Pollen Germination Rate Research Articles

Successful without sex – the enigmatic biology and evolutionary origin of coralroot bittercress (Cardamine bulbifera, Brassicaceae)

Cardamine bulbifera (Coralroot Bittercress) is one of the Central European enigmatic plant species. Although the species is wide-spread all over Europe, no reproduction via seeds has ever been observed. Instead dispersal of vegetative leaf-axillary bulbs assures effective propagation. In our study we analyzed different life stages and factors affecting sexual reproduction and seek for unravelling the evolutionary origin of this polyploid species. We combined studies on pollen quality and fertility, pollen-stigma interactions, growth performance, and reproductive success with common garden experiments, controlled pollination and genotyping analysis (AFLPs). We also tested the interplay of resource allocation either into developing fruits and seeds or into reproductive organs generated by vegetative means. Cytogenetic analyses were conducted addressing variation in chromosome numbers and ploidy level. Phylogenetic relationships among possible parental lineages of Eurasian Cardamine species were reconstructed based on whole plastome sequences and the entire nuclear encoded rDNA cistron. We have shown herein that sexual reproduction of Cardamine bulbifera is hindered at various stages of reproductive development. We did not find any complete interruption of reproductive development except final embryo arrest. We detected low pollen germination rates and slow pollen tube growth. Less than 25 % of flowers matured into siliques with most often low-quality seeds; only 2% of those seeds developed towards early stages of germination but arrested before primary root formation. Results are independent from genotypes or vegetative propagation. Phylogenetic data demonstrate close relationships to C. quinquefolia and C. abchasica, but don’t indicate a hybrid origin involving distant species from other lineages. Cardamine bulbifera is a fully functional sexual plant with attractive flowers, nectar production, viable pollen, functional ovules and no signatures of a sporophytic incompatibility system. Highly reduced seed set and failure in seedling formation may be causally linked to a polyploid origin in the Caucasus region. Long-term survival has been achieved by rapid transition towards vegetative propagation and subsequent range expansion.

Effect of methyl jasmonate on in-vitro pollen germination and tube elongation of Pinus nigra.

The purpose of the main research was to investigate the effects of methyl jasmonate (MeJA) (0.05, 0.25, 0.5, and 2.5mM) on the pollen germination and tube elongation of Pinus nigra. Total pollen germination rate increased after MeJA treatments while the most enhancement was observed at 0.05-mM MeJA. No germination was observed at 2.5-mM MeJA. Although the unipolar and bipolar germination were observed in all groups, no significant changes were observed in unipolar and bipolar pollen germination rates after MeJA treatments. Tube length increased only at 0.05-mM MeJA. Although branched tubes were observed in all groups, branched tube rate increased only at 0.05-mM MeJA. Although two branched, three branched, and consecutive branched tubes were observed in all groups, the most common branching type was two branched type in all groups. Although anisotropy of actin filaments in the shank and apex of unbranched tubes decreased after MeJA treatments, the most decrease was observed at 0.05-mM MeJA. Also, anisotropy of actin filaments in the shank and in pre-branching region of branched tubes decreased only at 0.25-mM MeJA. Anisotropy of both two apexes of a branched tube changed only at 0.25- and 0.5-mM MeJA. Callose accumulation in the apex of unbranched and branched tubes increased in parallel with the increase in MeJA concentration. However, more callose is accumulated in one apex than the other apex of a branched tube. In conclusion, MeJA affected the actin organization, changed the callose distribution, and altered the pollen tube growth of Pinus nigra.

Physiological Importance of Pectin Modifying Genes During Rice Pollen Development.

