wall Components in the Placentas, Ovules and Female Gametophytes of Utricularia during Pollination.

In most angiosperms, the female gametophyte is hidden in the mother tissues and the pollen tube enters the ovule via a micropylar canal. The mother tissues play an essential role in the pollen tube guidance. However, in Utricularia, the female gametophyte surpasses the entire micropylar canal and extends beyond the limit of the integument. The female gametophyte then invades the placenta and a part of the central cell has direct contact with the ovary chamber. To date, information about the role of the placenta and integument in pollen tube guidance in Utricularia, which have extra-ovular female gametophytes, has been lacking. The aim of this study was to evaluate the role of the placenta, central cell and integument in pollen tube pollen tube guidance in Utricularia nelumbifolia Gardner and Utricularia humboldtii R.H. Schomb. by studying the production of arabinogalactan proteins. It was also determined whether the production of the arabinogalactan proteins is dependent on pollination in Utricularia. In both of the examined species, arabinogalactan proteins (AGPs) were observed in the placenta (epidermis and nutritive tissue), ovule (integument, chalaza), and female gametophyte of both pollinated and unpollinated flowers, which means that the production of AGPs is independent of pollination; however, the production of some AGPs was lower after fertilization. There were some differences in the production of AGPs between the examined species. The occurrence of AGPs in the placental epidermis and nutritive tissue suggests that they function as an obturator. The production of some AGPs in the ovular tissues (nucellus, integument) was independent of the presence of a mature embryo sac.

Auxin regulated metabolic changes underlying sepal retention and development after pollination in spinach

BackgroundPollination accelerate sepal development that enhances plant fitness by protecting seeds in female spinach. This response requires pollination signals that result in the remodeling within the sepal cells for retention and development, but the regulatory mechanism for this response is still unclear. To investigate the early pollination-induced metabolic changes in sepal, we utilize the high-throughput RNA-seq approach.ResultsSpinach variety ‘Cornel 9’ was used for differentially expressed gene analysis followed by experiments of auxin analog and auxin inhibitor treatments. We first compared the candidate transcripts expressed differentially at different time points (12H, 48H, and 96H) after pollination and detected significant difference in Trp-dependent auxin biosynthesis and auxin modulation and transduction process. Furthermore, several auxin regulatory pathways i.e. cell division, cell wall expansion, and biogenesis were activated from pollination to early developmental symptoms in sepals following pollination. To further confirm the role auxin genes play in the sepal development, auxin analog (2, 4-D; IAA) and auxin transport inhibitor (NPA) with different concentrations gradient were sprayed to the spinach unpollinated and pollinated flowers, respectively. NPA treatment resulted in auxin transport weakening that led to inhibition of sepal development at concentration 0.1 and 1 mM after pollination. 2, 4-D and IAA treatment to unpollinated flowers resulted in sepal development at lower concentration but wilting at higher concentration.ConclusionWe hypothesized that sepal retention and development might have associated with auxin homeostasis that regulates the sepal size by modulating associated pathways. These findings advanced the understanding of this unusual phenomenon of sepal growth instead of abscission after pollination in spinach.

The genotypic response towards haploid induction in Turkish onion (Allium cepa L.) germplasm

Haploid induction efficiency of unpollinated flower buds in twenty-six Turkish onion germplasm were determined on two media, Dunstan and Short medium (BDS) and Murashige and Skoog’s medium (MS). On BDS medium, 5850 flower buds were cultured and the induction rate was 2.10% and a plant survival percentage of 1.62% (2 plants). On MS medium, 5850 flower buds were cultured and 175 plantlets were induced; induction rate was 2.99% and plant survival percentage was 13.71% (24 plants). The highest number of plantlets was obtained from genotype Sanliurfa 2; 27 plantlets on BDS medium while 45 plantlets on MS medium. Flow cytometry confirmed that out of the twenty-six plants, 4 plants were haploid (15.38%), 2 mixoploid (7.69%), 18 (69.23%) diploid and 2 tetraploid (7.69%).

