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Gametophytic self-incompatibility (GSI) has been widely studied in flowering plants, but studies of the mechanisms underlying pollen tube growth arrest by self S-RNase in GSI species are limited. In the present study, two leucine-rich repeat extensin genes in pear (Pyrus bretschneideri), PbLRXA2.1 and PbLRXA2.2, were identified based on transcriptome and quantitative real-time PCR analyses. The expression levels of these two LRX genes were significantly higher in the pollen grains and pollen tubes of the self-compatible cultivar 'Jinzhui' (harboring a spontaneous bud mutation) than in those of the self-incompatible cultivar 'Yali'. Both PbLRXA2.1 and PbLRXA2.2 stimulated pollen tube growth and attenuated the inhibitory effects of self S-RNase on pollen tube growth by stabilizing the actin cytoskeleton and enhancing cell wall integrity. These results indicate that abnormal expression of PbLRXA2.1 and PbLRXA2.2 is involved in the loss of self-incompatibility in 'Jinzhui'. The PbLRXA2.1 and PbLRXA2.2 promoters were directly bound by the ABRE-binding factor PbABF.D.2. Knockdown of PbABF.D.2 decreased PbLRXA2.1 and PbLRXA2.2 expression and inhibited pollen tube growth. Notably, the expression of PbLRXA2.1, PbLRXA2.2, and PbABF.D.2 was repressed by self S-RNase, suggesting that self S-RNase can arrest pollen tube growth by restricting the PbABF.D.2-PbLRXA2.1/PbLRXA2.2 signal cascade. These results provide novel insight into pollen tube growth arrest by self S-RNase., (© 2022 Society for Experimental Biology and John Wiley & Sons Ltd.)

Sorbitol is the primary substrate translocated from source to sink in pear species. Among the many sorbitol transporters (SOTs), some are known to be involved in sorbitol accumulation in fruit; however, their particular roles are unclear. In this study, we examined the transcriptome and metabolome of a variety of pear samples from six time points to identify those SOTs. Similar to previous studies, sorbitol and sucrose differed significantly between the leaf and fruit, and sorbitol was consistently observed at higher concentrations at all time points. Interestingly, we found that sorbitol accumulation in pear fruit was cooperatively mediated by SOT3, SOT6/20, SOT19/21, and SOT22. In particular, the up-regulated SOT6/20 and SOT19/21 in fruit under 1 mg L -1 abscisic acid and 10 mg L -1 indole acetic acid treatments, respectively, resulted in an increased sorbitol concentration. In addition, sorbitol concentration showed positive correlations to fructose and glucose concentrations, indicating a role for sorbitol in the determination of fruit sweetness. Together with the deduced process of sugar biosynthesis, transport, conversion, and accumulation in pear, our study provides a foundation for further research into sugar accumulation processes in pear fruit, contributing to the improvement of fruit quality., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In pear, sucrose was mainly distributed in vacuole; and the alternation of sucrose abundance was associated the change of vacuolar invertase (VI) activity during fruit storage. However, the molecular mechanism beneath such phenomenon has not been clarified until recently. For this, a combination of metabolite, enzyme activity, transcriptome, quantitative real-time PCR (qRT-PCR), bioinformation, subcellular localization, and transient overexpression assay was conducted in this study to identify the acid invertase 1 (PbrAc-Inv1) and invertase inhibitor 5 (PbrII5) involved in sucrose degradation during 'Housui' pear storage. Both PbrAc-Inv1 and PbrII5 were located in vacuolar membrane. PbrAc-Inv1 could accelerate sucrose degradation; on the other hand, PbrII5 could bind with PbrAc-Inv1 to form a inactive complex, downregulate the VI activity, and suppressed sucrose decomposition. Based on Bio-layer interferometry (BLI) result after domain substitution, the domain on the left of catalytic 'WEC-P/V-D' box in PbrAc-Inv1 might played a key role in its interaction with PbrII5., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Pear fruit exhibit a single sigmoid pattern during development, while peach and strawberry fruits exhibit a double sigmoid pattern. However, little is known about the differences between these two patterns., Results: In this study, fruit weights were measured and paraffin sections were made from fruitlet to maturated pear, peach, and strawberry samples. Results revealed that both single and double sigmoid patterns resulted from cell expansion, but not cell division. Comparative transcriptome analyses were conducted among pear, peach, and strawberry fruits at five fruit enlargement stages. Comparing the genes involved in these intervals among peaches and strawberries, 836 genes were found to be associated with all three fruit enlargement stages in pears (Model I). Of these genes, 25 were located within the quantitative trait locus (QTL) regions related to fruit weight and 90 were involved in cell development. Moreover, 649 genes were associated with the middle enlargement stage, but not early or late enlargement in pears (Model II). Additionally, 22 genes were located within the QTL regions related to fruit weight and 63 were involved in cell development. Lastly, dual-luciferase assays revealed that the screened bHLH transcription factors induced the expression of cell expansion-related genes, suggesting that the two models explain the single sigmoid pattern., Conclusions: Single sigmoid patterns are coordinately mediated by Models I and II, thus, a potential gene regulation network for the single sigmoid pattern was proposed. These results enhance our understanding of the molecular regulation of fruit size in Rosaceae.

