Some cytological and physiochemical features relating to non-storability of pistachio (Pistacia vera L.) pollen

Pollen grains may become desiccated after independence from parent plants and remain viable in an inactive dry state during presentation and dispersal, until the conditions for rehydration and germination are prepared. But some pollen types do not tolerate the desiccation state and lose the germination power soon after release, and therefore, are difficult to store. In this study, moisture content, germinability, cytology and dehydrin and phenolics contents were surveyed in pistachio pollen at fresh and desiccated states. Mature pollen lost 54.1% of its initial moisture after 48 h desiccation along with severe decrease in germinability. Light microscopy results indicated that a low rate of pollen grains have vegetative cell rupture caused by desiccation, but a higher rate of grains were intact in appearance. Numerous amyloplasts persisted after desiccation as a sensitivity indicator. A 16 kDa dehydrin band was detected by western blot method with higher content in desiccated than fresh samples. High performance liquid chromatography (HPLC) analysis showed that the total content of phenolics increased slightly by desiccation. These results indicate the insufficiency of dehydrin and phenolics accumulation for achievement of desiccation tolerance. Furthermore, the severe loss of germinability in desiccated pistachio pollen may be the result of deficiency in some other protective mechanisms that need further investigations.     

Strain-dependent viscoelastic behaviour and rupture force of single chondrocytes and chondrons under compression

The chondron in articular cartilage includes the chondrocyte and its surrounding pericellular matrix (PCM). Single chondrocytes and chondrons were compressed between two parallel surfaces by a micromanipulation technique to investigate their biomechanical properties and to discover the mechanical significance of the PCM. The force imposed on the cells was measured directly during deformation at various compression speeds and deformations up to cell rupture. When the deformation at the end of compression was 50%, relaxation showed that the cells were viscoelastic, but this viscoelasticity was generally insignificant at 30% deformation or lower. When the deformation was 70%, the cells had deformed plastically. Chondrons ruptured at a mean deformation of 85 ± 1%, whilst chondrocytes ruptured at a mean deformation of 78 ± 1%. Chondrons were generally stiffer than chondrocytes and showed less viscoelastic behaviour than chondrocytes. Thus, the PCM significantly influences the mechanical properties of the cells.     

The influence of relative humidity on the swelling of pollen grains in vitro

The volume of hydrated pollen grains of Petunia hybrida L. during swelling in germination medium increased three times. The volume of desiccated pollen grains increased only two times after transfer to the same medium. This difference in swelling ability is attributed to different rigidities of the pollen grain wall,ccaused by the different hydration states. The relationship between pollen grain swelling and germination metabolism with regard to relative humidity is discussed.Abbreviation RH relative humidity     

Strength of mid-logarithmic and stationary phase Saccharopolyspora erythraea hyphae during a batch fermentation in defined nitrate-limited medium

A method for measuring mechanical properties of Saccharopolyspora erythraea is reported with data from a batch fermentation. Briefly, hyphae were glued to the end of a tungsten filament mounted horizontally on a sensitive force transducer. Free ends of hyphae were trapped against a flat surface by a second probe. The force transducer and tungsten filament were then moved at a fixed rate, the hypha were strained, and the force resisting motion recorded. From these data the maximum force resisting motion is taken as the force at which breakage occurs. Hyphae from the mid-logarithmic phase of a simple batch fermentation on defined medium were found to have a breaking force of 890 +/- 160 nN (95% confidence), while stationary phase hyphae were weaker at 580 +/- 150 nN. Video recordings of the experiments allowed an approximation of breaking strain, which did not differ significantly between samples at 0.18 +/- 0.03. Electron microscopy was used to measure cell wall thickness, cell diameter, and hence cell wall cross-sectional area. The ultimate tensile strength was estimated to be 24 +/- 3 MPa with no difference between the two samples, the lower breaking force of the stationary phase hyphae being attributed to a thinner cell wall. Assuming a linear relationship between stress and strain, the elastic modulus was estimated to be 140 +/- 30 MPa. These values are comparable with other structural biological materials such as yeast cell walls and collagen.     

