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.     

Effect of ethylene on flower abscission: a survey

The effect of ethylene on flower abscission was investigated in monocotyledons and eudicotyledons, in about 300 species from 50 families. In all species studied except Cymbidium, flower abscission was highly sensitive to ethylene. Flower fall was not consistent among the species in any family studied. It also showed no relationship with petal senescence or abscission, nor with petal colour changes or flower closure. Results suggest that flower abscission is generally mediated by endogenous ethylene, but that some exceptional ethylene-insensitive abscission occurs in the Orchidaceae.     

番茄离体花柄脱落区多聚半乳糖醛酸酶提取纯化体系的优化

多聚半乳糖醛酸酶是植物器官脱落过程中的重要水解酶,实验以20μL.L-1乙烯处理的离体番茄花柄为试材,建立了与脱落相关的多聚半乳糖醛酸酶提取与纯化体系:以50 mmol.L-1乙酸缓冲液(pH=5.5)为提取液,加入0.1 mol.L-1NaCl、1 mmol.L-1DTT提取效果较好;将酶的粗提液低温浓缩后,经Sephadex G-75凝胶层析分离纯化,最佳流速为0.2 mL.min-1,适宜上样量为3.5 mL;再将凝胶层析分离的活性部分低温浓缩后,经CM Sepharose CL-6B离子交换层析再次纯化,流速为0.3 mL.min-1、洗脱液pH值5.5纯化效果最好。经上述提取纯化过程,得到了分子质量为30.2 kD的多聚半乳糖醛酸酶蛋白。该提取纯化体系为探讨与脱落相关酶的性质及其活性调控提供了参考。     

Shoot-tip abscission and adventitious abscission of internodes in mulberry (Morus alba)

In mulberry ( Morus alba L. cv. Shin-ichinose), shoot-tip abscission following the cessation of apical growth could be induced in different internodes, depending on the vigour of the shoot and its apex and other internal and external factors. In the lateral, short shoots of 1-year-old stems of low-pruned trees, the apical growth cessation and shoot-tip abscission (May–June) resulted primarily from the dominance of the upper, long shoots and intense competition among laterals along the stem. Decapitation of the laterals, before abortion of their apices took place (early May), readily caused adventitious abscission of the distal internode. Similar decapitation-induced, adventitious abscission of the distal internode of the upper, long shoots of 1-year-old stems of pruned trees also occurred (May–September), demonstrating that the abscission itself is not directly associated with photoperiod. In May and June, decapitation induced abscission primarily in parallel with or after sprouting of lateral buds and shoot elongation, while in July, August and September, the abscission was induced by decapitation and independently of sprouting. Shoot (stem) orientation positively affected the abscission, which is related to gravimorphic effects on buds and shoots on the lower and lateral sides of the horizontally trained stem. These results suggest that the vigour of shoots and apices is an important determinant of growth and apex abscission in mulberry.     

Hormonal regulation of secondary abscission in pear pedicels in vitro

In vitro cultivated pear, Pyrus communis L. cv. Beurré Hardy, pedicels cut above their primary abscission layer can form a secondary abscission layer, especially under the influence of auxins or cytokinins in the culture medium. The maximum percentage of abscission reached by auxin application was always higher than that by cytokinin. The presence of the flower was of no consequence to the abscission. Characteristic differences in abscission were observed between pear and apple pedicels. In contrast to apple (1) secondary abscission in pear could also be induced by cytokinins, and (2) the site of abscission in pear was dependent on the auxin concentration. At lower auxin concentrations abscission was induced in the basal parts of the pedicels inserted in the medium, whereas at higher auxin concentrations the abscission layer was formed in the terminal parts of the pedicels above the culture medium. A clear effect of gibberellins, ABA and CEPA could not be detected.     

Delay of flower senescence and abscission in Arabidopsis transformed with an FOREVER YOUNG FLOWER homolog from Oncidium orchid

The ectopic expression of FOREVER YOUNG FLOWER (FYF), a MADS box gene in Arabidopsis, caused significant delay of senescence and a deficiency of abscission in flowers of transgenic Arabidopsis. It was proposed that the function of the FYF gene was related to the regulation of senescence and abscission. This hypothesis was further supported by one line of evidence reported in this study. The evidence is the similar delay of flower senescence and abscission observed in transgenic Arabidopsis ectopically expressing OnFYF, an FYF homolog from the Oncidium orchid, a monocot. This data suggested that the function of FYF homologs in regulating flower senescence and abscission was highly conserved in both dicot and monocot plants.     

