Characterization of the pectin methyl-esterase gene family and its function in controlling pollen tube growth in pear (Pyrus bretschneideri).

Pectin methyl-esterases (PMEs) play crucial roles in plant growth. In this study, we identified 81 PbrPMEs in pear. Whole-genome duplication and purifying selection drove the evolution of PbrPME gene family. The expression of 47 PbrPMEs was detected in pear pollen tube, which were assigned to 13 clusters by an expression tendency analysis. One of the 13 clusters presented opposite expression trends towards the changes of methyl-esterified pectins at the apical cell wall. PbrPMEs were localized in the cytoplasm and plasma membrane. Repression of PbrPME11, PbrPME44, and PbrPME59 resulted in the inhibition of pear pollen tube growth and abnormal deposition of methyl-esterified pectins at pollen tube tip. Pharmacological analysis confirmed that reduced PbrPME activities repressed the pollen tube growth. Overall, we have explored the evolutionary characteristics of PbrPME gene family and found the key PbrPME genes that control the growth of pollen tube, which deepened the understanding of pear fertility regulation.

Effects of Melatonin Treatment of Postharvest Pear Fruit on Aromatic Volatile Biosynthesis.

Aroma affects the sensory quality of fruit and, consequently, consumer satisfaction. Melatonin (MT) is a plant growth regulator used to delay senescence in postharvest fruit during storage; however, its effect on aroma of pear fruit remains unclear. In this study, we assessed the effects of 0.1 mmol L-1 MT on volatiles and associated gene expression in the fruit of pear cultivars 'Korla' (Pyrus brestschneideri Rehd) and 'Abbé Fetel' (Pyrus communis L.). MT mainly affected the production of C6 aromatic substances in the two varieties. In 'Korla', MT inhibited expression of PbHPL, and reduced hydroperoxide lyase (HPL) activity and content of hexanal and (E)-hex-2-enal. In contrast, MT inhibited activity of lipoxygenase (LOX), reduced expression of PbLOX1 and PbLOX2, promoted PbAAT gene expression, increased alcohol acyltransferase (AAT) activity, and increased propyl acetate, and hexyl acetate content in 'Abbé Fetel' that similarly led to the reduction in content of hexanal and (E)-hex-2-enal. Content of esters in 'Abbé Fetel' pear increased with increasing postharvest storage period. Although mechanisms differed between the two varieties, effects on aroma volatiles mediated by MT were driven by expression of genes encoding LOX, HPL, and AAT enzymes.

Characterization of the Genes Involved in Malic Acid Metabolism from Pear Fruit and Their Expression Profile after Postharvest 1-MCP/Ethrel Treatment.

In this study, five genes involved in malic acid (MA) metabolism, including a cytosolic NAD-dependent malate dehydrogenase gene ( cyNAD-MDH), a cytosolic NADP-dependent malic enzyme gene ( cyNADP-ME), two vacuolar H+-ATPase genes ( vVAtp1 and vVAtp2), and one vacuolar inorganic pyrophosphatase gene ( vVPp), were characterized from pear fruit based on bioinformatic and experimental analysis. Their expression profile in "Housui" pear was tissue-specific, and their expression patterns during fruit development were diverse. During "Housui" pear storage, MA content decreased, which was associated with the downregulated transcripts of MA metabolism-related genes and cyNAD-MDH activity and higher cyNADP-ME activity. The response of MA metabolism to postharvest 1.5 µL L-1 1-MCP fumigation and 0.5 mL L-1 ethrel dipping was distinct: 1-MCP fumigation upregulated gene expression and cyNAD-MDH activity and suppressed cyNADP-ME activity, and thus maintained higher MA abundance when compared with those in the control; on the other hand, an opposite behavior was observed in ethrel-treated fruit.

[Effects of different phosphorus application rates on growth, 15N-urea absorption, and utilization characteristics of pear rootstocks.] / ä¾›ç£·æ°´å¹³å¯¹æ¢¨ç §æœ¨ç”Ÿé•¿å’Œ15N-å°¿ç´ å¸æ”¶åˆ©ç”¨ç‰¹æ€§çš„å½±å“.

