Pollen Tube Length Research Articles

Fountain streaming contributes to fast tip-growth through regulating the gradients of turgor pressure and concentration in pollen tubes.

Fountain streaming is a typical microfluidic pattern in plant cells, especially for cells with a high aspect ratio such as pollen tubes. Although it has been found that fountain streaming plays crucial roles in the transport of nutrients and metabolites, the positioning of organelles and the mixing of cytoplasms, its implications for the fast tip growth of pollen tubes remain a mystery. To address this, based on the observations of asiatic lily Lilium Casablanca, we developed physical models for reverse fountain streaming in pollen tubes and solved the hydrodynamics and advection-diffusion dynamics of viscous Stokes flow in the shank and apical region of pollen tubes. Theoretical and numerical results demonstrated that the gradients of turgor pressure and concentration of wall materials along the length of pollen tubes provide undamped driving force and high-efficiency materials supply, which are supposed to contribute to the fast tip-growth of pollen tubes. The sample experimental results show that the tip-growth will be abnormal when the gradients of turgor pressure change under osmotic stress induced by different concentrations of PEG-6000 (a dehydrant).

Effects of Ca2+ on in vitro pollen germination of three Acacia species

Abstract We investigated the effects of Ca2+ on in vitro pollen germination of Acacia auriculiformis, Acacia mangium, and Acacia crassicarpa under different concentrations of Ca2+ (50 mg.L−1, 100 mg.L−1, 150 mg.L−1, 200 mg.L−1, 250 mg.L−1, 300 mg.L−1, 350 mg.L−1 and 400 mg.L−1) in the present study. Our results revealed that Ca2+ could stimulate the pollen germination percentage and the pollen tube growth of A. auficuliformis and A. crassicarpa under a certain concentration. In vitro pollen germination of A. mangium did not require exogenous Ca2+. With high Ca2+ concentration, the pollen germination of A. auriculiformis, A. mangium, and A. crassicarpa were obviously inhibited. With the rise of Ca2+ concentration, the percentage of pollen germination, the pollen tube length, the pollen tube growth, and the number of pollen tube were increased. However, the pollen germination percentage decreased with high Ca2+ concentration.

Pollen aquaporins: What are they there for?

ABSTRACTIn order to provide more insight into the function of aquaporins during pollination, we characterized NIP4;1 and NIP4;2, 2 pollen-specific aquaporins of Arabidopsis thaliana. NIP4;1 and NIP4;2 displayed high amino acid identity. RT-PCR and GUS promoter analysis showed that they have different expression patterns. NIP4;1 is expressed at low levels in mature pollen, while NIP4;2 is highly expressed only during pollen tube growth. Single T-DNA nip4;1 and nip4;2 mutants and double amiRNA nip4;1 nip4;2 knockdowns showed reduced male fertility due to deficient pollen germination and pollen tube length. Functional assays in oocytes showed that NIP4;1 and NIP4;2 transport water and nonionic solutes. Here, the participation of the different pollen aquaporins in pollen hydration and pollen tube growth is discussed.

Pollen-Specific Aquaporins NIP4;1 and NIP4;2 Are Required for Pollen Development and Pollination in Arabidopsis thaliana.

In flowers with dry stigmas, pollen development, pollination, and pollen tube growth require spatial and temporal regulation of water and nutrient transport. To better understand the molecular mechanisms involved in reproductive processes, we characterized NIP4;1 and NIP4;2, two pollen-specific aquaporins of Arabidopsis thaliana. NIP4;1 and NIP4;2 are paralogs found exclusively in the angiosperm lineage. Although they have 84% amino acid identity, they displayed different expression patterns. NIP4;1 has low expression levels in mature pollen, while NIP4;2 expression peaks during pollen tube growth. Additionally, NIP4;1pro:GUS flowers showed GUS activity in mature pollen and pollen tubes, whereas NIP4;2pro:GUS flowers only in pollen tubes. Single T-DNA mutants and double artificial microRNA knockdowns had fewer seeds per silique and reduced pollen germination and pollen tube length. Transport assays in oocytes showed NIP4;1 and NIP4;2 function as water and nonionic channels. We also found that NIP4;1 and NIP4;2 C termini are phosphorylated by a pollen-specific CPK that modifies their water permeability. Survival assays in yeast indicated that NIP4;1 also transports ammonia, urea, boric acid, and H2O2 Thus, we propose that aquaporins NIP4;1 and NIP4;2 are exclusive components of the reproductive apparatus of angiosperms with partially redundant roles in pollen development and pollination.