Although cell wall dynamics, particularly modification of homogalacturonan (HGA, a major component of pectin) during pollen tube growth, have been extensively studied in dicot plants, little is known about how modification of the pollen tube cell wall regulates growth in monocot plants. In this study, we assessed the role of HGA modification during elongation of the rice pollen tube by adding a pectin methylesterase (PME) enzyme or a PME-inhibiting catechin extract (Polyphenon 60) to in vitro germination medium. Both treatments led to a severe decrease in the pollen germination rate and elongation. Furthermore, using monoclonal antibodies toward methyl-esterified and de-esterified HGA epitopes, it was found that exogenous treatment of PME and Polyphenon 60 resulted in the disruption of the distribution patterns of low- and high-methylesterified pectins upon pollen germination and during pollen tube elongation. Eleven PMEs and 13 PME inhibitors (PMEIs) were identified by publicly available transcriptome datasets and their specific expression was validated by qRT-PCR. Enzyme activity assays and subcellular localization using a heterologous expression system in tobacco leaves demonstrated that some of the pollen-specific PMEs and PMEIs possessed distinct enzymatic activities and targeted either the cell wall or other compartments. Taken together, our findings are the first line of evidence showing the essentiality of HGA methyl-esterification status during the germination and elongation of pollen tubes in rice, which is primarily governed by the fine-tuning of PME and PMEI activities.

Dissecting the distyly response to pollination using metabolite profiling in heteromorphic incompatibility system interactions of Plumbago auriculata Lam

Heteromorphic self-incompatibility (HetSI) is a strategy used to prevent selfing while favouring outcrossing in angiosperm. Although the genome, proteome and metabolome of homomorphic self-incompatibility (HomSI) have been investigated, metabolome findings have shown that energy deficiency is one of the factors leading to HomSI. However, the mechanism of HetSI remains unclear. This study investigates the alterations of metabolite fluxes in HetSI. Here, metabolic changes present in dimorphic styles as well as between self-incompatibility (SI) and self-compatibility (SC) pollinations of Plumbago auriculata Lam were simultaneously determined by gas chromatography–mass spectrometry (GC–MS). Fifty-three metabolites, mainly including other organic acids, amino acids, carbohydrates/glycosides, fatty acids/lipids, amines, amides, flavonoids and alcohols, were detected. The overall results showed that carbohydrates, which may affect pollen germination and pollen tube growth rate on stigmas, were abundant in S (short styles without pollination). Moreover, energy deficiency may not be a reason for HetSI because we found inflated levels of metabolites in SI pollinations. This study provided detailed insight into metabolic changes in HetSI and evidence for further studies of HetSI.

The in vitro germination and storage characteristics of Keteleeria fortunei var. cyclolepis pollen provide a reference for cross breeding.

Keteleeria fortunei var. cyclolepis is an ideal tree species for mountain afforestation, timber forests, and landscaping. Its pollination process can be affected by the rainy season, making it difficult to pollinate the massive female cones, which leads to a high abortion rate and low quality of seeds. Here, we observed the pollen morphology of K. f. cyclolepis using scanning electron and light microscopes, investigated the characteristics of its in vitro germination by the detached method, and explored the effect of different storage temperatures and times on the pollen germination rate and the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Our results indicated that the pollen of K. f. cyclolepis is a five-cell pollen, comprising one noumenon and two air sacs, both of which were oval in polar view. The optimal condition for pollen germination of K. f. cyclolepis was 240g/L sucrose + 70mg/L CaCl2 + 210mg/L H3BO3 at 24°C and pH6.0, resulting in a germination rate of 45.0%. The effects of different storage temperature and time on pollen germination rate varied significantly. The best storage temperature was - 80°C, at which the germination rate was 20.9% after 365days of storage, and the activity of three protective enzymes remained relatively high, representing relatively strong antioxidation and antiaging activity. Stepwise regression analysis showed that SOD was the main factor affecting the pollen germination rate of K. f. cyclolepis. The function of the three protective enzymes differed under various temperatures, for example, SOD served as a sensitive protective enzyme at room temperature, - 20°C and - 80°C, whereas both SOD and CAT served as sensitive protective enzymes at 4°C.

Effects of Colchicine on Populus canescens Ectexine Structure and 2n Pollen Production.