Three kinds of potted one-year-old pear rootstocks (Pyrus calleryana, P. pashia, and P. xerophila) and 15N trace technique were used to examine the effects of different phosphorus application rates (P0, P1, P2, P3 and P4 equivalent to 0, 50, 100, 150 and 200 kg·hm-2 P2O5, respectively) on plant growth and the characteristics of 15N-urea absorption and utilization. The results showed that, with the increases of phosphorus levels, plant height, ground diameter, dry mass, root surface area, root length, number of root tips, root activity, root respiration rate, Ndff values, and nitrogen use efficiency of rootstocks first increased and then decreased. However, the range of rise and fall of different rootstocks were distinct, and each index reached the highest level at different phosphorus levels. The plant height, diameter, dry mass of P. xerophila were the highest under the same phosphorus level, followed by P. pashia, and P. calleryana was the lowest. The root architecture parameters and root respiration rate showed the same trend, but Ndff values and nitrogen use efficiency performed different. Under different phosphorus levels, each index of P. xerophila reached the highest level at P3, but those of P. pashia and P. calleryana appeared at P2 and P1 rates, respectively. The Ndff values in stem were the highest among different organs of rootstocks at diffe-rent phosphorus levels, and the highest nitrogen use efficiency of P. xerophila, P. pashia and P. calleryana was 9.6%, 8.9% and 8.3%, respectively. The variations of plant growth and N absorption and utilization of different pear rootstocks across different phosphorus levels indicated that phosphorus fertilizer should be carry out reasonably in practice and give full consideration of phosphorus demands of plants.

B-BOX genes: genome-wide identification, evolution and their contribution to pollen growth in pear (Pyrus bretschneideri Rehd.).

BACKGROUND: The B-BOX (BBX) proteins have important functions in regulating plant growth and development. In plants, the BBX gene family has been identified in several plants, such as rice, Arabidopsis and tomato. However, there still lack a genome-wide survey of BBX genes in pear. RESULTS: In the present study, a total of 25 BBX genes were identified in pear (Pyrus bretschneideri Rehd.). Subsequently, phylogenetic relationship, gene structure, gene duplication, transcriptome data and qRT-PCR were conducted on these BBX gene members. The transcript analysis revealed that twelve PbBBX genes (48%) were specifically expressed in pear pollen tubes. Furthermore, qRT-PCR analysis indicated that both PbBBX4 and PbBBX13 have potential role in pear fruit development, while PbBBX5 should be involved in the senescence of pear pollen tube. CONCLUSIONS: This study provided a genome-wide survey of BBX gene family in pear, and highlighted its roles in both pear fruits and pollen tubes. The results will be useful in improving our understanding of the complexity of BBX gene family and functional characteristics of its members in future study.

Evaluation of Food Lures for Capture and Monitoring of Anastrepha fraterculus (Diptera: Tephritidae) on Temperate Fruit Trees.

The Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) is the main pest of fruit trees grown in temperate climates in the southern region of Brazil. The objective of this work was to evaluate the efficiency of the major commercial food lures used in Brazil for trapping and monitoring of A. fraterculus in plum, pear, and feijoa orchards. The assessed lures were hydrolyzed proteins of animal origin (CeraTrap) and plant origin (BioAnastrepha), torula yeast + borax (Torula), and grape juice. Response variables included the rate of adult capture (flies per trap per day, FTD) and the percentage of females captured. We also evaluated the number of times the weekly capture rate exceeded the traditional threshold of 0.5 FTD for each lure. Traps baited with grape juice, currently used for monitoring A. fraterculus in Southern Brazil, captured fewer adults and a lower percentage of females compared with the other lures. CeraTrap trapped a greater number of A. fraterculus adults and, in some cases, a lower percentage of females compared with the other lures in pears. Traps baited with CeraTrap had greater capture rates (FTD), particularly during the stages of fruit maturation and harvest, and even in years with low population density of A. fraterculus, thus demonstrating greater sensitivity in the detection of this pest. These results show that, in order to detect and monitor the presence of A. fraterculus in plum, feijoa, and pear crops, protein-based lures are superior to grape juice, especially the animal protein CeraTrap.