Stone cells negatively affect fruit quality because of their firm and lignified cell walls, so are targets for reduction in pear breeding programmes. However, there is only limited knowledge of the molecular mechanisms underlying the formation of stone cells. Here, we show that PbrMYB169, an R2R3 MYB transcription factor, of Pyrus bretschneideri positively regulates lignification of stone cells in pear fruit. PbrMYB169 was shown to be co-expressed with lignin biosynthesis genes during pear fruit development, and this co-expression pattern was coincident with stone cell formation in the fruit of Pyrus bretschneideri 'Dangshansuli'. The PbrMYB169 expression level was also positively correlated with stone cell content in 36 pear cultivars tested. PbrMYB169 protein significantly activated the promoter of lignin genes C3H1, CCR1, CCOMT2, CAD, 4CL1, 4CL2, HCT2, and LAC18 via binding to AC elements [ACC(T/A)ACC] in these promoters. Furthermore, overexpression of PbrMYB169 in transgenic Arabidopsis plants enhanced the expression of lignin genes, and increased lignin deposition and cell wall thickness of vessel elements, but did not change the ratio of syringyl and guaiacyl lignin monomers. In conclusion, PbrMYB169 appears to be a transcriptional activator of lignin biosynthesis and regulates secondary wall formation in fruit stone cells. This study advances the understanding of the regulation of lignin biosynthesis and provides valuable molecular genetic information for reducing stone cell content in pear fruit., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Ethylene response factor (ERF) has been widely studied in regulating fruit ripening in tomato, apple, banana and kiwifruit, but little is known in pear. In this study 1-methylcyclopropene (1-MCP) treatment, an inhibitor of ethylene perception, was conducted at approximately 30 days before harvest to delay fruit ripening in a climacteric white pear cultivar Yali. Transcriptome libraries were constructed and sequenced in pre-ripening, ripening, and 1-MCP treated fruits. Data analysis showed that 73 candidate genes related to fruit ripening were induced by 1-MCP, among which two were positively related, namely 1-aminocyclopropane-1-carboxyla oxidase and an ERF gene (designated as ACO54 and ERF24). Transient transformations in pear fruit revealed that over-expression of ACO54 enhance transcription level of ERF24 and most ripening-related genes. Meanwhile, over-expression of ERF24 raises expression level of ACO54 and partially ripening-related genes. Moreover, dual-luciferase and yeast-one-hybrid assays unravel an interaction between ERF24 and the ACO54 promoter. Therefore, the ERF24 could directly regulate ACO54 expression by binding to its promoter. These results suggested that the first identified ERF24 is involved in regulating fruit ripening in Chinese white pear., (© 2017 Scandinavian Plant Physiology Society.)

