Pollen Germination Research Articles

Pollen indices of Cedrus atlantica Manetti populations vary with geographical localities in the Moroccan Atlas Mountains

North Africa’s forests of Cedrus atlantica Manetti have declined drastically, by more than 58% in the last 130 years, and many stands are likely to disappear entirely in the coming decades. This study on the interactions between C. atlantica pollen characters (production, germination, and pollen tube length) and locality characters in Morocco, using seventy individuals from seven geographically distant populations, showed that pollen indices varied according to station. Pollen production was high in the populations of the Moudemam-1 and Seheb stations, intermediate in the Ait Oufella and Ait Ayach stations, and low in the Zerrouka, Ras Elma and Moudemam-2 stations. Pollen germination was very low for the populations in the Seheb and Moudemam-1 stations but high in the other stations. On the other hand, the longest pollen tubes were recorded in the Moudemam-1 population, while those in the other stations were shorter. These results show an inverse variation between the pollen indices characterizing the populations of the stations studied. The shortest pollen tube length classes [0-100] to [300-400] accounted for 85.98% of all classes and were assessed for the Zerrouka, Ait Oufella and Ait Ayach stations. The other classes were more represented or exclusive to the population of the Moudemam-1 station. These results could have implications not only for assessing pollen variations according to geographical localities but also for optimizing fertilization in cedar forests by selecting the best clones for this species.

Protein/Lipid ratio of pollen biases the visitation of bumblebees (Bombus ignitus Smith) to male-fertile cultivars of the Japanese pear (Pyrus pyrifolia Nakai).

Bees have been known to visit the male-fertile cultivars of self-incompatible flowering plants more frequently than the male-sterile cultivars, but the origin of this preference is poorly understood. Here, we demonstrate that this preference is driven by the higher protein/lipid ratio of male-fertile pollen compared with male-sterile pollen by way of two caged-behavioral assays with six cultivars. In the first assay, flower-naïve bumblebees (Bombus ignitus Smith) showed a significantly higher flower-visitation rate to male-fertile cultivars (pollen germination rate > 55%; > 14 visits/10 min) of the Japanese pear (Pyrus pyrifolia Nakai) than male-sterile cultivars (pollen germination rate ≤ 20%; > 6 visits/10 min). In the second, bees still preferred the anthers of male-fertile cultivars (5-9 visits/10 min) more than those of male-sterile ones (less than 1 visit in 10 min) even in the absence of all other organs (i.e., petals, pistil, nectar), indicating that pollen is responsible for the preference. We then analyzed the macronutrient content of the pollen and its visual cues, and found that the bee preference was highly correlated with the protein/lipid ratio (0.3-1.6) but not color variables such as (a)chromatic contrast, intensity, and spectral purity. We conclude that the protein/lipid ratio influences the foraging behavior of the bumblebees likely by serving as (1) a chemotactile cue while antennating, (2) a gustatory cue after intake, and (3) an olfactory cue. In addition, the low bee visitation rate to poorly viable pollen could be due to its low protein/lipid ratio.

Studies on pollen micro-morphology, pollen storage methods, and cross-compatibility among grape (Vitis spp.) genotypes.

