Pollen-pistil interactions in compatible pollination

Gold Nanoparticles-Induced Modifications in Cell Wall Composition in Barley Roots

The increased use of nanoparticles (NP) in different industries inevitably results in their release into the environment. In such conditions, plants come into direct contact with NP. Knowledge about the uptake of NP by plants and their effect on different developmental processes is still insufficient. Our studies concerned analyses of the changes in the chemical components of the cell walls of Hordeum vulgare L. roots that were grown in the presence of gold nanoparticles (AuNP). The analyses were performed using the immunohistological method and fluorescence microscopy. The obtained results indicate that AuNP with different surface charges affects the presence and distribution of selected pectic and arabinogalactan protein (AGP) epitopes in the walls of root cells.

Expression analysis of ethylene synthesis and signalling genes in kiwifruit stigmatic arms and their involvement in programmed cell death processes

Kiwifruit (Actinidia chinensis var. deliciosa (A. Chev) A. Chev.) is a widely cultivated crop due to the nutritional value of its fruits. Its commercialization is related to the fruit size, which is directly linked with the number of seeds and, consequently, with pollination. In this dioecious species pollination is dependent on a short effective pollination period which is related to a Programmed Cell Death (PCD) process. At the same time, this PCD process allows the growth of many pollen tubes. Several studies suggest that ethylene can play an important role in PCD in a number of systems. In this report, we determined the full sequence of the AcACS gene, encoding the enzyme that catalyses a rate-limiting step of the ethylene synthesis. Next, we monitored the expression pattern of this gene as well as of other genes involved in ethylene synthesis (ACO2-5) and signalling (AdERS1a, AdERS1b, AdETR1, AdETR2, AdETR3, AdCTR1, AdCTR2, AdEIL1) in pollinated and non-pollinated stigmatic arms of kiwifruit female flowers. The relative expression patterns observed for AcACS, ACOs and ethylene perception and signalling genes (AdERS1, AdETR1, AdCTR1 and AdEIL1) showed that they are expressed before anthesis. After anthesis, expression of the studied genes was detected earlier in pollinated than in non-pollinated stigmatic arms, as it was previously determined for PCD hallmarks. In addition, the expression pattern of the studied genes showed a clear relationship with the PCD hallmarks described in a previous report in the secretory tissue both in non-pollinated stigmatic arms (related to the short EPP in this species) and in pollinated ones (related to the growth of many pollen tubes during progamic phase). Overall, these results suggest an involvement of ethylene with PCD contributing to the high reproductive success of this species.

Protein Profiling Reveals Novel Proteins in Pollen and Pistil of W22 (ga1; Ga1) in Maize

Gametophytic factors mediate pollen-pistil interactions in maize (Zea mays L.) and play active roles in limiting gene flow among maize populations and between maize and teosinte. This study was carried out to identify proteins and investigate the mechanism of gametophytic factors using protein analysis. W22 (ga1); which did not carry a gametophytic factor and W22 (Ga1), a near iso-genic line, were used for the proteome investigation. SDS-PAGE was executed to investigate proteins in the pollen and pistil of W22 (ga1) and W22 (Ga1). A total of 44 differentially expressed proteins were identified in the pollen and pistil on SDS-PAGE using LTQ-FTICR MS. Among the 44 proteins, a total of 24 proteins were identified in the pollen of W22 (ga1) and W22 (Ga1) whereas 20 differentially expressed proteins were identified from the pistil of W22 (ga1) and W22 (Ga1). However, in pollen, 2 proteins were identified only in the W22 (ga1) and 12 proteins only in the W22 (Ga1) whereas 10 proteins were confirmed from the both of W22 (ga1) and W22 (Ga1). In contrary, 10 proteins were appeared only in the pistil of W22 (ga1) and 7 proteins from W22 (Ga1) while 3 proteins confirmed in the both of W22 (ga1) and W22 (Ga1). Moreover, the identified proteins were generally involved in hydrolase activity, nucleic acid binding and nucleotide binding. These results help to reveal the mechanism of gametophytic factors and provide a valuable clue for the pollen and pistil research in maize.

