Fruit thinning of peach trees

The present review deals with the importance of fruit thinning in peach.The date of treatment, the severity and the criteria underlying the practiceare discussed. Methods of fruit thinning are described, with particularemphasis on the use of chemical treatment as an alternative to handthinning. Strategies for chemical thinning are advanced.     

Developments in the chemical thinning of apple and pear

A literature review is presented on past and present experienceswith chemical flower and fruit thinning of apple and pear, amplifiedwith some data of recent trials with known and new flower thinners(mainly ethephon and ammonium thiosulphate) and fruit thinners (mainly1-napthylacetic acid (NAA), its amide (NAAm), carbaryl, ethephon,conjugates of NAA and NAAm and benzyladenine). Chemical-thinningpractices give quite unpredictable results. This inconsistency is atleast partly caused by weather factors, such as temperature and airhumidity, but tree factors are also involved. To solve this problem,climate-room and multi-site trials are proposed, together with anintergrated approach in elucidating background mechanisms and thedevelopment of new fruit thinning compounds.     

Cell division and cell enlargement in fruit of Lagenaria leucantha as influenced by pollination and plant growth substances

The effects of NAA (naphthaleneacetic acid), GA₃ (gibberellic acid), CPPU (N-(2-chloro-4-pyridyl)-N'-phenylurea) and pollination on fruit set, cell division and enlargement were studied in Lagenaria leucantha, an important vegetable. NAA and GA₃ were ineffective in inducing parthenocarpy, whereas CPPU induced parthenocarpic fruit significantly larger than fruit that resulted from pollination. Cell division, which occurred during the first 4 days after pollination was not reactivated by NAA or GA₃, but was effectively reactivated by CPPU. The cell number of the total cross-section of CPPU-treated fruit was 117.4% of that of pollinated fruit and 154.4% of that of unpollinated at 12 DAA (days after anthesis) respectively. The CPPU-induced parthenocarpic fruit had the largest cell cross-sectional area followed, successively, by pollinated fruit, NAA-treated fruit, GA₃-treated fruit and unpollinated fruit. These results indicate that CPPU induced parthenocarpic fruit growth by directly reactivating cell division and expansion.     

Cellulase and polygalacturonase involvement in the abscission of leaf and fruit explants of peach

Ethylene-induced abscission in leaf and fruit explants of peach involves different enzymes. In leaves abscission is accompanied by increased occurrence of cellulase forms differing in isoelectric point (pI 6.5 and 9.5). A polypeptide with a molecular mass of 51 kDa gives in a western blot a strong cross-reaction with an antibody raised against a maturation cellulase from avocado fruit. Cellulase activity is also found in abscising fruit explants but the amount is very low compared to that of the leaf explants. A northern analysis with a cellulase clone from avocado reveals the presence of two hybridizing mRNAs with a size of 2.2 kb and 1.8 kb, respectively. The steady-state level of the 2.2 kb mRNA is significantly increased by treatment with ethylene.Polygalacturonases are not detected in abscising leaves, but are strongly induced by ethylene in fruit explants. Of the three forms found, two are exopolygalacturonases while the third is an endoenzyme. Ethylene activates preferentially the endoenzyme and the basic exoenzyme but depresses the acid exopolygalacturonases. A northern analysis carried out with a cDNA coding for tomato endopolygalacturonase shows hybridization only with one endopolygalacturonase mRNA from in the fruit abscission zone. Treatment with ethylene causes an increase in the steady-state level of this mRNA. The differences in the enzyme patterns observed in fruit and leaf abscission zones and a differential enzyme induction suggest the feasibility to regulate fruit abscission in peach with the aid of antisense RNA genes.     

