Identification of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in pollen

Within 15 min after application of pollen to the stigma of carnation flowers (Dianthus caryophyllus L. cultivar ‘White Sim’), ethylene (C₂H₄) production by the gynoecium had increased substantially. Pollen germination did not start until 1 h after pollination. Analysis of materials removed from pollen by a brief rinse with an aqueous solvent showed the presence of high concentrations of the C₂H₄ precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). This compound, which was found to be present in pollen from a number of flower species and which increased in concentration as the anthers developed, may be an important mediator of the early response of flowers to pollination.     

The effect of silver thiosulphate pre-treatment on 1-aminocyclopropane-1-carboxylic acid content and action in cut carnations

Endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) levels, and the ACC → ethylene (C₂H₄) conversion of exogenously applied ACC in naturally senescing and silver thiosulphate (STS) pre-treated cut carnations, were investigated. Under natural conditions, increase in ACC accumulation coincided with the onset of the climacteric rise in C₂H₄ production. Flowers pre-treated with STS did not show this increase in ACC content. Exogenously applied ACC caused wilting within 24 h and an increase in C₂H₄ production up to 1300 nl/h/flower. Flowers successively treated with STS and ACC produced C₂H₄ at quantities much higher than the controls, but showed no wilting. Together, these data suggest that the binding of C₂H₄ to its receptor leads to an increase in the production of ACC and of C₂H₄. By blocking the C₂H₄ action, the silver ion inhibits the autocatalytic increase in C₂H₄ and the accompanying rise in ACC content.     

Inoculation of growing media with the rhizobacterium Variovorax paradoxus 5C-2 reduces unwanted stress responses in hardy ornamental species

Inoculation of growing media with plant growth promoting rhizobacteria (PGPR) has a number of potential benefits for the production of ornamental plants. Certain rhizobacteria synthesise the enzyme ACC deaminase, which cleaves ACC, the precursor of the plant hormone ethylene. Bacterial metabolism is now known to lead to a reduction in [ACC] in the plant transpiration stream and bacteria are hypothesised to act on ACC exuded from roots. This in turn reduces the ethylene generated in plants growing in growing media inoculated with these bacteria. Here we tested if applications of the ACC deaminase containing rhizobacteria Variovorax paradoxus⁵C–²could be of benefit to ornamental growers by reducing ethylene generation in stressed plants. Ethylene is produced at levels that are inhibitory to growth and development under a number of abiotic stresses. The propagation and production of hardy ornamentals is deleteriously affected by abiotic stresses that involve ethylene signalling, including drought and physical wounding. Inoculation of growing media with V. paradoxus 5C-2 lowered ethylene emission from mature leaves of Cytisus × praecox experiencing drought stress. In addition, bacterial inoculation of the growing media resulted in significantly reduced abscission of the mature leaves under drought treatment. Beneficial effects of inoculation where also found in the wounding response of Fargesia murielae following divisional propagation and late season senescence in Aquilegia × hybrida in response to drought stress. Together these results demonstrate that V. paradoxus⁵C–²has real potential for use on ornamental nurseries in situations where plant stresses are unavoidable.     

The effect of humidity in plantain ripening

An examination of the coordination of ripening changes in plantain fruits (Musa AAB, cultivar ‘Apem’) showed that water stress had no effect on the respiratory rate at the climacteric maximum nor on the time between initiation and maximum. Similarly, water stress had little or no effect on the coordination of changes in CO₂ and C₂H₄ evolution, although it slightly increased the magnitude of C₂H₄ production and of the ACC content of the pulp. Stressed and unstressed fruits showed similar synchronised ripening changes after 2 and 3 days from the commencement of the climacteric. However, after 1 day, peel colouration, pulp softening and total soluble solids were less in stressed than in unstressed fruits. The results are discussed in the light of reported work on dessert bananas (Musa AAA cultivars).     

Wound induced ethylene production from excised muskmelon fruit tissue

Summary

Previous studies indicate that physical damage or wounding increases the preclimacteric production of ethylene in muskmelon fruit (Cucumis melo L., var. reticulatus Naud.) by inducing 1-aminocylopropane-l-carboxylic acid (ACC) synthase and ACC oxidase. In our experiments, ethylene production increased in the cylinders of preclimacteric fruit tissue from an undetectable level to 125 nl g^?1 h^?1 within 24 h after excision but declined to less than 50 nl g^?1 at 48 h. Tissues subsampled from the inner portion of the original cylinder never exceeded 50 nl g^?1 h^?1 unless incubated for an additional 24 to 48 h after removal from the original cylinder. In contrast to ethylene production, ACC increased throughout all tissues in the original cylinder during the initial 48 h incubation. Wound induced increases in ACC were unaffected by inhibiting endogenous ethylene production with cobalt. The temporal and spatial patterns of wound induced ethylene production in preclimacteric muskmelon fruits are apparently determined by changes in the tissue’s ability to convert ACC to ethylene rather than the presence of ACC.     