The cellular mechanics of an invasive lifestyle

Invasive behaviour is the hallmark of a variety of cell types of animal, plant, and fungal origin. Here we review the purpose and mechanism of invasive growth and migration. The focus is on the physical principles governing the process, the source of invasive force, and the cellular mechanism by which the cell penetrates the substrate. The current experimental methods for measuring invasive force and the modelling approaches for studying invasive behaviour are explained, and future experimental strategies are proposed.

High-throughput sequencing of small RNAs from pollen and silk and characterization of miRNAs as candidate factors involved in pollen-silk interactions in maize

In angiosperms, successful pollen-pistil interactions are the prerequisite and guarantee of subsequent fertilization and seed production. Recent profile analyses have helped elucidate molecular mechanisms underlying these processes at both transcriptomic and proteomic levels, but the involvement of miRNAs in pollen-pistil interactions is still speculative. In this study, we sequenced four small RNA libraries derived from mature pollen, in vitro germinated pollen, mature silks, and pollinated silks of maize (Zea mays L.). We identified 161 known miRNAs belonging to 27 families and 82 novel miRNAs. Of these, 40 conserved and 16 novel miRNAs showed different expression levels between mature and germinated pollen, and 30 conserved and eight novel miRNAs were differentially expressed between mature and pollinated silks. As candidates for factors associated with pollen-silk (pistil) interactions, expression patterns of the two sets of differentially expressed miRNAs were confirmed by stem-loop real-time RT-PCR. Transcript levels of 22 predicted target genes were also validated using real-time RT-PCR; most of these exhibited expression patterns contrasting with those of their corresponding miRNAs. In addition, GO analysis of target genes of differentially expressed miRNAs revealed that functional categories related to auxin signal transduction and gene expression regulation were overrepresented. These results suggest that miRNA-mediated auxin signal transduction and transcriptional regulation have roles in pollen-silk interactions. The results of our study provide novel information for understanding miRNA regulatory roles in pollen-pistil interactions.

The post-pollination ethylene burst and the continuation of floral advertisement are harbingers of non-random mate selection in Nicotiana attenuata

The self-compatible plant Nicotiana attenuata grows in genetically diverse populations after fires, and produces flowers that remain open for 3 days and are visited by assorted pollinators. To determine whether and when post-pollination non-random mate selection occurs among self and non-self pollen, seed paternity and semi-in vivo pollen tube growth were determined in controlled single/mixed pollinations. Despite all pollen sources being equally proficient in siring seeds in single-genotype pollinations, self pollen was consistently selected in mixed pollinations, irrespective of maternal genotype. However, clear patterns of mate discrimination occurred amongst non-self pollen when mixed pollinations were performed soon after corollas open, including selection against hygromycin B resistance (transformation selectable marker) in wild-type styles and for it in transformed styles. However, mate choice among pollen genotypes was completely shut down in plants transformed to be unable to produce (irACO) or perceive (ETR1) ethylene. The post-pollination ethylene burst, which originates primarily from the stigma and upper style, was strongly correlated with mate selection in single and mixed hand-pollinations using eight pollen donors in two maternal ecotypes. The post-pollination ethylene burst was also negatively correlated with the continuation of emission of benzylacetone, the most abundant pollinator-attracting corolla-derived floral volatile. We conclude that ethylene signaling plays a pivotal role in mate choice, and the post-pollination ethylene burst and the termination of benzylacetone release are accurate predictors, both qualitatively and quantitatively, of pre-zygotic mate selection and seed paternity.