The knowledge of pollen morphology, suitable storage condition, and species compatibility is vital for a successful grapevine improvement programme. Ten grape genotypes from three different species, viz., Vitis vinifera L., Vitis parviflora Roxb., and Vitis champini Planc., were studied for their pollen structure and pollen storage with the objective of determining their utilization in grape rootstock improvement programs. Pollen morphology was examined through the use of a scanning electron microscope (SEM). The viability of the pollen was assessed using 2,3,5-triphenyltetrazolium chloride (TTC). In vitro pollen germination was investigated using the semi-solid medium with 10 % sucrose, 100 mg/L boric acid, and 300 mg/L calcium nitrate. The results revealed variations in pollen micro-morphology in 10 genotypes, with distinct pollen dimensions, shapes, and exine ornamentation. However, species-wise, no clear difference was found for these parameters. Pollen of V. parviflora Roxb. and Dogridge was acolporated and did not germinate. The remaining eight genotypes exhibited tricolporated pollen and showed satisfactory in vitro pollen germination. Storage temperature and duration interactions showed that, at room temperature, pollen of most of the grape genotypes can be stored for up to 1 day only with an acceptable pollen germination rate (>30 %). However, storage for up to 7 days was successfully achieved at 4 °C, except for 'Pearl of Csaba'. The most effective storage conditions were found to be at -20 °C and -196 °C (in liquid N2), enabling pollen storage for a period of up to 30 days, and can be used for pollination to overcome the challenge of asynchronous flowering. Four interspecific combinations were studied for their compatibility, among which V. parviflora Roxb. × V. vinifera L. (Pusa Navrang) and V. parviflora Roxb. × V. champini Planc. (Salt Creek) showed high cross-compatibility, offering their potential use for grape rootstock breeding. However, V. parviflora Roxb. × V. vinifera L. (Male Hybrid) recorded the lowest compatibility index among studied crosses. In the case of self-pollinated flowers from V. parviflora Roxb. and V. parviflora Roxb. × V. champini Planc. (Dogridge), pollen failed to germinate on the stigma due to male sterility caused by acolporated pollen. As a result, the flowers of these genotypes functioned as females, which means they are ideal female parents for grape breeding without the need for the tedious process of emasculation.

Heat stress at the bicellular stage inhibits sperm cell development and transport into pollen tubes.

For successful double fertilization in flowering plants (angiosperms), pollen tubes deliver two non-motile sperm cells towards female gametes (egg and central cell, respectively). Heatwaves, especially during the reproduction period, threaten male gametophyte (pollen) development, resulting in severe yield losses. Using maize (Zea mays) as a crop and grass model system, we found strong seed set reduction when moderate heat stress was applied for two days during the uni- and bicellular stages of pollen development. We show that heat stress accelerates pollen development and impairs pollen germination capabilities when applied at the unicellular stage. Heat stress at the bicellular stage impairs sperm cell development and transport into pollen tubes. To understand the course of the latter defects, we used marker lines and analyzed the transcriptomes of isolated sperm cells. Heat stress affected the expression of genes associated with transcription, RNA processing and translation, DNA replication, and the cell cycle. This included the genes encoding centromeric histone 3 (CENH3) and α-tubulin. Most genes that were mis-regulated encode proteins involved in the transition from metaphase to anaphase during pollen mitosis II (PM II). Heat stress also activated spindle assembly check point and meta- to anaphase transition genes in sperm cells. In summary, mis-regulation of the identified genes during heat stress at the bicellular stage results in sperm cell development and transport defects ultimately leading to sterility.

Pollen viability and longevity in Juniperus taxa native to Slovakia

Pollen viability, dispersion ability and longevity during deep-freezer storage were studied in three Juniperus taxa distributed in Slovakia. All these characteristics of pollen are closely related to the pollination and/or fertilization success of the junipers in nature. Pollen viability varied considerably between the three populations of J. communis and one population of each, J. sibirica and J. communis var. intermedia. Pollen germination rate ranged between 40.75% and 75.06%, and pollen tube length between 30.32 and 40.41 µm. A clear tendency indicates a higher germination rate of J. communis pollen from lower altitudes and reduced germination of J. sibirica and J. communis var. intermedia pollen from higher altitudes. The dispersion potential of the J. communis pollen during its shedding seems relatively low. In 2021, pollen cloud density was diluted at 68.1% at the 4 m distance from the test shrub, in 2022 of 52.1% at the 17 m distance from the pollen source. A deep-freezer storage of juniper pollen in a double-walled polyethylene bag with silica gel was not efficient enough, as indicated by the drop of pollen germination rate of 31.2% in J. communis and of 79.4% in J. sibirica during a 1-year storage period at − 81 °C.

Identification of self-incompatibility alleles in Quince (Cydonia oblonga Mill.).

