Overexpression of auxin/indole-3-acetic acid gene MdIAA24 enhances Glomerella leaf spot resistance in apple(Malus domestica)

Auxin is throughout the entire life process of plants and is involved in the crosstalk with other hormones,yet its role in apple disease resistance remains unclear.In this study,we investigated the function of auxin/indole-3-acetic acid(IAA)gene Md IAA24 overexpression in enhancing apple resistance to Glomerella leaf spot(GLS)caused by Colletotrichum fructicola(Cf).Analysis revealed that,upon Cf infection,35S::Md IAA24 plants exhibited enhanced superoxide dismutase(SOD)and peroxidase(POD)activity,as well as a greater amount of glutathione(reduced form)and ascorbic acid accumulation,resulting in less H_(2)O_(2)and superoxide anion(O_(2)^(-))in apple leaves.Furthermore,35S::Md IAA24 plants produced more protocatechuic acid,proanthocyanidins B1,proanthocyanidins B2 and chlorogenic acid when infected with Cf.Following Cf infection,35S::Md IAA24 plants presented lower levels of IAA and jasmonic acid(JA),but higher levels of salicylic acid(SA),along with the expression of related genes.The overexpression of Md IAA24 was observed to enhance the activity of chitinase andβ-1,3-glucanase in Cfinfected leaves.The results indicated the ability of Md IAA24 to regulate the crosstalk between IAA,JA and SA,and to improve reactive oxygen species(ROS)scavenging and defense-related enzymes activity.This jointly contributed to GLS resistance in apple.

Isolation of Trichoderma virens 6PS-2 and its effects on Fusarium proliferatum f. sp. Malus domestica MR5 related to apple replant disease in China

Apple replant disease(ARD) is primarily caused by biotic factors that seriously inhibits the development of apple industry. Therefore, the use of biological control measures to inhibit the main pathogens(such as Fusarium spp.) that cause ARD is of great significance to the sustainable development of the apple industry. Trichoderma virens 6PS-2, which exhibited antagonism toward a variety of pathogens, was screened from the rhizosphere soils of healthy apple trees(Malus robusta) in different replanted orchards in the Yantai and Zibo Cities, Shandong Province, China. Its fermentation extract inhibited the growth of pathogenic Fusarium proliferatum f. sp. Malus domestica MR5, which was proportional to the concentration. These substances also increased the hairy root volume and growth of Arabidopsis thaliana lateral roots. The phenotype of Malus hupehensis seedlings and microbial community structure in rhizosphere soils in greenhouse experiment using Highthroughput sequencing were analyzed, and the field experiment with grafted apple trees were used for further verification. Compared with the application of potato dextrose broth(PDB) medium, application of 6PS-2 spore suspension directly to replanted soils could improve the growth of M. hupehensis seedlings as well as the elongation of grafted apple trees. Concomitant decreases in the gene copy number of Fusarium and increases in the culturable bacteria/fungi were also observed in the greenhouse and field experiments. The abundance of Trichoderma,Bacillus, and Streptomyces increased significantly, but that of Fusarium, Pseudarthrobacter, and Humicola decreased. The content of esters, phenols,furans, and amino acids in root exudates of M. hupehensis seedlings increased, which significantly inhibited the multiplication of Fusarium, but was positively correlated with Bacillus and Trichoderma. In summary, T. virens 6PS-2 not only directly inhibits the activity of pathogenic Fusarium but also secrets secondary metabolites with antifungal and growth-promoting potential. In addition, 6PS-2 spore suspension can also promote the growth of plants to a certain extent, and change the soil microbial community structure of rhizosphere soils. It is believed that T. virens 6PS-2 has the potential for the alleviation of apple replant disease(ARD) in China.