F-box gene family, as one of the largest gene families in plants, plays crucial roles in regulating plant development, reproduction, cellular protein degradation and responses to biotic and abiotic stresses. However, comprehensive analysis of the F-box gene family in pear (Pyrus bretschneideri Rehd.) and other Rosaceae species has not been reported yet. Herein, we identified a total of 226 full-length F-box genes in pear for the first time. And these genes were further divided into various subgroups based on specific domains and phylogenetic analysis. Intriguingly, we observed that whole-genome duplication and dispersed duplication have a major contribution to F-box family expansion. Furthermore, the dynamic evolution for different modes of gene duplication was dissected. Interestingly, we found that dispersed and tandem duplicate have been evolving at a high rate. In addition, we found that F-box genes exhibited functional specificity based on GO analysis, and most of the F-box genes were significantly enriched in the protein binding (GO: 0005515) term, supporting that F-box genes might play a critical role for gene regulation in pear. Transcriptome and digital expression profiles revealed that F-box genes are involved in the development of multiple pear tissues. Overall, these results will set stage for elaborating the biological role of F-box genes in pear and other plants., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Sucrose transporters (SUTs) belong to the major facilitator superfamily. The function of SUTs has been intensively investigated in some higher plants, whereas that in pear fruit is unknown. In this study, the cloning and functional characterization of a sucrose transporter, PbSUT2, in pear (Pyrus bretschneideri Rehd. cv. 'Yali') fruits are reported. PbSUT2 encoded a protein of 498 amino acid residues, and was localized in the plasma membrane of transformed onion epidermal cells and Arabidopsis protoplasts. Phylogenetic analysis revealed that PbSUT2 belonged to the SUT4 clade. The phenotype of overexpression of PbSUT2 tomato plants included early flowering, higher fruit quantity and lower plant height. Overexpression of PbSUT2 in transgenic tomato plants led to increases in the net photosynthetic rate in leaves and sucrose content in mature fruit compared with wild-type tomato plants, and a decrease in the contents of glucose, fructose and total soluble sugars in mature fruits. These results suggested that PbSUT2 affected sucrose content in sinks and the flowering phase during tomato plant growth and development., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

The sugar transporter (ST) plays an important role in plant growth, development and fruit quality. In this study, a total of 75 ST genes were identified in the pear (Pyrus bretschneideri Rehd) genome based on systematic analysis. Furthermore, all ST genes identified were grouped into eight subfamilies according to conserved domains and phylogenetic analysis. Analysis of cis-regulatory element sequences of all ST genes identified the MYBCOREATCYCB1 promoter in sucrose transporter (SUT) and monosaccharide transporter (MST) genes of pear, while in grape it is exclusively found in SUT subfamily members, indicating divergent transcriptional regulation in different species. Gene duplication event analysis indicated that whole-genome duplication (WGD) and segmental duplication play key roles in ST gene amplification, followed by tandem duplication. Estimation of positive selection at codon sites of ST paralog pairs indicated that all plastidic glucose translocator (pGlcT) subfamily members have evolved under positive selection. In addition, the evolutionary history of ST gene duplications indicated that the ST genes have experienced significant expansion in the whole ST gene family after the second WGD, especially after apple and pear divergence. According to the global RNA sequencing results of pear fruit development, gene expression profiling showed the expression of 53 STs. Combined with quantitative real-time PCR (qRT-PCR) analysis, two polyol/monosaccharide transporter (PLT) and three tonoplast monosaccharide transporter (tMT) members were identified as candidate genes, which may play important roles in sugar accumulation during pear fruit development and ripening. Identification of highly expressed STs in fruit is important for finding novel genes contributing to enhanced levels of sugar content in pear fruit., (© The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Main Conclusion: Comparative and association analyses of the proteome and transcriptome for pear fruit development were conducted for the first time in this study. Pear fruit development involves complex physiological and biochemical processes, but there is still little knowledge available at proteomic and transcriptomic levels, which would be helpful for understanding the molecular mechanisms of fruit development and quality in pear. In our study, three important stages, including early development (S4-22), middle development (S6-27), and near ripening (S8-30), were investigated in 'Dangshansuli' by isobaric tags for relative and absolute quantitation (iTRAQ) labeling technology, identifying a total of 1,810 proteins during pear fruit development. The association analysis of proteins and transcript expression revealed 1,724, 1,722, and 1,718 associated proteins identified in stages S4-22, S6-27, and S8-30, respectively. A total of 237, 318, and 425 unique proteins were identified as differentially expressed during S4-22 vs S6-27, S6-27 vs S8-30, S4-22 vs S8-30, respectively, and the corresponding correlation coefficients of the overall differentially expressed proteins and transcripts data were 0.6336, 0.4113, and 0.7049. The phenylpropanoid biosynthesis pathway, which is related to lignin formation of pear fruit, was identified as a significantly enriched pathway during early stages of fruit development. Finally, a total of 35 important differentially expressed proteins related to fruit quality were identified, including three proteins related to sugar formation, seven proteins related to aroma synthesis, and sixteen proteins related to the formation of lignin. In addition, qRT-PCR verification provided further evidence to support differentially expressed gene selection. This study is the first to reveal protein and associated mRNA variations in pear during fruit development and quality conformation, and identify key genes and proteins helpful for future functional genomics studies, and provides gene resources for improvement of pear quality.

