Pollen Tube Length Research Articles

The role of microtubules in the growth of pollen tube tip

Pollen grains were sown on agar germination media containing increasing concentrations of the following disruptors, oryzalin and colchicines. Germination tube length was examined and results were evaluated. Treatment with oryzalin caused a slight but significant reduction in pollen germination while colchicines did not affect germination. All the microtubules (MTs) disruptors caused a decline in pollen tube length. The concentration that caused a significant reduction in tube length was 100 µM for oryzalin and 500 mM for colchicines. The effectiveness of these inhibitors varied. At the highest tested concentrations, oryzalin was more effective than colchicines in reducing tube length. In addition, MT disruptors induced tube curving. Curving was caused by disruption of the microtubules in the tip. We concluded that microtubules were involved in tip growth of pollen tubes. Therefore, the functional MT configuration is essential for the pollen tube to exert the penetration force. Key words: Pollen germination, pollen tube growth, inhibitor treatments, gelling agent.

BORON CONCENTRATION AFFECTS IN VITRO POLLEN GERMINATION AND TUBE GROWTH IN KIWIFRUIT (ACTINIDIA DELICIOSA) CULTIVAR 'MATUA'

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Plant Physiology from Cell to Fruit Production System BORON CONCENTRATION AFFECTS IN VITRO POLLEN GERMINATION AND TUBE GROWTH IN KIWIFRUIT (ACTINIDIA DELICIOSA) CULTIVAR 'MATUA'

FLOWER PERFORMANCE AND FRUIT PERSISTENCE IN ORGANIC 'KALAMATA' OLIVE

Organic olive farming is characterized by products with high biological value and increased market prices but in the same time is doubted for tree nutrition inefficiency and lower yield consistency. For two consecutive years, we studied flower biology in an irrigated ‘Kalamata’ olive orchard. Additionally, fruit persistence, from fruit set to harvest was monitored in monthly intervals. Flowering was realized between mid-April and mid-May with duration affected by air temperature. The average number of flowers/inflorescence was 22 and flower fertility was 78%. 52% of the staminate flowers were located in the basal section of inflorescence, 33% in the middle part and only 15% in the apical fraction. In vitro pollen germination was 58.9% and mean pollen tube length was 196 μm. 64% of the fruit set was abscised between late May and late June while during the next 6 months to December 21% of the initial fruit load was dropped. The average fruit yield was 35.7 kg/tree. Tree productivity of organic olive compared to conventional farms is also discussed.

Temperature-dependent enhancement of pollen tube growth observed in interspecific crosses between wild Cucumis spp. and melon (C. melo L.)

Wild Cucumis spp., which have resistance to various diseases, have the potential to be used for melon (C. melo L.) breeding. Nevertheless, few interspecific hybrids between melon and wild Cucumis spp. have been obtained because of strong reproductive barriers such as pollen–pistil incongruity and hybrid seed abortion. For this study, we examined the temperature conditions enhancing pollen tube growth and fruit set in interspecific crosses between melon and wild Cucumis spp. Before temperature-conditioned pollination, four wild Cucumis spp. were pollinated with the melon line ‘MR-1’ and two lines of C. anguria, PI 147065 and PI 320052, and a line of C. metuliferus, PI 526242, were selected for later experiments. These three lines were crossed reciprocally with ‘MR-1’ under controlled temperatures of 24–34°C at 2°C intervals. When ‘MR-1’ pistils were pollinated with three lines of wild Cucumis spp., pollen tube growth was arrested after germination at all temperatures. However, in the pistil of wild Cucumis spp., pollen tube growth of ‘MR-1’ was significantly greater at 32°C and at 34°C than that under 30°C. Furthermore, pollen tube length in pistils of PI 320052 and PI 526242 at 32°C was comparable to that of ‘MR-1’ self-pollination at 28°C. Fruit set frequency was also improved at 32°C. These results demonstrated that the pollen tube inhibition of Cucumis spp. interspecific crosses might be partially or fully recoverable in higher-temperature conditions. Moreover, 32°C is apparently the threshold temperature for promoting pollen tube growth in these cross combinations.