The stiffening of the cell walls observed during physiological softening of pears.

MAIN CONCLUSION: The Young's modulus of the primary cell walls of pears decreases linearly during the pre-harvest on-tree maturation and increases during postharvest storage, and does not correlate with firmness of fruit. The determination of mechanical properties of cell walls is indispensable for understanding the mechanism of physiological softening and deterioration of quality of fruits during postharvest storage. The Young's modulus of the primary cell walls from pear fruit (Pyrus communis L., cultivars 'Conference' and 'Xenia') during pre-harvest maturation and postharvest storage in an ambient atmosphere at 2 °C followed by shelf life was studied using atomic force microscopy (AFM). The results were related to the firmness of fruits, galacturonic acid content in water, chelator, sodium carbonate and insoluble pectin fractions, polygalacturonase and pectin methylesterase activities. The Young's modulus of the primary cell walls decreased linearly during the last month of pre-harvest maturation from 3.2 ± 1.8 to 1.1 ± 0.7 MPa for 'Conference' and from 1.9 ± 1.2 to 0.2 ± 0.1 MPa for 'Xenia' which correlated with linear firmness decrease. During postharvest storage the cell wall Young's modulus increased while firmness continued to decrease. Correlation analysis for the entire period of the experiment showed a lack of straightforward relation between the Young's modulus of primary cell walls and fruit firmness. The Young's modulus of cell walls correlated negatively either with galacturonic acid content in sodium carbonate soluble pectin ('Conference') or with insoluble pectin fractions ('Xenia') and positively with polygalacturonase activity. It was therefore evidenced that covalently linked pectins play the key role for the stiffness of fruit cell walls. Based on the obtained results, the model explaining the fruit transition from firm and crispy to soft and mealy was proposed.

Expression and regulation of pear 1-aminocyclopropane-1-carboxylic acid synthase gene (PpACS1a) during fruit ripening, under salicylic acid and indole-3-acetic acid treatment, and in diseased fruit.

In plants, the level of ethylene is determined by the activity of the key enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS). A gene encoding an ACC synthase protein was isolated from pear (Pyrus pyrifolia). This gene designated PpACS1a (GenBank accession no. KC632526) was 1488 bp in length with an open reading frame (ORF) encoding a protein of 495 amino acids that shared high similarity with other pear ACC synthase proteins. The PpACS1a was grouped into type-1 subfamily of plant ACS based on its conserved domain and phylogenetic status. Real-time quantitative PCR indicated that PpACS1a was differentially expressed in pear tissues and predominantly expressed in anthers. The expression signal of PpACS1a was also detected in fruit and leaves, but no signal was detected in shoots and petals. Furthermore, the PpACS1a expression was regulated during fruit ripening. In addition, the PpACS1a gene expression was regulated by salicylic acid (SA) and indole-3-acetic acid (IAA) in fruit. Moreover, the expression of the PpACS1a was up-regulated in diseased pear fruit. These results indicated that PpACS1a might be involved in fruit ripening and response to SA, IAA and disease.

Influence of rootstocks on growth, yield, fruit quality and leaf mineral element contents of pear cv. 'Santa Maria' in semi-arid conditions.