Genetic Diversity of Volatile Components in Xinjiang Wild Apple (Malus sieversii)

To evaluate genetic relationships using qualitative and/or quantitative differentiation of volatile components in Xinjiang Wild Apple （Malus sieversii （Lebed.） Roem.） and to acquire basic data for the conservation and utilization of the species, aroma components in ripe fruit of M. sieversii obtained from 30 seedlings at Mohe, Gongliu County, Xinjiang Autonomic Region, China, and in ripe fruit of 4 M. purnila cultivars （＇Rails＇, ＇Delicious＇, ＇Golden Delicious＇, and ＇Fuji＇） were analyzed using head space-solid phase microextraction and gas chromatography-mass spectrometry. The results indicated that the values of similarity coefficient concerning volatile types between the two species were in accordance with the evolution of M. pumila cultivars （forms）, and that M. sieversii seedlings showed considerable genetic variations in these aspects： the total content of volatile components, the classes and contents of each compound classes, the segregation ratio, and content of main components. The results showed significant difference among seedlings and wide genetic diversity within the populations. Comparison of the volatile components in M. sieversii with those in M. pumila cultivars showed that the common compounds whose number were larger than five with the contents over 0.04 mg/L simultaneously between M. sieversii and M. pumila cultivars belonged to esters, alcohols, aldehydes or ketones. This suggests fundamental identity in main volatile components of M. sieversii and M. pumila cultivars. The results above sustained the conclusion ＂M. sieversii is probably the ancestor ofM. purnila＂. However, there were 48 compounds present in M. puraila that were not detected in M. sieversii, including 6 character impact components （i.e., propyl acetate, （Z）-3-hexenal, 2-methyl-l-butanol acetate, pentyl acetate, 3-furanmethanol, and benzene acetaldehyde）. This suggested that in the domestication of M. pumila, introgression of other apple species, except for M. sieversii, by interspecies hybridization was possible. There were 177 compounds in total belonging to 11 classes detected in 30 M. sieversii seedlings, including esters, alcohols, ketones, aldehydes, acids, benzene ramifications, terpenes, heterocycles, hydrocarbon derivates, acetals, and lactones. Among them, acetals and lactones were not detected in M. pumila cultivars, 90 compounds were unique to M. sieversii, and 7 components （l-butanol, ethyl hutanoate, 1-hexanol, ethyl hexanoate, 3-octen-1-ol, ethyl octanoate, and damascenone） belonged to character impact odors. Thus, the potential of M. sieversii in ＂utilization conservation＂ is enormous as a rate germplasm on genetic improvement of M. pumila cultivars.

Aroma Volatile Compound Analysis of SPME Headspace and Extract Samples from Crabapple (Malus sp.) Fruit Using GC-MS

Volatile compounds from the ripened crabapple fruit of six varieties （Red Splendor, Strawberry Parfait, Pink Spire, Radiant, Sparkler, and Flame） were analyzed by the use of the SPME/GC/MS method. The changes in the volatiles between the ripened and upon full maturity fruit states were studied in Red Splendor and Strawberry Parfait. An effort was made to summarize an effective method for searching and identifying new idioplasms containing a particular fruit aroma within Malus. A total of 37 compounds were identified from the sample. The main aroma volatiles of the six varieties of fruit were comprised of 2-hexenal, 3-hexenal, hexanal, 2,4-hexadienal, benzaldehyde, diethyl phtbalate. The main volatile compound of the crabapple fruit was 2-hexenal, but the relative content percentages were different （45.37, 21.98, 33.56, 32.21, 38.60, and 45.88%）. The aroma components accumulated differently as the fruits ripened. The relative content of aldehydes and esters decreased as alcohols increased after the Red Splendor and Strawberry Parfait fruit ripened. For Red Splendor, the main volatile was still 2-hexenal, but the relative content decreased to 42.89%, and the relative content of alcohols increased by 13.86% as aldehydes and esters declined by 12.16 and 7.18%, respectively. For Strawberry Parfait, the main volatile was changed to cyclohexanol, and the relative content increased to 46.43%, while the relative content of alcohols increased by 49.03% as aldehydes and esters declined by 23.74 and 9.34%, respectively.

Molecular characterization of Apple necrotic mosaic virus identified in crabapple(Malus spp.) tree of China