Genome duplication and the evolution of conspecific pollen precedence

Conspecific pollen precedence can be a strong reproductive barrier between polyploid and diploid species, but the role of genome multiplication in the evolution of this barrier has not been investigated. Here, we examine the direct effect of genome duplication on the evolution of pollen siring success in tetraploid Chamerion angustifolium. To separate the effects of genome duplication from selection after duplication, we compared pollen siring success of synthesized tetraploids (neotetraploids) with that of naturally occurring tetraploids by applying 2x, 4x (neo or established) or 2x + 4x pollen to diploid and tetraploid flowers. Seed set increased in diploids and decreased in both types of tetraploids as the proportion of pollen from diploid plants increased. Based on offspring ploidy from mixed-ploidy pollinations, pollen of the maternal ploidy always sired the majority of offspring but was strongest in established tetraploids and weakest in neotetraploids. Pollen from established tetraploids had significantly higher siring rates than neotetraploids when deposited on diploid (4x(est) = 47.2%, 4x(neo) = 27.1%) and on tetraploid recipients (4x(est) = 91.9%, 4x(neo) = 56.0%). Siring success of established tetraploids exceeded that of neotetraploids despite having similar pollen production per anther and pollen diameter. Our results suggest that, while pollen precedence can arise in association with the duplication event, the strength of polyploid siring success evolves after the duplication event.

Pistil anatomy and pollen tube development in Polygala vayredae Costa (Polygalaceae)

Low seed ovule ratios have been observed in natural populations of Polygala vayredae Costa, a narrowly endemic species from the oriental pre-Pyrenees. To evaluate physical and nutritional constraints and pollen tube attrition in this endemic species, stigma and style anatomy, as well as pollen tube development along the pistil were investigated using light and fluorescence microscopy. The structural morphology of the stigmatic region was also examined with scanning electron microscopy. Pollen grains that reached the stigmatic papillae came into contact with a lipid-rich exudate and germinated easily. Although a large number of pollen grains reach the stigmatic papillae, few pollen tubes were able to grow into the style towards the ovary. The style was hollow, with the stylar channel beginning a few cells below the stigmatic papillae. Initially, the stylar channel area was small compared to other levels of the style, and was surrounded by lipid-rich, highly metabolic active cells. Furthermore, lipid-rich mucilage was detected inside the stylar channel. At subsequent style levels towards the ovary, no major reserves were detected histochemically. The reduced intercellular spaces below the stigmatic papillae and the reduced area of the stylar channel at its commencement are suggested to physically constrain the number of pollen tubes that can develop. In subsequent levels of the style, the stylar channel could physically support a larger number of pollen tubes, but the lack of nutritional reserves cannot be disregarded as a cause of pollen tube attrition. Finally, the number of pollen tubes entering the ovary was greater than the number of ovules, suggesting that interactions occurring at this level play a major role in the final reproductive outcome in this species.

The signal peptide peptidase is required for pollen function in Arabidopsis

The Signal Peptide Peptidases (SPP) are members of the Intramembrane Cleaving Proteases, which are involved in an array of protein-processing and intracellular signaling events in animals. Arabidopsis (Arabidopsis thaliana) has six genes encoding SPP-like proteins, the physiological functions of which are unknown. As a first step in defining the roles of the SPPs in plants, we examined the distribution and activities of Arabidopsis SPP (AtSPP; accession no. At2g03120), the SPP-like gene with the highest degree of similarity to human SPP. The protease is expressed at low levels throughout the plant, with the highest levels in emerging leaves, roots, and floral tissues. Homozygous plants carrying a T-DNA insertion mutation in AtSPP, spp-2, could not be recovered, and transmission of the mutant allele through pollen was reduced to less than 2% in reciprocal cross experiments. Although viable, pollen from spp-2 heterozygous plants exhibited a 50% reduction in germination rate and a disruption in male germ unit organization. These data demonstrate that AtSPP is required for male gametophyte development and pollen maturation in Arabidopsis.

Distinct short-range ovule signals attract or repel Arabidopsis thaliana pollen tubes in vitro

BACKGROUND

Pollen tubes deliver sperm after navigating through flower tissues in response to attractive and repulsive cues. Genetic analyses in maize and Arabidopsis thaliana and cell ablation studies in Torenia fournieri have shown that the female gametophyte (the 7-celled haploid embryo sac within an ovule) and surrounding diploid tissues are essential for guiding pollen tubes to ovules. The variety and inaccessibility of these cells and tissues has made it challenging to characterize the sources of guidance signals and the dynamic responses they elicit in the pollen tubes.