Triploid breeding is a central way to improve growth traits, timber quality, and stress resistance in Populus. In the present study, the morphology and viability of colchicine-induced 2n pollen, triploid production by crossing induced 2n pollen, and identification of genetic constitution of colchicine-induced 2n pollen were conducted in Populus canescens based on optimizing technology for inducing chromosome doubling in pollen. We found that the meiotic stage, injection time, and the interaction between the meiotic stage and injection time had highly significant effects on the 2n pollen production rate. The most effective treatment for inducing 2n pollen was to give 11 injections of 0.5% colchicine solution when pollen mother cells (PMCs) were at the pachytene stage. The highest 2n pollen production rate was 30.27 ± 8.69%. Colchicine occasionally affected ectexine deposition, and some narrow furrows were detected in the ectexine structure. However, no significant difference was observed in the pollen germination rate between natural 2n pollen and colchicine-induced 2n pollen. Moreover, 5 triploids derived from FDR-type 2n pollen were generated by crossing induced 2n pollen, suggesting that colchicine does not eliminate the function of colchicine-induced 2n pollen. However, slower growth of 2n pollen tubes was responsible for a lower triploid production rate.

In vitro pollen germination of Betula utilis, a typical tree line species in Himalayas

The study was conducted to determine the optimum medium for in vitro pollen germination for B. utilis based on germination percentages and length of the pollen tube. Studies about pollen germination and tube growth of B. utilis are limited. Therefore, this study aimed to investigate the effects of sucrose (1, 3, 5, 10 and 15%), boric acid (25, 50, 100 and 200 ppm), calcium nitrate (50, 100, 200, 300 and 400 ppm), magnesium sulfate (50, 100, 200 and 300 ppm) and potassium nitrate (50, 100 and 200 ppm) and time of incubation on pollen germination and tube growth. Pollen germination rates and tube growth were recorded periodically at 2, 4, 6, and 10 h. The length varied significantly with different concentrations and incubation time. The germination rate and pollen tube length varied significantly with different concentrations and incubation time. Pollen germination was maximal (98 ± 6.1%) when the germination medium contained 10% sucrose solution supplemented with 100 ppm H3BO3, 300 ppm Ca(NO3)2, 200 ppm MgSO4 and 100 ppm KNO3, after 6 h of incubation. In addition, results revealed that pollen grains collected immediately after anther dehiscence showed the best germination ability but gradually decreased with time.

Pollen germination is impaired by disruption of a Shaker K+ channel OsAKT1.2 in rice

Potassium homeostasis is essential for pollen development and pollen-pistil interactions during the sexual reproduction of flowering plants. Here, we described the role of a Shaker K+ channel, OsAKT1.2, in rice pollen germination and growth. OsAKT1.2 is specifically expressed in the tricellular pollen, mature pollen grains and growing pollen tubes. Using CRISPR gene editing, we found that knockout lines did not differ from wildtype in vegetative growth, but showed decreased pollen germination rate both in the germination medium and in vivo. OsAKT1.2-GFP fusion protein was localized in the plasma membrane and enriched at the pollen tube tip. OsAKT1.2 could complement the yeast strain which is deficient in K+ intake. These findings suggest that OsAKT1.2 is associated with pollen germination and tube elongation in rice.

Pollen performance modelling with an artificial neural network on commercial stone fruit cultivars

Pollen tube growth and pollen germination percentage are key factors for successful fruit set. Pollen performance is critical for the production and breeding of flowering plants and in agricultural systems in terms of fruit development. This study was carried out to predict pollen tube growth and pollen germination percentage in four stone fruits species (cherry (Prunus avium), apricot (Prunus armeniaca), plum (Prunus domestica), and peach (Prunus persica)) using a neural network. For this purpose, we measured pollen tube length and pollen germination rates under in vitro conditions. For the in vitro test, pollen grains of four stone fruit cultivars were sown in three different media and incubated at seven different temperatures for four incubation periods. A layered neural network was used for estimating the pollen germination rate and pollen tube length related to the in vitro condition. This study suggests a method for estimating the pollen germination rate and pollen tube length using artificial neural networks. The performed artificial neural networks produced an efficient prediction from in vitro data. The determination coefficients obtained between the observed and predicted data sets are 0.86 (for germination rate) and 0.81 (for tube length), indicating an accurate estimation of the in vitro data. In our case, the network that produced the best result had a 4:9:2 architecture.

