Rosaceae Plants Research Articles

Detection of Estrogenic and Anti‐estrogenic Activities of Dietary Plant Extracts by InVitro Reporter Assays

Phytoestrogens are plant polyphenolic compounds which structurally and functionally mimic the mammalian estrogen hormone. This study aimed to establish the estrogenic agonism and antagonism of some dietary plants in Ericaceae, Moraceae, Rosaceae, and Vitaceae families. A steroid‐regulated transcription system in Saccharomyces cerevisiae containing a human estrogen receptor alpha expression plasmid and a β‐galactosidase gene reporter plasmid was employed in this study. Estrogenic activities of plant extracts were detected by assessing their effects on estrogen receptor mediated transactivation of the reporter gene as compared to estradiol. The degree of the weak estrogenic activities of ethanolic fruit extracts ranked as follows: California grape (Vitis californica) > red raspberry (Rubus ideaus) > strawberry (Fragaria ananassa) > Blackberry (R. fruticosus). Fruit extracts of blueberry (Vaccinium corymbosum), jackfruit (Artocarpus heterophyllus) and black raspberry (R. occidentalis) exhibited no estrogenic activities. Some extracts showed anti‐estrogenic properties by lowering the transcriptional activity induced by estradiol in transgenic yeast. Black and red raspberry extracts showed anti‐estrogenic activities in dose‐dependent manner. Blackberry, blueberry, and jackfruit extracts lowered estradiol activity by 25‐35% at all concentrations used. Strawberry extract exhibited partial antagonism of estradiol at low concentrations and partial agonism at high concentrations. This study reports for the first time anti‐estrogenic activities of the above plant extracts and it may lead to detection of new more potent phytoestrogens for possible chemopreventive effects and cancer treatments.

Genome-wide characterization and analysis of F-box protein-encoding genes in the Malus domestica genome.

The F-box protein family is a large family that is characterized by conserved F-box domains of approximately 40-50 amino acids in the N-terminus. F-box proteins participate in diverse cellular processes, such as development of floral organs, signal transduction and response to stress, primarily as a component of the Skp1-cullin-F-box (SCF) complex. In this study, using a global search of the apple genome, 517 F-box protein-encoding genes (F-box genes for short) were identified and further subdivided into 12 groups according to the characterization of known functional domains, which suggests the different potential functions or processes that they were involved in. Among these domains, the galactose oxidase domain was analyzed for the first time in plants, and this domain was present with or without the Kelch domain. The F-box genes were distributed in all 17 apple chromosomes with various densities and tended to form gene clusters. Spatial expression profile analysis revealed that F-box genes have organ-specific expression and are widely expressed in all organs. Proteins that contained the galactose oxidase domain were highly expressed in leaves, flowers and seeds. From a fruit ripening expression profile, 166 F-box genes were identified. The expressions of most of these genes changed little during maturation, but five of them increased significantly. Using qRT-PCR to examine the expression of F-box genes encoding proteins with domains related to stress, the results revealed that F-box proteins were up- or down-regulated, which suggests that F-box genes were involved in abiotic stress. The results of this study helped to elucidate the functions of F-box proteins, especially in Rosaceae plants.

The application of multiplex fluorimetric sensor for the analysis of flavonoids content in the medicinal herbs family Asteraceae, Lamiaceae, Rosaceae.