Probing the distribution of plant hormones by immunocytochemistry

Taking advantage of the highly specific structuralrequirements of antibodies for binding, the detectionof plant hormones in tissue by immunolocalisationoffers a powerful tool to study the distribution ofthese signalling molecules. For instance, specificmonoclonal and polyclonal antibodies have been raisedfor abscisic acid, indole-3-acetic acid and a varietyof cytokinins. Immobilisation by chemical fixation orfreezing minimises diffusion of these low molecularweight compounds in plant tissues. Associated primaryantibodies in sections or permeabilised cells can bedetected by secondary antibodies linked to enzymes,fluorescent molecules or electron opaque markers,which allow detection by either light or electronmicroscopy. These techniques have already found theirapplication in various studies related to thephysiology of these plant hormones.     

类黄酮调节生长素的极性运输(综述)

生长素在植物体内是通过极性运输方式输送的,这个运输过程是一个严格调控的过程.目前对其调控机理尚不了解.植物体内广泛存在的类黄酮类物质影响生长素运输,对生长素运输起负调控作用.     

Significance of flower and fruit thinning on fruit quality

The effects of mechanical or chemical flower and fruit thinning on fruitquality were primarily by altering crop load. However, there were alsodirect effects of thinning agents. Fruit size was directly related tothinning intensity. In addition to crop load, age of wood, flower budquality, competition within clusters and canopy were important factorsaffecting the response to thinning. Short- and long-term thinningstudies identified two groups of quality components: Group 1characteristics include size, colour, skin performance, firmness andsugar and acid content of the fruit. Group 2 characteristics wererepresented by inorganic components, especially calcium and potassiumwhich are implicated in the susceptibility of fruit to physiologicaldisorders. While group 1 characteristics were improved by increasingthinning intensity, storability of the fruit was better at high than atlow crop loads. Therefore, a compromise between all quality requirementsmust be found for a good economic return. Establishing the trends ofthinning on the different quality parameters can help to select athinning strategy for local or regional conditions typically beingdetermined by growing and market conditions.     

Molecular cloning and sequencing of a cDNA for an auxin-repressed mRNA: correlation between fruit growth and repression of the auxin-regulated gene

A complementary DNA (cDNA) library has been constructed in gt10 from poly(A)⁺ mRNA isolated from auxin-deprived strawberry receptacles. By differential plaque filter hybridization, a cDNA (SAR5) to an auxin-repressed mRNA has been isolated. The expression of the auxin-repressed gene is studied at various stages of normal fruit development and in fruits of variant strawberry genotype using SAR5 as a probe. Northern analyses of RNA isolated from pollinated and unpollinated fruits of various developmental stages revealed that mRNA corresponding to the SAR5 clone is repressed during normal fruit development, and the level of SAR5 mRNA is regulated by endogenous auxin. Furthermore, results with both normal and variant genotype strawberry fruit indicate that there is a positive correlation between growth of strawberry fruit and repression of mRNA corresponding to the SAR5 clone. The SAR5 cDNA has been sequenced and is 723 nucleotides in length. The deduced protein has 111 amino acid residues with a molecular mass of 12.5 kDa. The putative polypeptide starts at nucleotide position 20 and ends at 352. The molecular weight of the predicted polypeptide is in agreement with the molecular weight of the in vitro translated polypeptide of hybrid selected mRNA. A comparison of the nucleotide and deduced amino acid sequence of SAR5 with nucleotide and protein sequences in data banks has not revealed any homology to known proteins.     

Ca2+对离体培养的番茄花柄脱落的影响以及脱落过程中离区内钙形态的变化

在自然条件下,Ca~(2 )对离体培养的番茄花柄脱落有抑制作用,而对经乙烯处理的则有显著的促进。无论是在自然还是乙烯条件下,未经任何处理的番茄花柄脱落过程中总钙与果胶酸钙含量下降,而水溶性钙含量升高,Ca~(2 )在不同程度上提高脱落过程中离区总钙、果胶酸钙和水溶性钙含量,尤其是在乙烯下的效果更显著,而经EGTA处理的则相反。     

Interaction of 4-chloroindole-3-acetic acid and gibberellins in early pea fruit development