Apple necrotic mosaic virus(ApNMV) was identified in crabapple trees with mosaic symptoms from Zaozhuang, Shandong Province, China, by reverse transcription polymerase chain reaction(RT-PCR) analysis. The complete nucleotide sequences of one isolate from crabapple(ApNMV-Hai) and two isolates from apple(ApNMV-Hua and-Qu) were determined. The sizes of genomic RNA1, 2 and 3 of the three isolates differed from those of the previously reported isolate ApNMV-P126 from Japanese apple, especially RNA3. Compared with the nucleotide(nt) sequence of RNA3 in isolate P126, those in the Hai and Qu isolates were 7 and 33 nt shorter, respectively, and that of isolate Hua was 7 nt longer. Alignment analyses showed that these differences in size were mainly due to differences in the lengths of the 5′ untranslated region(UTR) and the UTR region between the ORFs encoding the movement protein and the coat protein. In the phylogenetic trees constructed using the full genomic sequences of RNA1, 2 and 3, the isolate Hai clustered into a group with the isolate Qu in the RNA1 tree, but formed an individual branch in the RNA2 and 3 trees. Three recombination events were identified in the nucleotide sequences of RNA1 and 2 among the isolates ApNMV-Hai,-Hua, and-Qu. This is the first report of the full genome sequence of ApNMV in crabapple.

The Growth-Promoting Mechanism of Brevibacillus laterosporus AMCC100017 on Apple Rootstock Malus robusta

Plant growth-promoting rhizobacteria(PGPR) located in rhizobacteria soil are beneficial to plant growth and development. A PGPR strain AMCC100017 of Brevibacillus laterosporus synthesizes the plant hormone IAA in a tryptophan-dependent manner. In this study, the AMCC100017 strain was used to treat Malus robusta, an excellent natural rootstock for apple production, and assess its ability to promote growth. The fresh weight, dry weight, plant height, and lateral root growth of M. robusta were significantly increased with treatment. The presence of the AMCC100017 strain increased IAA content in M. robusta and promoted root secretion of tryptophan. Colonization of the strain in the roots allowed continuous synthesis of IAA and promoted plant growth. In addition, the photosynthetic efficiency in leaves increased after microbial treatment, and the utilization of nitrogen, zinc, iron, copper and magnesium in leaves was increased, which was conducive to photosynthesis.Interestingly, the activities of CAT and SOD, as well as the contents of ROS in plants colonized by AMCC100017 were increased compared to control plants, but the activities of POD and MDA contents were decreased. AMCC100017 strain affected the antioxidant capacity and stress resistance of plants. AMCC100017 strain increased the content of soluble protein and soluble sugar in plants, improved plant metabolic activity and stress resistance. Therefore, AMCC100017 not only increased IAA content and photosynthetic efficiency to promote M. robusta growth, but also affected plant through multiple metabolic pathways.

Forecasting Fruit Diameter of ‘Fuji' Apples (Malus pumila Mill)at Harvest During Early Growing Season

The fruit growth evolution on 35 tagged 'Fuji' apple trees was studied in three successive growing seasons from 1994 to 1996 to explore a new method for forecasting the fruit diameter at harvest during early growing season. Daily fruit growth rate (DFGR) (based on fruit diameter, fruit dry weight, fruit fresh weight, or fruit volume) during the early growing season, 30 - 50 d after full bloom (DAFB), or during mid-growing season (60-120 DAFB), displayed a strong positive linear correlation with the fruit diameter at harvest, and the correlation between the fruit diameter at harvest and DFGR during early and mid-growing season was much better than that between the fruit diameter at harvest and either fruit diameter at a given time or the relative growth rate during early or mid-growing season. The fruit diameters obtained in the field were compared with the mean fruit diameters estimated based on different criteria, such as DFGRs (based on fruit diameter, fruit dry weight, fruit fresh weight, or fruit volume) during early and mid-growing season, and fruit diameter at 120 DAFB. Results showed that daily growth rate of fruit diameter during 30 - 50 DAFB was the best criterion for forecasting fruit diameter at harvest. There was no significant difference in mean fruit diameter between the value measured in the field at harvest and that estimated based on the daily growth rate of fruit diameter during 30 - 50 DAFB (equations for forecasting: y = 153.571 x + 73.492) either for the individual trees or for different vigor groups of trees. Daily growth rate of fruit diameter during 30 - 50 DAFB can be used as the basis for forecasting fruit diameter at harvest.