The Quince (Cydonia oblonga Mill.), typically known for its self-compatibility, surprisingly presents a degree of self-incompatibility. This research focused on exploring the diversity within the self-incompatibility gene locus (S) in various C. oblonga genotypes. Through meticulous DNA sequencing, the study sought to unearth potential novel S alleles. In the process of genotyping the S gene across multiple quince genotypes, not only were the previously documented S1 and S2 alleles identified, but this investigation also uncovered two previously unrecognized alleles, termed S4 and S5. These alleles, particularly S4, emerged as the most prevalent among the tested genotypes. To corroborate the findings derived from DNA sequencing, the study employed pollen tube growth germination assays. These assays elucidated a higher pollen germination rate in the Ardabil2 genotype in contrast to Behta. Additionally, the study involved assessing pollen tube growth in both Ardabil2 and Behta through cross-pollination techniques, meticulously tracking the development of pollen tubes at various stages. Remarkably, the outcomes demonstrated that the Behta genotype possesses self-incompatibility, whereas the Ardabil2 genotype showcases a notable degree of self-compatibility. This groundbreaking discovery of new S alleles in quince not only affirms the species' self-compatibility but also sheds light on the complexities of allelic diversity and its impact on self-incompatibility. Such insights are invaluable for enhancing the yield of quince orchards through strategic breeding programs.

Study on the effects of pollen sources on the agronomic, biochemical, mineral, and pomological traits of date palm (Phoenix dactylifera L.) cv 'Deglet Nour' fruits in Degache Oases (Tunisia)

AbstractGiven the dioecious nature of date palms, selecting an effective pollinizer bearing a substantial quantity of high-quality pollen is imperative. In this study, we investigated the effects of 11 male date palm cultivars from Tunisia on the production of female trees, fruit sets, and the characteristics of 'Deglet Nour' cultivar dates. The comparison of pollen germination rates showed that ABD1 and P169 pollens exhibited outstanding viability, with 98.7% and 98.3%, respectively. On the other hand, P169 pollen had the highest germination rate, at 86.3%. The most remarkable fruit set (90.7%) and retention rate (69.7%) were observed in response to P13 pollen. In response to the P165 pollinator, the fruit stood out among the resulting fruits for their notable weight, averaging 11.6 g. In addition, pollination with P90 increased total soluble solids (measured at 74.4°Brix in the Tamr stage), whereas P7-pollinated fruits recorded the highest levels of reducing sugars, reaching 41%. Notably, the highest acidity levels were found in P7-pollinated fruits (0.29%), and pollen sources significantly influenced the fruits' mineral content.Moreover, regarding pomological characteristics, fruits pollinated with P4 attained maximum size, measuring 4.10 cm. Conversely, P7-pollinated fruits had a notable width of 2.02 cm. These findings illustrate the possibility of the selective application of high-value pollinizers and emphasize the direct influence of pollen sources on fruit quantity and quality.

Dynamic organelle changes and autophagic processes in lily pollen germination

Pollen germination is a crucial process in the life cycle of flowering plants, signifying the transition of quiescent pollen grains into active growth. This study delves into the dynamic changes within organelles and the pivotal role of autophagy during lily pollen germination. Initially, mature pollen grains harbor undifferentiated organelles, including amyloplasts, mitochondria, and the Golgi apparatus. However, germination unveils remarkable transformations, such as the redifferentiation of amyloplasts accompanied by starch granule accumulation. We investigate the self-sustained nature of amylogenesis during germination, shedding light on its association with osmotic pressure. Employing BODIPY 493/503 staining, we tracked lipid body distribution throughout pollen germination, both with or without autophagy inhibitors (3-MA, NEM). Typically, lipid bodies undergo polarized movement from pollen grains into elongating pollen tubes, a process crucial for directional growth. Inhibiting autophagy disrupted this essential lipid body redistribution, underscoring the interaction between autophagy and lipid body dynamics. Notably, the presence of tubular endoplasmic reticulum (ER)-like structures associated with developing amyloplasts and lipid bodies implies their participation in autophagy. Starch granules, lipid bodies, and membrane remnants observed within vacuoles further reinforce the involvement of autophagic processes. Among the autophagy inhibitors, particularly BFA, significantly impede germination and growth, thereby affecting Golgi morphology. Immunogold labeling substantiates the pivotal role of the ER in forming autophagosome-like compartments and protein localization. Our proposed speculative model of pollen germination encompasses proplastid differentiation and autophagosome formation. This study advances our understanding of organelle dynamics and autophagy during pollen germination, providing valuable insights into the realm of plant reproductive physiology.