Heat tolerance evaluation in commercial African violet cultivars using physiological and pollen parameters

High temperatures negatively affect the vegetative and reproductive growth of African violets thus decreasing their aesthetic and commercial values. No scientific information is currently available on cultivar tolerance to high temperatures in this plant. This study was conducted with the objective of evaluating heat tolerance in commercial African violet cultivars using a combination of physiological and pollen parameters and ranking the cultivars based on their cumulative temperature response index (CTRI). Physiological parameters including cell membrane thermostability (CMT), canopy temperature depression (CTD) and chlorophyll stability index (CSI) were analyzed using fully expanded leaves. In vitro pollen germination percentage (PG) and pollen tube length (PTL) were estimated at between 10 and 40°C. Cardinal temperatures (Tmin, Topt, and Tmax) of PG and PTL, as well as maximum PG percentage (PGmax) and maximum PTL (PTLmax), were estimated using the modified bilinear model. Results showed the different cultivars varied significantly for their CMT (5.39–74.07%), CTD (−1.65 to 0.61°C) and CSI (70.16–81.06%). They also differed for PG (mean of 54.43%), PTL (mean of 3109.08μm), and cardinal temperatures (Tmin=−2.5°C, Topt=24.9°C, and Tmax=49.9°C for PG; Tmin=3.4°C, Topt=26.0°C, and Tmax=43.1°C for PTL). The CTRI of each cultivar was calculated as the sum of individual stress response index (ISRI) derived from CMT, CTD, CSI, and PGmax, PTLmax, Tmin, Topt, and Tmax for PG and PTL. Among the thirty cultivars screened, the cultivars ‘Rob's Ooey Gooey’ and ‘Mac's Stop Sign’ had high CTRI values for the physiological and pollen parameters, singly or in combination, so are potential candidates to be used for the development of novel heat tolerant genotypes.

5-Aminolevulinic Acid Thins Pear Fruits by Inhibiting Pollen Tube Growth via Ca(2+)-ATPase-Mediated Ca(2+) Efflux.

Chemical fruit thinning has become a popular practice in modern fruit orchards for achieving high quality fruits, reducing costs of hand thinning and promoting return bloom. However, most of the suggested chemical thinners are often concerned for their detrimental effects and environmental problems. 5-Aminolevulic acid (ALA) is a natural, nontoxic, biodegradable, and environment-friendly plant growth regulator. One of its outstanding roles is improving plant photosynthesis and fruit quality. Here, results showed that applying 100–200 mg/L ALA at full bloom stage significantly reduced pear fruit set. Both in vivo and in vitro studies showed that ALA significantly inhibited pollen germination and tube growth. ALA decreased not only cytosolic Ca2+ concentration ([Ca2+]cyt) but also “tip-focused” [Ca2+]cyt gradient, indicating that ALA inhibited pollen tube growth by down-regulating calcium signaling. ALA drastically enhanced pollen Ca2+-ATPase activity, suggesting that ALA-induced decrease of calcium signaling probably resulted from activating calcium pump. The significant negative correlations between Ca2+-ATPase activity and pollen germination or pollen tube length further demonstrated the critical role of calcium pump in ALA's negative effect on pollen germination. Taken together, our results suggest that ALA at low concentrations is a potential biochemical thinner, and it inhibits pollen germination and tube growth via Ca2+ efflux by activating Ca2+-ATPase, thereby thinning fruits by preventing fertilization.