BACKGROUND: Rootstocks play an essential role to determining orchard performance of fruit trees. Pyrus communis and Cydonia oblonga are widely used rootstocks for European pear cultivars. The lack of rootstocks adapted to different soil conditions and different grafted cultivars is widely acknowledged in pear culture. Cydonia rootstocks (clonal) and Pyrus rootstocks (seedling or clonal) have their advantages and disadvantages. In each case, site-specific environmental characteristics, specific cultivar response and production objectives must be considered before choosing the best rootstock. In this study, the influence of three Quince (BA 29, Quince A = MA, Quince C = MC) and a local European pear seedling rootstocks on the scion yield, some fruit quality characteristics and leaf macro (N, P, K, Ca and Mg) and micro element (Fe, Zn, Cu, Mn and B) content of 'Santa Maria' pear (Pyrus communis L.) were investigated. RESULTS: Trees on seedling rootstock had the highest annual yield, highest cumulative yield (kg tree(-1)), largest trunk cross-sectional area (TCSA), lowest yield efficiency and lowest cumulative yield (ton ha(-1)) in the 10(th) year after planting. The rootstocks had no significant effect on average fruit weight and fruit volume. Significantly higher fruit firmness was obtained on BA 29 and Quince A. The effect of rootstocks on the mineral element accumulation (N, K, Ca, Mg, Fe, Zn, Cu, Mn and B) was significant. Leaf analysis showed that rootstocks used had different mineral uptake efficiencies throughout the early season. CONCLUSION: The results showed that the rootstocks strongly affected fruit yield, fruit quality and leaf mineral element uptake of 'Santa Maria' pear cultivar. Pear seedling and BA 29 rootstock found to be more prominent in terms of several characteristics for 'Santa Maria' pear cultivar that is grown in highly calcareous soil in semi-arid climate conditions. We determined the highest N, P (although insignificant), K, Ca, Mg, Fe and Cu mineral element concentrations on the pear seedling and BA 29 rootstocks. According to the results, we recommend the seedling rootstock for normal density plantings (400 trees ha(-1)) and BA 29 rootstock for high-density plantings (800 trees ha(-1)) for 'Santa Maria' pear cultivar in semi-arid conditions.

Influence of rootstocks on growth, yield, fruit quality and leaf mineral element contents of pear cv. 'Santa Maria' in semi-arid conditions

BACKGROUND: Rootstocks play an essential role to determining orchard performance of fruit trees. Pyrus communisand Cydonia oblonga are widely used rootstocks for European pear cultivars. The lack of rootstocks adapted to different soil conditions and different grafted cultivars is widely acknowledged in pear culture. Cydonia rootstocks (clonal) and Pyrus rootstocks (seedling or clonal) have their advantages and disadvantages. In each case, site-specific environmental characteristics, specific cultivar response and production objectives must be considered before choosing the best rootstock. In this study, the influence of three Quince (BA 29, Quince A = MA, Quince C = MC) and a local European pear seedling rootstocks on the scion yield, some fruit quality characteristics and leaf macro (N, P, K, Ca and Mg) and micro element (Fe, Zn, Cu, Mn and B) content of 'Santa Maria' pear (Pyrus communis L.) were investigated. RESULTS: Trees on seedling rootstock had the highest annual yield, highest cumulative yield (kg tree(-1)), largest trunk cross-sectional area (TCSA), lowest yield efficiency and lowest cumulative yield (ton ha(-1)) in the 10th year after planting. The rootstocks had no significant effect on average fruit weight and fruit volume. Significantly higher fruit firmness was obtained on BA 29 and Quince A. The effect of rootstocks on the mineral element accumulation (N, K, Ca, Mg, Fe, Zn, Cu, Mn and B) was significant. Leaf analysis showed that rootstocks used had different mineral uptake efficiencies throughout the early season. CONCLUSION: The results showed that the rootstocks strongly affected fruit yield, fruit quality and leaf mineral element uptake of 'Santa Maria' pear cultivar. Pear seedling and BA 29 rootstock found to be more prominent in terms of several characteristics for 'Santa Maria' pear cultivar that is grown in highly calcareous soil in semi-arid climate conditions. We determined the highest N, P (although insignificant), K, Ca, Mg, Fe and Cu mineral element concentrations on the pear seedling and BA 29 rootstocks. According to the results, we recommend the seedling rootstock for normal density plantings (400 trees ha(-1)) and BA 29 rootstock for high-density plantings (800 trees ha(-1)) for 'Santa Maria' pear cultivar in semi-arid conditions.