The Fruit Dropping Characters of Sweet Cherry and Its Interior Causes in Insufficient Chilling Zone

Attempts had been made to provide evidences insight into the pattern and physiological mechanism of sweet cherry fruit dropping. However, the fruit abscission pattern and mechanism underlying the heavy fruit dropping in insufficient chilling regions, especially the roles of interior factors including carbohydrates and hormones in abnormal fruit dropping, has not yet been better understood so far. Currently, four five-year-old sweet cherry (Prunus avium L.) cultivars, i.e., ‘Santina’, ‘Brooks’, ‘Sparkerry’ and ‘Black Pearl’, which were grown in Weining County (104.28° E, 26.86° N), Guizhou province of China, were used as materials to elucidate the physiological fruit abscission pattern of sweet cherry and the chief interior causes for the heavy fruit dropping in insufficient chilling region of China. It was explicated that the abscission pattern of sweet cherry fruit somewhat varied among the cultivars in a low chilling region. Higher rate of pollen germination and longer polar axis length was proved to be remarkably beneficial to fruit development. A comparative anatomic dissection of fruit stalk between the retention and dropped fruit elaborated that there is obvious difference in the microstructure with the progress of fruit development. The discrepancy was mostly showed by the cell space of abscission zone tissues for the dropped fruit enlarged gradually and was remarkably larger than that of the retention ones. Furthermore, the imbalance of endogenous hormones in fruit is a crucial trigger for fruit dropping with the progress of fruit development, particularly the active ZR, GA, as well as IAA levels in fruit are positively correlated to fruit setting, conversely, ABA played a negative role in fruit retention. Moreover, carbohydrate contents in retention fruit were considerably higher than that of the dropped ones during the fruit development, however, the contents of glucose and fructose in dropped fruit did not reach the required threshold which was possibly a vital cause leading to fruit abscission.

Panicle inclination influences pollination stability of rice (Oryza sativa L.)

ABSTRACTRice pollination occurs when pollen grains fall by gravity from the anther onto the stigma and has been thought to be assured under suitable conditions. However, the position of the stigma relative to the anther pores may affect pollination. The inclination of panicle, that is quite usual in agricultural scene, may change the relative position of anther and stigma. We investigated the effect of panicle inclination on pollination stability. Pots of rice at flowering stage were tilted at one of the four inclinations (0° = control, 15°, 30°, and 45°). We assessed pollination (numbers of total and germinated pollen grains on the stigma) and morphology of dehisced anthers. Inclination significantly affected the number of total and germinated pollen grains on the stigma: as it increased from 0° to 45°, the percentage of florets with <20 total pollen grains on the stigma (TP20) increased from 36.6% to 59.9%, and that of florets with <10 germinated pollen grains on the stigma (GP10) increased from 26.6% to 58.9%. Both an increase in TP20 and a decrease in the rate of pollen germination were major causes of the increase in GP10. Inclination did not affect anther morphology. A panicle inclination of ≥30°could greatly reduce rice production because rice fertilization requires >10 germinated pollen grains on the stigma. Uprightness of the panicle at flowering should be an important objective in rice breeding and production.Abbreviations: TP20: percentage of florets with <20 total pollen grains on the stigma; GP10: percentage of florets with <10 germinated pollen grains on the stigma