Haploid Induction via In Vitro Gynogenesis in Persian Shallot (Allium hirtifolium)

Abstract Haploid induction using in vitro cultures of unpollinated flowers has been recognized as an important tool to produce homozygous plants for genetic studies and breeding programs. In this study the potential of gynogenic haploid induction in four ecotypes of Allium hirtifolium under different combinations of benzylaminopurine (BAP) with 2,4-dichlorophenoxyacetic acid (2,4-D), or α-naphthaleneacetic acid (NAA) was investigated. Unpollinated flower buds were excised from an umbel 5 to 3 days before anthesis, and cultured onto B5 medium containing 7.5% sucrose and 2 mg·dm−3 BAP with auxin. The experiments revealed that NAA increased the percentage of gynogenesis induction and number of gynogenic embryos per flower in all ecotypes. Somatic organogenesis from basal callus or other floral parts was most effective on the media containing 2,4-D. Plants obtained by gynogenesis were haploid in 70–77% and plants from somatic tissue were mostly diploid.

Pollination elicits an accelerated reduction in nocturnal scent emission by flowers of the dioecious herb Silene latifolia

More than 85% of plants rely on biotic pollen vectors attracted by olfactory or visual signals. While these signals are beneficial for plant reproduction, they are also costly in terms of resource investment, and may involve additional costs related to herbivore attraction, transmission of diseases, and increased transfer of self-pollen among flowers of an individual plant. Given the potential costs of signalling to pollinators, we hypothesized that plants should cease signalling to pollinators as soon as the costs of being attractive exceed the benefits. Here, we used the herb Silene latifolia Poir., which is pollinated by the nocturnal seed-predator Hadena bicruris, to investigate the possible reduction of scent emission after pollination. We compared the progressive decrease of scent and attractive compound emission between pollinated and unpollinated flowers on an hourly basis, overnight. We found that total scent emission decreased significantly faster over time for pollinated than for non-pollinated flowers. Our findings suggest that the costs of maintaining the attractiveness of pollinated flowers of Silene latifolia exceed the benefits, which could be linked with the risks of parasitism.

Abnormalities in the ovule development of the European plum cultivar ‘Pozna Plava’ in the days following anthesis

Factors such as the stage of ovule maturity and longevity at flowering, when the stigma is able to receive the pollen, are significant in terms of fruit set. Various abnormalities during ovule development can often limit pollination, effective pollination period (EPP) and fruit set. In the plum cultivar ‘Pozna Plava’ (Prunus domestica L.), in the ovaries of open-pollinated flowers and of emasculated unpollinated flowers, we investigated abnormalities in the tissues of primary and secondary ovules during the time of anthesis until 10 days thereafter. At the same time, the viability of the ovules of the unpollinated flowers was examined. Abnormal ovules were considered those with degenerations in the egg apparatus, inverse arrangement of egg cells, more than eight nuclei in the embryo sac as well as degeneration of the nucellus and integuments. In primary ovules, the most frequent abnormality in open-pollinated and unpollinated flowers was the degeneration of the egg apparatus, with frequencies of 14.3–50.0% and 10.0–89.0%, respectively. In the secondary ovules, in both treatments, a completely different picture was obtained. The processes that led to abnormalities in the structure of the secondary ovules first occurred in the cells of the nucellus, while the elements of the embryo sac had a relatively normal cytological organisation. However, the observed abnormalities do not explain the low fruit set of this cultivar.

Differential deployment of sanctioning mechanisms by male and female host trees in a gynodioecious fig-wasp mutualism.

