Tube Growth Rate Research Articles

Pollen germination, tube growth and longevity in some cultivars of Vitis vinifera L.

The grapevines (Vitis vinifera, L.) are cultured widely in Maragheh and are made one of the most important commercial fruit crops of its regions. Most of the cultivars are growing with their fruits or are used in rasine, juice and fresh fruits forms. However, pollination is the main factor affecting fruit set and knowledge about pollen traits of cultivars is necessary to plan the vineyards establishment and breeding programs. This study was accomplished to investigate pollen traits of 15 main grape cultivars ('Fakhri', 'Hosaini', 'Khalili', 'Keshmeshi' ('Sefide bidaneh), 'Lale bidaneh', 'Garmian', 'Gizil uzum', 'Sahebi', 'Jigh jigha', 'Shahani', 'Soltanin', 'Rish baba', 'Syahe malahi', 'Razeghi' ('Peikami') and 'Tabarzeh') which are grown in Maragheh. Pollens of cultivars gathered and cultured in the in vitro medium contained sucrose, boric acid and agar. Pollen germination percentage and tube growth were studied by light microscope. Experiment was carried out based on completely randomized design was (CRD) and data were analyzed with SAS software. Pollen germination percentage and tube growth rate showed significant differences among all of the studied cultivars. Finally, cultivars 'Fakhri', 'Khalili', 'Keshmeshi' 'Lale bidane' and 'Rish baba' showed the highest range of pollen germination, tube growth rate, longevity and selected for vineyards establishment and breeding programs.

A microsystem-based assay for studying pollen tube guidance in plant reproduction

We present a novel microsystem-based assay to assess and quantify pollen tube behavior in response to pistil tissues. During plant reproduction, signals from female tissues (pistils) guide the sperm-carrying pollen tube to the egg cell to achieve fertilization and initiate seed development. Existing pollen tube guidance bioassays are performed in an isotropically diffusive environment (for example, a semi in vivo assay in petri dishes) instead of anisotropically diffusive conditions required to characterize guidance signal gradients. Lack of a sensitive pollen tube guidance bioassay has therefore compounded the difficulties of identifying and characterizing the guidance signals that are likely produced in minute quantities by the ovules. We therefore developed a novel microsystem-based assay that mimics the in vivo micro-environment of ovule fertilization by pollen tubes in the model research plant Arabidopsis thaliana. In this microdevice, the pollen tube growth rate, length and ovule targeting frequencies were similar to those obtained using a semi in vivo plate assay. As a direct measure of the microdevice's utility in monitoring pollen tube guidance, we demonstrated that in this device, pollen tubes preferentially enter chambers with unfertilized ovules, suggesting that the pollen tubes sense the concentration gradient and respond to the chemoattractants secreted by unfertilized ovules.

Influence of temperature on the in vitro pollen germination and pollen tube growth of various native Iranian almonds (Prunus L. spp.) species

Pollen germination and pollen tube growth was quantified among various native Iranian wild almonds (P. dulcis (Mill.) D. A. Webb, P. eleaegnifolia Mill., P. orientalis Mill., P. lycioides Spach, P. reuteri Bioss. et Bushe, P. arabica Olivier, P. glauca Browick and P. scoparia Spach in order to identify differences in the tolerance of pollen to temperature variations. Pollen germination and pollen tube growth were observed after incubation in darkness in a germination medium for 24 h at 10–50°C at 5°C intervals. Maximum pollen germination of the wild almond species and specify that 60% was obtained for P. orientalis pollen and 98% for P. scoparia. Pollen tube length ranged from 860 μm was obtained in P. lycioides and 1490 μm in P. scoparia. A modified bilinear model best described the response to temperature of pollen germination and pollen tube length. Almond species variation was found for cardinal temperatures (Tmin, Topt and Tmax) of pollen germination percentage and pollen tube growth. Mean cardinal temperatures averaged over eight almond species were 14.7, 24.2, and 43.7°C for maximum percentage pollen germination and 14.48, 25.3, and 44.4 °C for maximum pollen tube length. The principal component analysis (PCA) identified maximum percentage pollen germination and pollen tube length of the species, and Tmax for the two processes as the most important pollen parameters in describing a species tolerance to high temperature. PCA also classified Prunus L. spp. into four groups according to the tolerance of pollen to temperature variations. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating species for high temperature tolerance.