Communities of arbuscular mycorrhizal fungi in the roots of Pyrus pyrifolia var. culta (Japanese pear) in orchards with variable amounts of soil-available phosphorus.

We examined the colonization rate and communities of arbuscular mycorrhizal fungi (AMF) in the roots of Pyrus pyrifolia var. culta (Japanese pear) in orchards to investigate the effect of phosphorus (P) fertilization on AMF. Soil cores containing the roots of Japanese pear were collected from 13 orchards in Tottori Prefecture, Japan. Soil-available P in the examined orchards was 75.7 to 1,200 mg kg(-1), showing the extreme accumulation of soil P in many orchards. The AMF colonization rate was negatively correlated with soil-available P (P <0.01). AMF communities were examined on the basis of the partial fungal DNA sequences of the nuclear small-subunit ribosomal RNA gene (SSU rDNA) amplified by AMF-specific primers AML1 and AML2. The obtained AMF sequences were divided into 14 phylotypes, and the number of phylotypes (species richness) was also negatively correlated with soil-available P (P <0.05). It was also suggested that some AM fungi may be adapted to high soil-available P conditions. Redundancy analysis showed the significant effects of soil pH, available P in soil, and P content in leaves of P. pyrifolia var. culta trees on AMF distribution. These results suggested that the accumulation of soil-available P affected AMF communities in the roots of Japanese pear in the orchard environment.

Pollen factors controlling self-incompatibility strength in Japanese pear.

Japanese pear has a genetically controlled self-incompatibility system, but both the pollen-tube growth in a semi in vivo assay and fruit set after self-pollination differ considerably among cultivars. The percentage of styles in which pollen tubes have reached the base ranges from 0 to 36 %, a value determined by culture of styles in vitro, and fruit set ranges from 0.6 to 15.2 %. Based on these data, we have assigned a value for the self-incompatibility weakness to each cultivar. Here, we showed that pollen factors control the degree of self-incompatibility. When the pollen-tube growth of 13 cultivars was compared in a completely compatible 'Hougetsu' (S (1) S (7)) style, it differed a fair amount among cultivars and showed a significantly positive relation to self-incompatibility weakness (r = 0.707). The degree of self-incompatibility of pear is, therefore, determined by pollen factor(s) unrelated to the S-locus. Although the fruit set and fruit growth of 'Hougetsu' were not affected by the pollen donor, a positive relationship was also observed between seed number and self-incompatibility weakness (r = 0.972). However, in a style with no S-RNase production (genotype: S (4) (sm) S (4) (sm) ), the relationship disappeared (r = 0.341) and pollen-tube growth was promoted by 12-36 % except in one cultivar. These results suggest that S-RNase functions as a cytotoxin on compatible pollen in a cultivar-dependent manner, and that the degree of inhibition is determined by pollen factor(s) unrelated to the S-locus. The pollen factor also functions on S-RNase in incompatible styles, resulting in a different degree of self-incompatibility.

Effects of ripening, 1-methylcyclopropene and ultra-high-pressure pasteurisation on the change of volatiles in Chinese pear cultivars.

BACKGROUND: Aroma is one important fruit sensory attribute influenced by the volatile constituents related to species, variety and technological treatments. We analysed the variations of volatile compounds in five pear cultivars and investigated their changes related to different pear organs, different ripening stages, 1-MCP treatment and ultra-high-pressure pasteurisation. RESULTS: Considerable variations exist in the quantity of 10 volatile compounds among five pear cultivars. Their levels generally showed an increasing trend when collected at later harvest time in Ya pear. In Whangkeumbae pear, most volatile compounds reached their maximum levels in skin and pulp. After treating pears with 42 µmol L(-1) 1-methylcyclopropene (1-MCP), the levels of volatiles remained basically unchanged or only slightly increased in Ya pear during a shelf life of 21 days. When Huangguan pear juice was pasteurised by using ultra-high pressure, the levels of volatiles significantly changed during the shelf life. CONCLUSION: The volatile compositions of five different Chinese pear cultivars differ considerably. The levels of these volatiles vary along with ripening stages and pear tissues. A moderate concentration of 1-MCP could keep the levels of volatile compounds basically unchanged during storage and ultra-high-pressure pasteurisation could change the levels of volatiles significantly during the following shelf life.