Calcium Forms, Subcelluar Distribution and Ultrastructure of Pulp Cells as Influenced by Calcium Deficiency in Apple (Malus pumila) Fruits

Calcium in Red Fuji and Starkrimson apples during storage were fractionated by sequentextracting. Localization and distribution of calcium and influence of calcium nutritionon cell ultrastructure were observed by transmission electron microscopy combined within situ precipitation of calcium with an improved method of potassium pyroantimonatetechnique. Results indicated that spraying calcium solution on surface of young fruitsincreased contents of calcium in all forms. During storage, contents of soluble calciumand pectic calcium declined and those in calcium phosphate, calcium oxalate and calciumsilicate increased. Calcium contents of Red Fuji in all forms were higher than those ofStarkrimson, indicating that calcium accumulating capability of Red Fuji fruits precededthat of Starkrimson. Under transmission electron microscopy, calcium antimonite precipitates(CaAP) was mainly distributed in cell wall, tonoplast, nuclear membrane and nucleoplasm,much more CaAP deposited in vacuole. Calcium deficiency during storage leads to decreaseof CaAP in locations mentioned above, disappearance of compartmentation, and entrance ofCaAP to cytoplasm. Transformation from soluble calcium and pectic calcium to calciumphosphate, oxalate and damages of biomembranes structuraly and functionally resultedfrom calcium deficiency during storage were the crucial causation of physiologicaldisorder.

An apple (Malus domestica) AP2/ERF transcription factor modulates carotenoid accumulation

Color is an important trait for horticultural crops.Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health.Here,we identified an APETALA2(AP2)/ETHYLENE RESPONSE FACTOR(ERF)transcription factor named MdAP2-34 in apple(Malus domestica Borkh.).MdAP2-34 expression exhibited a close correlation with carotenoid content in‘Benin Shogun’and‘Yanfu 3’fruit flesh.MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway.The major carotenoid contents of phytoene andβ-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin,yet the predominant compound of lutein showed no obvious difference,indicating that MdAP2-34 regulates phytoene andβ-carotene accumulation but not lutein.MdPSY2-1(phytoene synthase 2)is a major gene in the carotenoid biosynthesis pathway in apple fruit,and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34.In addition,overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents.Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple,and this research is valuable for accelerating the apple breeding process.

Genome-wide identification of the radiation sensitivity protein-23(RAD23)family members in apple(Malus×domestica Borkh.)and expression analysis of their stress responsiveness

Radiation sensitivity proteins-23 （RAD23） are DNA repair factors participate in the ubiquitin/proteasome system （UPS）. Although the genome-wide analysis of RAD23 family members has been conducted in some species, little is known about RAD23 genes in apple （Malusxdomestica Borkh.）. We analyzed this gene family in M. domestica in terms of genomic locations, protein and promoter structures, and expressions in response to stresses. Various members showed a ubiqui- tous pattern of expression in all selected apple parts. Their expressions were altered under chilling, heat, and hydrogen peroxide treatments, as well as abscisic acid （ABA） treatment and water deficiency, suggesting their possible roles in plant stress responses. These results provide essential information about RAD23 genes in apple and will contribute to further functional studies.

Identification and expression of the CEP gene family in apple (Malus×domestica)

Plant peptide hormones play important roles in plant growth and development. Among these hormones, the C-TERMINALLYENCODED PEPTIDE（CEP） belongs to a newly found peptide family that regulates root development in Arabidopsis as well as in other species. However, nothing is known about the CEP genes in apple（Malus×domestica, MdCEP）. In this study, a total of 27 apple CEP genes were identified through a genome-wide analysis and were phylogenetically divided into three classes（Ⅰ, Ⅱ and Ⅲ）. The predicted MdCEP genes were distributed across 10 of 17 chromosomes with different densities. Next, the gene structures and motif compositions of the MdCEP genes were analyzed. Subsequently, the expression analysis suggested that the MdCEP genes were highly activated in roots and that MdCEP23 may play an important role in regulating the growth and development of roots. Moreover, all of the MdCEP genes were responsive to multiple abiotic stresses, indicating that MdCEP genes may be involved with various aspects of physiological processes in apple. Nearly one-third of MdCEP genes had a significant response to low nitrogen treatment. Most of the MdCEP genes were up-regulated under stress, including mannitol, polyethylene glycol（PEG） and abscisic acid（ABA）, suggesting that MdCEP genes may be involved in the drought stress response. This study provides insight into the putative functions of the MdCEP genes using a genome-wide analysis of the CEP gene family.