Key Message: This research reveals the different expression patterns of anthocyanin biosynthesis enzyme genes and transcription factors in six red-skinned pear cultivars with different genetic backgrounds. Skin color is an important feature of pear fruits, with red skin generally attracting consumers. However, great differences of coloration exist in different pear cultivars. To elucidate the characteristics of pigmentation in pear cultivars with different genetic backgrounds, six cultivars, belonging to P. communis, P. pyrifolia, P. ussuriensis, P. bretschneideri, and a hybrid of P. communis × P. pyrifolia, were used to detect pigment concentrations, expressions of seven anthocyanin biosynthesis enzyme genes, and three related transcription factor genes. Results showed that the occidental pears 'Starkrimson' and 'Red Bartlett' colored at the beginning of fruit setting, but color decreased with fruit maturity; the other four cultivars showed low anthocyanin accumulations and the contents increased during fruit development, but also decreased at later stages. The expression patterns of genes encoding enzymes indicated that ANS and UFGT were decisive genes for anthocyanin biosynthesis for red-skinned pear, and their different expressions led to the coloration differences between occidental and oriental pears. The expression patterns of transcription factors indicated that the different co-expression of MYB10 and bHLH33 genes and the different expressions of WD40 are involved in the differential regulation mechanisms of anthocyanin biosynthesis and coloration pattern between occidental and oriental pears.

Pear (Pyrus spp) is an important fruit crop, grown in all temperate regions of the world, with global production ranked after grape and apples among deciduous tree crops. A high-density linkage map is a valuable tool for fine mapping quantitative trait loci (QTL) and map-based gene cloning. In this study, we firstly constructed a high-density linkage map of pear using SNPs integrated with SSRs, developed by the rapid and robust technology of restriction-associated DNA sequencing (RADseq). The linkage map consists of 3143 SNP markers and 98 SSRs, 3241 markers in total, spanning 2243.4 cM, with an average marker distance of 0.70 cM. Anchoring SSRs were able to anchor seventeen linkage groups to their corresponding chromosomes. Based on this high-density integrated pear linkage map and two years of fruit phenotyping, a total of 32 potential QTLs for 11 traits, including length of pedicel (LFP), single fruit weight (SFW), soluble solid content (SSC), transverse diameter (TD), vertical diameter (VD), calyx status (CS), flesh colour (FC), juice content (JC), number of seeds (NS), skin colour (SC), and skin smooth (SS), were identified and positioned on the genetic map. Among them, some important fruit-related traits have for the first time been identified, such as calyx status, length of pedicel, and flesh colour, and reliable localization of QTLs were verified repeatable. This high-density linkage map of pear is a worthy reference for mapping important fruit traits, QTL identification, and comparison and combination of different genetic maps., (© The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

The present study was conducted to reveal the effect of bags with different colors on the fruit coloration of 'Yunhongli No. 2'. The differences in fruit skin color, chlorophyll, flavonoids, total phenol, anthocyanin contents and the activities of related enzymes involved in anthocyanin synthesis among different bagging treatments were evaluated. The results showed that dark treatment at the fruit development stage was beneficial to skin coloration after bag removing. After removing bags, the anthocyanin content in the treatment of natural light was highest and the red coloration of the fruit skin were best, followed by the treatment of white bags. The different bagging treatments significantly affected the contents of chlorophyll, flavonoids, total phenol, anthocyanin in the fruit skin, thereby affected the skin coloration. The activities of related enzymes for anthocyanin synthesis showed significant differences among the different bagging treatments. The correlation analysis suggested that the anthocyanin content was significantly positively related with the activities of dihydroflavonol 4-reductase (DFR) and UDP-glucose flavonoid-3-O-glucosyltransf-erase (UFGT), however, it had no significant correlation with the activity of phenylalanin ammo-nialyase (PAL).