乙烯和1-MCP的竞争性作用对月季花器官乙烯生成量及相关基因表达的影响

 以探讨月季切花不同花器官的乙烯生物合成和对乙烯的感受为目的,以切花月季‘Samantha’为试材,进行了乙烯和1-MCP交叉处理,测定花朵各器官乙烯生成量,Rh-ACS3、Rh-ACO1和Rh-ETR3基因的表达。结果表明,1-MCP前处理或后处理均能有效抑制花瓣、雌蕊和花托中由于外源乙烯造成的内源乙烯生成量增加。在基因表达方面,Rh-ACS3、Rh-ACO1和Rh-ETR3在花瓣和雌蕊中对乙烯处理的诱导表达均可被1-MCP前处理或后处理有效抑制,而在花托中,这种抑制主要针对Rh-ETR3。这些结果说明,1-MCP对乙烯的竞争性抑制作用主要发生在花瓣、雌蕊和花托上,其竞争效果在乙烯处理前或乙烯处理后均有效。     

Influence of ethanol on ethylene biosynthesis and flower senescence of cut carnation

Ethanol in the holding-solution inhibited climacteric ethylene (C₂H₄) biosynthesis and decreased the respiration rate 60% during a 7-day period in cut carnation flowers. Conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to C₂H₄ was inhibited by adding ethanol to the holding-solution. Simultaneously, ACC-induced senescence in carnation flowers was inhibited by ethanol. Ethanol was the most effective alcohol in delaying carnation flower senescence of the tested series methanol, ethanol, propanol, tert-butanol and n-butanol. Ovary development was also inhibited in carnation flowers by ethanol. The senescence of Easter lily flowers (Lilium longiflorum) and tulip flowers (Tulipa gesneriana) was not delayed by ethanol.     

Cultivar and anatomical analysis of corolla enlargement of petunia (Petunia hybrida Vilm.) by cytokinin application

We found that the corolla of petunia (Petunia hybrida Vilm.) could be conspicuously enlarged by the separate application of three cytokinins: forchlorfenuron (CPPU), N⁶-benzylaminopurine (BA), and zeatin. To obtain the same enlargement as that achieved by CPPU, approximately 30 and 900 times the concentration of BA and zeatin, respectively, were required. CPPU at 3.2 μmol/L increased the limb area of the corollas of 15 cultivars to between 1.3 and 2.4 times (1.8 times on average) the size of the control area. The increase was negatively correlated (R = 0.58) with the “genetic” limb area (i.e., that of the untreated plant). The enlargement of the corolla caused by cytokinin application was mainly attributed to an increase in cell number in most cultivars. This increase resulted from a high rate of cell proliferation and from prolongation of the cell proliferation phase during corolla development. This anatomical change caused by cytokinin application was similar to the anatomical difference among cultivars because genetic differences in limb area resulted mainly from differences in cell number.     

Identification of Petunia hybrida cultivars that diurnally emit floral fragrances

In order to identify genetic resources for breeding fragrant petunias for use as bedding plants, volatile compounds released by day from the flowers of 40 commercial Petunia hybrida cultivars were analyzed using a solid-phase micro-extraction technique coupled with GC–MS. The three cultivars with solid deep-blue flowers that accumulate malvidin in corollas with high tissue pH were found to emit abundant iso-eugenol as the principal floral fragrance. Several other cultivars that emitted considerable amounts of methylbenzoate and/or benzylbenzoate from the flower were also identified. Association between the floral fragrance and the other floral traits such as floral anthocyanin composition and corolla-tissue pH was discussed.     