BackgroundThe aim of our research work was to quantify total flavonoid contents in the leaves of 13 plant species family Asteraceae, 8 representatives of family Lamiaceae and 9 plant species belonging to family Rosaceae, using the multiplex fluorimetric sensor. Fluorescence was measured using optical fluorescence apparatus Multiplex(R) 3 (Force-A, France) for non-destructive flavonoids estimation. The content of total flavonoids was estimated by FLAV index (expressed in relative units), that is deduced from flavonoids UV absorbing properties.ResultsAmong observed plant species, the highest amount of total flavonoids has been found in leaves of Helianthus multiflorus (1.65 RU) and Echinops ritro (1.27 RU), Rudbeckia fulgida (1.13 RU) belonging to the family Asteraceae. Lowest flavonoid content has been observed in the leaves of marigold (Calendula officinalis) (0.14 RU) also belonging to family Asteraceae. The highest content of flavonoids among experimental plants of family Rosaceae has been estimated in the leaves of Rosa canina (1.18 RU) and among plant species of family Lamiaceae in the leaves of Coleus blumei (0.90 RU).ConclusionsThis research work was done as pre-screening of flavonoids content in the leaves of plant species belonging to family Asteraceae, Lamiaceae and Rosaceae. Results indicated that statistically significant differences (P > 0.05) in flavonoids content were observed not only between families, but also among individual plant species within one family.

Exploring new roles for therpoSgene in the survival and virulence of the fire blight pathogenErwinia amylovora

Erwinia amylovora causes fire blight in economically important plants of the family Rosaceae. This bacterial pathogen spends part of its life cycle coping with starvation and other fluctuating environmental conditions. In many Gram-negative bacteria, starvation and other stress responses are regulated by the sigma factor RpoS. We obtained an E.amylovora rpoS mutant to explore the role of this gene in starvation responses and its potential implication in other processes not yet studied in this pathogen. Results showed that E.amylovora needs rpoS to develop normal starvation survival and viable but nonculturable (VBNC) responses. Furthermore, this gene contributed to stationary phase cross-protection against oxidative, osmotic, and acid stresses and was essential for cross-protection against heat shock, but nonessential against acid shock. RpoS also mediated regulation of motility, exopolysaccharide synthesis, and virulence in immature loquats, but not in pear plantlets, and contributed to E.amylovora survival in nonhost tissues during incompatible interactions. Our results reveal some unique roles for the rpoS gene in E.amylovora and provide new knowledge on the regulation of different processes related to its ecology, including survival in different environments and virulence in immature fruits.

Control of Plant Defense Mechanisms and Fire Blight Pathogenesis through the Regulation of 6‐Thioguanine Biosynthesis in Erwinia amylovora

Fire blight is a devastating disease of Rosaceae plants, such as apple and pear trees. It is characterized by necrosis of plant tissue, caused by the phytopathogenic bacterium Erwinia amylovora. The plant pathogen produces the well-known antimetabolite 6-thioguanine (6TG), which plays a key role in fire blight pathogenesis. Here we report that YcfR, a member of the LTTR family, is a major regulator of 6TG biosynthesis in E. amylovora. Inactivation of the regulator gene (ycfR) led to dramatically decreased 6TG production. Infection assays with apple plants (Malus domestica cultivar Holsteiner Cox) and cell cultures of Sorbus aucuparia (mountain ash, rowan) revealed abortive fire blight pathogenesis and reduced plant response (biphenyl and dibenzofuran phytoalexin production). In the presence of the ΔycfR mutant, apple trees were capable of activating the abscission machinery to remove infected tissue. In addition to unveiling the regulation of 6TG biosynthesis in a major plant pathogen, we demonstrate for the first time that this antimetabolite plays a pivotal role in dysregulating the plant response to infection.

In Vitro Antiviral Activity of a Series of Wild Berry Fruit Extracts against Representatives of Picorna-, Orthomyxo- and Paramyxoviridae