Evaluation of viability and germination of pollen grains of three local caprifig cultivars and their effect on some characteristics of fig fruits (Ficus carica L.)

This research was carried out in fig fields in the village of Kafar-Jales, in the north of Syria. The analyses were conducted in the laboratories of the Faculty of Agriculture at Idlib University during the 2022 farming season, to evaluate the viability and germination of three local varieties of Caprifig (Bunduqi, Azraq, Panjani). The morphological characteristics, the date of the exodus of insects (Blastophaga psenes) from male fruits, the quantity of pollen, and the percentage of germination and viability were studied on four nutritive media at a temperature of 27°C. The measurements were taken after 24 h, 48 h, and 72 h. These three pollinators were used to pollinate three varieties of edible figs (white Satehi, Safrawi, and Habashi) to study the effect of pollen source on the productive characteristics of edible fig fruits. The result showed significant superiority of the Bunduqi cultivar over the rest of the cultivars in traits of the fruit’s early ripening, pollen quantity, and date of departure of insects. The Azraq cultivar is found to be superior to Bunduqi and Panjani cultivars in the germination rate of pollen at all stages of the experiment and in all used media. The addition of stigma flower extract in culture media increased germination percentage by 35% for all studied Caprifig cultivars. The addition of 10% sucrose in the cultivation environment increased the percentage of pollen germination by 20%. The cultivars that were inoculated with the Panjani pollinator outperformed the characteristics of the length, diameter, and weight, demonstrating that the fruit’s quality characteristics are affected by the genotype of the pollinator used. The results of this research can be beneficial for both fig growers and plant breeders, as they help to select the best pollinators and contribute to the development and improvement of the quality of the cultivated fig fruits.

Effects of UV-B radiation on pollen germination and tube growth: A global meta-analysis

Despite widespread recognition of pollen's potential sensitivity to ultraviolet-B (UV-B) radiation (280–315 nm), there remains ongoing debate surrounding the extent and mechanisms of this effect. In this study, using published data on pollen germination and tube growth including 377 pair-wise comparisons from 77 species in 30 families, we present the first global quantification of the effects of UV-B radiation on pollen germination and tube growth, along with its underlying mechanisms. Our results showed a substantial reduction in both pollen germination and tube growth in response to UV-B radiation, affecting 90.9 % and 84.2 % of species, respectively. Notably, these reductions exhibited phylogenetic constraints, highlighting the role of evolutionary history in shaping the sensitivity of pollen germination and tube growth to UV-B radiation. A negative correlation between elevation and the sensitivity of pollen tube growth was detected, suggesting that pollens from plants at higher elevations exhibit greater resistance to UV-B radiation. Our investigation also revealed that the effects of UV-B radiation on pollen germination and tube growth were influenced by a range of abiotic and biotic factors. Nevertheless, the intensity and duration of UV-B radiation exposure exhibited the highest explanatory power for the effects on both pollen germination and tube growth. This suggests that the responses of pollens to UV-B radiation are profoundly influenced by its dose, a critical consideration within the context of global change. In conclusion, our study provides valuable insights into the diverse responses of pollen germination and tube growth to UV-B radiation, highlighting the environment and species-dependent nature of pollen's susceptibility to UV-B radiation, with substantial implications for our understanding of the ecological and agricultural consequences of ongoing changes in UV-B radiation.

Tomato plant response to heat stress: a focus on candidate genes for yield-related traits.