Optimization of Agrobacterium-mediated transformation parameters for Melastomataceae spp. using green fluorescent protein (GFP) as a reporter

Agrobacterium-mediated transformation for both Melastoma malabathricum and Tibouchina semidecandra were optimized using green fluorescent protein (GFP) as a reporter. The binary vector pCAMBIA1304 harboring the modified green fluorescent protein (mgfp) gene driven by the CaMV 35S promoter was used. Parameters optimized were bacterial strain, bacterial concentration, pre-culture period, co-cultivation period, immersion time, acetosyringone concentration and wounding type. Results obtained were based on the percentage of GFP expression which was observed 3 days post-transformation. Agrobacterium tumefaciens strain LBA4404 and EHA105 at concentration 1 × 10⁷ cfu ml⁻¹ (OD_600nm 0.8) showed the highest virulence on M. malabathricum and T. semidecandra, respectively. Four days of pre-culture and 2 days of co-cultivation were optimum for M. malabathricum transformation, while 3 days of pre-culture and co-cultivation for T. semidecandra. Result also showed that 60 min of immersion and addition of 200 μM acetosyringone gave the highest percentage of positive transformants for both M. malabathricum and T. semidecandra. Mild wounding also significantly increased the efficiency of M. malabathricum transformation.     

Effects of ethylene,abscisic acid and auxin on fruit abscission in water dropwort (Oenanthe stolonifera DC.)

Fruit abscission in water dropwort (Oenanthe stolonifera DC.) was investigated by measuring fruit removal force (FRF) affected by fruit ages and plant hormones. FRF decreased rapidly 30 days after anthesis (DAA). Ethylene evolution increased rapidly at 35 DAA and ABA concentration increased gradually after 20 DAA. ACC and ethephon decreased the FRF of fruit explants and the promoting effect of ACC was delayed by silver thiosulphate and cycloheximide, but not by norbornadiene and actinomycin D. ABA enhanced fruit abscission without increasing ethylene evolution. However, the observation that CoCl₂ delayed abscission induced by ABA indicates possible involvement of ethylene in the ABA effect. Treatment with NAA, fenoprop and IAA had no effect on 30 DAA fruit explants, but IAA delayed abscission of 25 DAA explants. This suggests that the effect of auxins may differ with fruit age when used as control agents.     

Midday depression of photosynthesis is related with carboxylation efficiency decrease and D1 degradation in bayberry (Myrica rubra) plants

Diurnal patterns of photosynthesis in two-year-old Myrica rubra young trees under natural conditions were studied by measuring gas exchange, chlorophyll fluorescence parameters and D1 protein. When measured on a clear day, the diurnal changes of net photosynthetic rate (P_n), stomatal conductance (G_s) and apparent quantum yield (AQY) show two daily maxima; the maximum value occurred at about 09:00 h, then declined, and reached the lowest values at about 13:00 h then increased to reach the second maxima at about 15:00 h. However, with the consistent decline of P_n and G_s in the afternoon, the ratio of intercellular CO₂ concentration (C_i) to atmospheric CO₂ concentration (C_a) increased. In addition, carboxylation efficiency (CE) and RUBP regeneration declined as the afternoon progressed. In the morning, the maximum yield of fluorescence after dark adaptation (F_m) and maximal photochemical efficiency of PSII (F_v/F_m) decreased continuously until it reached its minimum at 13:00 h, while the reverse occurred in the later afternoon. The quantum yield of PSII (Φ_PSII) declined after 09:00 h; in contrast, initial fluorescence (F_o) increased. A decrease in the rate of Q_A reduction and an increase in inactive PSII reaction centers was observed as the day progressed. Non-photochemical quenching (qN) and its slow-relaxing (qS) component increased at about midday, while the fast-relaxing component (qF) declined. The amount of inactive PSII centers was significantly enhanced, while F_v/F_m, Φ_PSII, qS and rate of Q_A reduction were significantly reduced by DTT (dithiothreitol), an inhibitor of the xanthophyll cycle. The D1 protein was significantly degraded at 13:00 h relative to that at 09:00 h during the course of the day. These results suggest that stomatal and non-stomatal limitations, which decreased carboxylation and photochemical efficiency, may cause the midday depression; and that non-stomatal limitations may be due to the decrease in RuBPCase activity and degradation of D1 protein, which causes decreased photoprotection at midday.     

