第八章-生物技术保鲜

1、第八章 生物技术保鲜,植物采后腐败,Number of efficient chemical and physical treatments can be used to preserve fresh foods Ideal way to preserve foods (plant) Genetically programme to foods to do the job by themselves with any human intervention,Once plant tissues are harvested, they engage in an accelerated senesc

2、ence process that leads to spoilage Plant organ senescence Natural process Controlled by gene Harvestingdetaching organs from main plants Adding a strong stress component speeding up the decay,Genetic engineering has the potential to slow down the natural senescence processes and alleviate the stres

3、s responses from harvested tissues,Fruits ACC, 1-aminocyclopropane-1-carboxylic acid,(1) Manipulating ACS- Transgenic tomato,Antisense gene inactivation Bearing inverted copies of antisense of ACS Complete inhibition of endogenous ethylene production Failed to ripen Develop orange color, kept on air

4、 up to 150days after pollination Control :60 days Reversible by exogenous ethylene 6 days Control:1-2days,Transgenic tomatoes,Non-ripening,Ripening,(2) Manipulating ACO,ACO Final enzyme on the biosynthetic pathway Antisense gene of ACO in tomato Reduced levels of ethylene Extended ripening period Ri

5、pening was delayed by the suppression of the ACC oxidase gene,Manipulating ACO-Examples,Melon Strong silencing of ACO Suppression of ethylene production Enhanced storage capacity VS. control Tomato Remaining firmer Resistant to chilling injury (2C, 3 weeks),(3) Depletion of SAM and ACC,Bacterial gen

6、e coding ACC deaminase (脱氨基酶)tomato Ethylene reduced Firmness increased A gene encoding SAM hydrolase tomato Ethylene reduced Fruit stayed firmer,(4) Inhibition of ethylene receptor,Ethylene is perceived by the cell by a family of receptors Success Suppress the expression of Nr (C2H4 receptor) Fruit

7、s with very low levels of the Nr gene expression showed delayed ripening.,Non-climacteric fruits,Little is known about the mechanisms controlling fruit ripening Economic importance Important agronomic trait : firmness Ripening usually accompanied by increase of softening Manipulation of fruit firmne

8、ss can lead to longer effective period of consumer acceptability and reduced losses,Manipulation of fruit firmness -the case of strawberry,Transgenic strawberry plants Fruit-ripening-specific pectate lyase (果胶裂解酶)gene had been silenced No difference was observed in color, shape or weight Clear diffe

9、rence in firmness Microscopic analysis of the fruits cell walls in transgenic fruits displayed a lower degree of swelling than control fruits,Drawback,Yield reduced Avoid using tissue specific promoters Silencing the pectate liase gene only in ripening fruits instead in all plant tissues,3.Methods f

10、or reducing spoilage in vegetables,Edible vegetables come in all shapes, developmental stages and colors Leafy vegetables are the most economically important type Lettuce letis Spinach Endive endaiv 菊莴苣 Radicchio菊苣 Witloof 菊苣,Senescence is a highly regulated stage in the life of the leaf it is coord

11、inated by a set of genes senescence-associated genes or SAGS Control process is quite complex Number of external and internal parameters can influence the rate of senescence,Reducing spoilage in vegetables,Ethylene receptor Ethylene is intimately linked to senescence and its role as a senescence ind

12、ucer has been firmly established Ethylene insensitive plants Mutagenize（诱变） to disrupt ethylene perception,Cytokinins(细胞分裂素),Antagonistic to ethylene delaying the onset of senescence in leaves During the senescence process, there is a drop in cytokinin levels manipulate cytokinin biosynthesis to del

13、ay senescence in leaves Bacterial gene coding for enzyme for biosynthesis of cytokinins Cytokinins level elevated Delay in leaf senescence,Antisense of ACO,Flower vegetables (cauliflower and broccoli) are quite popular but the fresh market opportunities are limited by their poor post-harvest life es

14、pecially in broccoli Ethylene play a crucial role in the control of senescence in many flowers Broccoli produces a significant amount of ethylene after harvest strong influence on the rate of senescence,Transgenic broccoli carrying antisense copies of a tomato ACO gene Ethylene lower than controls (

15、72h after harvesting) Respiration rate decrease (98h after harvest),4. Enhancing plant resistance to fungal and bacteria,One of the most promising resistance strategies use of cell wall lytic enzymes to degrade or damage the fungal cell wall Major components: chitin and glucan Several kinds of chiti

16、nases and glucanases have now been cloned,transgenic plants an increased degree of resistance to fungal pathogens bacterial resistance is difficult to accomplish,Safety of Transgenic Foods/GMO/GEO,FDA 1992 Federal Register statement The agency is not aware of any information showing that foods deriv

17、ed by these new methods differ from other foods in any meaningful or uniform way, or that, as a class, foods developed by the new techniques present any different or greater safety concern than foods developed by traditional plant breeding.,Regulatory process for transgenic crops in the U.S.,Institu

18、tional Biosafety Committee Animal and Plant Health Inspection Service (APHIS) of USDA Food and Drug Administration (FDA) Environmental Protection Agency (EPA),GM Food Label Required,European Unions 10/2003: Labeling & traceability 04/2004: EC 1829/2003 & EC 1830/2003 Other counties Japan, Korea, Chi

19、na, Australia, New Zealand, India More than 35 countries have GMO regulations under consideration,Proposed FDA policy for voluntary labeling,Not genetically modified,X Virtually all commercial foods have been genetically modified.,GMO free,X “Free” implies zero, which is difficult to verify.,Proposed FDA policy for voluntary labeling,Genetically engineered,This product contains cor