RESULTS

Here we developed an in vitro assay to study pollen tube guidance to excised A. thaliana ovules. Using this assay we discerned the temporal and spatial regulation and species-specificity of late stage guidance signals and characterized the dynamics of pollen tube responses. We established that unfertilized A. thaliana ovules emit diffusible, developmentally regulated, species-specific attractants, and demonstrated that ovules penetrated by pollen tubes rapidly release diffusible pollen tube repellents.

CONCLUSION

These results demonstrate that in vitro pollen tube guidance to excised A. thaliana ovules efficiently recapitulates much of in vivo pollen tube behaviour during the final stages of pollen tube growth. This assay will aid in confirming the roles of candidate guidance molecules, exploring the phenotypes of A. thaliana pollen tube guidance mutants and characterizing interspecies pollination interactions.

Antisense phenotypes reveal a role for SHY, a pollen-specific leucine-rich repeat protein, in pollen tube growth

SHY, a pollen-specific gene identified in a screen for genes upregulated at pollen germination, encodes a leucine-rich repeat (LRR) protein that is predicted to be secreted. To test if SHY plays an important role during pollen germination, we generated transgenic plants expressing an antisense (AS) copy of the SHY cDNA in pollen. Primary transformants exhibited poor seed set, but homozygous lines could be identified. In these lines, nearly all pollen tubes failed to reach the ovules; tube growth was arrested at the apex of the ovary and the pollen tubes exhibited abnormal callose deposits throughout the tube and in the tips. We show that a SHY::eGFP fusion protein is targeted to the cell wall. The structure of the SHY protein is nearly identical to other extracellular matrix glycoproteins that are composed of LRRs, such as the polygalacturonase inhibitor proteins (PGIP) of plants. PGIPs may function as defense proteins by inhibiting fungal endo-polygalacturonases, but enzyme assays with extracts of AS-SHY pollen do not support such an inhibitor role for SHY. The tomato ortholog of SHY interacts with a tomato receptor kinase (LePRK2) in yeast two-hybrid and pull-down assays; this, and the AS-SHY phenotypes, suggest instead that SHY might function in a signal transduction pathway mediating pollen tube growth.

Botrytis cinerea Infection in Grape Flowers: Defense Reaction, Latency, and Disease Expression

ABSTRACT Inflorescences of field-grown grapevines (Vitis vinifera L. cv. Gamay) were inoculated with a Botrytis cinerea conidia suspension or dried conidia at different stages during bloom in moist weather. Approximately 10% of the conidia germinated within 72 h, resulting in two to three times more latent infections than uninoculated controls in pea-size (7 mm in diameter) berries. In surface-sterilized pea-size berries, latent B. cinerea was present predominantly in the receptacle area. After veraison, latent B. cinerea also was found in the style and, in mature berries, latent colonies were distributed throughout the pulp. Inoculation at full bloom led to the highest disease severity (66%) at harvest, compared with 38% in controls. Stilbene stress metabolites in the flowers were measured by high-performance liquid chromatography. Resveratrol accumulated mainly after pre-bloom and full-bloom inoculation, but did not prevent infection. Piceid levels did not change following inoculation, while epsilon-viniferin was found in necrotic tissues only, and pterostilbene and alphaviniferin were not detected at all. B. cinerea conidia suspensions also were applied to various locations on flowers of pot-grown cvs. Pinot Noir and Chardonnay. Inoculation of the receptacle area, but not that of the stigma and ovary, resulted in latent infections. Stilbene synthesis was similar to the field results, with resveratrol accumulating mainly in the calyptra and receptacle area. Constitutive soluble phenolic compounds (mainly derivatives of quercetin and hydroxy-cinnamic acid) were present at high concentrations in the calyptra but at low levels in the receptacle area. These experiments confirmed bloom as a critical time for B. cinerea infection in grapes and suggest that the most likely site of infection is the receptacle area or cap scar exposed at anthesis. Stilbenes may have a limited role in inhibition of flower infection and latency in susceptible grape cultivars, and epsilon-viniferin may be a by-product rather than a deterrent of infection.