Overexpression of SlOFP20 affects floral organ and pollen development

The OVATE gene was initially identified in tomato and serves as a key regulator of fruit shape. There are 31 OFP members in the tomato genome. However, their roles in tomato growth and reproductive development are largely unknown. Here, we cloned the OFP transcription factor SlOFP20. Tomato plants overexpressing SlOFP20 displayed several phenotypic defects, including an altered floral architecture and fruit shape and reduced male fertility. SlOFP20 overexpression altered the expression levels of some brassinosteroid (BR)-associated genes, implying that SlOFP20 may play a negative role in the BR response, similar to its ortholog OsOFP19 in rice. Moreover, the transcript accumulation of gibberellin (GA)-related genes was significantly affected in the transgenic lines. SlOFP20 may play an important role in the crosstalk between BR and GA. The pollen germination assay suggested that the pollen germination rate of SlOFP20-OE plants was distinctly lower than that of WT plants. In addition, the tomato pollen-associated genes SlCRK1, SlPMEI, LePRK3, SlPRALF, and LAT52 were all suppressed in the transgenic lines. Our data imply that SlOFP20 may affect floral organ and pollen development by modulating BR and GA signaling in tomato.

The vitality of the Serbian spruce (Picea omorika) pollen during the long-term cryopreservation

This article studies differences in the vitality (germination rate and pollen tube length) of fresh pollen and pollen stored at −20 °C for 14 years of Serbian spruce (Picea omorika [Pančić] Purkyne). Fresh pollen was sampled from 24 trees from a Serbian spruce seed stand area on the site of Bela zemlja (43° 48′ 32″ N, 19° 44′ 25″ E) in the area of Mount Zlatibor (Serbia) in two successive years. Six nutrition media with different sucrose concentrations (0%, 5%, 10%, 15%, 20% and 25% aqueous solution) were used to assess the vitality of the pollen. Variance analysis shows significant differences among years of pollen sampling, years of cryopreservation, trees, and sucrose treatments for pollen germination for both germination rate and pollen tube length. The results indicate that climate conditions preceding the pollen maturation period had an impact on the pollen quality as well as on the pollen vitality during the years of cryopreservation. Inter-individual variability (differences between trees genetic variability) was very pronounced and enabled selection of pollinator trees that retained their initial vitality during the period of cryopreservation. This periodicity in Serbian spruce full flowering might have significant practical application in the breeding of this important species.

High Temperature Reduces the Viability of Pollen from Upland Cotton in China

The viability of pollen grains from upland cotton (Gossypium hirsutum L.) has an important influence on fertilization and fiber yield and quality, and high temperature adversely affects cotton pollen grain development. However, the effects of high temperature on the vigor of pollen grains and cultivars having pollen grains resistant to high temperature in different regions have not been reported. The purpose of this study was to evaluate how high temperatures influence the viability of pollen from upland cotton and determine the high‐temperature risk to pollen vigor in upland cotton cultivars in major cotton‐producing regions in China. In this study, pollen grain germination was performed in vitro by culturing pollen grains in medium to detect cotton pollen grain viability. Pollen germination rates decreased significantly when the maximum daily temperature was ≥35°C for three consecutive days. The resistance of pollen vigor to high temperatures significantly differed among cultivars. According to the average annual number of days with temperatures ≥35°C from June to August in the main cotton‐producing areas in China within a 10‐yr period, the risk of high temperature affecting pollen vigor can be divided into five levels. Seventeen cultivars (lines) resistant to high temperatures were selected from 206 upland cotton cultivars, and four simple sequence repeat (SSR) markers were found to be associated with pollen germination rates under high temperature. This study clarified the degree of high‐temperature risk in major cotton‐producing areas in China and provided guidance for the selection of suitable heat‐resistant cultivars.Core Ideas Pollen germination rates decreased significantly when the maximum daily temperature was ≥35°C for three consecutive days. The heat resistance index was calculated to evaluate the differences in the heat resistance among the different cultivars. Resistance of pollen vigor to high temperature significantly differed among cultivars. Four simple sequence repeat markers associated with pollen germination rates under high temperature were identified.

