Role of ethylene receptors during senescence and ripening in horticultural crops

The past two decades have been rewarding in terms of deciphering the ethylene signal transduction and functional validation of the ethylene receptor and downstream genes involved in the cascade. Our knowledge of ethylene receptors and its signal transduction pathway provides us a robust platform where we can think of manipulating and regulating ethylene sensitivity by the use of genetic engineering and making transgenic. This review focuses on ethylene perception, receptor mediated regulation of ethylene biosynthesis, role of ethylene receptors in flower senescence, fruit ripening and other effects induced by ethylene. The expression behavior of the receptor and downstream molecules in climacteric and non climacteric crops is also elaborated upon. Possible strategies and recent advances in altering the ethylene sensitivity of plants using ethylene receptor genes in an attempt to modulate the regulation and sensitivity to ethylene have also been discussed. Not only will these transgenic plants be a boon to post-harvest physiology and crop improvement but, it will also help us in discovering the mechanism of regulation of ethylene sensitivity.     

成串采收对番茄果实采后乙烯合成及贮藏品质的影响

为研究成串采收对番茄果实采后乙烯合成及贮藏品质的影响,对广西田阳县两个栽培区两种嫁接砧木的串收番茄的采后生理指标进行测定,探讨了该采收方式对番茄果实采后保鲜的作用机制。结果表明:整个贮藏期,不同栽培区不同嫁接砧木的番茄成串采收的果实,乙烯生成量明显低于对照的常规单果采收。其中,砧木1号Ⅰ区的串收番茄的乙烯生成量,采后5 d即下降至最低点(0.35 nL·g~(-1)·h~(-1)),显著低于其对照(1.36 nL·g~(-1)·h~(-1)),其他栽培区和砧木组合的串收番茄,在采后15 d乙烯生成量达到最低值。串收番茄的类胡萝卜素、番茄红素和抗坏血酸等果实内天然抗氧化物质的含量,在贮藏前期快速升高,且峰值显著高于对照。此外,成串采收处理还一定程度抑制了果实后熟阶段可溶性糖的积累和可滴定酸的分解。因此,番茄成串采收处理,可能通过抑制果实采后乙烯的合成,同时提高类胡萝卜素、番茄红素和抗坏血酸的水平,并且推迟糖和酸等营养物质的后熟变化进程,实现其延长果实货架期,提高商品品质的作用。     

柿果实采后氧化还原电位与乙烯合成和相关酶活性的关系

该研究以广西特色柿品种‘恭城月柿''为材料,在采后贮藏过程中对其氧化还原电位(ORP)、乙烯生物合成量、硬度、色差、抗氧化酶及细胞壁降解酶活性的变化进行了测定,初步探讨柿果实氧化还原电位与乙烯生物合成和相关酶活性的关系。结果表明:贮藏期果实的硬度整体呈下降趋势,乙烯利处理果实的硬度从采后3 d即急速下降,至贮藏末期始终显著低于对照。贮藏前14 d果实转色较缓慢,采后15 d乙烯利处理果实的总色差ΔE值快速上升至29.6,转色完全,显著高于对照的11.9。在贮藏前期处理和对照果实的ORP均稳定在7.5 mv·g^-1,采后15 d乙烯利处理果实的ORP快速上升至11.9 mv·g^-1,是对照组的1.4倍。乙烯利处理果实的乙烯生物合成量在贮藏前期呈较低水平,采后15 d乙烯生成量急剧增加至0.372 μL·kg^-1·h^-1的高峰,对照乙烯生成量则始终维持在0.033 μL·kg^-1·h^-1的较低水平。可见,乙烯生成量的增加与ORP的上升关系密切。此外,抗氧化酶中的过氧化物酶(POD)和细胞壁降解酶中的β-D-半乳糖苷酶(β-D-Gal)活性与ORP呈极显著正相关,表明二者受果实ORP变化的影响。因此,经乙烯利处理柿果实的ORP贮藏末期显著上升,促进乙烯生物合成量的急剧增加,诱导抗氧化酶POD和细胞壁降解酶 β-D-Gal活性增强,导致果实急速后熟软化。柿果实ORP可能作为开关调控1-氨基环丙烷-1-羧酸(ACC)生成乙烯这一生物化学反应,即打破ORP的稳定状态引发乙烯合成的启动。     

Abscission: ethylene and light control

The role of ethylene in light control of leaf abscission im mung bean, Vigna radiata (L.) Wilczek cv Jumbo, cuttings was examined. While red light inhibits and far-red light promotes loss of break strength in abscission zones as compared with dark controls, changes in the rate of abscission could not be associated with changes in the rate of ethylene production. Reducing ethylene synthesis in tissue with aminoethoxyvinylglycine did not alter the effects of red or far-red light on abscission. Far-red light appeared to increase and red light appeared to decrease tissue sensitivity to ethylene.     