Effects of foliar and fruit addition of sodium selenate on selenium accumulation and fruit quality.

BACKGROUND: We investigated the effects of the foliar and fruit application of sodium selenate on selenium (Se) accumulation, fruit growth and ripening in peach and pear. Trials were conducted in two growing seasons. In 2008 selenate was applied at a rate of 0.1 and 1.0 mg Se L⁻¹ to the leaves of peach. In 2009 selenate was applied at a rate of 1 mg Se L⁻¹ via foliar (LT) or fruit (FT) application to peach and pear. RESULTS: The foliar addition of selenate to peach resulted in an increase in Se concentration both in leaves and fruit. The higher Se content in fruit resulted in an increase in flesh firmness and a decrease in soluble solid content. LT significantly increased the Se content in the leaves and fruit of peach and pear, and leaves showed the highest Se concentrations. FT increased the fruit Se concentration in both crops, and it was more effective than LT in increasing Se content. After storage, flesh firmness decreased in all treatments, but it was significantly higher in FT compared to LT and control samples. CONCLUSION: Foliar and fruit selenium spraying appeared effective in increasing the Se content of fruit in peach and pear. The enhanced Se concentration affected the shelf life of fruit, delaying the reduction in flesh firmness and fruit ripening, thus positively affecting fruit storage.

Influence of cultivar, harvest time, storage conditions, and peeling on the antioxidant capacity and phenolic and ascorbic acid contents of apples and pears.

Apple and pear fruits are important sources of secondary plant metabolites and one of the major sources of dietary phenolics consumed all year round. The aim of this work was to identify the main variables influencing phenolic content and antioxidant capacity in apples. Higher phenolic and antioxidant contents were observed in some varieties (such as the Delbar Estival apple and Durondeau pear). Storage conditions were important. Our results also showed that fruits should be consumed rapidly after purchase and with their peel. After one week of domestic storage, the ascorbic acid content was found to decrease by 75%. Peeling led to a more than 25% decrease in total phenolics and ascorbic acid. The harvest time (at normal ripeness) had only a limited impact, but significant year-to-year variations were observed. In conclusion, well-chosen and well-stored apples and pears may contribute to an antioxidant-rich diet if consumed rapidly and with their peel.

Differential expression of proteins in red pear following fruit bagging treatment.

Fruit bagging is a very effective method for study of fruit qualities and anthocyanin synthesis. The characterization of differentially expressed proteins that were isolated from both bagged and normal fruit skin tissue is apparently an essential parameter for understanding the effect of shading on fruit qualities and to understand the mechanism of fruit coloring in Pyrus communis. Proteome maps of both bagged and normal P. communis 'Placer' fruit skin were obtained by performing two-dimensional electrophoresis analysis and compared to assess the extent to which protein distribution differed in pear skin. The comparative analysis showed 38 differentially expressed proteins between the two samples: with three protein spots up-regulated and 35 down-regulated in the bagged fruit. Differentially expressed protein spots were subjected to matrix-assisted laser desorption ionization time of flight (MALDI-TOF) analysis and the data compared to that of known proteins to deduce their possible functions. Of these, 21 protein spots were identified and classified into functional classes. These identified proteins were mainly involved in photosynthesis, signal transduction, energy pathway, protein folding and assembly, and carbohydrate and acidity metabolisms, and were under-expressed in bagged fruit skins. This work provides a first characterization of the proteome changes in response to fruit bagging treatment in red pears.

Pollen density on the stigma affects endogenous gibberellin metabolism, seed and fruit set, and fruit quality in Pyrus pyrifolia.