The effect of temperature on pollen germination and pollen tube growth of pear cultivars

The effect of three different temperatures (8, 16 and 24?C) on pollen germination and length of pollen tube in vitro was investigated in four pear cultivars (?Butirra Precoce Morettini?, ?Williams?, ?Conference? and ?Abate Fetel?). The temperature showed a significant effect on in vitro pollen germination. The highest pollen germination was determined at a temperature of 24?C (53.25%), somewhat lower at 16?C (44.72%) and the lowest at 8?C (23.16%). The temperature effect was significantly more pronounced on the length of pollen tube. Pollen tube length was about three times higher at the temperatures of 16 and 24?C compared to 8?C. The temperature of 8?C was not sufficient for pollen germination and pollen tube growth in pear cultivars. However, temperatures of 16 and 24?C were optimal for pollen germination and pollen tube growth.

Effect of nickel on pollen germination and pollen tube length in Arabis alpina (Brassicaceae)

In this work we studied and compared the toxic effect of nickel (Ni) on pollen germination and pollen tube length in Arabis alpina L. collected from serpentine and non-serpentine populations distributed in the Rila mountains, Bulgaria. Pollen grains were treated with prepared standard solutions of 100, 300, 500, and 700 μM Ni as NiCl2 in distilled water. A nutritional medium was also used to assess pollen germination. Nickel inhibited pollen germination and pollen tube elongation in both serpentine and non-serpentine plants. The percentage of germinated pollen in serpentine plants treated with Ni was higher than in non-serpentine plants but there was no difference in pollen tube elongation between groups. However, pollen tubes showed abnormalities such as coiling and swelling of the tip, or burst, and varied considerably among the samples. A complete break of pollen tube elongation is due to such abnormalities. Also, decreased pollen fertility in both populations was found. The plants from serpentines were less sensitive to (i.e. more tolerant of) elevated Ni concentrations commonly found in serpentine soils.

Microsporogenesis and meiotic abnormalities in different ‘Oblačinska’ sour cherry (Prunus cerasus L.) clones

The Oblačinska sour cherry (Prunus cerasus) is a mixture of different clones with similar tree and fruit characteristics that is indigenous to and widely planted in commercial orchards in Serbia. Sour cherry, including Oblačinska sour cherry clones, exhibits irregular meiosis which may contribute to low fruit set in some selections. The goal of this study was to examine the process of microsporogenesis and to determine if meiosis and its anomalies effect the in vitro pollen germination and pollen tube length in four ‘Oblačinska’ sour cherry clones that differ in fruit set and yields. All clones displayed varying degrees of chromosomal abnormalities in all meiosis sub-phases. The abnormalities became evident from late pachytene with more than half of the pollen mother cells (PMC) showing abnormal conjugation of chromosomes in metaphase I. The lowest number of PMCs with laggards was in clone III/9 and the highest in clone XIII/1. In second division, the univalent and multivalent association was observed at metaphase-II, the lagging and stickiness in anaphase-II, and the phenomenon persisted up to the microspore stage. In all four ‘Oblačinska’ clones, PMCs exhibited cytomixis phenomena, however, it was only observed in the second experimental year. Cytomixis differed among the four clones but was equally frequent in all stages of meiosis. The syncytia formed, most often consisted of 2–3 PMCs that were at the same phase of meiosis, and exhibited common cytoplasm and occasionally nuclear fusion. In vitro pollen germination and pollen tube length significantly differed between the clones. Most probably abnormalities during meiosis, regardless of the good results of pollen germination, influenced the reduced potential clones XI/3 and XIII/1.

Growth, Photosynthesis and Pollen Performance in Saline Water Treated Olive Plants under High Temperature

Olive cultivation in hot arid areas is hindered by the scarcity of irrigation water. The exploitation of saline water has been proposed as a solution to partially cover plant water demands. This paper presents the effects of salinity [0, 60 and 120 mM sodium chloride (NaCl)] on physiological and reproductive functions of cultivars Koroneiki and Amphissis in a closed hydroponic system. Shoot growth was markedly reduced in high salinity dose in Amphissis (−81%) and Koroneiki (−75%). The photosynthetic rate was significantly reduced at 120 mM NaCl for both cultivars, as well as chlorophyll and carotenoids content (43% and 44%, respectively). The Na+ content in all plant parts increased in both salinity doses especially in Amphissis while K concentration decreased for both cultivars. Inflorescences in Amphissis were severely damaged due to salinity. Consequently, pollen sampling and in vitro germination study was only feasible for Koroneiki. Indeed, Koroneiki pollen germination was reduced at 60 mM NaCl (−42%) and at 120 mM NaCl (−88%). Pollen tube length was also reduced by 15% and 28% for the middle and high salinity dose, respectively. The results of the present study indicate that Amphissis is more sensitive in high salinity doses compared to Koroneiki and that reproductive functions are severely affected by salinity.