Oligomerization studies show that the kinase domain of the tomato pollen receptor kinase LePRK2 is necessary for interaction with LePRK1

LePRK1 and LePRK2 are two pollen-specific receptor-like kinases from Solanum lycopersicum that are involved in signaling during pollen-pistil communication. Previously, we showed that both proteins interact in pollen and when expressed in yeast. We also showed that pollen tube length was regulated by phosphorylation of specific residues in the juxtamembrane domain of LePRK2. To determine the domains responsible for the interaction between LePRK1 and LePRK2, we constructed a series of deletions, expressed them in yeast and determined their association by co-immunoprecipitation assays. We show that deletions containing extracellular domains of LePRK1 and LePRK2 were glycosylated in yeast and were sufficient for interaction with the corresponding full-length receptor. The juxtamembrane domain of LePRK1 was sufficient for its interaction with LePRK2, whereas LePRK2 required its kinase domain for interaction with LePRK1. These findings suggest a role for the juxtamembrane domain of LePRK2 in mediating intracellular dimerization and thus receptor kinase phosphorylation.

Pollen studies of Jatropha (Jatropha curcas L.)

The present investigation was undertaken at the Farm of All India Coordinated Research Project on Under Utilized Crops, Regional Research Station, S.D. Agricultural University, Sardarkrushinagar during the year 2002 and 2003. Pollen grains were creamish yellow and sticky. They were Spheroidal or globular in distilled water and acetocarmine with three to four germspores. The mean pollen size in distilled water was 90.5 and 83.5 μm in lower and upper tier of stamen, respectively, while in acetocarmine 82 and 89 μm in upper and lower tier of stamens, respectively. The pollen viability was quite high (95.04 to 98.77%). Maximum pollen germination (35.49%) and pollen tube length (265.19 μ) was recorded in 15 % sucrose solution with 0.005% boric acid.

A novel pollen tube growth assay utilizing a transmitting tract-ablated Nicotiana tabacum style

Sexual plant reproduction requires multiple pollen-pistil interactions from the stigma (pollen adhesion, hydration, and germination) to the ovary (fertilization). Understanding the factors that regulate pollen tube growth is critical to understanding the processes essential to sexual reproduction. Many pollen tube growth assays (PTGAs) have shorter and slower pollen tube growth when compared to pollen tube growth through the style. The identification and study of factors that regulate pollen tube growth have been impeded by a lack of an efficient and reproducible PTGA. The objective of this research is to develop a robust assay for Nicotiana tabacum pollen tube growth in an environment that supports sustained and normal growth yet is amenable to testing the effects of specific factors. In this paper, we introduce a novel PTGA, which uses pistils from N. tabacum that lack a mature transmitting tract (TT) due to tissue-specific ablation. The TT-ablated style supports normal pollen tube growth and the hollow structure of the style allows modification of the growth environment by direct injection of test material. This PTGA is robust and allows for rapid and accurate measurement of pollen tube length and pollen tube morphology, supporting pollen tube growth from 20 to 35°C and at pH ranging from 4.8 to 7.6. Use of the ablated style for a PTGA is a novel method for the culture of pollen tubes with sustained growth in vivo while permitting the application of treatments to the growing pollen tubes.