In some insect nursery pollination mutualisms, plant hosts impose net costs to uncooperative "cheater" symbionts. These "sanctions" promote mutualism stability but their precise adaptive nature remains unclear. In fig-wasp mutualisms host trees (Ficus spp.) are only pollinated by female agaonid wasps whose larvae only use galled fig flowers as food. In actively pollinated systems, if wasps fail to pollinate, sanctions can result via fig abortion, killing all wasp offspring, or by increased offspring mortality within un-aborted figs. These sanctions result from selective investment to pollinated inflorescences, a mechanism present in almost all angiosperms. To more fully understand how selective investment functions as sanctions requires the measurement of variation in their costs and benefits to both hosts and symbionts. Gynodioecious fig-tree-fig-wasp mutualisms are particularly suitable for this because pollen and wasps are produced only in the figs of "male" trees and seeds only in the figs of "female" trees. Male and female trees thus incur different net costs of pollen absence, and costs of sanctions to pollen-free "cheater" wasps only occur in male trees. We used the actively pollinated host tree Ficus hispida and introduced into male and female figs either 1, 3, 5, 7, or 9 all pollen-laden "cooperative" (P+) or all pollen-free "cheater" (P-) wasps. Abortion in both male and female trees was highest in P- figs, with P- fig abortion higher in females (~90%) than in males (~40%). Fig abortion was negatively associated with foundress number mainly in P+ figs; in P- figs abortion was only weakly associated with the number of "cheater" wasps, especially in female figs. In un-aborted male figs, wasp offspring mortality was higher in P- figs than in P+ figs, and in P- figs correlated positively with foundress (cheater) number. Increased offspring mortality was biased against female wasp offspring and likely resulted from reduced larval nutrition in unpollinated flowers. Variation in selective investment to P- figs thus reflects costs and benefits of pollen absence/presence to hosts, variation that translates directly to net costs to cheater wasps.

Ovule senescence and unusual pollen tube growth in the ovary of sweet cherry as affected by pistilar genotype and temperature

The study of ovule senescence in the ovaries of four sweet cherry cultivars (‘Karina᾿, ‘Kordia᾿, ‘Regina᾿ and ‘Summit᾿) in the environmental conditions of West Serbia was carried out. Monitoring of ovaries was performed using the fluorescence microscopy method, on emasculated and pollinated flowers (cross-pollination variant), non-emasculated open-pollinated flowers (open pollination variant), and emasculated unpollinated flowers (unpollinated variant). In cross- and open pollination variants, the rate of unusual pollen tube growth in the ovary, fertilization percentage and fruit set were determined. The tendency in the appearance of fluorescence, as an indicator of ovule senescence, showed strong genotypic dependence ‒ it was the most and the least pronounced in the ovaries of ‘Kordia’ and ‘Regina’, respectively, in all the flower categories. Investigation of unusual pollen tube growth, fertilization percentage and fruit set, considered from the aspect of ovule senescence and cultivars’ behaviour as female (pollinated), pointed to their specific relations and complex dependence on the air temperature before and during the flowering. Flower emasculation and pollination also influenced ovule senescence, and this impact was unequal by genotypes, i.e. those having better ovule vitality in general, had also better ovule vitality in the conditions of emasculation, and pollination absence. The results imply different adaptation of cultivars to higher temperatures before and during the flowering, pointing to the further investigation related to the good adaptability of genotypes to air temperatures in reproductive sense, which is a basic indicator of good adaptability in general.

Mating systems and avoidance of inbreeding depression as evolutionary drivers of pollen limitation in animal-pollinated self-compatible plants.