In vitro Teasle Gourd Pollen Germination and Pollen Tube Development as Affected by Sucrose, Boric Acid, and Inorganic Salts

ABSTRACTThe rapid rate of pollen tube formation in vitro exhibited by some plant species has become a model system for studying growth and development in plants during the past decades. In vitro pollen germination and pollen tube characters were examined as they were affected by nutrient media in Teasle gourd [Momordica subangulata Blume ssp. renigera (G. Don) de Wilde]. Concentrations of sucrose or boric acid, applied separately or in combination, and inorganic salts (potassium nitrate, magnesium sulfate, calcium nitrate) were used as growth media. The best pollen germination (49.82%), highest pollen tube length (77.81 μm), and maximum recovery (36.73%) of intact pollen tube were with 20% sucrose + 0.025% boric acid. Use of inorganic salts in low concentrations negated the benefits of sucrose or boric acid. Germination of pollen grain and subsequent growth of pollen tubes are at least in part physiologically independent in this crop. Considerable rupturing of pollen tubes in boron-deficient media and integration of pollen tubes in calcium-rich media occurred. Sucrose and boric acid beneficially influenced pollen germination and pollen tube formation in teasle gourd.

Arabidopsis Qc-SNARE genes BET11 and BET12 are required for fertility and pollen tube elongation.

Key message BET11 and 12 are required for pollen tube elongation.Pollen tubes are rapidly growing specialized structures that elongate in a polar manner. They play a crucial role in the delivery of sperm cells through the stylar tissues of the flower and into the embryo sac, where the sperm cells are released to fuse with the egg cell and the central cell to give rise to the embryo and the endosperm. Polar growth at the pollen tube tip is believed to result from secretion of materials by membrane trafficking mechanisms. In this study, we report the functional characterization of Arabidopsis BET11 and BET12, two genes that may code for Qc-SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors). Double mutants (bet11/bet12) in a homozygous/heterozygous background showed reduced transmission of the mutant alleles, reduced fertilization of seeds, defective embryo development, reduced pollen tube lengths and formation of secondary pollen tubes. Both BET11 and BET12 are required for fertility and development of pollen tubes in Arabidopsis. More experiments are required to dissect the mechanisms involved.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-015-0102-x) contains supplementary material, which is available to authorized users.

Seed set, pollen morphology and pollen surface composition response to heat stress in field pea.

Pea (Pisum sativum L.) is a major legume crop grown in a semi-arid climate in Western Canada, where heat stress affects pollination, seed set and yield. Seed set and pod growth characteristics, along with in vitro percentage pollen germination, pollen tube growth and pollen surface composition, were measured in two pea cultivars (CDC Golden and CDC Sage) subjected to five maximum temperature regimes ranging from 24 to 36 °C. Heat stress reduced percentage pollen germination, pollen tube length, pod length, seed number per pod, and the seed-ovule ratio. Percentage pollen germination of CDC Sage was greater than CDC Golden at 36 °C. No visible morphological differences in pollen grains or the pollen surface were observed between the heat and control-treated pea. However, pollen wall (intine) thickness increased due to heat stress. Mid-infrared attenuated total reflectance (MIR-ATR) spectra revealed that the chemical composition (lipid, proteins and carbohydrates) of each cultivar's pollen grains responded differently to heat stress. The lipid region of the pollen coat and exine of CDC Sage was more stable compared with CDC Golden at 36 °C. Secondary derivatives of ATR spectra indicated the presence of two lipid types, with different amounts present in pollen grains from each cultivar.