TOMATO POLLEN STORAGE AT FREEZE AND CRYOGENIC TEMPERATURE - EFFECTS ON VIABILITY AND FECUNDITY

Storage at cryogenic temperatures is considered a successful method of retaining pollen viability in many plant species. Storage at ­20°C has also been reported as a convenient method of pollen preservation with satisfactory results. In this study, the effects of two storage methods on tomato pollen viability and fecundity have been compared. Tomato pollen was stored at ­20°C using CaCl2 as desiccant and at ­196°C after modification of its moisture content to 6.5-7% (wet weight basis). After 6, 8, 10, 12 and 18 months, in vitro pollen germination and pollen tube growth were tested following rehydration for 3 h at 100% R.H. and 15°C, and incubation for 6 h on semisolid substrate (1% agar, 12% sucrose and 50 mg L-1 H3BO3). Respiration activity was measured in pollen stored at both ­20 and ­196°C for 6 and 12 months in liquid substrate (12% sucrose and 50 mg L-1 H3BO3). Fecundity of stored pollen was assessed by artificial pollinations conducted at the same time. Pollen stored at ­20°C retained high in vitro germination for 10 months. However, after only 6 months at ­20°C, pollen tube length and respiration activity declined with a negative impact on pollen fecundity, as indicated by the reduced number of seeds per fruit in fruits obtained by artificial pollination. Pollen germination ability significantly declined after 12 months. On the other hand, pollen stored at ­196°C for 18 months exhibited similar in vitro germination, pollen tube growth and respiration activity to those recorded for fresh pollen. Furthermore, artificial pollination with cryogenically stored pollen resulted in similar fruit set and number of seeds per fruit to those observed after artificial pollination with fresh pollen.

Investigation on pollen viability and longevity in Malus pumila L., Pyrus commonis L., and Cydonia oblonga L., in vitro

The most important goal of fruit growers is obtaining high quantity and quality yield in fruit industry which depends on sufficient fruit setting. Pollination and fertilization are the basic factors which affect fruit setting volume. Commercial fruit trees in Iran belong to stone and pome fruits of Rosaceae family with gametophytic self-incompatibility, making necessary the selection of favorable pollinizer in breeding and orchard planning programs. Therefore, knowledge about pollen traits of the species and cultivars in this family is one of the main issues for growers and breeders. In this research, pollen germination, tube growth and longevity were studied in some cultivars and selected favorable genotypes of three species including; apple, pear and quince. Pollen traits were investigated after 35 days maintenance in 0°C, using in vitro medium containing 16% sucrose, 4 ppm acid boric and 1% agar. Cultured pollens were incubated in dark condition at 25°C for 24 h and then, pollen germination percentage and pollen tube length were evaluated using Light-Microscope. Results showed significant differences among cultivars and genotypes of each three studied species for pollen germination, tube growth and longevity characteristics. Key words: Apple, pear, quince, pollen traits, longevity and in vitro condition.

Screening Ornamental Pepper Cultivars for Temperature Tolerance Using Pollen and Physiological Parameters

Temperature affects reproductive potential, aesthetic, and commercial value of ornamental peppers (Capsicum annuum L.). Limited information is available on cultivar tolerance to temperature stress. An experiment was conducted using pollen and physiological parameters to assess high and low temperature tolerance in ornamental peppers. In vitro pollen germination (PG) and pollen tube length (PTL) of 12 morphologically diverse ornamental pepper cultivars were measured at a range of temperatures, 10 to 45 °C with 5 °C increments. Cell membrane thermostability (CMT), chlorophyll stability index (CSI), canopy temperature depression (CTD), and pollen viability (PV) were measured during flowering. From the modified bilinear temperature–PG and PTL response functions, cardinal temperatures (Tmin, Topt, and Tmax) for PG and PTL and maximum PG (PGmax) and PTL (PTLmax) were estimated. Cultivars varied significantly for PG, PTL, cardinal temperatures for PG and PTL, and all three physiological parameters. Cumulative temperature response index (CTRI) of each cultivar, calculated as the sum of 12 individual temperature responses derived from PV, PGmax, PTLmax, Tmin, Topt, and Tmax for PG and PTL, CMT, CTD, and CSI were used to distinguish differences among the cultivars and classify for high (heat) and low (cold) temperature tolerance. Based on CTRI–heat, cultivars were classified as heat-sensitive (‘Black Pearl’, ‘Red Missile’, and ‘Salsa Yellow’), intermediate (‘Calico’, ‘Purple Flash’, ‘Sangria’, and ‘Variegata’), and heat-tolerant (‘Chilly Chili’, ‘Medusa’, ‘Thai Hot’, ‘Explosive Ember’, and ‘Treasures Red’). Similarly, cultivars were classified for cold tolerance as cold-sensitive, moderately cold-sensitive, moderately cold-tolerant, and cold-tolerant based on CTRI–cold. ‘Red Missile’ and ‘Salsa Yellow’ were classified as cold-tolerant. Cultivar screening using pollen parameters will be ideal for reproductive temperature tolerance, whereas physiological parameters will be suitable for screening vegetative temperature tolerance. The identified heat- and cold-tolerant cultivars are potential candidates in breeding programs to develop new ornamental and vegetable pepper genotypes for high and low temperature tolerance.