Effects of 1-aminocyclopropane carboxylic acid on the rate of ethylene release from detached fruiting spurs and on fruit abscission in apple

Summary

1-Aminocyclopropane carboxylic acid (ACC) was applied to apple (Malus × domestica Borkh.) trees or to individual fruiting spurs between full bloom (FB) and 31 d after full bloom (DAFB; mean fruit diameter of 20 mm) to determine the effects of ACC on the ethylene released from detached spurs and on fruit abscission. The rate of ethylene release from detached fruiting spurs increased 1 d after applying 50 mg l^–1 ACC at full bloom or 16 DAFB (mean fruit diameter of 10 mm), but ACC had a reduced effect on the rate of ethylene release when it was applied 31 DAFB (mean fruit diameter of 20 mm). ACC reduced fruit set in ‘GoldRush’ apple in a concentration-dependent manner in 2009 and in 2010, but had no thinning activity on ‘Pink Lady’ in 2010. ACC at 200 mg l^–1 resulted in the yellowing and abscission of ‘GoldRush’ spur leaves in 2009, but not in 2010. The effects of combining ACC and 5 mg l^–1 naphthaleneacetic acid on fruit set in ‘GoldRush’ apple were additive. The application of 200 mg l^–1 ACC when fruit are ca. 10 mm in diameter may therefore be a useful chemical thinning treatment for apple fruit.     

Effect of salicylic acid on jasmonic acid-related defense response of pea seedlings to wounding

Interactions between jasmonic acid (JA) and salicylic acid (SA) signaling pathways play important roles in the regulation and fine-tuning of induced defenses which are activated by pathogen, insect attack, or wounding. In this study, endogenous SA and JA level in pea seedlings presented opposite trends in response to wounding. Results exhibited that SA impaired the resistance to wounding of pea seedlings by means of suppressing the action of JA. Based on the fact that the wound-induced PPO activity was suppressed by SA, it could be concluded further that SA had negative effect on JA-related defense response. However, synergy between JA and SA also existed in phenolic metabolism related to PAL. Moreover, endogenous SA and salicylic acid 2-O-β-d-glucose (SAG) levels in wounded pea seedlings also appeared opposite variation tendency, and newly synthesised SAG was detected. In contrast to SA, SAG showed some synergistic action in JA-related defense response in terms of MDA, PPO activity and PAL activity, which was quite different from SA. In conclusion, these results revealed both the negative effect and some synergistic effect of SA on JA-related defense of pea in response to wounding, particularly the role of SAG.     

Influence of temperature and bark injuries on the development of Phytophthora cactorum and P. Citrophthora on peach trees

The effect of temperature and bark injuries on the occurrence of crown rot of peach trees caused by P. cactorum and P. citrophthora were examined in field and laboratory. Lesions developed at 35 °C (the complete range of temperatures tested) but maximum development occurred at 20–25 °C. Greatest growth of these fungi on cornmeal agar (CMA) also occurred between 15 and 30 °C. Both pathogens could infect injured trees up to 20 days after wounding, but could not infect uninjured plants or plants wounded 40 and 30 days before inoculation, respectively. This study showed that temperature is a critical factor for the development of Phytophthora crown rot of peach trees. In addition, crown rot developed from recent wounds inoculated with agar plugs of Phytophthora.     

Effects of genotype and stigma development stage on seed set following intra- and inter-specific hybridization of Dianthus spp.

The caryophyllaceae is a family of flowering plants commonly known as the pink or carnation family. Members of this family are widely grown as ornamental plants. The species Dianthus chinensis, Dianthus barbatus, and Dianthus superbus include notable examples of such ornamental varieties. Intra- and inter-specific hybridization is important for the breeding of improved varieties and, therefore, it is desirable to optimize the efficiency of cross-pollination procedures within this family. Here, we conducted intra-specific pollination using four lines of D. chinensis, and inter-specific pollination between D. chinensis, D. barbatus and D. superbus genotypes. For each of these crosses we recorded information of pollen viability, stigma development stage at time of pollination, pollen germination on the stigma surface and pollen tube elongation within the stigma, and final seed set. Pollen viability levels were determined at the start of anther dehiscence, which occurred on day 1 of flower opening. The genotypes D. chinensis var. ‘Bz2’, D. barbatus var. ‘Xb’, and D. superbus wild species ‘Qm’ all displayed good levels of pollen viability (i.e. between 68% and 75%); D. chinensis vars. ‘H58III’, ‘H68I’ and ‘H6II’ showed lower levels of pollen viability (i.e. between 32% and 51%). In each Dianthus line, the stigma organs were observed to undergo morphological changes during the 1–7 d following flower opening. We have characterized these changes as five distinct development stages, namely, ‘column’ (day 1), ‘Y-like’ (day 2), ‘Y-shaped with slight curve’ (days 3–4), ‘Y-shaped horn-like’ (days 5–6), and ‘wilting’ (day 7). Pollen was artificially applied to stigma organs at each of these development stages and aniline blue staining was used to follow pollen tube germination on the stigma surface and pollen tube elongation down the length of the stigma. This showed that the ‘Y-shaped slightly curved’ stigma stage (3–4 d) was optimal for pollination. The ‘Y-shaped horn-like’ stage (5–6 d) was also receptive to pollination. By contrast, the earlier ‘Y-shaped’ (2 d) and ‘column’ (1 d) stages, and also the later ‘wilting’ (7 d) stage, were far less receptive. Parallel field experiments were conducted in which seed set was measured following the artificial pollination of flowers at different development stages. These data also indicated that the optimal time for pollination was during 3–4 d of flower opening. This conclusion held true for both intra- and inter-specific crosses of the various Dianthus lines. Thus, stigma receptivity in Dianthus does not become optimal until 3–4 d after flower opening. Since anther dehiscence occurs at 1 d (i.e. when stigma are at the unreceptive ‘column’ stage), this suggests that Dianthus employs a delayed self-fertilization strategy. We also found a significant effect of genotype on pollen tube growth and seed-set values. The highest numbers of seed per flower were achieved when the D. superbus wild species ‘Qm’ was the female parent in inter-specific crosses. Thus, genotype and stigma development are identified as key factors that determine the success of cross-pollination in Dianthus lines.     