Low temperature (LT) negatively affects fertilization processes of flowering plants. Pollen tube growth is generally inhibited under LT stress; however, the mechanism(s) underlying this inhibition remain(s) largely unknown. Pollen tubes are tip-growing and the presence of tip-localized reactive oxygen species (ROS) is necessary for cellular functioning. Disruption of tip-localized ROS was observed in pear pollen tubes in vitro under low temperature of 4 °C (LT4). Diphenylene iodonium chloride, an NADPH oxidase (NOX) inhibitor, suppressed hydrogen peroxide formation in the cell walls of the subapical region in pear pollen tubes. Under LT4 stress, ROS disruption in pear pollen tubes mainly resulted from decreased NOX activity in the plasma membrane, indicating that NOX was the main source of ROS in this process. Moreover, LT4 remarkably decreased mitochondrial oxygen consumption and intracellular ATP production. The endocytosis, an energy-dependent process, disruption in pear pollen tubes under LT4 may be mediated by mitochondrial metabolic dysfunctions. Our data showed ROS and endocytosis events in pear pollen tubes responding to LT4 stress., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

The pear cultivar 'Zaoguan' (S(4)S(34)) is the a self-compatible descendant of 'Yali' (S(21)S(34)) × 'Qingyun'(S(4)S(9)). Two self-incompatible cultivars 'Xinya' and 'Yaqing', also S-genotyped as S(4)S(34) for the S-RNase gene, were used as controls. Field pollination data revealed that 'Zaoguan' displayed SC, whereas 'Xinya' and 'Yaqing' showed self-incompatibility (SI) upon self-pollination. Reciprocal pollinations between the varieties showed that most of the 'Zaoguan' flowers pollinated with 'Xinya' or 'Yaqing' pollen set fruits but that few of the 'Xinya' or 'Yaqing' flowers set fruit when pollinated with 'Zaoguan' pollen. The pollen performance was monitored with fluorescence microscopy, and we observed that 'Zaoguan' accepted self-pollen as well as 'Xinya' or 'Yaqing' pollen, whereas 'Xinya' or 'Yaqing' rejected self-pollen and 'Zaoguan' pollen. The S(34)-RNase but not the S(4)-RNase could be detected in all selfed progeny of 'Zaoguan'. Comparisons of the 2D-PAGE profiles of the stylar extracts from the three cultivars showed that the S(4)-RNase protein expressed normally, but the S(34)-RNase of 'Zaoguan' was not found. Thus, we concluded that the stylar S(34) products were defective in 'Zaoguan' and that the S (4)-allele functioned normally. The nucleotide sequences of the S(4)- and S(34)-RNase of 'Zaoguan' showed no differences from those of 'Xinya' or 'Yaqing', and they transcribed normally. These results indicate that SC in 'Zaoguan' was due to the loss of the S(34)-RNase caused by unknown post-transcriptional factors., (© Springer Science+Business Media B.V. 2011)

Pear (Pyrus pyrifolia L.) possesses an S-RNase-based gametophytic self-incompatibility (GSI) system, and S-RNase, the self-incompatibility (SI) determinant in the pistil, has also been implicated in the rejection of self-pollen and genetically identical pollen. We have demonstrated that S-RNase depolymerises actin cytoskeleton, triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube, which indicates programmed cell death (PCD) may occur in SI response of Pyrus pyrifolia. Recently, we have identified that S-RNase specifically disrupted tip-localized reactive oxygen species (ROS) of incompatible pollen tube via arrest of ROS formation in mitochondria and cell walls in Pyrus pyrifolia. Furthermore, tip-localized ROS disruption not only decreased the Ca(2+) current and depolymerised the actin cytoskeleton, but it also induced nuclear DNA degradation in the pollen tube. The results mentioned above indicate that a cascade signal pathway may occur in SI of Pyrus pyrifolia and PCD is used to terminate the incompatible pollen tubes growth. In this addendum, we review the cascade signal pathway of Pyrus pyrifolia SI.