Breakdown of middle lamella pectin by ●OH during rapid abscission in Azolla

Azolla, a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that occurs in Azolla, breakdown of wall components of abscission zone cells by ^●OH is involved. Experimentally generated ^●OH caused the rapid separation of abscission zone cells from detached roots and the rapid shedding of roots from whole plants. Electron microscopic observations revealed that ^●OH rapidly and selectively dissolved a well‐developed middle lamella between abscission zone cells and resultantly caused rapid cell separation and shedding. Treatment of abscission zones of Impatiens leaf petiole with ^●OH also accelerated the separation of abscission zone cells. However, compared with that of Azolla roots, accelerative effects in Impatiens were weak. A large amount of ^●OH was cytochemically detected in abscission zone cells both of Azolla roots and of Impatiens leaf petioles. These results suggest that ^●OH is involved in the cell separation process not only in the rapid abscission in Azolla but also in the abscission of Impatiens. However, for rapid abscission to occur, a well‐developed middle lamella, a unique structure, which is sensitive to the attack of ^●OH, might be needed.     

Costs and benefits of non‐random seed release for long‐distance dispersal in wind‐dispersed plant species

The dispersal ability of plants is a major factor driving ecological responses to global change. In wind‐dispersed plant species, non‐random seed release in relation to wind speeds has been identified as a major determinant of dispersal distances. However, little information is available about the costs and benefits of non‐random abscission and the consequences of timing for dispersal distances. We asked: 1) to what extent is non‐random abscission able to promote long‐distance dispersal and what is the effect of potentially increased pre‐dispersal risk costs? 2) Which meteorological factors and respective timescales are important for maximizing dispersal? These questions were addressed by combining a mechanistic modelling approach and field data collection for herbaceous wind‐dispersed species. Model optimization with a dynamic dispersal approach using measured hourly wind speed showed that plants can increase long‐distance dispersal by developing a hard wind speed threshold below which no seeds are released. At the same time, increased risk costs limit the possibilities for dispersal distance gain and reduce the optimum level of the wind speed threshold, in our case (under representative Dutch meteorological conditions) to a threshold of 5–6 m s^–1. The frequency and predictability (auto‐correlation in time) of pre‐dispersal seed‐loss had a major impact on optimal non‐random abscission functions and resulting dispersal distances. We observed a similar, but more gradual, bias towards higher wind speeds in six out of seven wind‐dispersed species under natural conditions. This confirmed that non‐random abscission exists in many species and that, under local Dutch meteorological conditions, abscission was biased towards winds exceeding 5–6 m s^–1. We conclude that timing of seed release can vastly enhance dispersal distances in wind‐dispersed species, but increased risk costs may greatly limit the benefits of selecting wind conditions for long‐distance dispersal, leading to moderate seed abscission thresholds, depending on local meteorological conditions and disturbances.     

Polygalacturonase: a candidate gene for the soft flesh and deciduous fruit mutation in Capsicum

The soft flesh and deciduous fruit of pepper (Capsicum spp.) originated from the wild C. frutescens BG 2816 accession is a complete dominant trait controlled by the S gene. We constructed an F₂ population from a cross of BG 2816 (SS) and the bell-type C. annuum cultivar Maor (ss) and determined that S cosegregated with the tomato fruit-specific endo-polygalacturonase (PG) gene. The soft flesh and deciduous fruit phenotypes were observed together in all F₂ individuals, indicating a pleiotropic effect of PG on the two traits. We mapped S to pepper chromosome 10 in the region corresponding to that in which PG was previously mapped in tomato. Northern, RT-PCR and western analyses and enzyme activity assays, collectively, indicated that PG is not detected in green, breaker or red fruits of Maor, nor in green fruits of BG 2816. Accumulation of PG mRNA and protein was detected in the fruits of BG 2816, and it increased during ripening from breaker to red stages. The sequence analysis of partial PG cDNA isolated from BG 2816 revealed high homology (87% identity) with the tomato PG. The resemblance of the soft flesh and deciduous fruit phenotypes to PG-associated phenotypes in other fruit crops, the complete linkage between Sand PG, and the greater expression of PG in the fruits of BG 2816 than in those of Maor, all strongly indicate that PG is a candidate gene for S.     