乙烯受体抑制剂在园艺作物上的应用研究（综述）

本文从乙烯受体抑制剂的特性,作用特点及效应等方面,概述其在园艺作物上的研究进展和应用情况,并展望今后的研究方向。     

The use of sewage sludge and horticultural waste to develop artificial soil for plant cultivation in Singapore

Greenhouse pot experiments were performed with Ipomoea aquatica (Kang Kong) to evaluate artificial soil produced from poor fertility subsoil, horticultural compost, and sewage sludge. The addition of horticultural compost and sewage sludge to subsoil substantially improved plant growth, improved the physical properties of subsoil and enriched subsoil by essential nutrients for plants. The effect was enhanced when the two ingredients were added to subsoil together. The highest yield of biomass of I. aquatica was observed in artificial soil prepared by mixing subsoil with 4% (wet weight/wet weight) of horticultural compost and 2% (dry weight/wet weight) of sewage sludge. The contents of heavy metals in plants, grown in the artificial soil, were significantly lower than toxic levels. The artificial soil could be recommended for urban landscaping and gardening in Singapore.     

Application of bacteriophages in post-harvest control of human pathogenic and food spoiling bacteria

Bacteriophages have attracted great attention for application in food biopreservation. Lytic bacteriophages specific for human pathogenic bacteria can be isolated from natural sources such as animal feces or industrial wastes where the target bacteria inhabit. Lytic bacteriophages have been tested in different food systems for inactivation of main food-borne pathogens including Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Salmonella enterica, Shigella spp., Campylobacter jejuni and Cronobacter sakazkii, and also for control of spoilage bacteria. Application of lytic bacteriophages could selectively control host populations of concern without interfering with the remaining food microbiota. Bacteriophages could also be applied for inactivation of bacteria attached to food contact surfaces or grown as biofilms. Bacteriophages may receive a generally recognized as safe status based on their lack of toxicity and other detrimental effects to human health. Phage preparations specific for L. monocytogenes, E. coli O157:H7 and S. enterica serotypes have been commercialized and approved for application in foods or as part of surface decontamination protocols. Phage endolysins have a broader host specificity compared to lytic bacteriophages. Cloned endolysins could be used as natural preservatives, singly or in combination with other antimicrobials such as bacteriocins.     

From researcher to farmer: The use of extension programs to transfer biological control technology in developed countries

Effective use of biological control by the pest manager requires knowledge of the biologies of the pests and natural enemies, and their interactions with their environment and agronomic practices. Manufacturers provide information for products such as microbial pesticides and entomophagous arthropods used in augmentative biological control. However, information about process-oriented methods such as classical (importation) biological control and conservation of natural enemies is not often available to the farmer. Governmental extension programs are one method for providing practical biological control information, but availability in developed countries varies considerably. Examples of transfer of biological control information are provided for New Zealand, Canada, and Australia. In the United States, the Extension Service, a branch of the U.S. Department of Agriculture, provides partial funding and coordination for pest management educational programs conducted at the national, regional, state and local levels. In a twelve-state region of the North Central United States, university extension and research entomologists have developed a coordinated program to educate county extension personnel, farmers, and private consultants about the use of biological controls in pest management. The details of this model program are discussed. The paper concludes with a discussion of the educational constraints that must be overcome to successfully increase the adoption of biological control.     