自交不亲和甘蓝亲和花粉授粉早期差异蛋白质分析

 为从蛋白质的角度揭示自交不亲和甘蓝亲和授粉早期花粉与柱头相互作用,将蛋白质组学方法应用于自交不亲和性甘蓝柱头与亲和花粉互作早期差异蛋白质的研究。结果表明,亲和授粉后3 ~ 5 min与1 h对比,有116个差异蛋白质点,而授粉后1 h与2 h差异不显著。按照特异表达与变化量大的蛋白质点优先原则,初步选取差异点中71个点做质谱分析,鉴定出31个可信差异蛋白质。与亲和授粉后3 ~ 5 min组相比,1 h组中特异表达蛋白质有19个,上调表达9个,下调表达3个。31种蛋白质的生物信息学分析表明,有两种蛋白与前人发现的与花粉管在柱头中生长发育相关蛋白相同,其他29种参与包括胁迫与防御应答在内多种生理过程。对早期差异蛋白中这种“既有促进花粉管发育的蛋白,也有与防御相关蛋白”现象分析表明,花粉管生长性侵入柱头的过程有可能伴随着柱头抗性的提高。     

A new form of genetic female sterility in Capsicum annuum L.

During evaluation of genotypes of pepper (Capsicum annuum L.), a female-sterile mutant was observed in one line. The mutant also exhibited flat stem and rosette branching-habit. The stamens were functional and pollen fertility was normal. Style and stigma were petaloid and non-functional. A single recessive gene caused the sterility and the other aberrant characteristics. The possible use of this mutant in a hybrid seed production programme in pepper is indicated.     

Effect of brassinosteroids on drought resistance and abscisic acid concentration in tomato under water stress

The effect of brassinosteroid (BR) on relative water content (RWC), stomatal conductance (g_s), net photosynthetic rate (PN), intercellular CO₂ concentration (Ci), lipid peroxidation level, activities of antioxidant enzymes and abscisic acid concentration (ABA) in tomato (Lycopersicon esculentum) seedlings under water stress was investigated. Two tomato genotypes, Mill. cv. Ailsa Craig (AC) and its ABA-deficient mutant notabilis (not), were used. Water stress was achieved by withholding water and both the AC and not plants were treated with 1 μM 24-epibrassinolide (EBR) or distilled water as a control. The RWC, g_s, Ci and PN were significantly decreased under water stress. However, EBR treatment significantly alleviated water stress and increased the RWC and PN. EBR application also markedly increased the activities of antioxidant enzymes (catalase, ascorbate peroxidase and superoxide dismutase) while it decreased g_s, Ci and the contents of H₂O₂ and malondialdehyde (MDA). Interestingly, ABA concentration in AC and not plants was markedly elevated after EBR treatment although the increasing rate and amplitude of ABA in not plants treated by EBR was significantly lower than those in AC plants. Our study suggested that amelioration of the drought stress of tomato seedlings may be caused by EBR-induced elevation of endogenous ABA concentration and/or the activities of antioxidant enzymes.