High temperature limits in vivo pollen tube growth rates by altering diurnal carbohydrate balance in field-grown Gossypium hirsutum pistils

It has recently been reported that high temperature slows in vivo pollen tube growth rates in Gossypium hirsutum pistils under field conditions. Although numerous physical and biochemical pollen–pistil interactions are necessary for in vivo pollen tube growth to occur, studies investigating the influence of heat-induced changes in pistil biochemistry on in vivo pollen tube growth rates are lacking. We hypothesized that high temperature would alter diurnal pistil biochemistry and that pollen tube growth rates would be dependent upon the soluble carbohydrate content of the pistil during pollen tube growth. G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures but at the same developmental stage. Diurnal pistil measurements included carbohydrate balance, glutathione reductase (GR; EC 1.8.1.7), soluble protein, superoxide dismutase (SOD; EC 1.15.1.1), NADPH oxidase (NOX; EC 1.6.3.1), adenosine triphosphate (ATP), and water-soluble calcium. Soluble carbohydrate levels in cotton pistils were as much as 67.5% lower under high temperature conditions (34.6 °C maximum air temperature; August 4, 2009) than under cooler conditions (29.9 °C maximum air temperature; August 14, 2009). Regression analysis revealed that pollen tube growth rates were highly correlated with the soluble carbohydrate content of the pistil during pollen tube growth ( r 2 = 0.932). Higher ambient temperature conditions on August 4 increased GR activity in the pistil only during periods not associated with in vivo pollen tube growth; pistil protein content declined earlier in the day under high temperatures; SOD and NOX were unaffected by either sample date or time of day; pistil ATP and water soluble calcium were unaffected by the warmer temperatures. We conclude that moderate heat stress significantly alters diurnal carbohydrate balance in the pistil and suggest that pollen tube growth rate through the style may be limited by soluble carbohydrate supply in the pistil.

Pollen Viability and Pollen Tube Growth of IPB's Papaya

The purpose of the research was to examine the pollen germination process and growth rate of pollen tubes of papaya. Pollen tube growth of nine genotypes of papaya (IPB 1, IPB 2, IPB 3, IPB 4, IPB 5, IPB 7, IPB 8, IPB 9, and IPB 10) was investigated in this experiment in order to study their pollen germination rate and pollen viability. The fresh pollen were excised from the fl owers of papaya grown at Tajur Field Station of Research Center for Tropical Fruit, Bogor Agricultural University (IPB), Bogor. The extracted pollen was cultured aseptically on the Brewbaker and Kwack medium (pH 7.3) at ambient temperature of 26-28 °C. Pollen germination and pollen tube growth was observed under optical microscope with 100 and 400 magnifi cation. Papaya pollen viability was not associated with size-based categories of papaya fruits. IPB 4 had the longest pollen tube at fi rst 30 minutes after germination (115.5 µm), whereas IPB 10 had the shortest (99.5 µm). The distance from stigma to ovary in hermaphrodite fl owers varies with genotypes, ranging from 7.38 to 13.44 mm. Average length of pollen tube within four hours of germination for small papaya fruit category (IPB 1, IPB 3, and IPB 4) was 1,030.67 ± 19.14 μm, while the distance between stigma and ovary was short (14.85 ± 2.19 mm) so that the expected of fertilization process occurred sooner. At the end of the experiment (four hours after germination), IPB 1 genotype had the longest pollen tube (1,052 µm) while IPB 9 genotype (913 µm) had the shortest pollen tube. Genotype with the highest percentage of germination at the end experiment was IPB 2 (65.65%), whereas the lowest was IPB 7 (42.56%).

Quantifying growth mechanics of living, growing plant cells in situ using microrobotics

Plant cell growth is a fundamental process during plant development and the developmental biology society has studied cell growth from various aspects using physiological, biochemical, genetic, mathematical and modelling approaches. Recent advances in the field of biology demonstrate a need for investigation and quantification of the mechanics of growth at individual cellular levels. Here, we describe a microrobotic system capable of performing automated mechanical characterisation of living plant cells in situ as these cells proliferate and grow. The microrobotic measurement system employs a single-axis capacitive MEMS microforce sensor, a multi-axis positioning system with position feedback, a high-resolution optical microscope and a custom–user interface for the guiding of the automated measurement process. The system has been applied to measure mechanical properties of Lilium pollen tubes approximately 20 µm wide. The measurements were performed in growth medium, and the observed growth rate of the pollen tubes is about 20 µm per minute. For the mechanical characterisation of pollen tubes, nano-Newton level loads and nanometric indentations are applied. The force-deformation data obtained show a difference in stiffness from the tip to the apex demonstrating that the developed measurement system is a promising tool for better understanding the mechanics of plant cell growth.