Climate change and global warming represent the main threats for many agricultural crops. Tomato is one of the most extensively grown and consumed horticultural products and can survive in a wide range of climatic conditions. However, high temperatures negatively affect both vegetative growth and reproductive processes, resulting in losses of yield and fruit quality traits. Researchers have employed different parameters to evaluate the heat stress tolerance, including evaluation of leaf- (stomatal conductance, net photosynthetic rate, Fv/Fm), flower- (inflorescence number, flower number, stigma exertion), pollen-related traits (pollen germination and viability, pollen tube growth) and fruit yield per plant. Moreover, several authors have gone even further, trying to understand the plants molecular response mechanisms to this stress. The present review focused on the tomato molecular response to heat stress during the reproductive stage, since the increase of temperatures above the optimum usually occurs late in the growing tomato season. Reproductive-related traits directly affects the final yield and are regulated by several genes such as transcriptional factors, heat shock proteins, genes related to flower, flowering, pollen and fruit set, and epigenetic mechanisms involving DNA methylation, histone modification, chromatin remodelling and non-coding RNAs. We provided a detailed list of these genes and their function under high temperature conditions in defining the final yield with the aim to summarize the recent findings and pose the attention on candidate genes that could prompt on the selection and constitution of new thermotolerant tomato plant genotypes able to face this abiotic challenge.

Avaliação da viabilidade do pólen em algumas variedades de crisântemo em spray no período de armazenamento

Abstract In producing chrysanthemum hybrids, more seed sets per fruit are preferred. Only successful pollination and fertilization allow seeds to de-velop. High pollen viability and pollen germination rate are intimately correlated with successful fertilization. Chrysanthemum pollen and their storage duration have only been the subject of a relatively few investigations. The study aimed to determine pollen's viability and germination during the 4 days, which were kept at 24 ºC. In the present study, two different Chrysanthemum species (Chrysanthemum coronarium L. and Chrysanthemum segetum L.) and two commercial Chrysanthemum varieties (Chic and Haydar) that belong to Chrysanthemum morifolium Ramat. species as spray chrysanthemum pollens were used for experimental material. The grains pollen were stored in an incubator which was 24 ºC and 60% humidity. The pollen viability was tested with TTC (2,3,5 Triphenyl Tetrazolium Chloride) staining test and pollen germination was evaluated hanging drop method with modified ME3-m medium, daily for 4 days including day 0. The results showed that the viability and germination of all pollens used in this study decreased day by day. Depending on the species/varieties, the viability rates ranged from 12.83% to 32.04% on the first day and between 0.57-2.33% on the last day. Pollen germination rates differed between 16.76% - 3.45% on the 0th day and 0.0-0.17% on the 4th day.

Effects of Putrescine and Spermine on Pollen Germination Levels of Some Olive Cultivars

In this study, it is aimed to determine the effects of putrescine and spermine on pollen germination levels of 8 olive cultivars. Arbequina, Gemlik, Halhalı, Karamani, Kozan yerli, Saurani, Sayfi and Şami olive cultivars were used as material. In the study, 5 spermine doses (0,25mM, 0,125 mM, 0,025 mM, 0,05 mM and 0,005 mM) and 5 putrescine doses (0,20 mM, 0,10 mM, 0,05 mM, 0,025 mM and 0,1 mM) added to basal germination medium (15% sucrose + 1% agar + 100 ppm Boric acid) were tested for determining the effects on pollen germination of olive cultivars. Basal media was used for Control treatment. In terms of pollen germination media, pollen germination levels were increased with lower putrescine and higher spermine levels. In Sayfi olive cultivar, while pollen viability rate was 42,74%, pollen germination was 0,00% in control treatments. However, pollen germination was increased for Sayfi olive cultivar with 0,20 mM and 0,10 mM putrescine (3,64% and 3,40%, respectively) and 0,25 mM, 0,125 mM and 0,05 mM Spermine (12,56%, 4,73% and 3,40%, respectively). In conclusion, polyamine treatments were increased the low germinated cultivars. So, polyamine treatments reveal the potential of the pollen especially in low-germinated pollens.