Wild berry species are known to exhibit a wide range of pharmacological activities. They have long been traditionally applied for their antiseptic, antimicrobial, cardioprotective and antioxidant properties. The aim of the present study is to reveal the potential for selective antiviral activity of total methanol extracts, as well as that of the anthocyanins and the non-anthocyanins from the following wild berries picked in Bulgaria: strawberry (Fragaria vesca L.) and raspberry (Rubus idaeus L.) of the Rosaceae plant family, and bilberry (Vaccinium myrtillis L.) and lingonberry (Vaccinium vitis-idaea L) of the Ericaceae. The antiviral effect has been tested against viruses that are important human pathogens and for which chemotherapy and/or chemoprophylaxis is indicated, namely poliovirus type 1 (PV-1) and coxsackievirus B1 (CV-B1) from the Picornaviridae virus family, human respiratory syncytial virus A2 (HRSV-A2) from the Paramyxoviridae and influenza virus A/H3N2 of Orthomyxoviridae. Wild berry fruits are freeze-dried and ground, then total methanol extracts are prepared. Further the extracts are fractioned by solid phase extraction and the non-anthocyanin and anthocyanin fractions are eluted. The in vitro antiviral effect is examined by the virus cytopathic effect (CPE) inhibition test. The results reveal that the total extracts of all tested berry fruits inhibit the replication of CV-B1 and influenza A virus. CV-B1 is inhibited to the highest degree by both bilberry and strawberry, as well as by lingonberry total extracts, and influenza A by bilberry and strawberry extracts. Anthocyanin fractions of all wild berries strongly inhibit the replication of influenza virus A/H3N2. Given the obtained results it is concluded that wild berry species are a valuable resource of antiviral substances and the present study should serve as a basis for further detailed research on the matter.

Host acceptance behavior of the parasitoid Aphelinus mali and its aphid-host Eriosoma lanigerum on two Rosaceae plant species

The presence of a natural enemy in a habitat refuge is no guarantee of emigration by these into crop fields, when pest population outbreaks occur. Parasitoids from a refuge may not prefer foraging on the pest crop, exhibiting host fidelity, and therefore not constituting a source of natural enemies for improving biological control. An effective refuge must not only be a suitable sink for natural enemies, providing an acceptable host when these are not present in the crop, but it must also be a suitable source of parasitoids that readily accept the aphid-host on the crop. Therefore, crop-originated parasitoids would have to accept pests from the refuge as hosts to lay eggs in, and refuge-originated parasitoids would have to accept and lay eggs in pests from the crop. We here study the host fidelity of populations of Eriosoma lanigerum originating from two host plants (firethorn and apple) through reciprocal transfer experiments. Thereafter, the host fidelity of parasitoids from populations in the two host plants (firethorn and apple) was assessed. Reciprocal transfer experiments of parasitoids did not show an association between apple-originated parasitoids and their preference for any of the aphid hosts. Conversely, parasitoids from firethorn exhibited a higher number of attacks and in less time when aphids from apple were offered, suggesting a preference for apple-originated aphids. If future field work confirms these findings, firethorn could become an important management tool for enhancing biological control of woolly apple aphid in apple orchards, without being a substantial source of aphids.

Apple SSRs present in coding and noncoding regions of expressed sequence tags show differences in transferability to other fruit species in Rosaceae

Zhou, Y., Li, J., Korban, S. S. and Han, Y. 2013. Apple SSRs present in coding and noncoding regions of expressed sequence tags show differences in transferability to other fruit species in Rosaceae. Can. J. Plant Sci. 93: 183–190. Simple sequence repeat markers derived from expressed sequence tags (ESTs) are referred to as eSSRs. To develop molecular markers for non-model plants in Rosaceae, we investigated the transferability of apple eSSRs across seven fruit trees, belonging to four genera and 11 species of the Rosaceae family, including peach, quince, pear, loquat, apricot, cherry, and plum. Of the 98 apple eSSRs tested, 86 successfully amplified PCR products in at least one of the fruit tree species. Five apple eSSRs produced amplicons in more than five fruit tree species, and were deemed as a widely transferable Rosaceae marker set. Frequency of transferability of apple eSSRs across all seven fruit trees of Rosaceae varied widely among genera and species, with an average transferability of 29.0%. Overall, apple eSSRs transferred more easily to peach and pear than to plum and loquat. Interestingly, apple eSSRs present in coding sequences (CDS) showed higher levels of transferability to other fruit trees than those present in noncoding or untranslated regions (UTRs). Interestingly, apple eSSRs present in 5'UTRs showed lower frequencies of transfer than those present in 3'UTRs. The latter finding suggested that 5'UTRs might have diverged more rapidly than 3'UTRs in Rosaceae.