Sexual selection: an evolutionary force in plants?

Sexual selection has traditionally been used to explain exaggerated sexual traits in male animals. Today the concept has been developed and various other sexually related traits have been suggested to evolve in the same manner. In nearly all new areas where the theory of sexual selection has been applied, there has been an intense debate as to whether the application is justified. Is it the case that some scientists are all too ready to employ fashionable ideas? Or are there too many dogmatic researchers refusing to accept that science develops and old ideas are transformed? Maybe the controversies are simply a reflection of the difficulty of defining a theory under constant re-evaluation. Thus, we begin by summarizing the theory of sexual selection in order to assess the influence of sexual selection on the evolution of plant morphology. We discuss empirical findings concerning potentially affected traits. Although we have tried to address criticisms fairly, we still conclude that sexual selection can be a useful tool when studying the evolution of reproductive traits in plants. Furthermore, by including the evidence from an additional kingdom, a fuller understanding of the processes involved in sexual selection can be gained.

Pollination modulates expression of the PPAL gene, a pistil-specific beta-expansin

Using differential screening we isolated a pistil-specific cDNA clone corresponding to a 1.2 kb mRNA and encoding a 32.5 kDa protein. The amino acid sequence shared similarity with that of group-I grass pollen allergens, which are known to have expansin activity. This clone, which later showed to share homology also with beta-expansins, was named PPAL. The PPAL mRNA was specifically expressed in the secretory zone of the stigma and in the epidermal layer of the placenta. The accumulation level of the transcript increased during pollination, and the protein was secreted in the stigmatic exudate of the tobacco flower. We suggest here that PPAL is a new expansin, acting as a cell-wall-loosening agent during pollination.

A role for arabinogalactan proteins in gibberellin-induced alpha-amylase production in barley aleurone cells

Arabinogalactan proteins (AGPs) are plant proteoglycans that have been implicated in plant growth and development. The possible involvement of AGPs in the action of gibberellin (GA), a class of plant hormones, was examined by applying beta-glucosyl Yariv reagent (beta-Glc)3Y, a synthetic phenyl glycoside that interacts selectively with AGPs, to barley aleurone protoplasts. Gibberellin induces transcription and secretion of alpha-amylases in the protoplasts. Induction of alpha-amylase was clearly inhibited by (beta-Glc)3Y but not by (alpha-Gal)3Y, a negative control of the Yariv reagent that does not interact with AGPs. Transfection analysis, using an alpha-amylase promoter-GUS fusion gene in the protoplasts, indicated that the transcriptional activation of the alpha-amylase promoter was inhibited specifically by (beta-Glc)3Y. These observations are the first indication of an involvement of AGPs in a plant hormone function. The inhibitory effect of (beta-Glc)3Y was not observed when aleurone layers or half-seed grains were used. This result, together with the fact that protoplasts do not have cell walls, suggests that the AGPs that function in alpha-amylase induction reside at the plasma membrane. An aleurone-specific AGP was detected by reversed-phase HPLC, and supported the idea that an AGP may play an important role in aleurone-specific events. The possible mechanism of AGP function in gibberellin-induced alpha-amylase production is discussed.

Genetic and epigenetic processes in seed development

Seed development has emerged as an important area of research in plant development. Recent research has highlighted the divergent reproductive strategies of the male and female genomes and interaction between genetic and epigenetic control mechanisms. Isolation of genes involved in embryo and endosperm development is leading to an understanding of the regulation of these processes at the molecular level. A thorough grasp of these processes will not only illuminate an important area of plant development but will also have an impact on agronomy by helping to facilitate food production. An understanding of seed development is also likely to clarify the molecular mechanisms of apomixis, a fascinating process of asexual seed production present in many plants.