Analysis of Leaf Volatiles of Crabapple (<i>Malus</i>sp.) Individuals in Different Aphids’ Resistance

The aim of this experiment was to analyze the leaf volatiles of crabapple (Malus sp.) individuals at different aphid’s resistance, to ascertain the particular ingredients which has lure or aversion effects on aphid, and to provide reference for finding out a simple method to control effectively aphids. Volatiles of leaves from twenty-one different crabapple individuals were evaluated with the method of head space-solid phase micro-extraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS). Volatiles profiles of them were then compared. There are one hundred eighty-six kinds of volatiles were detected with varied contents found in different individuals. And all plants contain eight kinds of common components: 3-Hexen-1-ol, acetate, (Z)-, 4-Hexen-1-ol, (Z)-, n-Decanal, n-Tetradecane, .alpha.-Farnesene, Diethyl Phthalate, Oxime-, methoxy-phenyl- and Dibenzofuran-, wherein the relative content of higher have 3-Hexen-1-ol, acetate, (Z)- and 4-Hexen-1-ol, (Z)-. Specific volatile substances in high resistance plants contain 3-Hexenal, (Z)- and 2-Hexenal, (E)-. Leaf volatiles differ in twenty-one crabapple individuals. High resistance plants specific volatile substances contains 3-Hexenal, (Z)-, 2-Hexenal, (E)- and other small molecular volatile substances, and no-resistance plants all have .beta.-Farnesene.

Genome-wide identification and expression analyses of homeodomain-leucine zipper family genes reveal their involvement in stress response in apple(Malus×domestica)

The homeodomain-leucine zipper(HD-Zip)family has been shown to perform amultitude of functions during plant development and stress responses;however,the familymembers and functions have not been identified in apple(Malus×domestica).In this study,83 HD-Zips(MdHDZs)were identified in the apple genome.They were assembled into four subgroups according to the classification in Arabidopsis,where MdHDZs in the same subgroup had similar gene structures and conserved protein motifs.Putative cis-element analysis of MdHDZs promoter regions uncovered numerous elements related to the response of stress and plant hormones.In addition,twelve transcripts of the MdHDZs showed different expression patterns under salt,drought,low temperature and ABA stresses by quantitative reverse transcription-PCR(qRT-PCR)assay.To further explore the function of MdHDZs in apple,MdHDZ3 was selected to verify its function under salt,low temperature and ABA stresses;and genetic transformation was used to obtain MdHDZ3 transgenic apple calli.The results demonstrated that MdHDZ3 increased sensitivity to salt,low temperature and abscisic acid in apple calli,suggesting that MdHDZ3 plays an important role in response to stresses.Subcellular localization and three-dimensional structural analysis revealed that MdHDZ3 was a nuclear-localized protein.Taken together,these findings provide potential information for further identification of HD-Zip proteins in apple.

Influences of open-central canopy on photosynthetic parameters and fruit quality of apples(Malus×domestica)in the Loess Plateau of China

Although open-central canopy(OCC)is popular in apple(Malus×domestica)orchards in Loess Plateau of China,its relevant photosynthetic mechanisms have not been elucidated.In this study,changes in photosynthetically active radiation(PAR),gas exchange,chlorophyll fluorescence quenching and fruit quality in apple trees were measured in OCC and compared with those in the conventional condensed round and large canopy(RLC).Results showed that light intercepted at different orientations was 44%higher by OCC than that by RLC.The improved light environment within OCC remarkably increased leaf maximum net photosynthetic rate(Pnmax)and significantly decreased stomatal limitation.Under high light,the ratio of photorespiratory rate to gross photosynthetic rate(Pr/Pg)in OCC was higher than that in RLC.Moreover,reversible component in non-photochemical quenching(r(qE))was increased,while irreversible component(r(qI))was decreased in OCC than in RLC.As a result,the fruit quality in OCC was greatly boosted as evidenced by the significantly increased single fruit weight,fruit flesh firmness and fruit soluble solid contents and the sharply decreased fruit titratable acid contents.PAR intercepted by the canopy and the fruit soluble solid contents,leaf Pnmaxor single fruit weight were positively correlated,while PAR or Pnmaxwas negatively correlated with the fruit titratable acid contents.Accordingly,the improved crown light environment and the enhanced leaf photosynthetic performance and photoprotective capacity in OCC led to the boosted fruit quality.

Genetic and environmental control of fruit maturation,dry matter and firmness in apple(Malus×domestica Borkh.)