Diurnal pollen tube growth rate is slowed by high temperature in field-grown Gossypium hirsutum pistils

For Gossypium hirsutum pollination, germination, and pollen tube growth must occur in a highly concerted fashion on the day of flowering for fertilization to occur. Because reproductive success could be influenced by the photosynthetic activity of major source leaves, we hypothesized that increased temperatures under field conditions would limit fertilization by inhibiting diurnal pollen tube growth through the style and decreasing subtending leaf photosynthesis. To address this hypothesis, G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures while at the same developmental stage (node 8 above the cotyledons). Collection and measurement were conducted at 06:00, 09:00, 12:00, 15:00, and 18:00 h on August 4 (34.6 °C maximum air temperature) and 14, 2009 (29.9 °C maximum air temperature). Microclimate measurements included photosynthetically active radiation, relative humidity, and air temperature. Pistil measurements included pistil surface temperature, pollen germination, pollen tube growth through the style, fertilization efficiency, fertilized ovule number, and total number of ovules per ovary. Subtending leaf measurements included leaf temperature, photosynthesis, and stomatal conductance. Under high temperatures the first measurable pollen tube growth through the style was observed earlier in the day (12:00 h) than under cooler conditions (15:00 h). Also, high temperature resulted in slower pollen tube growth through the style (2.05 mm h −1) relative to cooler conditions (3.35 mm h −1), but there were no differences in fertilization efficiency, number of fertilized ovules, or ovule number. There was no effect of sampling date on diurnal photosynthetic patterns, where the maximum photosynthetic rate was observed at 12:00 h on both dates. It is concluded that, of the measured physiological and reproductive processes, pollen tube growth rate showed the greatest sensitivity to high temperature under field conditions.

Pollen density on the stigma affects endogenous gibberellin metabolism, seed and fruit set, and fruit quality in Pyrus pyrifolia

To clarify the relationship between pollen density and gametophytic competition in Pyrus pyrifolia, gametophytic performance, gibberellin metabolism, fruit set, and fruit quality were investigated by modifying P. pyrifolia pollen grain number and density with Lycopodium spores. Higher levels of pollen density improved seed viability, fruit set, and fruit quality. Treatments with the highest pollen density showed a significantly increased fruit growth rate and larger fruit at harvest. High pollen density increased germination rate and gave a faster pollen tube growth, both in vivo and in vitro. Endogenous gibberellin (GA) concentrations increased in pollen tubes soon after germination and the concentration of two growth-active GAs, GA3, and GA4, was positively correlated to final fruit size, cell numbers in the mesocarp, and pollen tube growth rate. These two GAs appear to be biosynthesized de novo in pollen tube and are the main pollen-derived bioactive GAs found after pollen germination. GA1 levels in the pollen tube appear to be related to a pollen–style interaction that occurred after the pollen grains landed on the stigma.

Effects of anion channel blockers NPPB and DIDS on tobacco pollen tube growth and its mitochondria state

Influence of anion channel blockers NPPB and DIDS on pollen tube growth and its mitochondria functioning was studied by means of fluorescence microscopy and flow cytometry. NPPB (40 microM) blocked pollen tube growth completely, but did not change its diameter. DIDS (20-80 microM) caused pollen tube swelling and bursting, suggesting that DIDS-sensitive channels take part in the regulation of pollen tube osmotic balance. The osmotic effect of low DIDS concentration (20 (Mkappa)M) was not accompanied by changes in the tube growth rate. The mapping of membrane potential on the pollen tube plasmalemma using Di-4-ANEPPS revealed the involvement of NPPB-sensitive but not DIDS-sensitive anion channels in the maintenance of the longitudinal membrane potential gradient along the tube surface. The study of isolated pollen mitochondria showed that DIDS increased their capacity to take up potential-dependent dye DiOC5(3), i. e. caused hyperpolarization of mitochondrial membranes. At the same time DIDS influenced on intramitochondrial ROS content and excretion of ROS from mitochondria. Thus, NPPB and DIDS differently influenced on transmembrane potential distribution along pollen tube plasmalemma, on its osmotic balance, and on mitochondria functioning. This set of data suggests that pollen tube growth is dependent on activity of anion channels that differ in localization and functions.