To clarify the relationship between pollen density and gametophytic competition in Pyrus pyrifolia, gametophytic performance, gibberellin metabolism, fruit set, and fruit quality were investigated by modifying P. pyrifolia pollen grain number and density with Lycopodium spores. Higher levels of pollen density improved seed viability, fruit set, and fruit quality. Treatments with the highest pollen density showed a significantly increased fruit growth rate and larger fruit at harvest. High pollen density increased germination rate and gave a faster pollen tube growth, both in vivo and in vitro. Endogenous gibberellin (GA) concentrations increased in pollen tubes soon after germination and the concentration of two growth-active GAs, GA(3), and GA(4), was positively correlated to final fruit size, cell numbers in the mesocarp, and pollen tube growth rate. These two GAs appear to be biosynthesized de novo in pollen tube and are the main pollen-derived bioactive GAs found after pollen germination. GA(1) levels in the pollen tube appear to be related to a pollen-style interaction that occurred after the pollen grains landed on the stigma.

Compatible and self-incompatible pollination in Pyrus communis displays different polyamine levels and transglutaminase activity.

The polyamine (PA) content and the transglutaminase (TGase) activity have been investigated in Pyrus communis pollination with compatible and self-incompatible (SI) pollen in order to deepen their possible involvement in the progamic phase of plant reproduction. The PA distribution as free, perchloric acid (PCA)-soluble and PCA-insoluble fractions in ungerminated (UGP), germinating pollen (GP), styles and pollinated styles with compatible and SI pollens is discussed in the light of a possible role during pollination. Generally, the conjugated PAs both in PCA-soluble and PCA-insoluble fractions were higher than the free form. Within the conjugated PAs, the PCA-insoluble ones were the highest with the exception of the not pollinated styles. As TGase mediates some of the effects of PAs by covalently binding them to proteins, the activity of this enzyme, never checked before in styles and pollinated styles, was examined. In the SI styles, the TGase activity is higher in comparison to style-pollinated with compatible pollen, and high molecular mass cross-linked products were formed, suggesting an involvement of TGase in SI response. This is the first evidence on the presence of this enzyme activity in not pollinated and pollinated styles.

[The effect of G protein regulator on pollen germination and [Ca2+]i variation in Pyrus serotina Rehd. pollen].

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.

European, Chinese and Japanese pear fruits exhibit differential softening characteristics during ripening.

Softening characteristics were investigated in three types of pear fruit, namely, European pear 'La France', Chinese pear 'Yali', and Japanese pear 'Nijisseiki'. 'La France' fruit softened dramatically and developed a melting texture during ripening, while 'Yali' fruit with and without propylene treatment showed no change in flesh firmness and texture during ripening. Non-treated 'Nijisseiki' did not show a detectable decrease in flesh firmness, whereas continuous propylene treatment caused a gradual decrease in firmness resulting in a mealy texture. In 'La France', the analysis of cell wall polysaccharides revealed distinct solubilization and depolymerization of pectin and hemicellulose during fruit softening. In 'Nijisseiki', propylene treatment led to the solubilization and depolymerization of pectic polysaccharides to a limited extent, but not of hemicellulose. In 'Yali', hemicellulose polysaccharides were depolymerized during ripening, but there was hardly any change in pectic polysaccharides except in the water-soluble fraction. PC-PG1 and PC-PG2, two polygalacturonase (PG) genes, were expressed in 'La France' fruit during ripening, while only PC-PG2 was expressed in 'Nijisseiki' and neither PC-PG1 or PC-PG2 was expressed in 'Yali'. The expression pattern of PC-XET1 was constitutive during ripening in all three pear types. PG activity measured by the reducing sugar assay increased in all three pears during ripening. However, viscometric measurements showed that the levels of endo-PG activity were high in 'La France', low in 'Nijisseiki', and undetectable in 'Yali' fruits. These results suggest that, in pears, cell wall degradation is correlated with a decrease in firmness during ripening and the modification of both pectin and hemicellulose are essential for the development of a melting texture. Furthermore, the data suggest that different softening behaviours during ripening among the three pear fruits may be caused by different endo-PG activity and different expression of PG genes.