Using Colchicine to Create Poinsettia (Euphorbia pulcherrima × Euphorbia cornastra) Mutants with Various Morphological Traits

Commercially available novel cultivars of poinsettia, obtained through interspecific hybridization, were subject to colchicine-based mutagenesis to recover their fertility, enabling subsequent breeding. Mutagenic treatment was conducted at different concentrations of colchicine with either lanolin or cotton serving as the matrix. The results indicated that 1 day was the optimal duration of colchicine treatment and that suitable colchicine concentration varied by cultivar. Moreover, one-time treatment gave higher rates of both polyploidy and morphological mutant production than two-times treatment. Specifically, the poinsettia cultivars Dulce Rosa (5 mg·g−1 colchicine with lanolin; 10 mg·mL−1 colchicine with cotton) and Princettia-Hot Pink (15 mg·g−1 colchicine with lanolin; 10 mg·mL−1 colchicine with cotton) yielded relatively high polyploidy production efficiency and morphological mutation rate. Consequently, a total of three polyploidy mutants of ‘Dulce Rosa’ and 19 polyploidy mutants of ‘Princettia-Hot Pink’ were obtained. Both cultivars had mutants with recovered fertility, with pollen germination rate of up to 27.5%. Moreover, unexpected non-polyploidy mutants with various morphological trait variations were also obtained.

Pollen Performance of ‘Red Lake’ and ‘Rosenthal’ Currant (Ribes rubrum) Cultivars

Objective: The aim of this study is to test the performance of the pollen grains of ‘Red Lake’ and ‘Rosenthal’ blackcurrant varieties. Pollen morphological homogeneity ratio, pollen viability ratio and germination rate at different temperatures were investigated.Material and Methods: In this study, pollen germination, viability and quality of pollens belongs to ‘Red Lake’ and ‘Rosenthal’ currant cultivars were studied. For the fertilization biology studies, phenologic observations were first noted. In order to determine the pollen performance, morphological homogeneity, pollen viability (TTC staining test) and germination rates (agar in plate) were determined. In addition, the effect of different temperature conditions (15 °C, 20 0C, 25 0C, 30 0C) on pollen germination was noted and the most suitable germination temperature was determined for each cultivar. The effect of different incubation times (6h, 12h, 24h, 48h) on germination capacity was also determined.Results: Morphological homogeneity value of the pollen of the two cultivars was quite high and higher pollen viability should be obtained from morphologically homogenous pollens. Effect of different temperatures on pollen germination percentage was found to be statistically different (p&amp;lt;0.05) for both cultivars.Conclusions: 150C was the optimum temperature to obtain the highest pollen germination for ‘Red Lake’ while 200C was the optimum for ‘Rosenthal’ pollen grains. Increasing incubation period for both cultivars increased overall pollen germination rate.

Low soil temperature and drought stress conditions at flowering stage affect physiology and pollen traits of rice

Low temperature and drought stress are the major constraints in rice productivity worldwide. This study investigated the influence of low soil temperature and/or drought stress on physiology and pollen traits of two rice genotypes viz., Guinongzhan and Yueza 763 at flowering stage. The experiment included four treatments, i.e., under the greenhouse natural growth conditions (UC) taken as control, drought stress (DS), the soil water potential was kept at −0.035 to −0.045 MPa (DS), low soil temperature (LT) maintained at 19 to 21°C, combined LT and DS (LT+DS, LD). Results showed that LT, DS, and LD substantially reduced net photosynthetic rate (Pn) and the maximal photochemical efficiency of PSII (Fv/Fm), whilst transpiration rate (Tr) was markedly enhanced by under LT in both rice genotypes. The malondialdehyde (MDA) contents were enhanced under LT, DS, and LD in Guinongzhan, whilst the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were regulated by LT, DS, and LD in both rice genotypes. Furthermore, anther dehiscence rate, pollen numbers on stigma, pollen viability and pollen germination rate, and anther starch contents were obviously reduced under LT and DS of both rice genotypes. Stress conditions substantially reduced the yield and yield components, i.e., effective panicles, seed set percentage, grain/panicles, 1000-grain weight, and grain yield of both genotypes and the effects were more apparent in Guinongzhan than those in Yueza 763 whilst combined LT and DS proved more damaging than individual stress.