In pea, normal pod (pericarp) growth requires the presence of seeds; and in the absence of seeds, gibberellins (GAs) and/or auxins can stimulate pericarp growth. To further characterize the function of naturally occurring pea GAs and the auxin, 4-chloroindole-3-acetic acid (4-Cl-IAA), on pea fruit development, profiles of the biological activities of GA3, GA1, and 4-Cl-IAA on pericarp growth were determined separately and in combination on pollinated deseeded ovaries (split-pericarp assay) and nonpollinated ovaries. Nonpollinated ovaries (pericarps) responded differently to exogenous GAs and 4-Cl-IAA than pollinated deseeded pericarps. In nonpollinated pericarps, both GA3 and 4-Cl-IAA stimulated pericarp growth, but GA3 was significantly more active in stimulating all measured parameters of pericarp growth than 4-Cl-IAA. 4-Cl-IAA, GA1, and GA3 were observed to stimulate pericarp growth similarly in pollinated deseeded pericarps. In addition, the synergistic effect of simultaneous application of 4-Cl-IAA and GAs on pollinated deseeded pericarp growth supports the hypothesis that GAs and 4-Cl-IAA are involved in the growth and development of pollinated ovaries.     

Induction of alcohol dehydrogenase by plant hormones in alfalfa seedlings

Six-day-old alfalfa (Medicago sativa L.) seedlings were treated with auxin, abscisic acid (ABA), cytokinin and gibberellin to determine the effect of these plant hormones on induction of alcohol dehydrogenase (ADH). The ADH activity was increased at concentrations greater than 1 M for auxin and ABA and 3 M for cytokinin, respectively, and all increases were found within 6 h after treatments. However, ADH activity remained almost unchanged in the seedlings treated with gibberellin. At 100 M doses, the activities in the seedlings were 4.0-, 3.6- and 2.1-fold greater than that of non-treated seedlings for auxin, ABA and cytokinin, respectively.     

Immunogold localization of trans-zeatin riboside in embryo and endosperm during early fruit drop of Malus domestica

The specificity of a monoclonal antibody IgG1, raised against trans-zeatin riboside-keyhole limpet hemocyanin conjugate, was investigated by means of inhibition experiments with soluble competing antigens. A competitive enzyme immunoassay was set up, with immobilized antigen. The analysis of the cross reaction profile enabled a study of the specificity of the antigen-antibody interaction. The antibody was able to distinguish the trans form of zeatin riboside from the cis form (cross reaction index = 1 %); cross reactions with ribose, adenine, adenosine and other related heterologous antigens were not detectable over the range of concetration tested. The recognition centres for the antibody seem to be the purine ring and the R substituent, especially in its hydroxymethyl group. Employment of this monoclonal antibody to localize cytokinins in control and shedding affected fruits of Malus domestica Borkh. evidenced high content of trans-zeatin riboside in developing seeds, differences in its content in embryo and endosperm, and a strong reduction of its content in the tissues of drop fruits. This decrease may be an important component responsible for early fruit abscission. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of fruit thinning agents on apple tree canopy photosynthesis and dark respiration

Effects on photosynthesis of the fruit thinning agents naphthaleneaceticacid (NAA) and three commercial plant growth regulator formulations,naphthaleneacetic acid ('Rhodofix') and naphthaleneacetamide('Amidthin') and 2-chloroethylphosphonic acid('Ethrel')were evaluated with respect to the stress they impose on the fruit tree, usingthe alternate-bearing sensitive apple cv. 'Elstar'. This work wasbased on the hypothesis that plant stress in the form of large reductions inleaf photosynthesis are a pre-requisite for successful fruit thinning. A newtechnology was employed for continuous recording of tree canopyphotosynthesis, dark respiration and carbon balance of apple trees. This wasbased on six canopy chambers, which enclosed apple trees under naturalconditions in the field, with on-line measurements and continuous analysis ofCO₂ exchange and automated data acquisition. All employed thinningagents reduced whole tree canopy photosynthesis consistently by3–34% on the five days following their application, withphotosynthesis still declining thereafter in the case of the NAA and'Amid-thin' application. The reduction after application of either'Rhodofix' or 'Ethrel', declined within five days, suchthat most of the original photosynthetic potential was restored, indicatingacceptable phytotoxicity of these three plant growth regulators at theconcentrations used. The effects on dark respiration differed markedly. NAA and'Ethrel' increased dark respirationover-proportionally by up to 106%, whereas 'Amid-thin' and'Rhodofix' decreased it by up to 46%inthe first night after application, thereby drastically affecting the carbonbalance of the tree in opposite ways. These results are integrated into ahypothesis linking basipetal auxin transport, phloem loading, translocation anddeficiency of photoassimilates.     