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.

Mutations in Two Putative Phosphorylation Motifs in the Tomato Pollen Receptor Kinase LePRK2 Show Antagonistic Effects on Pollen Tube Length

The tip-growing pollen tube is a useful model for studying polarized cell growth in plants. We previously characterized LePRK2, a pollen-specific receptor-like kinase from tomato (1). Here, we showed that LePRK2 is present as multiple phosphorylated isoforms in mature pollen membranes. Using comparative sequence analysis and phosphorylation site prediction programs, we identified two putative phosphorylation motifs in the cytoplasmic juxtamembrane (JM) domain. Site-directed mutagenesis in these motifs, followed by transient overexpression in tobacco pollen, showed that both motifs have opposite effects in regulating pollen tube length. Relative to LePRK2-eGFP pollen tubes, alanine substitutions in residues of motif I, Ser(277)/Ser(279)/Ser(282), resulted in longer pollen tubes, but alanine substitutions in motif II, Ser(304)/Ser(307)/Thr(308), resulted in shorter tubes. In contrast, phosphomimicking aspartic substitutions at these residues gave reciprocal results, that is, shorter tubes with mutations in motif I and longer tubes with mutations in motif II. We conclude that the length of pollen tubes can be negatively and positively regulated by phosphorylation of residues in motif I and II respectively. We also showed that LePRK2-eGFP significantly decreased pollen tube length and increased pollen tube tip width, relative to eGFP tubes. The kinase activity of LePRK2 was relevant for this phenotype because tubes that expressed a mutation in a lysine essential for kinase activity showed the same length and width as the eGFP control. Taken together, these results suggest that LePRK2 may have a central role in pollen tube growth through regulation of its own phosphorylation status.

In vitro study of pollen traits after short storage in some almond, apricot and sweet cherry favorable genotypes

Iran is one of the most important producers of almond, apricot and sweet cherry known as stone fruits belong to genus Prunus of Rosaceae family. Most of the stone fruit trees are gametophytically self-incompatible which makes necessary the selection of favorable pollinizer in orchard planning programs for producing positive crop. However, study of main pollen traits is one of the most important issues for growers and breeders. In this research, main pollen traits including germination, tube growth and longevity were investigated in some favorable selected genotypes of three Prunus species including almond, apricot and sweet cherry. Pollen traits of five genotypes from each species were studied after six weeks storage in 4°C using the in vitro medium containing 10% sucrose and 1.2% agar. Pollen Germination Percentage (PGP) and Pollen Tube Length (PTL) were studied by Light-Microscope. Analysis of data was showed significant differences among the species and genotypes. PGP and PTL were normal after six weeks storage in 4°C especially; in almond and sweet cherry genotypes which showed high PGP and PTL in compared with apricot genotypes. Finally, the best genotypes of each species were selected for orchard establishment and breeding programs. Key words: Rosaceae family, almond, apricot, cherry, pollen traits and in vitro.