The molecular and genetic basis of pollen-pistil interactions

Over the past decade or so, there has been significant progress towards elucidating the molecular events occurring during pollination in flowering plants. This process involves a series of complex cellular interactions that culminates in the fusion between male and female gametes. The process also regulates crucial events such as pollen adhesion, hydration, pollen tube growth and guidance to the ovules. Additionally, in many instances, incompatibility mechanisms that control the acceptance or rejection of pollen alighting on a recipient plant play a major role in the pollination process. In this article we aim to review our current understanding of the components that are implicated in enabling the pollen to deliver the male gametes to the ovary and the molecular mechanisms by which they are thought to act. Contents Summary 565 I. Introduction 565 II. Adhesion of pollen to the stigma 566 III. Pollen hydration 567 IV. Pollen germination and initial growth on the stigma surface 568 V. Pollen tube growth through the style and pollen tube guidance 569 VI. Control of pollen viability by incompatibility responses 572 1. Self incompatibility (SI) 573 Gametophytic SI 573 SI in the Solanaceae 573 SI in Papaver 575 Sporophytic SI 577 SI in Brassica 577 SI in Ipomoea 579 2. Interspecific incompatibility responses 579 VII. Conclusions and perspective 580 References 580.

A pollen tube growth-promoting arabinogalactan protein from nicotiana alata is similar to the tobacco TTS protein

Upon germination on the stigma, pollen tubes elongate in the stylar transmitting tract, aided by female factors, with speed and directionality not mimicked in in vitro pollen tube growth cultures. We have shown that a stylar transmitting tissue arabinogalactan protein (AGP) from Nicotiana tabacum (tobacco), TTS protein, stimulates pollen tube growth in vivo and in vitro and attracts pollen tubes grown in a semi-in vivo culture system. It has been reported that the self-incompatible Nicotiana alata produced a stylar glycoprotein, GaRSGP, which had a backbone polypeptide that shared 97% identity with those of TTS proteins but some of its properties were different from those described for TTS proteins. We report here the characterization of a family of stylar transmitting tissue glycoproteins from N. alata that is virtually identical to tobacco TTS proteins and which we refer to as NaTTS proteins. Like their tobacco counterparts, NaTTS proteins are recognized by the traditional AGP-diagnostic reagent beta-glucosyl Yariv reagent, and they are also recognized by JIM13, a monoclonal antibody against AGP. NaTTS proteins also stimulate pollen tube elongation in vitro and attract pollen tubes in a semi-in vivo pollen tube culture system. Biochemical and immunological characterization of NaTTS proteins revealed that they have extraordinary variability in the extent of sugar modifications of their polypeptide backbones. The extent of sugar modifications on NaTTS proteins significantly affects their biochemical properties, influences how they interact with the transmitting tissue extracellular matrix, and affects their solubility from this matrix. Our results suggest that the strategy used to purify GaRSGP only recovered a less glycosylated, more tightly extracellular matrix-bound sub-population of the entire spectrum of N. alata TTS proteins.

Uncoupling secretion and tip growth in lily pollen tubes: evidence for the role of calcium in exocytosis

Cytoplasmic calcium concentration ([Ca2+]i) and extracellular calcium (Ca2+o) influx has been studied in pollen tubes of Lilium longliflorum in which the processes of cell elongation and exocytosis have been uncoupled by use of Yariv phenylglycoside ((beta-D-Glc)3). Growing pollen tubes were pressure injected with the ratio dye fura-2 dextran and imaged after application of (beta-D-Glc)3, which binds arabinogalactan proteins (AGPs). Application of (beta-D-Glc)3 inhibited growth but not secretion. Ratiometric imaging of [Ca2+]i revealed an initial spread in the locus of the apical [Ca2+]i gradient and substantial elevations in basal [Ca2+]i followed by the establishment of new regions of elevated [Ca2+]i on the flanks of the tip region. Areas of elevated [Ca2+]i corresponded to sites of pronounced exocytosis, as evidenced by the formation of wall ingrowths adjacent to the plasma membrane. Ca2+o influx at the tip of (beta-D-Glc)3-treated pollen tubes was not significantly different to that of control tubes. Taken together these data indicate that regions of elevated [Ca2+]i, probably resulting from Ca2+o influx across the plasma membrane, stimulate exocytosis in pollen tubes independent of cell elongation.