• The regulation of plant potassium (K+) channels has been extensively studied in various systems. However, the mechanism of their regulation in the pollen tube is unclear. • In this study, the effects of heme and carbon monoxide (CO) on the outward K+ (K+(out)) channel in pear (Pyrus pyrifolia) pollen tube protoplasts were characterized using a patch-clamp technique. • Heme (1 μM) decreased the probability of K+(out) channel opening without affecting the unitary conductance, but this inhibition disappeared when heme was co-applied with 10 μM intracellular free Ca²+. Conversely, exposure to heme in the presence of NADPH increased channel activity. However, with tin protoporphyrin IX treatment, which inhibits hemeoxygenase activity, the inhibition of the K+(out) channel by heme occurred even in the presence of NADPH. CO, a product of heme catabolism by hemeoxygenase, activates the K+(out) channel in pollen tube protoplasts in a dose-dependent manner. The current induced by CO was inhibited by the K+ channel inhibitor tetraethylammonium. • These data indicate a role of heme and CO in reciprocal regulation of the K+(out) channel in pear pollen tubes., (© 2010 Nanjing Agricultural University. New Phytologist © 2010 New Phytologist Trust.)

Pear (Pyrus pyrifolia L.) has an S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. However, RNA degradation might be only the beginning of the SI response, not the end. Recent in vitro studies suggest that S-RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia, and it seems that a relationship exists between self S-RNase, actin depolymerization and DNA degradation. To further uncover the SI response in pear, the relationship between self S-RNase and tip-localized reactive oxygen species (ROS) was evaluated. Our results show that S-RNase specifically disrupted tip-localized ROS of incompatible pollen tubes via arrest of ROS formation in mitochondria and cell walls. The mitochondrial ROS disruption was related to mitochondrial alteration, whereas cell wall ROS disruption was related to a decrease in NADPH. Tip-localized ROS disruption not only decreased the Ca(2+) current and depolymerized the actin cytoskeleton, but it also induced nuclear DNA degradation. These results indicate that tip-localized ROS disruption occurs in Pyrus pyrifolia SI. Importantly, we demonstrated nuclear DNA degradation in the incompatible pollen tube after pollination in vivo. This result validates our in vitro system in vivo.

Pear (Pyrus pyrifolia L.) has a S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. No studies, however, have examined the extent of organelle alterations during the SI response in Pyrus pyrifolia. Consequently, this study focused on the alterations to mitochondria and nuclear DNA in incompatible pollen tubes of the pear. Methylthiazolyldiphenyl-tetrazolium bromide was used to evaluate the viability of pollen tubes under S-RNase challenge. The results showed that the viability of the control and compatible pollen tubes decreased slightly, but that of the incompatible pollen and pollen tubes began to decline at 30 min. The mitochondrial membrane potential (Delta psi(mit)) was also tested with rhodamine 123 30 min after SI challenge, and was shown to have collapsed in the incompatible pollen tubes after exposure to S-RNase. Western blotting 2 h after SI challenge confirmed that the Delta psi(mit) collapse induced leakage of cytochrome c into the cytosol. Swollen mitochondria were detected by transmission electron microscopy as early as 1 h after SI challenge and the degradation of nuclear DNA was observed by both 4,6-diamidino-2-phenylindole and transferase-mediated dUTP nick-end labeling. These diagnostic features of programmed cell death (PCD) suggested that PCD may specifically occur in incompatible pollen tubes.