Comparative Study of in Vitro and in Vivo Inflorescence of Feathered Amaranth

This study aimed to compare the inflorescence, florets and pollen formed by the plantlets of feathered amaranth [Celosia argentea var. plumosa (Burvenich) Voss] developed and grown under in vitro conditions with those formed by the plants grown under in vivo conditions. Plantlets were first derived from nodal explants of feathered amaranth cultured on Murashige and Skoog (MS) semi-solid medium under in vitro aseptic conditions, and then the plantlets produced in vitro inflorescences, florets and pollen. In parallel, inflorescences, florets and pollen of plants raised from feathered amaranth seeds under in vivo conditions were obtained for the comparative purpose. The results revealed that florets from both sources were largely similar except the size. The in vitro florets were mainly smaller than those of the in vivo ones. Also in vivo pollen exhibited a higher germination percentage and average pollen tube length than in vitro pollen when cultured on a pollen germination medium.

Screening and validation of tomato genotypes under heat stress using Fv/Fm to reveal the physiological mechanism of heat tolerance

Cultivation of tomatoes at high temperatures negatively affects growth and yield. Our aim was to screen tomato genotypes under heat stress for differences in the maximum quantum efficiency of photosystem II (Fv/Fm) and uncover the physiological traits for heat tolerance in a three-step process. Initially, 67 tomato genotypes were ranked according to Fv/Fm. Two genotypes with higher Fv/Fm (heat-tolerant group) and two genotypes with lower Fv/Fm (heat-sensitive group) were selected from the initial screening. Second, the physiological responses of the four genotypes to seven days of heat stress (36/28°C) were analyzed in detail. Third, pollen germination and fruit set of the four genotypes were investigated at high temperature conditions in the field. The results showed that the heat-tolerant group maintained higher leaf pigment content and higher total phenolic content (TPC) than the heat-sensitive group under heat stress. The heat-tolerant group maintained unaltered stomata and pore area and net photosynthesis rate (PN) but increased stomatal conductance (gs) under heat stress compared with the control. Chloroplasts in the heat-tolerant group maintained a normal shape, whereas the chloroplasts in the heat-sensitive group became swollen with decomposed starch grain after heat stress. The heat-tolerant group exhibited a higher pollen germination rate (%), longer pollen tube length and higher fruit set rate compared with the heat-sensitive group at high temperatures in the field. Thus, we concluded that Fv/Fm is an early indicator of heat stress tolerance and that the responses of tomatoes to heat stress were identical in widely different growing conditions. The stay-green trait, improved ability of stomata regulation and higher contents of reactive oxygen species scavengers seemed to be part of the protective mechanisms in heat-tolerant tomatoes.

Ultraviolet-B radiation or heat cause changes in photosynthesis, antioxidant enzyme activities and pollen performance in olive tree

The present study attempts to determine how some physiological and reproductive functions of olive tree (Olea europaea L., cv. Koroneiki) respond to enhanced UV-B radiation or heat. Enhanced UV-B radiation was applied to (1) three-year-old potted plants in an open nursery (corresponded to ca. 16% ozone depletion), and (2) in vitro cultured pollen samples (220 μmol m−2 s−1, PAR = 400−700 nm + UV-B at 7.5, 15.0, or 22.5 kJ m−2 d−1). Potted olive plants were also subjected to high temperature (38 ± 4°C) for 28 h to mimic heat levels regularly measured in olive growing areas. A significant effect of UV-B on photosynthetic rate was observed. However, enhanced UV-B radiation did affect neither chlorophyll nor carotenoid content, supporting previous reports on hardiness of the photosynthetic apparatus in olive. Increased superoxide dismutase activity was observed in UV-B-treated olive plants (+ 225%), whereas no effect was found in the plants under heat stress. Neither UV-B and nor heat did affect H2O2 accumulation in the plant tissues. However, the same treatments resulted in enhanced lipid peroxidation (+ 18% for UV-B and + 15% for heat), which is likely linked to other reactive oxygen species. The increased guaiacol peroxidase activity observed in both treatments (+ 32% for UV-B and + 49% for heat) is related to the defense against oxidative membrane damage. The observed reduction in pollen germination (20–39%) and tube length (11–44%) could have serious implications on olive yields, especially for low fruit-setting cultivars or in years and environments with additional unfavorable conditions. UV-B and heat effects described here support the hypothesis that plant response to a given stressor is affected by the overall context and that a holistic approach is necessary to determine plant strategies for climate change adaptation.