Seasonal Variations in Pollen Germination Ability, Reproductive Function of Pistils, and Seeds and Fruit Yield in Papaya (Carica papaya L.) in Okinawa

To improve the fruit and seed productivity in hermaphrodite ‘Sunrise Solo’ and female ‘Wonder Flare’, we investigated seasonal variations in the frequency of sexually altered abnormal misshapen flowers (carpelloid and pentandoria flowers) and female sterile flowers, fruit and seed yield, pollen germination ability, and the reproductive function of pistils under greenhouse cultivation conditions in Okinawa, Japan. In ‘Sunrise Solo’, the percentages of abnormal misshapen flowers were 42–66% from July to October (average temperature: 25.6–30.5°C), though they were below 10% from February to March (14.6–16.8°C) and December to January (16.9–18.1°C). The percentages of female sterile flowers were low (below 10%) from March to November (16.8–30.5°C), but high (13–37%) from December to February (14.6–18.1°C). Seed and fruit yield increased in May (24.6°C) and November (19.4°C), but decreased from January to March (14.6–18.1°C) and July to September (28.2–30.5°C). Pollen germination rates (52–87%) were high from April to June (22.2–27.2°C) and October to November (19.4–25.6°C) and pollen tube length was long (208–272 μm) during the same periods, while the rates were low (5–32%) and the tube length was short (63–134 μm) from January to March (14.6–18.1°C); moreover, no germinated pollen was found from July to September (28.2–30.5°C). These results of the seasonal fluctuation in pollen germination ability were supported by pollen germination tests performed in an incubation chamber, i.e., pollen germination rates were high (72–80%) between 20 and 25°C, but low (0–56%) below 15°C and above 30°C; however, the pistils of ‘Sunrise Solo’ and ‘Wonder Flare’ retained their reproductive function even during the period of low (16.7°C) and high (29.5–30.5°C) temperatures, i.e., fruit and seed yields were improved by pollination using pollen (germination rate: about 35%) collected from plants cultivated in an open field during the high temperature period or pollen preserved at sub-zero temperatures during the low and high temperature periods. These results indicate that fruit and seed production in papaya under low or high temperature conditions is unfavorable for pollen germination, but could be improved by artificial pollination with preserved pollen.

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%).

Distribution of Callose Synthase, Cellulose Synthase, and Sucrose Synthase in Tobacco Pollen Tube Is Controlled in Dissimilar Ways by Actin Filaments and Microtubules

Callose and cellulose are fundamental components of the cell wall of pollen tubes and are probably synthesized by distinct enzymes, callose synthase and cellulose synthase, respectively. We examined the distribution of callose synthase and cellulose synthase in tobacco (Nicotiana tabacum) pollen tubes in relation to the dynamics of actin filaments, microtubules, and the endomembrane system using specific antibodies to highly conserved peptide sequences. The role of the cytoskeleton and membrane flow was investigated using specific inhibitors (latrunculin B, 2,3-butanedione monoxime, taxol, oryzalin, and brefeldin A). Both enzymes are associated with the plasma membrane, but cellulose synthase is present along the entire length of pollen tubes (with a higher concentration at the apex) while callose synthase is located in the apex and in distal regions. In longer pollen tubes, callose synthase accumulates consistently around callose plugs, indicating its involvement in plug synthesis. Actin filaments and endomembrane dynamics are critical for the distribution of callose synthase and cellulose synthase, showing that enzymes are transported through Golgi bodies and/or vesicles moving along actin filaments. Conversely, microtubules appear to be critical in the positioning of callose synthase in distal regions and around callose plugs. In contrast, cellulose synthases are only partially coaligned with cortical microtubules and unrelated to callose plugs. Callose synthase also comigrates with tubulin by Blue Native-polyacrylamide gel electrophoresis. Membrane sucrose synthase, which expectedly provides UDP-glucose to callose synthase and cellulose synthase, binds to actin filaments depending on sucrose concentration; its distribution is dependent on the actin cytoskeleton and the endomembrane system but not on microtubules.