From the anther to the proctodeum: Pear (Pyrus communis) pollen digestion in Osmia cornuta larvae

Modifications of the pollen grains of Pyrus communis Linneaus that occur during the digestion by Osmia cornuta (Latreille) larvae were studied histochemically. We compared the features of the pollen grains found in the anthers, in the larval cell provisions and in the alimentary canal of the 5th instar larvae. Modifications were already evident in the provisions and consisted of protoplast protrusions through the apertures and a decrease in the number of starch-containing pollen grains. After pollen grains were ingested by the larvae, the protoplast appeared retracted from the pollen wall. Pollen digestion began in the anterior part of the midgut, where we observed: (1) disorganised intine at the apertures; (2) disappearance of DAPI staining of nuclear pollen DNA; (3) fewer pollen grains containing starch than in the anthers; (4) some empty pollen grains. Pollen grains in the proctodeum appeared extremely compressed and crushed. Some grains appeared to be unaffected by the digestive process. We hypothesise that the protrusion of the intine and of the protoplast from the apertures in bee provisions could be considered a kind of pre-treatment necessary to initiate the digestion process in the larval alimentary canal.     

Single adhesive nanofibers from a live diatom have the signature fingerprint of modular proteins

The adhesive and mechanical properties of a cell-substratum adhesive secreted by live diatom cells were examined in situ using atomic force microscopy. The resulting force curves have a regular saw-tooth pattern, the characteristic fingerprint of modular proteins, and when bridged between tip and surface can repeatedly be stretched and relaxed resulting in precisely overlaying saw-tooth curves (up to approximately 600 successive cycles). The average rupture force of the peaks is 0.794 +/- 0.007 (mean +/- SE) nN at a loading rate of 0.8 microm/s and the average persistence length is 0.026 +/- <0.001 (mean +/- SE) nm (fit using the worm-like chain model). We propose that we are pulling on single adhesive nanofibers, each a cohesive unit composed of a set number of modular proteins aligned in register. Furthermore, we can observe and differentiate when up to three adhesive nanofibers are pulled based upon multimodal distributions of force and persistence length. The high force required for bond rupture, high extensibility (approximately 1.2 microm), and the accurate and rapid refolding upon relaxation, together provide strong and flexible properties ideally suited for the cell-substratum adhesion of this fouling diatom and allow us to understand the mechanism responsible for the strength of adhesion.     

Enhanced airborne radioactivity during a pine pollen release episode

 A single episode of pine pollen release in the highly contaminated area of Novozybkov, Russian Federation, which led to enhanced atmospheric concentrations of ¹³⁷Cs is discussed. The pollen grains were sampled by a rotating arm impactor and analysed by gamma-spectrometry for ¹³⁷Cs activity and by image analysis for their size. In the vicinity of a forest, a maximum concentration of 4.5±0.4 mBq m^–3 was measured, and a mean activity per pollen grain of 260±80 nBq was determined. The emission rate of the Novozybkov mixed pine forest was estimated to be approximately 400 Bq m^–2 per year. Because of the large size of pine pollen grains (about 50 μm) and the short emission period of 5–8 days per year, the estimated potential annual inhalation doses are very low. Biological emissions including pollen release may be a source of increased airborne radionuclide concentrations at larger distances from the source areas as well. Received: 2 October 1998 / Accepted in revised form: 30 January 1999     

希茉莉（Hamelia patens Jacq.）花粉发育时期快速检测

茜草科希茉莉（Hamelia patens Jacq.）的花粉用DAPI（4’,6-diamidino-2-phenylindole）直接染色不能观察到花粉核,本研究探索出适宜在DAPI染色前处理希茉莉花粉壁的水浴加热-氧化方法,使得希茉莉花粉核能在荧光显微镜下清晰地显示出来,从而快速检测花粉所处的发育阶段。结果表明：（1）单核花粉和二核花粉最适宜的水浴加热温度和时间分别为65℃、20~50 min和55℃、20~40 min;（2）花粉发育阶段与花朵、花药长度的对应关系为：花朵0.90~1.00 cm、花药0.50~0.60 cm时对应花粉的四分体时期,花朵1.10~1.60 cm、花药0.60~0.85 cm时对应单核花粉时期,花朵1.80~2.70 cm（花冠裂片张开前）、花药0.91~1.01 cm时对应二核花粉时期。     