Effects of improved post-harvest handling on the chemical constituents and quality of carrageenan in red alga,Kappaphycus alvarezii Doty

Red alga Kappaphycus alvarezii Doty is an important commercial species widely cultivated in southeast Asian countries for its polysaccharide, kappa-carrageenan. Common post-harvest handling technique involves sun-drying of harvested seaweed on platforms at the farms. Quantity and quality of carrageenan varies depending on the duration and care taken during the post-harvest handling of the raw seaweed. In this study, dynamics of moisture content, water activity index (aw), carrageenan yield, and carrageenan quality were investigated by subjecting the seaweed to three post-harvest methods: (1) freeze-drying (FD), (2) shade-drying (SD), and (3) direct sun-drying (DSD). Seaweed dried under FD and SD produced high yield (56–58 %), superior gel strength (1,454–1,424 g cm^?2), high viscosity (57–58 cPs), and low syneresis (15–17 %). But, carrageenan extracted from DSD seaweed gave 28 % lower yield, 38 % lower gel strength, 27 % lower viscosity, and 8–9 % higher syneresis. In addition, gelling temperature and melting temperature of the DSD carrageenan were lower by 4 and 9 °C, respectively. Molecular size analyses of carrageenan extracted from seaweed dried under FD and SD contained carrageenan of 700 KDa (80 %) and 200 KDa (4–10 %). However, carrageenan extracted from DSD seaweed contained smaller carrageenan molecules, 460 KDa (55 %), 210 KDa (25 %), and <100 KDa (20 %). Further, scanning electron microscope images illustrated the severe effects of DSD on the morphology of seaweed cells. Therefore, SD technique was found to be the best post-harvest processing technique that gave quality carrageenan in a high quantity. Due to its simplicity and low cost, it is a practical approach to be practiced in southeast Asian countries.     

Endogenous and exogenous ethylene induces needle abscission and cellulase activity in post-harvest balsam fir (Abies balsamea L.)

Post-harvest needle loss is a major problem for balsam fir and other Christmas tree species. Recent evidence has implicated ethylene as a signal responsible for post-harvest needle abscission, but enzymological changes remain unknown. The objective of this study was to identify and quantify cellulase activity associated with endogenous and exogenous ethylene-induced abscission. An experiment was designed with three treatments (control, endogenous ethylene, or exogenous ethylene) with five replicates. Key response variables include needle retention duration, xylem pressure potential, ethylene evolution rate, and cellulase activity. Two complimentary methods were used to assess cellulase activity: a cellulose plate digestion and zymography. The results confirm ethylene as a signal for post-harvest abscission and identify ethylene-induced cellulase. Ethylene evolution was typically between 15 and 16 μL g⁻¹ h⁻¹, but there was no difference among the three treatments. However, exogenous ethylene significantly decreased needle retention by 60% and resulted in a sixfold decrease in xylem pressure potential. In addition, cellulase activity increased by 8- and 12-fold in endogenous and exogenous ethylene-induced abscission, respectively, compared to the control. Identification of ethylene-induced cellulase activity has increased our understanding of the post-harvest needle abscission process and confirms ethylene’s role as a signal molecule.     

Polyamines and ethylene in the removal of embryonal dormancy in apple seeds

Putrescine (Put), spermidine (Spd) and spermine (Spm) were found in seeds of apple ( Malus domestica Borkh. cv. Antonovka), in amounts that increased in the order given. The levels slowly decreased during 30 days of stratification. Exogenous polyamines (PAs) affected germination of isolated embryos in a way dependent on the type of polyamine, its concentration, and the state of the embryo dormancy. The effect of Put and Spd on germination was stimulatory, while that of Spm was inhibitory. Stimulation of germination was also observed when embryos were treated with arginine, ornithine and methionine. Canavanine inhibited germination, and this effect was reversed by arginine or Put. Ethephon, aminooxyacetic acid (AOA) and aminoethoxyvinylglycine (AVG) present during seed stratification had no effect on the levels of endogenous PAs. Put and Spd did not change ethylene production, neither during seed stratification nor during embryo germination, whereas Spm reduced ethylene evolution. The data suggest that Spm plays a role in the maintenance of dormancy by preventing ethylene production, while Put and Spd participate in dormancy removal, independently of ethylene.     

The role of ethylene in photoperiodic control of bulbing in Allium cepa

Bulb formation in Allium cepa L. cv. Dorata di Parma, was promoted by ethylene (Ethrel 120 mg l⁻¹) treatments. Application of the antiethylene complex silverthiosulphate (0.01 m M ) inhibited ethylene-induced bulb formation, but did not affect photoperiod-induced bulb formation. When the inhibitor of ethylene biosynthesis, aminoethoxyvinylglycine, was applied at 0.04 to 4 mg l⁻¹ to onion plants under inductive photoperiodic conditions the bulb promotion was unaffected. Therefore, Ethrel-induced bulb formation does not appear to be related to endogenous control of bulbing.