Activity of pear fruit malic enzyme; its regulation by metabolites

Sigmoid kinetics are reported for the pear malic enzyme (l-malate NADP oxidoreductase, EC 1.1.1.40). Responses have been obtained from possible allosteric effectors. The physiological significance of these responses to metabolites is discussed in relation to a regulatory role of this enzyme in maturation.     

The march of the PINs: developmental plasticity by dynamic polar targeting in plant cells

Development of plants and their adaptive capacity towards ever‐changing environmental conditions largely depend on the spatial distribution of the plant hormone auxin. At the cellular level, various internal and external signals are translated into specific changes in the polar, subcellular localization of auxin transporters from the PIN family thereby directing and redirecting the intercellular fluxes of auxin. The current model of polar targeting of PIN proteins towards different plasma membrane domains encompasses apolar secretion of newly synthesized PINs followed by endocytosis and recycling back to the plasma membrane in a polarized manner. In this review, we follow the subcellular march of the PINs and highlight the cellular and molecular mechanisms behind polar foraging and subcellular trafficking pathways. Also, the entry points for different signals and regulations including by auxin itself will be discussed within the context of morphological and developmental consequences of polar targeting and subcellular trafficking.     

Relationship between reflectance spectra of host plant surfaces and visual detection of host fruit by Rhagoletis pomonella flies

ABSTRACT. Within host trees, male and female Rhagoletis pomonella (Walsh) flies locate visually individual fruit of apple and hawthorn, which are sites of mating and oviposition. By measuring the diffuse reflectance spectra of both fruit and foliage and by using artificially pigmented natural fruit and artificial fruit mimics, we show that fruit hue is not as important in R. pomonella fruit detection as is intensity contrast of dark fruit against a bright background of light transmitted through foliage or skylight. In discussing the fruit detection system of R. pomonella , we compare it to that of vertebrate fruit consumers and seed dispersers.     

Molecular cloning of cDNAs for auxin-induced mRNAs and developmental expression of the auxin-inducible genes

By differential hybridization, two auxin-inducible cDNA clones (SAR1 and SAR2) have been isolated from a cDNA library constructed to poly(A)⁺ mRNA from auxin-treated strawberry receptacles. Both the clones have been used as probes to study the expression of the auxin-induced genes in pollinated and unpollinated fruits of various stages of development and in different organs. A high level of auxin-induced mRNAs is found in pollinated fruits as compared to unpollinated fruits of the same age, suggesting that the expression of the auxin-induced genes is developmentally regulated and the level of auxin-induced mRNAs is regulated by endogenous auxin. Furthermore, our data on the expression of SAR1 and SAR2 genes in pollinated and unpollinated fruits revealed a positive correlation between growth of strawberry fruit and the induction of mRNA corresponding to the SAR1 and SAR2 clones. Ethylene has no effect on the expression of the auxin-induced mRNAs. SAR1 mRNA is not detected in other parts of strawberry plants whereas SAR2 mRNA is present in roots. Furthermore, mRNA corresponding to SAR1 and SAR2 is not detected in other auxin-responsive plant systems such as pea epicotyls and bean explants.