Pollen histochemistry and pollen : ovule ratios in Zingiberaceae

BACKGROUND AND AIMS: Pollen grains of 37 species from 11 genera in the family Zingiberaceae were examined to assess qualitatively starch or lipid contents; the pollen grain and ovule numbers per flower and pollen : ovule ratios were also counted and calculated. Pollen : ovule ratios were studied to reveal patterns of variation in the Zingiberaceae. METHODS: Freshly open flowers with dehiscing anthers were collected at random from plants growing in natural habitats or in botanical gardens. Presence of lipids or starch in pollen grains was tested by Sudan solution and IKI solution, respectively, and examined under a microscope. To estimate the pollen and ovule numbers per flower, one anther from each bud was carefully dissected and all pollen grains were counted; ovaries were carefully dissected out of each flower and counted. Whenever possible, at least 10-15 buds were used in the determination. KEY RESULTS: Thirty-three of all the 37 species examined had starchy pollen. Starch was not found in only four species and lipid was not found in only one species; among the four tribes in subfamily Zingiberoideae, all species of Zingibereae and Globbeae had pollen with no starch, Alpineae and Hedychieae had pollen with and without starch, whereas, all species of subfamily Costoideae had starchy pollen with abundant lipids. The mean pollen : ovule ratios in the members of the Zingiberaceae investigated range from 3.25 +/- 1.56 to 616.52 +/- 117.83. CONCLUSIONS: The pollen nutrition types seemed not related to mating systems. The pollen : ovule ratios in members of the Zingiberaceae with the same breeding system are noticeably lower than those recorded by previous authors. The lower pollen : ovule ratios in this family are presumed to be related to the highly efficient pollination systems, mediated by pollen which can be quite glutinous and the relatively large stigma area. In most of the Alpinia species the anaflexistylous flowers have much larger numbers of pollen grains and higher pollen : ovule ratios than the cataflexistylous flowers. There are significant differences in mean pollen grain numbers and pollen : ovule ratios between different life forms but ovule numbers are approximately the same.     

Dynamic dorsoventral stiffness assessment of the ovine lumbar spine

Posteroanterior spinal stiffness assessments are common in the evaluating patients with low back pain. The purpose of this study was to determine the effects of mechanical excitation frequency on dynamic lumbar spine stiffness. A computer-controlled voice coil actuator equipped with a load cell and LVDT was used to deliver an oscillatory dorsoventral (DV) mechanical force to the L3 spinous process of 15 adolescent Merino sheep. DV forces (48 N peak, approximately 10% body weight) were randomly applied at periodic excitation frequencies of 2.0, 6.0, 11.7 and a 0.5-19.7 Hz sweep. Force and displacement were recorded over a 13-22 s time interval. The in vivo DV stiffness of the ovine spine was frequency dependent and varied 3.7-fold over the 0.5-19.7 Hz mechanical excitation frequency range. Minimum and maximum DV stiffness (force/displacement) were 3.86+/-0.38 and 14.1+/-9.95 N/mm at 4.0 and 19.7 Hz, respectively. Stiffness values based on the swept-sine measurements were not significantly different from corresponding periodic oscillations (2.0 and 6.0 Hz). The mean coefficient of variation in the swept-sine DV dynamic stiffness assessment method was 15%, which was similar to the periodic oscillation method (10-16%). The results indicate that changes in mechanical excitation frequency and animal body mass modulate DV spinal stiffness.     