Cryptic self‐incompatibility and distyly in Hedyotis acutangula Champ. (Rubiaceae)

Distyly, floral polymorphism frequently associated with reciprocal herkogamy, self- and intramorph incompatibility and secondary dimorphism, constitutes an important sexual system in the Rubiaceae. Here we report an unusual kind of distyly associated with self- and/or intramorph compatibility in a perennial herb, Hedyotis acutangula. Floral morphology, ancillary dimorphisms and compatibility of the two morphs were studied. H. acutangula did not exhibit precise reciprocal herkogamy, but this did not affect the equality of floral morphs in the population, as usually found in distylous plants. Both pin and thrum pollen retained relatively high viability for 8 h. The pollen to ovule ratio was 72.5 in pin flowers and 54.4 in thrum flowers. Pistils of pin flowers remained receptive for longer than those of thrum flowers. No apparent difference in the germination rate of pin and thrum pollen grains was observed when cultured in vitro, although growth of thrum pollen tubes was much faster than that of pin pollen tubes. Artificial pollination revealed that pollen tube growth in legitimate intermorph crosses was faster than in either intramorph crosses or self-pollination, suggesting the occurrence of cryptic self-incompatibility in this species. Cryptic self-incompatibility functioned differently in the two morphs, with pollen tube growth rates after legitimate and illegitimate pollination much more highly differentiated in pin flowers than in thrum flowers. No fruit was produced in emasculated netted flowers, suggesting the absence of apomixis. Our results indicate that H. acutangula is distylous, with a cryptic self-incompatibility breeding system.

Pollen behaviour and fertililization impairment in Bambara groundnut (Vigna subterrenea [L.] Verdc.)

Two field experiments were conducted in April and August, 2007 cropping season at the Department of Crop Science research farm, University of Nigeria, Nsukka, to evaluate the pollen germination potentials and the pollen tube growth of thirteen bambara groundnut cultivars. The harvested pollen grains were exposed for 0, 5, 10 and 15 min durations to ambient conditions before in vitro germination. Pollen germination and pollen tube growth were tested using a medium containing 10 g sucrose, 100 mg/l boric acid and 300 mg/l calcium nitrate made up to 100 ml with deionized water. The results showed that cultivars, had significant effect on the pollen germination only at the late planting. The early and late planting results showed that pollens incubated immediately after harvest had the highest germination percentage,while pollen exposed for five minutes prior to germination showed very poorgermination. Pollens exposed beyond five minutes after harvest did not germinate. The cultivars significantly (P < 0.05) affected the pollen tube growth at both early and late planting dates. The pollen tube growth decreased drastically with increase in duration of pollen exposure. The pollen tube had an exponential growth rate at the on set of the pollen tube growth, followed by lag and stationary growth phases in the pollen tube growth curves. The exponential, logistic and Gomperzt growth models were used to estimate the best fit model for the pollen tube growth in bambara groundnut cultivars. In the early planting, the average straightness (R2) value of these models for growth estimate were 98.4, 98.6 and 98.5%, respectively. During the late planting, the average R2 values were 91.5, 96.6 and 96.6%, respectively. The three models are therefore considered suitable for the computation of the pollen tube growth rates. The principal component and cluster analyses were used to groupthe cultivars in relation to the levels of pollen survival under ambient conditions. At early planting, cultivar Bg-01 had moderate surviving pollen grains while Bg-08, Bg-09, Bg-10 and Bg-11 were found to have poor surviving pollens. At late planting, cultivar Bg-04 and Bg-07 had high survival pollens while Bg-01 had poor pollen survival. Key words: Pollen behaviour, pollination, fertilization, Bambara groundnut, Vigna subterranea (L.) Verdc.