Oxynetra: Facies and DNA Barcodes Point to a New Species from Costa Rica (Hesperiidae: Pyrginae: Pyrrhopygini)

Oxynetra stangelandi Grishin & Burns, new species, from high elevations of Area de Conservacion Guanacaste (ACG) in northwestern Costa Rica, is most similar to Oxynetra hopfferi Staudinger, known from mountains of central and southern Costa Rica and western Panama. These hesperiid species differ mainly in body color pattern and in DNA barcodes. We compare their barcodes, nucleotide by nucleotide, together with barcodes of a congener and a species of the related genus Olafia, and use the barcode data to show phylogenetic relationships. We describe the new species, its discovery, its male and female genitalia, and its life history as a cloud forest herbivore of Prunus annularis (Rosaceae). In ACG, no other skippers feed on this plant species, and no other skippers of the tribe Pyrrhopygini feed on plants in the family Rosaceae. Various stages of O. stangelandi belong to mimicry complexes. Although our adults, which are reared from wild-caught caterpillars, are split between the sexes (4 males, 6 females), there are scarcely any females of Oxynetra in the world's museums.

Occupational allergic contact dermatitis caused by weeds of the Compositae, Fabaceae and Rosaceae plant families

Occupational allergic contact dermatitis caused by weeds of the Compositae, Fabaceae and Rosaceae plant families

Gene‐for‐gene relationship in the host–pathogen system Malus × robusta 5–Erwinia amylovora

Fire blight is a destructive bacterial disease caused by Erwinia amylovora affecting plants in the family Rosaceae, including apple. Host resistance to fire blight is present mainly in accessions of Malus spp. and is thought to be quantitative in this pathosystem. In this study we analyzed the importance of the E. amylovora effector avrRpt2(EA) , a homolog of Pseudomonas syringae avrRpt2, for resistance of Malus × robusta 5 (Mr5). The deletion mutant E. amylovora Ea1189ΔavrRpt2(EA) was able to overcome the fire blight resistance of Mr5. One single nucleotide polymorphism (SNP), resulting in an exchange of cysteine to serine in the encoded protein, was detected in avrRpt2(EA) of several Erwinia strains differing in virulence to Mr5. E. amylovora strains encoding serine (S-allele) were able to overcome resistance of Mr5, whereas strains encoding cysteine (C-allele) were not. Allele specificity was also observed in a coexpression assay with Arabidopsis thaliana RIN4 in Nicotiana benthamiana. A homolog of RIN4 has been detected and isolated in Mr5. These results suggest a system similar to the interaction of RPS2 from A. thaliana and AvrRpt2 from P. syringae with RIN4 as guard. Our data are suggestive of a gene-for-gene relationship for the host-pathogen system Mr5 and E. amylovora.

СОДЕРЖАНИЕ ФЛАВОНОИДОВ В НЕКОТОРЫХ ПРЕДСТАВИТЕЛЯХ СЕМЕЙСТВА ROSACEAE JUSS. ИЗ ПРИРОДНЫХ ПОПУЛЯЦИЙ ЛЕСОСТЕПНОЙ ЗОНЫ ЗАПАДНОЙ СИБИРИ

Last years more and more attention it is given to search of new herbs containing considerable percent of flavonoids and working out of preparations from the vegetative raw materials used in national medicine. The maintenance of flavonoids in vegetative raw materials is the major indicator of its biological value. The purpose of the present work – maintenance research of flavonoids in an elevated and underground part of plants of family Rosaceae. It is analysed on 16 samples of leaves and roots and 14 samples of flowers of the wild-growing plants representing to populations from a forest-steppe zone of Western Siberia. It is established that the maximum maintenance of flavonoids in leaves and flowers characterizes plants Alchemilla vulgaris (5,0 and 4,8%) and Filipendula vulgaris (3,8 and 8,3%), accordingly