The temperature optima for pollen germination and pollen tube growth of coconut (Cocos nucifera L.) strongly depend on the growth temperature

Abstract Understanding trait variation in response to temperature is important to predict how crops respond to rising temperature. Although we have a sound understanding of the effects of increasing temperature on growth and development of crops, a robust assessment of how crop reproductive processes are affected by climate warming is still lacking. In this study, we experimentally investigate how the growth temperature affects the cardinal temperatures of in vitro pollen germination of widely distributed tree crop species Cocos nucifera L. (cultivar Sri Lankan Tall). We hypothesize that temperature optima for pollen germination and pollen tube growth would be determined by the growth temperature. Our results showed that the temperature optima of pollen germination and pollen tube growth were higher at relatively warmer sites (sites where the mean annual temperature ∼ 28°C) compared to the cooler sites (sites where the mean annual temperature ∼ 22°C). The two processes were better coordinated at warmer sites. We speculate that tropical tree species that are currently growing in relatively cooler environments may have the capacity to perform their reproductive physiological functions in future warmer climates without any substantial negative impacts. Findings of this study should prove useful in quantifying the potential impacts of climate warming on tropical agro-ecosystems, improving the representation of plant reproduction in crop models.

Bio-positive effects of ionizing radiation on pollen: The role of ROS.

The concept of 'hormesis' is defined as a dose-response relationship whereby low doses of various toxic substances or physical stressors trigger bio-positive effects in diverse biological systems, whereas high doses cause inhibition of cellular performance (e.g. growth, viability). The two-sided phenomenon of specific low-dose stimulation and high-dose inhibition imposed by a 'hormetic-factor' has been well documented in toxicology and pharmacology. Multitudinous factors have been identified that correspondingly cause hormetic effects in diverse taxa of animals, fungi, and plants. This study particularly aims to elucidate the molecular basis for stimulatory implications of ionizing radiation (IR) on plant male gametophytes (pollen). Beyond that, this analysis impacts general research on cell growth, plant breeding, radiation protection, and, in a wider sense, medical treatment. For this purpose, IR-related data were surveyed and discussed in connection with the present knowledge about pollen physiology. It is concluded that IR-induced reactive oxygen species (ROS) have a key role here. Moreover, it is hypothesized that IR-exposure shifts the ratio between diverse types of ROS in the cell. The interrelation between ROS, intracellular Ca2+-gradient, NADPH oxidases, ROS-scavengers, actin dynamics, and cell wall properties are most probably involved in IR-hormesis of pollen germination and tube growth. Modulation of gene expression, phytohormone signalling, and cellular antioxidant capacity are also implicated in IR-hormesis.

Optimization of Pollen Germination Medium and Pollen Collection in Two Japanese Strawberry Cultivars

Optimization of Pollen Germination Medium and Pollen Collection in Two Japanese Strawberry Cultivars

Diurnal versus nocturnal pollination in a subalpine wetland: From network structure to plant reproduction

Diurnal and nocturnal pollinators are fundamental for the functioning of natural ecosystems and food security. However, differences between diurnal and nocturnal pollination networks and the contribution of these pollinators to plant fecundity have not been assessed comprehensively within a community context. In the Dajiuhu subalpine wetland of central China, we supplemented data from an intensive field survey with the analysis of pollen loads carried by diurnal and nocturnal pollinators to compare the structures of diurnal and nocturnal pollination networks using network parameters. Simultaneously, we compared the contribution of diurnal and nocturnal pollinators to plant reproduction of the nine dominant species based on stigma pollen placement. We found that although diurnal and nocturnal pollination networks exhibited a similar structural organisation, the diurnal network displayed greater stability and broader interaction with pollinators and plants compared to the nocturnal network. However, nocturnal pollinator species tended to establish less generalised interactions with the available floral resources. Both diurnal and nocturnal pollinators played a significant role in plant reproduction, and nocturnal pollination can result in greater pollen germination. In terms of stability, the lower redundancy of links within nocturnal networks suggests they may be more vulnerable to the temporary or permanent disappearance of plant resources in the study area. Our findings highlight the differences in the contributions of diurnal and nocturnal pollinators to plant reproduction at the community level, demonstrating that nocturnal pollinators are not redundant in maintaining species diversity in communities. This knowledge should play a pivotal role in preventing future pollination declines and improving pollinator conservation efforts.