Anther structure and pollen development in Melicoccus lepidopetalus (Sapindaceae): An evolutionary approach to dioecy in the family

Anther and pollen development in staminate and pistillate flowers of dioecious Melicoccus lepidopetalus (Sapindaceae) were examined by light and electron microscopy. Young anthers are similar in both types of flowers; they consist of epidermis, endothecium, two to four middle layers and a secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents compressed epidermal cells and endothecium cells with fibrillar thickenings. A single locule is formed in the theca by dissolution of the septum and pollen grains are shed at two-celled stage. The mature anthers of pistillate flowers differ anatomically from those of staminate flowers. The epidermis is not compressed, the endothecium does not develop fibrillar thickenings, middle layers and tapetum are generally persisting, and the stomium is nonfunctional. Microspore degeneration begins after meiosis of microspore mother cells. At anthesis, uninucleate microspores and pollen grains with vegetative and generative nuclei with no cytokinesis are observed. Some pollen walls display an abnormal exine deposition, whereas others show a well formed exine, although both are devoid of intine. These results suggest that in the evolution towards unisexuality, the developmental differences of anther wall tissues and pollen grains between pistillate and staminate flowers might become more pronounced in a derived condition, such as dioecy.     

A planar biaxial constitutive relation for the luminal layer of intra-luminal thrombus in abdominal aortic aneurysms

The rupture risk of abdominal aortic aneurysms (AAAs) is thought to be associated with increased levels of wall stress. Finite element analysis (FEA) allows the prediction of wall stresses in a patient-specific, non-invasive manner. We have recently shown that it is important to include the intra-luminal thrombus (ILT), present in approximately 70% of AAA, into FEA simulations of AAA. All FEA simulations to date assume an isotropic, homogeneous material behavior for this material. The purpose of this work was to investigate the multi-axial biomechanical behavior of ILT and to derive an appropriate constitutive relation. We performed planar biaxial testing on the luminal layer of nine ILT specimens obtained fresh in the operating room (9 patients, mean age 71+/-4.5 years, mean diameter 5.9+/-0.4 cm), and a constitutive relation was derived from this data. Peak stretch and maximum tangential modulus (MTM) values were recorded for the equibiaxial protocol in both the circumferential (theta) and longitudinal (L) directions. Stress contour plots were used to investigate the presence of mechanical anisotropy, after which an appropriate strain energy function was fit to each of the specimen datasets. The peak stretch values for the luminal layer of the ILT were (mean+/-SEM) 1.18+/-0.02 and 1.13+/-0.02 in the theta and L directions, respectively (p=0.14). The MTM values were 20+/-2 and 23+/-3N/cm(2) in the theta and L directions, respectively (p=0.37). From these results and our observation of the symmetry of the stress contour plots for each specimen, we concluded that the use of an isotropic strain energy function for ILT is appropriate. Each specimen data set was then fit to a second-order polynomial strain energy function of the first invariant of the left Cauchy-Green strain tensor, resulting in an accurate fit (average R(2)=0.92+/-0.02; range 0.80-0.99). Comparison of our previously reported, uniaxially derived constitutive relation with the biaxially derived relation derived here shows large differences in the predicted mechanical response, underscoring the importance of the appropriate experimental methods used to derive constitutive relations. Further work is merited in an effort to produce more accurate predictions of wall stresses in patient-specific AAA, and viscoelastic behaviors of the ILT.     

Knee joint reaction force during tibial diaphyseal lengthening: a study on a rabbit model