Determination of the effects of growth regulators on pollen viability and germination level of tulip

The present study was focused on determining the effects of brassinosteroid, naphthalene acetic acid and gibberellic acid on in vitro pollen germination and pollen viability of tulip. Knowledge on different sources of pollen is an important issue for ornamental plant growers or breeders especially in crossing procedures for tulip. Flower bud formation and inflorescence is affected by bulb size, environment, irrigation, nutrition and many other factors. In some ornamental plants pollen quality as well as cultivar affect viability and germination characteristics. Tulipa greigii 'Pinocchio' was used as a pollen source which was tested for its ability to germinate in vitro on a medium (1% agar and 20% sucrose) containing three different group of hormones, gibberellic acid (GA3), naphthalene acetic acid (NAA) and epibrassinolide (EBR). After 24 h of incubation, pollen were evaluated and germination ratios were determined. The results indicate that pollen germination was significantly affected by growth regulators while pollen viability and germination rates were altered according to the concentrations and the type of the growth regulators. The highest average value of the pollen germination rate (42.95%) was determined in the concentration of 0.1 mg L(‑1) EBR treatment in Tulipa greigii 'Pinocchio', while the highest value (92.47%) for the pollen viability was obtained from epibrassinolide (EBR) in comparison to the other hormones.

The Effect of Air Pollution on Developmental Stages and Pollen Germination, Pollen Tube Growth and Fruit Set of the Apple Cultivars ‘Golden Delicious’ and ‘Golab’

In this study, the effect of industrial air pollution on developmental stages and pollen germination, pollen tube growth and fruit set of the apple cultivars ‘Golden Delicious’ and ‘Golab’ was studied. For this purpose, the flowers of the apple cultivars used were collected in early spring among the trees of the same age from Astaneh region as the non-polluted region, the region around the refinery as the semi-polluted region, and the Gavar region as the polluted region. The results of the variance analysis showed that the highest rate of pollen germination and pollen tube growth was associated with ‘Golden Delicious’ cultivar in Astaneh region; while, the lowest rate was related to the ‘Golab’ cultivar in Gavar region. The least amount of fruit set was related to pollen grains belonging to Gavar and refinery regions, whereas pollen grains from Astaneh region led to the highest amount of fruit set. Evaluation of the developmental stages of the anthers and pollen grains by light microscopy and SEM images of pollen grains showed that pollen grains from trees in polluted regions lost their normal forms and developed wrinkles. The results indicated that the effect of pollution on production of pollen grains with abnormal shape in the ‘Golab’ cultivar was more than the ‘Golden Delicious’ cultivar. Therefore, it is recommended for areas with air pollution to cultivate ‘Golden Delicious’ instead of ‘Golab’.

Temperature stress interferes with male reproductive system development in clementine (Citrus clementina Hort. ex. Tan.)

AbstractMale gametophyte development is a critical phase of the plant life cycle due to its high sensitivity to environmental stresses. The rise in the average global temperature, often accompanied by extreme fluctuations, has an important impact on biological processes. Among those, male gametophytes are particularly sensitive to temperature stress during flower bud development and anthesis. Male gametophyte development was extensively studied in several plant species, but little information is available about the effects of temperature stress on male gametophyte development in the genus Citrus. We evaluated the effects of cold and hot temperatures during microsporogenesis and microgametogenesis on one of the most economically valuable citrus species, the “Comune” clementine (Citrus clementina Hort. ex. Tan.). The effect of constant temperature on the androecium was evaluated by a time course histological analysis performed on the anthers and by monitoring in vitro pollen germination. The results revealed how suboptimal hot and cold temperatures induce drastic alterations on the morphology of the tapetal cells, microspores and mature pollen grains. Shifting from the optimal temperature affected the timing of starch depletion in the anther walls, such as epidermis, endothecium and middle layer, influencing the pollen germination rate and pollen tube growth. To the best of our knowledge this is the first study attempting to assess how temperature stress affects male reproductive development in citrus. A better understanding of the mechanisms underlining male sterility will provide novel insights to elucidate the physiology of this agronomical important quality trait.