For any given genotype,the environment in which an apple is grown can influence the properties of the fruit considerably.While there has been extensive research on the mechanism of the genetic control of fruit quality traits,less effort has been made to investigate the way that these genetic mechanisms interact with the environment.To address this issue,we employed a large‘Royal Gala’בBraeburn’population of 572 seedlings replicated over sites in three climatically diverse apple-growing regions in New Zealand.Phenotyping for traits including fruit maturation timing,firmness and dry matter content was performed at each of these three sites for a single growing season(2011),and at two sites(Motueka and Hawke’s Bay)for two seasons(2009 and 2010).The phenotype data collected over 2 years at two sites enabled the detection of 190 quantitative trait loci(QTL)that controlled these traits regardless of year or growing location,as well as some chromosomal loci that influenced the traits in a single given environment or year.For those loci that were environmentally stable over three sites,there was an interdependency of fruit maturation date,dry matter content and storage potential within this population,with two regions on Linkage Groups(LGs)10 and 16 strongly contributing.If these loci were used in a marker-assisted selection programme to select for progeny bearing firmer fruit,this would have the unintentional consequence of selecting,high dry matter content,later maturing apples.In addition,a further 113 new QTLs with a smaller effect were identified,some of which were exhibited only in a single growing environment,demonstrating the underlying complexity of control of traits determining fruit quality,in addition to the need for being aware of environmental effects when developing new apple varieties.

Effects of Exogenous Manganese (Mn) on Mineral Elements, Polyamines and Antioxidants in Apple Rootstock Malus robusta Rehd.

Manganese(Mn)is one of the essential microelements in all organisms.However,high level of Mn is deleterious to plants.In this study,the effects of exogenous manganese application on mineral element,polyamine(PA)and antioxidant accumulation,as well as polyamine metabolic and antioxidant enzyme activities,were investigated in Malus robusta Rehd.,a widely grown apple rootstock.High level of Mn treatments decreased endogenous Mg,Na,K and Ca contents,but increased Zn content,in a Mn-concentration-dependent manner.Polyamine metabolic assays revealed that,except the content of perchloric acid insoluble bound(PIS-bound)spermine,which increased significantly,the contents of putrescine(Put),spermidine(Spd)and spermine(Spm)all decreased progressively,accompanied with the decreased activities of arginine decarboxylase(ADC,EC 4.1.1.19)and ornithine decarboxylase(ODC,EC 4.1.1.17),and the increased activities of diamine oxidase(DAO,EC 1.4.3.6)and polyamine oxidase(PAO,EC 1.5.3.3).Further antioxidant capacity analyses demonstrated that contents of anthocyanin,non-protein thiols(NPT)and soluble sugar,and the activities of guaiacol peroxidase(POD,EC 1.11.1.7),catalase(CAT,EC 1.11.1.6)and superoxide dismutase(SOD,EC 1.15.1.1),also increased upon different concentrations of Mn treatments.Our results suggest that endogenous ion homeostasis is affected by high level of Mn application,and polyamine and antioxidant metabolism is involved in the responses of M.robusta Rehd.plants to high level of Mn stress.

Effects of Abscisic Acid on Drought Resistance in Apple Rootstock Malus baccata Seedlings

[Objective] Abscisic acid （ABA）, a plant endogenous hormone, plays an important role in plant responses to adverse environments. This study was to explore the effects of exogenous ABA on the drought resistmlce of apple rootstocks under simulated drought condition induced by polyethylene glycol （PEG）. [Method] Apple （Malus baccata） seedlings were employed as test material. There were five treatments （T1-5） designed as ABA application rates at 0 （T1）, 25 （T2）, 50 （T3）, 75 （T4） and 100 （T5） μmol/L in the hydroponic experiments. The changes of the relative leaf water content （RLWC）, root activity, malondialdehyde （MDA） content, proline （Pro） content, superoxide dismutase （SOD） activity and peroxidase （POD） activity were assayed under PEG stress. All indices were analyzed by principal component analysis （PCA） to evaluate the optimal ABA concentration alleviating drought stress. [Result] The different concentration of ABA could increase Pro content and antioxidant enzyme activities, relieve the descent of RLWC and decrease MDA content. Low levels of ABA increased root activity, whereas the high concentrations （T3-T5） inhibited it. Statistical analysis based on the PCA indicated that the cumulative contribution rate of the first two principal components was raised to 96.457%, and the PCA in the T2 scored the highest. [Conclusion] The exogenous ABA could decrease the damage caused by drought stress to Malus baccata seedlings and enhance the ability of drought tolerance by increasing osmolyte content, anti- oxidative enzyme activity and reducing the level of membrane lipid peroxidation. The optimal concentration of ABA was 25 μmol/L.