Organ-specific and Agamous-regulated expression and glycosylation of a pollen tube growth-promoting protein

Transmitting tissue-specific (TTS) protein is a pollen tube growth-promoting and attracting glycoprotein located in the stylar transmitting tissue extracellular matrix of the pistil of tobacco. The TTS protein backbones have a deduced molecular mass of about 28 kDa, whereas the glycosylated stylar TTS proteins have apparent molecular masses ranging between 50 and 100 kDa. TTS mRNAs and proteins are ectopically produced in transgenic tobacco plants that express either a cauliflower mosaic virus (CaMV) 35S promoter-TTS2 transgene or a CaMV 35S-promoter-NAG1 (NAG1 = Nicotiana tabacum Agamous gene) transgene. However, the patterns of TTS mRNA and protein accumulation and the quality of the TTS proteins produced are different in these two types of transgenic plants. In 35S-TTS transgenic plants, TTS mRNAs and proteins accumulate constitutively in vegetative and floral tissues. However, the ectopically expressed TTS proteins in these transgenic plants accumulate as underglycosylated protein species with apparent molecular masses between 30 and 50 kDa. This indicates that the capacity to produce highly glycosylated TTS proteins is restricted to the stylar transmitting tissue. In 35S-NAG transgenic plants, NAG1 mRNAs accumulate constitutively in vegetative and floral tissues, and TTS mRNAs are induced in the sepals of these plants. Moreover, highly glycosylated TTS proteins in the 50- to 100-kDa molecular mass range accumulate in the sepals of these transgenic, 35S-NAG plants. These results show that the tobacco NAGI gene, together with other yet unidentified regulatory factors, control the expression of TTS genes and the cellular capacity to glycosylate TTS proteins, which are normally expressed very late in the pistil developmental pathway and function in the final stage of floral development. The sepals in the transgenic 35S-NAG plants also support efficient pollen germination and tube growth, similar to what normally occurs in the pistil, and this ability correlates with the accumulation of the highest levels of the 50- to 100-kDa glycosylated TTS proteins.

Molecular analysis of a pistil-specific gene expressed in the stigma and cortex of Solanum tuberosum

A gene, sts14, coding for a highly expressed mRNA in pistils of Solanum tuberosum, was isolated. Northern blot and in situ analyses demonstrated that the gene was expressed throughout pistil development in both the stylar cortex and the stigma. The deduced STS14 protein displays similarity to the pathogenesis-related PR-1 proteins. A possible function for protection or guidance of the pollen tubes through the pistil is discussed.

Extensin-like Glycoproteins in the Maize Pollen Tube Wall

We recently described the cloning and characterization of Pex1, a maize pollen-specific gene with an extensin-like domain. Here, we report that antibodies raised against a Pex fusion protein and a Pex synthetic peptide recognize a protein doublet with an apparent molecular mass of ~300 kD as well as larger proteins in pollen extracts. These proteins were not detected in extracts of seedling, endosperm, ear, silk, root, leaf, wounded leaf, meiotic tassel, or young microspore. After deglycosylation, only the protein doublet was detected by the anti-Pex antiserum, suggesting that the higher molecular mass proteins represent a glycosylated form of the Pex proteins. The anti-Pex antiserum was also used in immunolocalization experiments with in vitro-germinated pollen. With the aid of a confocal light microscope, the Pex proteins were localized to the pollen tube wall. The Pex proteins could not be removed with high salt, SDS, or chaotropic or reducing agents, suggesting a very tight association with the pollen tube wall. Immunocytochemical analysis at the ultrastructural level localized the Pex proteins to the intine in mature pollen and to the callosic sheath of the pollen tube wall in germinated pollen. Localization to the pollen tube wall strongly suggests that the Pex proteins play a role in pollen tube growth during pollination.