The role of pollen in the changing environmental conditions of Scots pine

Rapid climate warming poses a challenge to forest trees adapted to cooler conditions. However, a genetic safety net may exist for wind pollinated tree species in the form of long distance gene flow mediated by pollen containing alleles that are (pre)adapted to a warmer climate. In order to examine long distance gene flow in Scots pine (Pinus sylvestris L.), we monitored flowering phenology in central, northern, and northernmost Finland and measured the amount and viability of airborne pollen over four years. Viable airborne pollen grains were detected during female flowering periods and prior to local pollen shedding in all study sites. Depending on the year and study site, female flowers were exposed only to pollen originating elsewhere for between one and four days. Foreign airborne pollen represented 2.3% of all viable grains detected and varied between years and study sites. Artificial pollination trials were conducted to evaluate the effect of pollen origin on seed siring success. Pollen genotypes originating from southern Finland sired 76% and 48% of seeds in competition experiments where pollen from both populations was introduced simultaneously into the female strobilus. Furthermore, we investigated the importance of pollen arrival order by introducing pollen of northern and southern genotypes in to the strobilus at two-hourly intervals. Northern genotypes sired 76% of the analysed seeds when injected first but when southern genotypes were supplied first, both pollen types enjoyed equal success. The first pollen grain in the pollen chamber did not always fertilize the ovum. Instead there is likely a more subtle and complex form of competition between genotypes and their pollen grains. To examine chemically-mediated pollen interactions we conducted an in vitro germination experiment where different genotypes were in chemical but not physical contact. Both positive and negative interactions were found. We found highly negative effects in the germinability of northern pollen grains when in contact with southern pollen, and an increase in the germinability of southern pollen when in contact with northern pollen. There was no variation in the size of dry pollen grains between sources, but after hydration and germination, northern pollen grains were larger than southern pollen. Genotypes with high hydration rates had low germinability and slow pollen tube growth rates. This suggests that early germination and growth of the pollen tube is more dependent on pollen storage materials and less dependent on water intake. Pollen source affected the outcome of competition experiments and therefore is an important factor in long distance gene flow. However, genotype also plays a role and must be taken into account.

Vacuolar sorting receptors (VSRs) and secretory carrier membrane proteins (SCAMPs) are essential for pollen tube growth

Vacuolar sorting receptors (VSRs) are type-I integral membrane proteins that mediate biosynthetic protein traffic in the secretory pathway to the vacuole, whereas secretory carrier membrane proteins (SCAMPs) are type-IV membrane proteins localizing to the plasma membrane and early endosome (EE) or trans-Golgi network (TGN) in the plant endocytic pathway. As pollen tube growth is an extremely polarized and highly dynamic process, with intense anterograde and retrograde membrane trafficking, we have studied the dynamics and functional roles of VSR and SCAMP in pollen tube growth using lily (Lilium longiflorum) pollen as a model. Using newly cloned lily VSR and SCAMP cDNA (termed LIVSR and LISCAMP, respectively), as well as specific antibodies against VSR and SCAMP1 as tools, we have demonstrated that in growing lily pollen tubes: (i) transiently expressed GFP-VSR/GFP-LIVSR is located throughout the pollen tubes, excepting the apical clear-zone region, whereas GFP-LISCAMP is mainly concentrated in the tip region; (ii) VSRs are localized to the multivesicular body (MVB) and vacuole, whereas SCAMPs are localized to apical endocytic vesicles, TGN and vacuole; and (iii) microinjection of VSR or SCAMP antibodies and LlVSR small interfering RNAs (siRNAs) significantly reduced the growth rate of the lily pollen tubes. Taken together, both VSR and SCAMP are required for pollen tube growth, probably working together in regulating protein trafficking in the secretory and endocytic pathways, which need to be coordinated in order to support pollen tube elongation.

Transparent conducting oxide glass grown with TiO 2-nanotube array for dye-sensitized solar cell

An arc ion plating (AIP) deposition system was employed to produce metal titanium layer on transparent conducting oxide glass, and followed by anodically oxidizing to form a TiO 2-nanotube array electrode. A dye-sensitized solar cell (DSC) was then assembled as ITO glass/[TiO 2-nanotube (N3 dye)]/I 2 + LiI electrolyte/Pt/ITO glass. Anodizing bath composition was varied, and post-annealing was carried out. Consequent changes in the TiO 2-nanotube array microstructure and photovoltaic efficiency of the assembled DSC device were revealed. Experimental results show that a 5-μm thick metal titanium layer can be obtained after 45 min AIP deposition. The metal titanium layer underwent complete conversion into XRD-amorphous TiO 2-nanotube array after anodic oxidation for 2 h. The tube can reach 10.7 μm long with tube inner diameter 92 nm. The ammonium fluoride in the anodizing bath accelerates the tube growth rate. Thermal annealing at temperatures over 250 °C works best on anatase crystallization of the TiO 2-nanotube. An ultimate photovoltaic efficiency 1.88% (active area 1 cm 2) of the assembled DSC device can be obtained for the TiO 2-nanotube grown ITO glass annealed at 350 °C.