The in vivo passive knee joint reaction force was measured in a rabbit model of tibial diaphyseal lengthening. This was based on the assumption that limb lengthening creates soft tissue tension that compresses the joint surface and generates the joint contact force. A measurement method was developed that involved the distraction of the joint and the determination of the distraction force that just separates the joint surfaces. Sixteen immature (mean+/-SD age=9+/-0.6 weeks) New Zealand White rabbits underwent 30% (left) tibial diaphyseal lengthening at a rate of two 0.4mm incremental lengthenings per day. The knee joint reaction force was measured at the end of lengthening (8 rabbits, mean+/-SD age=14+/-0.6 weeks) and five weeks after lengthening (8 rabbits, mean+/-SD age=19+/-0.7 weeks). An instrumented bilateral distractor and an extensometer were fixed cross the knee joint. The joint distraction force and distraction displacement were measured when the joint was distracted in steps and after the section of the Achilles tendon. The joint reaction force on the lengthened side was significantly higher than the control side at both time points (mean+/-SD 44.4+/-7.8 N v. 27.2+/-4.0 N at the end of lengthening, 44.3+/-S6.5 N v. 31.3+/-3.0 N at 5 weeks after lengthening). The contribution of the gastrocnemius to the joint reaction force on the lengthened side was also significantly higher than the control side at both time points (mean+/-SD 9.0+/-1.3N v. 2.8+/-0.8 N at the end of lengthening, 5.3+/-1.4N v. 2.7+/-0.5N at 5 weeks after lengthening). There were significant knee and ankle joint contractures at the end of lengthening, as evidenced by decreased range of motion (mean+/-SD 27+/-8 degrees and 36+/-13 degrees, respectively), which remained 5 weeks after lengthening (mean+/-SD 26+/-6 degrees and 35+/-8 degrees, respectively). The gastrocnemius contributed about 20% of the joint reaction force, indicating that changes in the other intra- and extra-articular structures due to joint contracture may be more important in generating the joint reaction force.     

Ectopic expression of Arabidopsis thaliana plasma membrane intrinsic protein 2 aquaporins in lily pollen increases the plasma membrane water permeability of grain but not of tube protoplasts

To investigate the role of aquaporin-mediated water transport during pollen grain germination and tube growth, Arabidopsis thaliana plasma membrane intrinsic proteins (PIPs) were expressed in pollen of Lilium longiflorum (lily). Successful expression of AtPIPs in particle-bombarded lily pollen grains was monitored by co-expression with fluorescent proteins and single-cell RT-PCR, and by measuring the water permeability coefficient (P(os)) in swelling assays using protoplasts prepared from transformed pollen grains and tubes. Expression of AtPIP1;1 and AtPIP1;2 in pollen grains resulted in P(os) values similar to those measured in nontransformed pollen grain protoplasts (6.65 +/- 2.41 microm s(-1)), whereas expression of AtPIP2 significantly increased P(os) (AtPIP2;1, 13.79 +/- 6.38; AtPIP2;2, 10.16 +/- 3.30 microm s(-1)). Transformation with combinations of AtPIP1 and AtPIP2 did not further enhance P(os). Native pollen tube protoplasts showed higher P(os) values (13.23 +/- 4.14 microm s(-1)) than pollen grain protoplasts but expression of AtPIP2;1 (18.85 +/- 7.60 microm s(-1)) did not significantly increase their P(os) values. Expression of none of the tested PIPs had any effect on pollen tube growth rates. The ectopic expression of AtPIP2s in lily pollen increased the water permeability of the plasma membrane in pollen grains, but not in pollen tubes. The measured endogenous water permeability does not limit water uptake during tube growth, but has to be regulated to prevent tube bursting.     

On the size of Corylus avellana L. pollen mounted in silicone oil

A considerable variation in the size of modern Corylus avellana pollen mounted in silicone oil was noticed. It turned out that a residue of the silicone oil solvent (benzene) prevents shrinkage of the pollen grains, and that size-variations may be due to more or less incomplete evaporation of the solvent. Evaporation at 50[ddot]C is more effective than evaporation at room temperature. Diffusion of solvents from a plastic spatula and from the slide-sealing material may cause a swelling of the pollen. The size of pollen grains compressed by the cover slip may increase slightly due to deformation. Size changes with storage up to 17 years are random, compressed grains do not swell, and the average changes are insignificant. The size of Corylus pollen from various modern collections is compared.     