Genome-wide identification and functional characterization of the MdCLE peptide family in apple(Malus×domestica)

The CLAVATA3/EMBRYO SURROUNDING REGION-related(CLE)peptides are critical for stem cell homeostasis in plant shoot and root apical meristem.Although CLE genes have been reported in numerous plants,there is limited information for apple.Here,twenty-five MdCLE genes were identified fromapple genome(Apple Genome V1.0 predicted peptides).Analysis of chromosomal location showed that the 25 MdCLE genes were located on 12 of 17 apple chromosomes.Genetic structure analysis showed that 21 of 25 the MdCLE genes were intron-free.Expression patterns showed thatmost of the MdCLE genes showed higher expression levels in leaves and root compared with the other tissues.In addition,expression analysis demonstrated that MdCLE genes had different gene expression patterns for abiotic stress treatment,suggesting their potential roles in acclimation of apple to adverse environments.The 25 MdCLE genes encoded 19 different CLE peptides,and they were divided into two groups depending on their effects on the inhibition of Arabidopsis root growth.Our results suggest that MdCLE genesmay have an important but redundant function in regulating plant growth and development,and this work provides valuable references for further investigation of the biological functions of MdCLE genes.

Some Aspects of Physical-mechanical Properties of Apple (Malus domestica) Cultivars for High Techniques in Manufacturing

Several mechanical and physical properties of five apple cultivars(Black, Apricot, Jester, Big Ariane and Medium Ariane) had been estimated. The results showed that there were important significant differences among the cultivars in most of the parameters that were measured. Among the cultivars, Black cultivar had the highest fruit mass(207.65 g), followed by Big Ariane(188.34 g) and Medium Ariane(137.49 g). The actual fruit volume(cm~3) ranged from 61.77(Apricot) to 269.67(Black). The highest geometric, arithmetic, square and equivalent mean diameter values were observed for Big Ariane. The surface area and projected area of cultivars were between 14.53-69 cm~2 and 45.56-165.33 cm~2, respectively. The maximum coefficient of static friction was obtained on plastic followed by steel, iron and glass; the maximum coefficient of dynamic friction was obtained on glass followed by steel, plastic and iron.

Physical mapping of three fruit ripening genes: Endopolygalacturonase, ACC oxidase and ACC synthasefrom apple (Malus x domestica) in an apple rootstock A106 (Malus sieboldii)

The apple rootstock, A106 (Malus sieboldii), had 17 bivalents in pollen mother cells at meiotic metaphase 1,and 17 chromosomes in a haploid pollen cell. Karyotypes were prepared from root-tip cells with 2n= 34 chromosomes. Seven out of 82 karyotypes (8.5%) showed one pair of satellites at the end of the short arm of chromosome 3. C-bands were shown on 6 pairs of chromosomes 2, 4,6, 8, 14, and 16 near the telomeric regions of short arms.Probes for three ripening-related genes from Malus x domestica: endopolygalacturonase (EPG,0. 6 kb ) , ACC oxidase (1.2 kb), and ACC synthase (2 kb) were hybridized in situ to metaphase chromosomes of A106. Hybridization sites for the EPG gene were observed on the long arm of chromosome 14 in 15 out of 16 replicate spreads and proximal to the centromere of chromosomes 6 and 11. For the ACC oxidase gene, hybridization sites were observed in the telomeric region of the short arm of chromosomes 5 and 11 in 87% and 81% of 16 spreads respectively proximal to the centromere of chromosome 1 in 81% of the spreads, and on the long arm of chromosome 13 in 50% of the spreads. Twenty five spreads were studied for the ACC synthase gene and hybridization sites were observed in the telomeric region of the short arm of chromosome 12 in 96% of the spreads, chromosomes 9 and 10 in 76% of the spreads, and chromosome 17 in 56% of the spreads.