The effects of G protein regulators and stylar S-RNase on the growth and [Ca(2+)](i) changes of the Pyrus pyrifolia pollen tube were investigated using Laser Confocal Scanning Microscope (LCSM). The results indicated that: (1) The growth of 'Housui' pollen tube could be inhibited by its stylar S-RNase and pertussis toxin (PTX), the inhibitor of heterotrimeric G protein. While 'Kousui' stylar S-RNase had little effect on the growth of 'Housui' pollen tube; cholera toxin (CTX), the activator of heterotrimeric G protein, could promote pollen tube growth and eliminate the suppression of stylar S-RNase on the growth of self-pollen tube, but the growth of 'Housui' pollen tube could be arrested under the co-action of PTX and S-RNase from 'Kousui' Fig.1). (2) Treatments with different stylar S-RNase and G protein regulators could have different effects on the change in [Ca(2+)](i) in the tip of pollen tube (Figs.2,3). The treatment with 'Housui' stylar S-RNase could induce the decrease of fluorescence gradient of [Ca(2+)](i) along the tip of self-pollen tube (Figs.2A, 3A), and the treatment with CTX could markedly elevate [Ca(2+)](i) in the tip of pollen tube showed (Fig.3C). The way of [Ca(2+)](i) changed in 'Housui' pollen tube under the co-action of CTX and its stylar S-RNase showed the compositive effect of the two respective treatment (Fig.3A, C, E), but the effect of the co-action of PTX and 'Kousui' stylar S-RNase showed increase in [Ca(2+)](i) in the pollen tube in 18 min after treatment, and then decrease between 18-36 min (Fig.3F). These results suggest that during self or cross pollination, the control of the growth of Pyrus pyrifolia pollen tube is by the synergistic effect of stylar S-RNase, G protein and [Ca(2+)](i) in the pollen tube.

This paper studied the effects of 0.3 mmol x L(-1) SNP on the antioxidant enzymes and reactive oxygen in pear leaves infected by Physalosproa piricola Nose. The results showed that compared with CK1 (spraying leaves with water and infecting with P. piricola Nose), 0.3 mmol x L(-1) SNP could increase the activities of leaf POD, SOD, CAT and PPO and the contents of leaf ASA, GSH and proline by 39.41%, 21.11%, 41.61%, 13.04%, 44.45%, 48.32% and 33.80%, while decrease the contents of leaf MDA and H2O2 and the generating rate of O2- by 20.45%, 6.93% and 6.27%, respectively, indicating that lower concentration SNP could reduce the damage of P. piricola Nose to pear leaves.

Pears (Pyrus pyrifolia L.) have an S-RNase-based gametophytic self-incompatibility system, and S-RNases have also been implicated in self-pollen or genetically identical pollen rejection. Tip growth of the pollen tube is dependent on a functioning actin cytoskeleton. In this study, configurations of the actin cytoskeleton in P. pyrifolia pollen and effects of stylar S-RNases on its dynamics were investigated by fluorescence and confocal microscopy. Results show that actin filaments in normal pollen grains exist in fusiform or circular structures. When the pollen germinates, actin filaments assembled around one of the germination pores, and then actin bundles oriented axially throughout the shank of the growing tube. There was a lack of actin filaments 5-15 microm from the tube tip. When self-stylar S-RNase was added to the basal medium, pollen germination and tube growth were inhibited. The configuration of the actin cytoskeleton changed throughout the culturing time: during the first 20 min, the actin configurations in the self-pollen and tube were similar to the control; after 20 min of treatment, the actin filaments in the pollen tube gradually moved into a network running from the shank to the tip; finally, there was punctate actin present throughout the whole tube. Although the actin filaments of the self-pollen grain also disintegrated into punctate foci, the change was slower than in the tube. Furthermore, the alterations to the actin cytoskeleton occurred prior to the arrest of pollen tube growth. These results suggest that P. pyrifolia stylar S-RNase induces alterations in the actin cytoskeleton in self-pollen grains and tubes.

The effects of the cholera toxin (CTX) and pertussis toxin (PTX), which can activate and antagonize respectively the heterotrimeric G protein, on pollen germination, pollen tube growth and the dynamic of cytosolic free calcium concentration ([Ca(2+)]i) in pear pollen were investigated using Laser Confocal Scanning Microscope (LCSM). The results show that CTX could stimulate pollen germination and tube growth while PTX had the opposite effect. CTX and PTX had marked influence on the dynamic of pollen [Ca(2+)]i. The CTX treatment had no significant effect on the changes in pollen [Ca(2+)]i during pollen germination, but induced specific signaling of "calcium transient" in pollen. Treatment with PTX caused decline of pollen [Ca(2+)]i in the first 18 min after treatment. These data suggested that the regulation of pollen germination and tube growth in Pyrus serotina may involve in heterotrimeric G protein, which can stimulate specific change of pollen [Ca(2+)]i.