Dalsze studia cyto-embriologiczne di-, tetra- i oktoploidaluych form Trifolium [Further cyto-embryological studies on di, tetra- and octoploid forms of Trifolium

In the course of this study no significant differences in the length of pollen-tubes of ecological types collected from natural stations (<i>Trifolium pratense</i> L. var. spontaneum Willk., <i>T. hybridum</i> L. and <i>T. repens</i> L,) were found as compared with their polyploid forms obtained in the experimental way. Disorders in fertilization, decay of unfertilized embryo sacs, and degeneration of embroys were observed more frequently on a percentage basis in the polyploid forms. Embryo and endosperm development were similar in the initial species and in the experimentally obtained polyploids.

Pollen study of wild Noni (Morinda tomentosaHeyne ex Roth)

The mean size of pollen grains of Morinda tomentosa varied in different media with comparatively larger size in distilled water. The pollen viability varied between 83.47 to 95.53% among the accessions. Fifteen to twenty per cent solo sucrose medium appeared precise for pollen germination. The boric acid addition irrespective of concentration (0.005 and 0.01%) in sucrose medium of different concentrations impacted the pollen germination. The germination was highest (85.26%) when 0.005% boric acid was added to 10% sucrose solution. Further, the lower concentration of boric acid (0.005%) evinced better germination of pollen grains than higher concentration of boric acid. The average pollen tube length was maximum (62.42 μ) in 15% sucrose solution while it was minimum (14.36 μ) in 30% sucrose solution indicating intermediate concentration of sucrose medium as appropriate for growth of pollen tube. The addition of boric acid to sucrose medium evinced clear impact on growth of pollen tube with maximum average pollen tube length of 120.74 μ recorded in 15% sucrose medium fortified with 0.005% boric acid.

A novel in vitro germination method revealed the influence of environmental variance on the pecan pollen viability

Pecan is one of the most important horticultural nut crops in the world. Germination tests are vital to the safe application of artificial pollination and cross breeding of pecan. Although many in vitro germination methods have been proposed, the realization of robust and reproducible methods to induce morphologically normal growth pollen tubes in vitro for detailed dynamic observation has often proved challenging in pecan. We employed a mixing and spreading method to realize the uniform distribution and germination on agarose medium, which resulted in the unprecedented level of germinational repeatability and observability. With this method, we investigated the influence of environmental variance on the in vitro germination of pecan pollen. The data from germination rate, burst rate, pollen tube length and germination speed indicated the pecan pollen had an optimal germination temperature at 25°C but optimal rehydration temperature at 16°C which was lower than minimum germination temperature. And this optimal rehydration temperature was harmful to pollen germination if pollen was ready to germinate after rehydration. It helped researchers understand the mechanism of probable promotion of high day/low night temperatures to pollen germination in nature. Results further revealed that pecan pollen didn’t lose their viability rapidly in first several days at ambient conditions but changed to a different rehydration and germination condition. In addition, we proposed here a new germination speed parameter GT50 to indicate the early change of pollen viability.

Mitochondrial dysfunction mediated by cytoplasmic acidification results in pollen tube growth cessation in Pyrus pyrifolia.

The length of pollen tubes grown in synthetic media is normally shorter than those grown in vivo. However, the mechanism(s) underlying the cessation of pollen tube growth under culture conditions remain(s) largely unknown. Here, we report a previously unknown correlation between vacuolar function and the cell's ability to sustain mitochondrial functions in pear pollen tubes. The pear pollen tubes in vitro grew slowly after 15 hours post-cultured (HPC) and nearly ceased growth at 18 HPC. There was increased malondialdehyde content and membrane ion leakage at 15 HPC compared with 12 HPC. Furthermore, cytoplasmic acidification mainly mediated by decreased vacuolar H(+)-ATPase [V-ATPase, Enzyme Commission (EC) 3.6.1.3] activity was observed in pollen tubes after 15 HPC, and this further resulted in mitochondrial dysfunction, including mitochondrial structure disruption, mitochondrial membrane potential collapse and decreases in both oxygen consumption and ATP production. Our findings suggest that vacuoles and mitochondria intimately linked in regulating pollen tube elongation.