Most theory addressing the evolution of pollen limitation in flowering plants focuses on stochasticity in the relative abundance of plant and pollinator populations affecting trade-offs in resource allocation to ovule production or pollinator attraction vs. seed maturation. Mating system evolution is an underappreciated but potentially widespread additional mechanism for the evolutionary emergence of pollen limitation in animal-pollinated self-compatible plants. We model individual plant flowering phenologies influencing both pollinator attraction and geitonogamous self-fertilization caused by pollinator movements among flowers within plants, incorporating demographic but not environmental stochasticity. Plant phenology and the resulting pollen limitation are analysed at evolutionarily stable equilibria (ESS). Pollen limitation is measured by two quantities: the proportion of unpollinated flowers and the reduction in maternal fitness caused by inbreeding depression in selfed seeds. When pollinators visit multiple flowers per plant, pollen limitation is never minimized at an ESS and results from the evolution of flowering phenologies balancing the amount and genetic composition (outbred vs. inbred) of pollen receipt. Results are consistent with previous theory demonstrating that pollen limitation can be an evolved property, not just a constraint; they complement existing models by showing that plant avoidance of inbreeding depression constitutes a genetic mechanism contributing to evolution of pollen limitation, in addition to ecological mechanisms previously studied.

Floral nectary and osmophore of Epipactis helleborine (L.) Crantz (Orchidaceae)

The analysis of flowers collected at different stages of anthesis provides strong evidence to conclude that the shell-shaped hypochile and the knobs of epichile form a nectary. The scent comes from the aromatic constituents of nectar and the epichile tissue and the apices of all tepals (osmophores). The comparison between pollinated and unpollinated flowers revealed that the anthesis of unpollinated flowers lasted up to the 16th day. The nectariferous secretory cells formed single-layered epidermis and several layers of underlying parenchyma built by small, isodiametric cells with thin walls and dense cytoplasm, relatively large nuclei, supplied by collateral vascular bundles. During the floral lifespan, the residues of secreted material were higher on the hypochile cells. The lipoid-carbohydrate material and lipid globules in the cell walls and in the cytoplasm were localised. The abundance of starch grains was observed at the beginning of anthesis and their gradual reduction during the flower lifespan. At the end of anthesis in unpollinated flowers, the lipoid-carbohydrate-phenolic materials have been demonstrated. The phenolic material was the same as in plastoglobuli. The features such as irregular plasmalemma, the secretory vesicles that fuse with it, fully developed dictyosomes, numerous profiles of ER indicate vesicle-mediated process of secretion. The substances could be transported by vesicles to the periplasmic space via granulocrine secretion and then to the external surface. Both micro-channels and slightly developed periplasmic space were visible in the hypochile epidermis. This is the first time for anatomical survey of secretory tissue in pollinated and unpollinated flowers of E. helleborine.

Influence of Culture Media and Their Compositions on Haploid Induction in Indian Short Day Onion

Two media, Gamborg’s medium (B5) and Murashige and Skoog’s medium (MS) with various combinations, were used to study their effect on haploid induction efficiency from unpollinated flowers or ovaries in tropical short day onion. In B5 medium, highest induction efficiency (1.9%) was observed on HAP18 followed by HAP17 and HAP05 whereas in MS medium, HAP40 recorded highest induction frequency (5.0%) followed by HAP32. Kinetin, meta-topolin, thidiazuron did not influence embryo induction. Sucrose at 7.5% in B5 medium and at 10% in MS medium was found to be optimum for induction. Days for plantlet induction were 98.9 ± 3.9 days in B5 medium and 83.1 ± 2.7 days in MS medium. Induction rate of 0.51% and survival of 27.8% in B5 medium and induction rate of 0.72% and survival of 33% in MS medium were observed. Three haploids, 1 mixoploid and 1 diploid in B5 medium and 2 haploids, one diploid in MS medium were obtained. Flow cytometry and cytology confirmed the status of haploid plants. MS medium was found to be better than B5 medium and newer combinations for haploid induction were identified. Plant Preservative Mixture (PPM™) at 1 mg/l was found to be efficient for inhibiting contamination from field grown flower buds. These combinations will be helpful in devising new strategies for faster and higher rate of haploid induction in tropical short day Indian cultivars.