Floral biology studies in wild melon [Cucumis melo L. ssp. agrestis (Naudin) Pangalo var. agrestis Naudin

Studies on floral morphology, phenology and biology of wild melon revealed that the ratio of staminate and pistillate flowers was 3.40:1. The longevity of the male flowers were between 5 and 6 days, whereas, female flowers between 6 and 7 days. Anthesis was observed from 4.00 am to 10.00 am, while, the anther dehiscence started from 5.00 am which was continued to 7.00 am. The peak anthesis was observed from 8.00 am to 9.00 am and anther dehiscence from 6.00 am to 6.30 am. Freshly opened flowers showed pollen viability up to 98.35%, decreased upon closure and crashed to 17.48% in 3 days. Pollen germination was occurred after 15 minutes of incubation and continued up to 24 h of incubation. The stigma receptivity lasts from one to two days of anthesis. Major pollinator of wild melons observed was honey bee, mostly visited between 9:00 am to 6:00 pm.

Pollen reaction of mutant tomato forms to abiotic stress factors

The article presents the results of screening accessions of the mutant tomato gene pool (125 genotypes) based on the response of their pollen to abiotic stress factors (high, low temperatures, drought) in order to study their potential and identify genetic sources/donors of resistance. The studies were carried out in open ground conditions from 2015 to 2017 and in summer greenhouses from 2017 to 2019. High heterogeneity of the genotype-specific response of pollen of mutant forms to various stress factors was shown: with a lethal outcome to all factors (10 genotypes); highly resistant to all stressors (20 genotypes); combining resistance: to high and low temperatures (7 genotypes), to high temperature and drought (9 genotypes), to cold and drought (4 genotypes); resistant only: to high (14 genotypes) or low (17 genotypes) temperatures, drought (6 genotypes). Mutant forms (38 genotypes) with high intrapopulation variability in pollen germination and the ability to form long pollen tubes under various stressors were also identified. It was established that resistance to heat, cold and drought according on traits of the male gametophyte was determined by different genetic systems.

The RALF signaling pathway regulates cell wall integrity during pollen tube growth in maize.

Autocrine signaling pathways regulated by RAPID ALKALINIZATION FACTORs (RALFs) control cell wall integrity during pollen tube germination and growth in Arabidopsis (Arabidopsis thaliana). To investigate the role of pollen-specific RALFs in another plant species, we combined gene expression data with phylogenetic and biochemical studies to identify candidate orthologs in maize (Zea mays). We show that Clade IB ZmRALF2/3 mutations, but not Clade III ZmRALF1/5 mutations, cause cell wall instability in the sub-apical region of the growing pollen tube. ZmRALF2/3 are mainly located in the cell wall and are partially able to complement the pollen germination defect of their Arabidopsis orthologs AtRALF4/19. Mutations in ZmRALF2/3 compromise pectin distribution patterns leading to altered cell wall organization and thickness culminating in pollen tube burst. Clade IB, but not Clade III ZmRALFs, strongly interact as ligands with the pollen-specific Catharanthus roseus RLK1-like (CrRLK1L) receptor kinases Z. mays FERONIA-like (ZmFERL) 4/7/9, LORELEI-like glycosylphosphatidylinositol-anchor (LLG) proteins Z. mays LLG 1 and 2 (ZmLLG1/2), and Z. mays pollen extension-like (PEX) cell wall proteins ZmPEX2/4. Notably, ZmFERL4 outcompetes ZmLLG2 and ZmPEX2 outcompetes ZmFERL4 for ZmRALF2 binding. Based on these data, we suggest that Clade IB RALFs act in a dual role as cell wall components and extracellular sensors to regulate cell wall integrity and thickness during pollen tube growth in maize and probably other plants.