Annuario della societa botanica italiana 1934

Apple research has undergone great improvements in the last years, in both quantitative and qualitative terms. Huge amount of data are now available, especially as far as the early development and the ripening phase are concerned. Moreover, the recent release of the apple genome sequence is significantly speeding up research, allowing on one hand to shed light on the most critical aspects of fruit development with almost immediate practical implications and, on the other hand, to identify new molecular markers that will improve the future breeding programs. In this context, apple is being increasingly considered as a model for fruit development studies, although many gaps still exist in apple research. These gaps are being filled by coupling the next generation high-throughput technologies with new physiological approaches, aimed at achieving both new basic knowledge and innovative tools to improve the final quality of the fruit. In this review, the available information on the regulatory aspects of apple fruit development will be reported and discussed in the light of the future perspectives of apple research.     

葡萄采后果粒脱落及保鲜贮藏

葡萄穗粳和果柄的呼吸强度与乙烯生成显著高于果粒,并呈现呼吸跃变型变化。落粒果柄中GA消失,ABA增加。降低贮藏温度、外源GA,NAA,AOA处理能抑制落粒,ABA、乙烯利则增加落粒率。剪去穗梗和果柄后果粒和果柄间不再形成离层,表明穗梗和果柄在落粒过程中起重要作用。     

Ethylene-promoted tomato flower abscission and the possible involvement of an inhibitor

The abscission zone in tomato (Lycopersicon esculentum (L.) Mill. flower pedicels is morphologically distinguishable prior to separation and is delineated by an indentation of the epidermis. Exposure of excised pedicels with the flower attached to ethylene results in abscission within 12 h and this can be accelerated by flower removal. Abscission of excised pedicels with the flower removed takes place in the absence of exogenous ethylene but this is delayed by pretreatment with aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. The data presented support the hypothesis that flower tissue is the source of an abscission inhibitor.Abbreviations AVG aminoethoxyvinyl glycine - IAA indole-3-acetic acid     

Effect of Crinipellis perniciosa Infection on Abscission of Cacao Cotyledons, Reserve Mobilization and Dry Matter Partitioning

Infection by Crinipellis perniciosa on cacao seedlings prevented the abscission of cotyledons which normally abscise within 32–61 days from seed sowing. The early growth and development of control and artificially inoculated seedlings was investigated for root dry mass (RDM), shoot dry mass (SDM), shoot‐to‐root ratio (SRR), total dry mass (TDM), cotyledonary dry mass (CDM) and cotyledonary water content (CWC). Cotyledonary reserve mobilization was estimated at 69 and 56% at 5 weeks and 79 and 64% at 8 weeks in control and infected seedlings, respectively. Infection induced the enlargement of tissues but was not accompanied by an increase in dry mass. Infection both delayed and reduced the utilization of cotyledonary food reserves resulting in slower accumulation of RDM, SDM and TDM culminating in a reduction of growth by a factor of 1.6 at 8 weeks. However, the SRR of inoculated plants was similar to that of control plants, suggesting that the balance between the root and shoot systems exists which is unchanged by the effect of the pathogen. CWC was decreased upon senescence to an average of 65% at abscission. The prevention of cotyledonary abscission in infected seedlings is suggested to be due in part to the CDM remaining above a critical level of 20% of the initial CDM. The implication of this response in relation to the infection biology of the pathogen is discussed.     

A Cholesterol‐Dependent Endocytic Mechanism Generates Midbody Tubules During Cytokinesis

Cytokinesis is the final stage of cell division and produces two independent daughter cells. Vesicles derived from internal membrane stores, such as the Golgi, lysosomes, and early and recycling endosomes accumulate at the intracellular bridge (ICB) during cytokinesis. Here, we use electron tomography to show that many ICB vesicles are not independent but connected, forming a newly described ICB vesicular structure – narrow tubules that are often branched. These ‘midbody tubules’ labelled with horseradish peroxidase (HRP) within 10 min after addition to the surrounding medium demonstrating that they are derived from endocytosis. HRP‐labelled vesicles and tubules were observed at the rim of the ICB after only 1 min, suggesting that midbody tubules are likely to be generated by local endocytosis occurring at the ICB rim. Indeed, at least one tubule was open to the extracellular space, indicative of a local origin within the ICB. Inhibition of cholesterol‐dependent endocytosis by exposure to methyl‐β‐cyclodextrin and filipin reduced formation of HRP‐labelled midbody tubules, and induced multinucleation following ICB formation. In contrast, dynamin inhibitors, which block clathrin‐mediated endocytosis, induced multinucleation but had no effect on the formation of HRP‐labelled midbody tubules. Therefore, our data reveal the existence of a cholesterol‐dependent endocytic pathway occurring locally at the ICB, which contributes to the accumulation of vesicles and tubules that contribute to the completion of cytokinesis.