Influence of pollination on seed content and mealiness development in ‘Forelle’ pear as detected with X-ray micro- and nano-computed tomography (CT)

'Forelle' pear fruit is prone to mealiness. The aim of this study was to establish whether pollination and seed development influence the mealiness and tissue structure by characterising microstructural differences using X-ray computed tomography (CT). Flowers of five mature 'Forelle' trees were emasculated and hand cross-pollinated with 'Early Williams Bon Chretien' pollen. Another five trees were emasculated without hand pollination. After harvesting and storage for 8 weeks at -0.5°C and subsequent ripening for 7 d at 20°C, nine pollinated and nine unpollinated pears were subjected to X-ray CT. A non-destructive X-ray micro-CT was used to visualise the internal structure of the whole fruit and to investigate seed development and density variations in regions next to viable or aborted seeds. A source voltage of 100 kV and electron current of 100 μA resulted in a resolution of 75 μm. Additional high resolution (3 μm) scans were performed on a section of the neck and equator, respectively. Nano-CT allowed for characterisation and quantification of microstructural parameters at cellular level. Fruits without viable seeds was more prone to mealiness compared to fruit with viable seeds. Differences in tissue density next to viable and aborted seeds were observed, with the region next to viable seeds being denser. Pollinated fruit had a lower porosity, indicating that these fruits may have a better source of hormones due to the viable seeds, resulting in lower mealiness incidence. Mealiness is associated with a high porosity and larger cells. Although not significant (P>0.05), fruit from unpollinated flowers was associated with larger cells, higher porosities and low connectivity between cells. This study demonstrated that X-ray CT is useful for characterising and quantifying microstructural differences related to mealiness in seeded and parthenocarpic 'Forelle' pears.

Does lack of pollination extend flower life?

Across angiosperm species, the longevity of individual flowers can range from fixed to highly plastic. The orchid family is noteworthy for frequent reports of species in which flower lifespans are greatly prolonged if flowers are not pollinated. Less dramatic cases of pollination-induced senescence of anthesis have been reported for various species in other families, but such reports are scattered. Frequently, such findings are peripheral components of more general pollination studies. Because pollination-dependent plasticity can ameliorate phenological dislocations between plants and pollinators, it is worthwhile to conduct systematic surveys of its magnitude and taxonomic distribution. As a start, we report a set of experiments comparing the active lifespans of pollinated flowers to those of unpollinated controls in a set of nine species from a local subalpine flora. In all species, unpollinated flowers had longer mean times of receptiveness than pollinated ones, although the differences in means were often small. Three species exhibited significantly extended floral longevity in the absence of pollination.

Downregulating a Type I Metacaspase in Petunia Accelerates Flower Senescence

Metacaspases are cysteine proteases from plants, fungi, and protozoans that have structural similarity to metazoan caspases. They play a critical role in programmed cell death (PCD) induced by developmental cues and environmental signals. In this study, a type I metacaspase (PhMC1) was identified and characterized from Petunia ×hybrida ‘Mitchell Diploid’ (MD) (petunia). The recombinant PhMC1 had activity against the metacaspase substrate Boc-GRR-AMC (GRR). Activity was highest at pH 7–9 and was dependent on the active site C237. Quantitative polymerase chain reaction (qPCR) showed that PhMC1 transcripts increased at a later stage of petal development, when corollas were visibly senescent in both pollinated and unpollinated flowers. Gene expression patterns were similar to that of the senescence-related gene PhCP10, a homolog of Arabidopsis thaliana (arabidopsis) AtSAG12. PhMC1 transcripts were upregulated in the petals by ethylene treatment. This ethylene regulation did not require protein synthesis, indicating that PhMC1 is a primary ethylene response gene. Metacaspase-like activity against Boc-GRR-AMC increased in protein extracts from senescing petals. RNAi was used to knock down the expression of PhMC1. Transgenic PhMC1 petunias had no abnormal, vegetative growth phenotypes under normal greenhouse conditions, but flower senescence was accelerated by an average of 2 days.