The joint evolution of mating system and pollen performance: Predictions regarding male gametophytic evolution in selfers vs. outcrossers

Abstract Studies of sexual selection in plants historically have focused on pollinator attraction, pollen transfer, gametophytic competition, and post-fertilization discrimination by maternal plants. Pollen performance (the speeds of germination and pollen tube growth) in particular is thought to be strongly subject to intrasexual selection, but the effect of mating system on this process has not been rigorously evaluated. Here we propose four predictions derived from the logic that pollen performance should evolve with mating system as an adaptive response to: (1) the competitive environment among pollen genotypes and (2) variation among female genotypes regularly encountered by a given pollen genotype. First, as previously predicted, due to the higher potential for intense selection among diverse pollen genotypes in outcrossing relative to selfing taxa, pollen should evolve to germinate and/or to grow more rapidly in outcrossers than in selfers. Second, due to stronger selection on pollen performance in outcrossing than in selfing taxa, heritable variation in pollen tube growth rate is more likely to be purged in outcrossers. In selfers, by contrast, genetic variation in pollen tube growth rates may readily accumulate because selfing reduces the number of genetically distinct male gametophytes likely to be deposited on any given stigma, thereby relaxing selection on male gametophytic traits. A summary of published studies presented here provides preliminary support for this prediction. Third, due to the high probability that the pollen of outcrossing individuals will be exposed to multiple pistil genotypes, we predict that the pollen of habitually outcrossing taxa will evolve to perform more consistently across female genotypes than the pollen of selfing taxa. Fourth, we predict that epistatic interactions between pollen and pistil genotypes are more likely to evolve in selfers than in outcrossers. We suggest several empirical approaches that may be used to test these predictions.

Incidence and post-pollination mechanisms of nonrandom mating in Arabidopsis thaliana

Compatible pollinations from many different taxa display nonrandom mating. Here we describe a system for examining questions of nonrandom mating in Arabidopsis thaliana. Using this system, we demonstrate that Arabidopsis thaliana displays nonrandom mating between distinct accessions. Statistical analysis of these data demonstrates aspects of both pollen competition and male-female complementarity in these matings. Cytological experiments implicate pollen germination and pollen tube growth rates as possible causal factors in these nonrandom mating efficiencies.

Effects of Temperature and the Combination of Liquid Lime Sulfur and Fish Oil on Pollen Germination, Pollen Tube Growth, and Fruit Set in Apples

Effects of temperature and the combination of liquid lime sulfur (LLS) and fish oil (FO) applied during bloom on pollen germination and pollen tube growth in flowers and fruit set were examined in apples (Malus ×domestica Borkh.). Percent germination of pollen of ‘Manchurian’ crabapples and ‘Golden Delicious’ apple flowers on the stigmatic surface of ‘Golden Delicious’ pistils increased with increasing temperature from 13 to 29 °C in the first 24 and 48 h after pollination, respectively, but not thereafter. Pollen tube growth rate in the style increased quadratically with increasing temperature from 13 to 29 °C. ‘Manchurian’ was a more effective pollenizer of ‘Golden Delicious’ than was ‘Golden Delicious’ pollen. For example, at 24 or 29 °C, some ‘Manchurian’ pollen tubes grew to the base of ‘Golden Delicious’ styles by 24 h after pollination. On the other hand, no ‘Golden Delicious’ pollen tube grew to the base of a ‘Golden Delicious’ style regardless of temperature and time. Pollen tube growth rate in the style increased with increasing day/night temperature from 7/0 to 24/7 °C. The time required for pollen tubes to grow to the base of styles decreased with increasing day/night temperature from 13/2 to 24/7 °C. Only ≈36 h was required for pollen tubes to grow to the base of style at 24/7 °C, whereas pollen tubes grew very slowly and no pollen tubes grew to the base of style at 7/0 °C regardless of pollen source. LLS + FO, applied 4 or 24 h after pollination, inhibited pollen germination, pollen tube growth in the style, fertilization, and fruit set, but it had no effect when applied 48 h after pollination. These results suggest that LLS + FO applied at this bloom stage causes flower or fruit abscission most likely by inhibiting pollen germination, pollen tube growth in the style, and fertilization.