Designing universal primers for the isolation of DNA sequences encoding Proanthocyanidins biosynthetic enzymes in Crataegus aronia

BackgroundHawthorn is the common name of all plant species in the genus Crataegus, which belongs to the Rosaceae family. Crataegus are considered useful medicinal plants because of their high content of proanthocyanidins (PAs) and other related compounds. To improve PAs production in Crataegus tissues, the sequences of genes encoding PAs biosynthetic enzymes are required.FindingsDifferent bioinformatics tools, including BLAST, multiple sequence alignment and alignment PCR analysis were used to design primers suitable for the amplification of DNA fragments from 10 candidate genes encoding enzymes involved in PAs biosynthesis in C. aronia. DNA sequencing results proved the utility of the designed primers. The primers were used successfully to amplify DNA fragments of different PAs biosynthesis genes in different Rosaceae plants.ConclusionTo the best of our knowledge, this is the first use of the alignment PCR approach to isolate DNA sequences encoding PAs biosynthetic enzymes in Rosaceae plants.

Molecular characterization and expression analysis of chalcone synthase gene during flower development in tree peony ( Paeonia suffruticosa )

Chalcone synthase (CHS, EC: 2.3.1.74) is a key enzyme in the flavonoid and anthocyanin biosynthesis pathway. In order to investigate the role of CHS in tree peony flower coloration mechanism, we isolated and characterized the CHS gene from Paeonia suffruticosa cv. Yu Ji Yan Zhuang and analyzed its spatial and temporal expression patterns during floral development. The cDNA sequence of the CHS gene in P. suffruticosa (Ps-CHS 1, genbank accession no. GQ483511) was 1475 bp in full length containing an opening reading frame (ORF) of 1185 bp that encoded a 394 amino acid polypeptide. Bioinformatic analysis showed that, Ps-CHS1 possessed all the conserved active sites for the CHS function as well as the family signature. Sequence alignment and phylogenetic analysis revealed that Ps-CHS1 shared high homology with CHS from plants in Salicaceae, Malvaceae and Rosaceae. The homology-based structural modeling showed that Ps-CHS1 had the typical structure of CHS. Southern blot analysis indicated that CHS was encoded by a small multigene family in the genome of tree peony. Anthocyanidin content in full-opening flower petals accumulated to the highest level. Real-time polymerase chain reaction amplification (PCR) analysis indicated that, Ps-CHS 1 showed the highest transcript abundance in petals, moderate levels in sepals, low levels in leaves and stamens, and the lowest levels in carpels. Ps-CHS 1 was actively expressed during flower development and increased gradually until reached maximal expression when flower fully opened. These results indicated that PsCHS 1 was involved in the flower pigmentation of tree peony.

Systematics of genus Gnomoniopsis (Gnomoniaceae, Diaporthales) based on a three gene phylogeny, host associations and morphology

Species of Gnomoniopsis are leaf- and stem-inhabiting pyrenomycetes that infect plants in Fagaceae, Onagraceae and Rosaceae. Morphology and analyses of DNA sequences from three ribosomal DNA and protein coding regions, namely β-tubulin, translation elongation factor 1α (tef-1α) and the ITS region including ITS1, 5.8S rDNA and ITS2, were used to define species in Gnomoniopsis. Secondary structural alignment of the ITS region across four genera in Gnomoniaceae was used to increase the potential number of homologous positions in the ITS alignment. Ascospore isolates were grown from newly collected specimens. Type specimens were compared with these specimens to determine their identity. In this paper a recent concept of Gnomoniopsis is confirmed with phylogenetic resolution of additional species. Four new combinations and one new species are proposed. Nine species are described and illustrated, and a key is provided to the 13 species currently recognized in Gnomoniopsis.