EFFECT OF TEMPERATURE AND GERMINATION MEDIA ON A VIABILITY OF POLLEN GRAIN OF FIVE PISTACHIO MALE STRAINS

This experiment was conducted to evaluate the effect of germination media and three temperatures on five male strains of pistachio at research center of agriculture faculty – Aleppo,(Arab center),.In this experiment, the rates of pollen germination were tested in different germination media (sucrose 10%, sucrose 10%+0.25 gr. boric acid P L. and sucrose 10%+0.0625 gr. boric acid P L.) with 3 temperature levels( 10,20 and 30◦c) .The media was contain 3 gr. agar per liter of water. The results showed that male strain 36 was gave the best germination rate, (78.33 % and tube length 796.1micron) as compared with other strains ,and male strain 47 was the lower (63.11%,511.3 micron) tube germination and tube length (63.11%,511.3 micron) respectively, but all were gave high rates of germination. sucrose 10% media gave the best germination rate (77.07%) and sucrose 10%+ 0.25 gr. boric acid P L. gave the lowest germination rate (62.2%), sucrose 10%+0. 0.25 gr. boric acid P L. gave highest tube germination length (777.68micron), where as 10% sucrose +0.0 625gr. boric acid P L. was the lowest tube length (499.88micron) .On the other hand, 30◦c gave the best germination rate and pollen tube germination length (88.73%and 1005.26 micron), however 10◦c gave lowest rates of these parameters (45.53% and, 244.3 micron) for germination rate and tube pollen length respectively. Generally, all media were gave highest significant results in germination rates and pollen tube length for all strains at all temperatures. we conclude that sucrose 10%was better media for pollen germination and sucrose 10%+0. 25 gr. boric acid P L.was the best for pollen tube length .

Biological characteristics of pollens in some genotypes of Rosa canina as main factors affecting fruit set

Rosa canina is a medicinal plant that its fruits have many important medicinal properties but unknown for many people's especially in Iran. However, this crop can be produced commercially and its orchards can be established such as other fruit trees. This research was carried out for studing pollen germination and tube growth as main factors affecting fruit set, in some Hashtroud and Maragheh indigenous genotypes of R. canina. Experiment was carried out based on completely randomized design (CRD) in ten genotypes (treatments) with four repeats. Pollens were cultured in an in-vitro medium containing 15% Sucrose, 0.01% Boric Acid and 1.2%. Agar and then maintained in 24°C in controlled condition. After 24 h pollens germination and growth were stopped with cholorophorm. Finally, pollen germination percentage (PGP) and pollen tube length (PTL) were measured by means of Light-Microscope at least in 7 randomized selected squares in each Petri Dish (repeats). Data analyzed with SAS software and results showed significant differences between studied characteristics of genotypes. Key words: Rosa canina, pollen germination, pollen tube growth, in vitro.

Recognition specificity of self-incompatibility in Pyrus and Malus

Pyrus displays gametophytic self-incompatibility controlled by a single highly polymorphic gene complex termed S locus, which comprises a stylar-expressed gene (S-RNase) tighlty linked with a pollen expressed gene, that determines the specificity of the self-incompatibility locus. Deduced amino acid sequence of ‘Meigetsu’ S 8 -RNase in Pyrus pyrifolia and ‘Kuerlexiangli’ S 28 -RNase in P. sinkiangensis showed 100% identity. S 3 -RNase in Malus spectabilis was also found to be similar to S 8 -RNase in P. pyrifolia with 96.9% identity in the deduced amino acid sequence. The intron, which is generally highly polymorphic between alleles, was also remarkably well conserved within these allele pairs. The intron of PpS 8 -RNase showed 95.3 and 91.9% identity with PsS 28 -RNase and MsS 3 -RNase, respectively. Pollen tube growth in styles, pollen tube length in artificial media containing different S-RNases and segregation of S haplotypes in F1 plants revealed commonality of the recognition specificity between PpS 8 -RNase and PsS 28 -RNase and between PpS 8 -RNase and MsS 3 -RNase. Results suggested that PpS 8 -RNase, PsS 28 -RNase and MsS 3 -RNase have maintained the same recognition specificity after the divergence of the two species and that amino acid substitutions found between PpS 8 -RNase and MsS 3 -RNase do not alter the recognition specificity.