Atomic force microscopy of pollen grains,cellulose microfibrils,and protoplasts

Summary Atomic force microscopy (AFM) holds unique prospects for biological microscopy, such as nanometer resolution and the possibility of measuring samples in (physiological) solutions. This article reports the results of an examination of various types of plant material with the AFM. AFM images of the surface of pollen grains ofKalanchoe blossfeldiana andZea mays were compared with field emission scanning electron microscope (FESEM) images. AFM reached the same resolutions as FESEM but did not provide an overall view of the pollen grains. Using AFM in torsion mode, however, it was possible to reveal differences in friction forces of the surface of the pollen grains. Cellulose microfibrils in the cell wall of root hairs ofRaphanus sativus andZ. mays were imaged using AFM and transmission electron microscopy (TEM). Imaging was performed on specimens from which the wall matrix had been extracted. The cell wall texture of the root hairs was depicted clearly with AFM and was similar to the texture known from TEM. It was not possible to resolve substructures in a single microfibril. Because the scanning tip damaged the fragile cells, it was not possible to obtain images of living protoplasts ofZ. mays, but images of fixed and dried protoplasts are shown. We demonstrate that AFM of plant cells reaches resolutions as obtained with FESEM and TEM, but obstacles still have to be overcome before imaging of living protoplasts in physiological conditions can be realized.Abbreviations AFM atomic force microscope - FESEM field emission scanning electron microscope - PyMS pyrolysis mass spectrometry - TEM transmission electron microscope     

Male gametophyte in maize: Influences of the gametophytic genotype

Summary Size and variation in pollen samples were investigated in several successively selfed generations. A significant decrease in mean diameter of pollen grains accompanied inbreeding; also decreased variation in pollen size from individual plants was observed. Since loss of developmental homeostasis in the sporophyte could affect variation in the gametophyte, sporophytic characters were observed as a control. The main conclusion reached in this study was that pollen diameter is influenced by the gametophytic genotype.     

More than a leak sealant. The mechanical properties of callose in pollen tubes

While callose is a well-known permeability barrier and leak sealant in plant cells, it is largely unknown whether this cell wall polymer can also serve as a load-bearing structure. Since callose occurs in exceptionally large amounts in pollen, we assessed its role for resisting tension and compression stress in this cell. The effect of callose digestion in Solanum chacoense and Lilium orientalis pollen grains demonstrated that, depending on the species, this cell wall polymer represents a major stress-bearing structure at the aperture area of germinating grains. In the pollen tube, it is involved in cell wall resistance to circumferential tension stress, and despite its absence at the growing apex, callose is indirectly involved in the establishment of tension stress resistance in this area. To investigate whether or not callose is able to provide mechanical resistance against compression stress, we subjected pollen tubes to local deformation by microindentation. The data revealed that lowering the amount of callose resulted in reduced cellular stiffness and increased viscoelasticity, thus indicating clearly that callose is able to resist compression stress. Whether this function is relevant for pollen tube mechanics, however, is unclear, as stiffened growth medium caused a decrease in callose deposition. Together, our data provide clear evidence for the capacity of cell wall callose to resist tension and compression stress, thus demonstrating that this amorphous cell wall substance can have a mechanical role in growing plant cells.     

Nasal vestibule wall elasticity: interactions with a nasal dilator strip.

We studied the effect of an adhesive external nasal dilator strip (ENDS) on external nasal geometry in 20 healthy Caucasian adults (10 men, 10 women; age 21-45 yr). The recoil force exerted by ENDS was estimated by bending the device (n = 10) with known weights. In the horizontal direction, a small/medium-sized ENDS in situ exerted a unilateral recoil force of 21.4-22.6 g. Application of ENDS resulted in a displacement of the lateral nasal vestibule walls that had both anterosuperior and horizontal components and that was maintained over an 8-h period. The resultant unilateral nasal vestibule wall displacement at the tip of the device was at 47.6 +/- 2.0 degrees to the horizontal (as related to the plane of the device when in situ) and had a magnitude of 3.5 +/- 0.1 mm. ENDS increased external nasal cross-sectional area by 23.0-65.3 mm2. Nasal vestibule wall compliance was estimated at 0.05-0.16 mm/g. Thus ENDS applies a relatively constant abducting force irrespective of nasal width. Variable responsiveness to ENDS may be related to differences in elastic properties of the nasal vestibule wall.