Development and population growth of Stephanitis pyri (F.) (Heteroptera: Tingidae) at five temperatures

Pear lace bug, Stephanitis pyri (F.) (Heteroptera: Tingidae) is a pest of apple and pear trees and ornamental Rosaceae plants in Mediterranean countries and palearctic region. The aim of this study is to determine the effects of temperatures on S. pyri in the laboratory. Development and fecundity of S. pyri reared on apple leaves (Pyrus malus L.) were investigated at five constant temperatures (20, 23, 26, 29 and 32 ± 1°C) and a 16L:8D photoperiod. Longevity was determined to be 12.6 days at 32°C and 58.7 days at 20°C for females, and 9.7 and 37.7 days for males. Females laid 186.9 eggs per female with the highest number achieved during 28.5 days of oviposition period at 26°C. Female lifetime fecundity was reduced at 32°C (40.0 eggs per female). While the net reproductive rate (R0) was highest at 26°C, the intrinsic rate of natural increase (rm) was highest at both 26 and 32°C. The mean generation time (G) was estimated to be 27.2–78.4 days at 20 and 32°C, respectively. The longest development times for egg and total nymph stages were obtained as 22.0 and 24.9 days, respectively, at 20°C. S. pyri developed fastest from egg to egg in 24.3 days at 32°C. The lower developmental threshold (T0) was 9.7°C and the thermal constant (K) was 517.3 degree-days for S. pyri. Thus, S. pyri is calculated to have 3.8 theoretical generations in Tekirdag. The optimum developmental temperature for S. pyri was 26°C.

The phytoalexin-inducible multidrug efflux pump AcrAB contributes to virulence in the fire blight pathogen, Erwinia amylovora.

The enterobacterium Erwinia amylovora causes fire blight on members of the family Rosaceae, with economic importance on apple and pear. During pathogenesis, the bacterium is exposed to a variety of plant-borne antimicrobial compounds. In plants of Rosaceae, many constitutively synthesized isoflavonoids affecting microorganisms were identified. Bacterial multidrug efflux transporters which mediate resistance toward structurally unrelated compounds might confer tolerance to these phytoalexins. To prove this hypothesis, we cloned the acrAB locus from E. amylovora encoding a resistance nodulation division-type transport system. In Escherichia coli, AcrAB of E. amylovora conferred resistance to hydrophobic and amphiphilic toxins. An acrB-deficient E. amylovora mutant was impaired in virulence on apple rootstock MM 106. Furthermore, it was susceptible toward extracts of leaves of MM 106 as well as to the apple phytoalexins phloretin, naringenin, quercetin, and (+)-catechin. The expression of acrAB was determined using the promoterless reporter gene egfp. The acrAB operon was up-regulated in vitro by the addition of phloretin and naringenin. The promoter activity of acrR, encoding a regulatory protein involved in acrAB expression, was increased by naringenin. In planta, an induction of acrAB was proved by confocal laser scanning microscopy. Our results strongly suggest that the AcrAB transport system plays an important role as a protein complex required for virulence of E. amylovora in resistance toward apple phytoalexins and that it is required for successful colonization of a host plant.