Post-pollination mechanisms in Nicotiana longiflora and N. plumbaginifolia: pollen tube growth rate, offspring paternity and hybridization

In natural populations where interfertile species coexist, conspecific and heterospecific pollen can be delivered to the stigmas. Post-pollination mechanisms might determine the seed siring success of different pollen donors within species as well as the chances for hybridization between species. Nicotiana longiflora and N. plumbaginifolia occur in sympatry in Northwest Argentina, where they have overlapping flowering seasons and share floral visitors. We explored (1) pollen tube growth rates for outcross versus self pollen in single-donor pollinations; (2) siring success of self versus outcross pollen donors in competitive pollinations, and (3) possibilities for hybridization by performing two- (outcross conspecific vs. heterospecific) and three-pollen donor (self vs. outcross vs. heterospecific) crosses. In N. longiflora, both pollen tube growth rate and siring success favored outcross pollen over self pollen and strong rejection of heterospecific pollen. In N. plumbaginifolia, pollen tube growth rate was similar for self and outcross pollen, self pollen sired similar numbers of offspring than outcross pollen and heterospecific pollen sired roughly the same number of progeny than self pollen. Results suggest that in natural sympatric populations, interspecific crosses would likely lead to unidirectional hybridization with N. plumbaginifolia as the seed parent.

H +-ATPase in the plasma membrane of Arabidopsis pollen cells is involved in extracellular calmodulin-promoted pollen germination

In this paper, the role of the plasma membrane (PM) H +-ATPase in extracellular calmodulin (CaM)-promoted pollen germination and in tube growth of Arabidopsis thaliana was investigated. Pollen germination, pollen tube growth rate, free cytosolic Ca 2+ concentration ([Ca 2+] cyt) and Ca 2+ channel activity in the PM of pollen cells were measured. In response to fusicoccin or CaM treatment, in vitro pollen germination and pollen tube growth rate, [Ca 2+] cyt and activity of a hyperpolarization-activated Ca 2+-permeable channel increased. Sodium vanadate inhibited the promotion of these parameters by extracellular CaM. The results suggest that H +-ATPase may be involved in extracellular CaM-regulated pollen germination and in tube growth by modulation of the hyperpolarization-activated Ca 2+ channel in the PM of A. thaliana pollen cells.

Analysis of the tip-to-base gradient of CaM in pollen tube pulsant growth using in vivo CaM–GFP system

Ca(2+)-CaM signaling is involved in pollen tube development. However, the distribution and function of CaM and the downstream components of Ca(2+)-CaM signal in pollen tube development still need more exploration. Here we obtained the CaM-GFP fusion protein transgenic line of Nicotiana tobacum SRI, which allowed us to monitor CaM distribution pattern in vivo and provided a useful tool to observe CaM response to various exogenous stimulations and afforded solid evidences of the essential functions of CaM in pollen tube growth. CaM-GFP fusion gene was constructed under the control of Lat52-7 pollen-specific promoter and transformed into Nicotiana tobacum SRI. High level of CaM-GFP fluorescence was detected at the germinal pores and the tip-to-base gradient of fluorescence was observed in developing pollen tubes. The distribution of CaM at apical dome had close relationship with the pulsant growth mode of pollen tubes: when CaM aggregated at the apical dome, pollen tubes stepped into growth state; When CaM showed non-polarized distribution, pollen tubes stopped growing. In addition, after affording exogenous Ca(2+), calmidazolium (antagonism of CaM) or Brefeldin A (an inhibitor of membrane trafficking), CaM turned to a uniform distribution at the apical dome and pollen tube growth was held back. Taken together, our results showed that CaM played a vital role in pollen tube elongation and growth rate, and the oscillation of tip-to-base gradient of CaM was required for the normal pulsant growth of pollen tube.