Assimilation of Nitrogen Dioxide in Selected Plant Taxa

AbstractThe production of a novel “nitrogen‐dioxide‐philic plant” that can grow with NO2 as the sole nitrogen source was investigated as a possible solution to pollution. 217 plant taxa were screened for the assimilation of NO2, among them 50 wild herbaceous plants collected from roadsides, 60 cultivated herbaceous plants and 107 cultivated woody plants. It was discovered that the NO2‐derived reduced nitrogen [μg N/mg dry weight] differed by a factor of 657 between the highest (Eucalyptus viminalis, 6.57) and lowest (Tillandsia ionantha and T. caputmedusae, 0.01) level in the 217 taxa. The capability of plants to assimilate NO2 was also found to change in a family‐dependent manner. Compositae, Myrtaceae, Salicaceae and Solanaceae had taxa with high NO2 assimilation capability, while none of the Gramineae, Theaceae and Rosaceae plants examined showed high NO2 assimilation capability. The 217 taxa included two species of the Solanaceae family (tobacco and petunia), both of which showed a high NO2 assimilation and their reduced nitrogen derived from NO2 was the third and twenty‐sixth highest. This suggested that the Solanaceae family includes plants of high NO2 assimilation.Therefore, in this study eight taxa of the Solanaceae family and four taxa of other families were investigated for NO2 assimilation in the same manner as reported previously by the fumigation of plants with 15N‐labelled NO2 followed by the mass spectroscopic analysis based upon the reduced nitrogen derived from NO2. The eight taxa Solanaceae included tobacco (Nicotiana tabacum) and petunia (Petunia X hybrida), ground cherry (Physalis alkekengi var. franchetii), tomato (Lycopersicon esculentum), datura (Datura innoxia), potato vine (Solanum jasminoides), red pepper (Capsicum annuum) and green pepper (Capsicum annuum var. grossum SENDTN.). The four taxa included two ivy cultivars (Hedera helix “Pittsburgh” and Hedera helix “Wonder”), an evergreen creeper (Ficus thunbergii) and kenaf (Hibiscus cannabinus).Among the twelve taxa, kenaf, tobacco and ground cherry showed the highest, second and third highest values, respectively, of reduced nitrogen derived from NO2 in plants, which reflects the capability to assimilate NO2‐nitrogen. The quantitative significance of these findings is discussed in relation to the reduction of nitrogenous pollution by the atmospheric NO2 pollution.

The nectary as the primary site of infection by Erwinia amylovora (Burr.) Winslow et al.: a mini review

Erwinia amylovora is the causative agent of fire blight, a bacterial disease existing as an unsolved problem in most countries where pome fruits like apple (Malus domestica) and pear (Pyrus communis) or ornamental plants of Rosaceae are grown. The primary site of colonization is the open flower. As for the establishment of the disease, the importance of various organs within the flowers is considerably different. The usual place for developing a large epiphytic population is the stigma. The actual infection will be attained by the external washing (rain, heavy dew) of bacteria from the stigma to the hypanthium. The bacteria penetrate through the openings of the nectary, so, the nectarthodes are the main entrance sites for them. Nectar is an excellent medium for growth of fire blight bacteria. Most often, however, the incidence of disease is significantly less than the percentage of colonized flowers. Little is known about the interrelationships of free mois- ture, nectar sugar concentration, ovary water potential, fine-structural characteristics of nectary versus the disease incidence and severity. The aim of this paper is to review the ecology and infection biology of Erwinia amylovora on floral surfaces and in floral tissues.

Ribonuclease inhibitors in Malus x domestica (common apple): isolation and partial characterization.

A ribonuclease inhibitory activity was detected in the fruits of common apple, Malus x domestica, cv. Fuji, and purified by affinity chromatography on ribonuclease A-Sepharose. It inhibited hydrolysis of cyclic-2':3'-CMP by bovine pancreatic ribonuclease A with an apparent inhibition constant of about 5 x 10(-8) M. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of the purified protein gave two peaks corresponding to the mass numbers of 55,658 and 62,839, while three bands of 43-, 34-, and 21-kDa were detected by SDS-PAGE. These results suggested that the inhibitor preparation was a mixture of two proteins comprised of 43- and 21-kDa subunits or of 34- and 21-kDa subunits. Attempts to separate these two proteins were unsuccessful. Amino acid composition and N-terminal amino acid sequence of these subunits were also identified and N-terminal sequences showed some similarity to that of cottonseed storage globulin. The significance of the presence of ribonuclease inhibitors in apple fruits is not clear, but it might allow some speculation about their possible involvement in the control of the self-incompatibility ribonuclease of Rosaceae plants.