Increased pigmentation was apparent in stems, petioles, main leaf veins,and sepals. lc-containing lines had 10 to 20 times higher levels of total anthocyanins than controls. In addition,antioxidant activity of lc-containing lines was 1.5 times higher than that of controls .The unique flavor and odor of alliums is derived from the hydrolysis of organosulfur compounds, which produces pyruvate, ammonia, and volatile sulfur compounds . This reaction is catalyzed by the enzyme alliinase,which is contained in vacuoles within cells and released upon disruption of the tissue . Variations in the ratios of these volatile sulfur compounds are responsible for the difference in flavors and odors between Alliumspecies . Along with health and nutritional benefits associated with these compounds, these thiosulfides are also major contributors to the bitter taste of some onions. Three sets of transgenic onion plants containingantisense alliinase gene constructs have been recently produced . Results from the antisense bulb alliinase lines have been much more encouraging, and three lineswere produced with barely detectable bulb alliinase levels and activity. Progress has been confounded by the poor survival of transgenic plants. Crossing a non-transgenic open-pollinated parental line with a transgenic parental plant carrying a single transgene in the hemizygous state has conducted to a transgenic hybrid onion seed from these transgenic lines.

Some resulting seed produced by the non-transgenic parents will be hemizygous for the transgene and can be selected to give F1 heterozygous individuals containing the transgene. Self-fertilizationof these individuals produces homozygous, hemizygous, aeroponic tower garden system and null F2 progeny for the transgene locus. These homozygousindividuals can then be used to generate the bulk seed required for the production of commercialtransgenic onion lines with less bitter taste. In attempts to reduce bitterness in lettuce, Sun et al.  cloned the gene for the sweet and taste, modifying protein miraculin from the pulp of berries of Richadella dulcifica, a West African shrub. This gene, with the CaMV 35S promoter, was introduced into the lettuce cultivar “Kaiser”using A. tumefaciens GV2260. Expression of this gene in transgenic plants led to the accumulation of significant concentrations of the sweet-enhancing protein. People suffering diabetes may use Miraculin as a food sweetener,which is active at extremely low concentrations. The first successful study conducted to engineer the taste of tomato fruit involved transformation of tomato with the thaumatin gene from the African plant katemfe.Thaumatin is a sweet-tasting protein. Fruit fromT2 transgenic plants tasted sweeter than the control plants, leaving a unique and sweet-specific aftertaste.Food safety can also be enhanced through transgenic approaches. The first transgenic cassava plants became available in the mid-1990s as plants with reduced cyanogenic content, which can benefit resource-poor people in rural Asia and Africa where this starchy root crop is the base of their diet.Some vegetables, mainly tomato, are also genetically modified to become a vaccine delivery. Plant delivery of oral vaccines has attracted much attention because this strategy offers several advantages over vaccine delivery by injection. Oral vaccines also offer the hope of more convenient immunization strategies anda more practical means of implementing universal vaccination programs worldwide.Transgenic tomato plants potentially can bring several positive effects and improve human health. McGarvey et al. engineered tomato plants of cultivar “UC82b” to express a gene encoding a glycoprotein,which coats the outer surface of the rabies virus. The recombinant constructs contained the G-protein gene from the environmental risk assessment strain of rabies virus. The G-protein was expressed in leaves and fruit of the transgenic plants,and it was found localized in Golgi bodies, vesicles, plasmalemma, and cell walls of vascular parenchyma cells.Ma et al.  overexpressed hepatitis E virus  open reading frame 2 partial gene  in tomato plants to investigate its expression in transformants, the immunoactivity of expressed products, and explore the feasibility of developing a new type of plant-derived HEV oral vaccine. The recombinant protein was produced at 61.22 ng/g fresh weight in tomato fruits and 6.37 47.9 ng/g fresh weight in the leaves of the transformants.

It was concluded that the HEV-E2 gene was correctly expressed in transgenic tomatoes and that the recombinant antigen derived had normal immunoactivity. These transgenic tomato plants are valuable tools for the development of edible oral vaccines. Chen et al.  developed an effective antiviral agent against enterovirus 71 ,which causes seasonal epidemics of hand, foot, and mouth disease associated with fatal neurological complications in young children, by transforming the gene for VP1 protein—a previously defined epitope and also a coat protein of EV71—in tomato plant. VP1 protein was first fused with sorting signals to enable it to be retained in the endoplasmic reticulum of tomato plant, and its expression level increased to 27 mg/g in fresh tomato fruit.Transgenic tomato fruit expressing VP1 protein was then used as an oral vaccine, and the development of VP1-specific fecal IgA and serum IgG were observed in BALB/c mice. Additionally, serum from mice fed transgenictomato could neutralize the infection of EV71 to rhabdomyosarcoma cells,dutch buckets for sale indicating that tomato fruit expressingVP1was successful in orally immunizing mice. Moreover, the proliferation of spleen cells from orally immunizedmice was stimulated by VP1 protein and provided further evidence of both humoral and cellular immunity.Results of this study not only demonstrated the feasibility of using transgenic tomato as an oral vaccine to generate protective immunity in mice against EV71 but also the probability of enterovirus vaccine development.The Gram-negative bacterium Yersinia pestis causes plague, which has affected human health since ancient times. It is still endemic in Africa, Asia, and the American continent. There is the urgent need for a safe and cheap vaccine due to the increasing reports of the incidence of antibiotic-resistant strains and concern with the use of Y. pestis as an agent of biological warfare. Out of all the Y. pestis antigens tested, only F1 and Vinducepresent a good protective immune response against a challenge with the bacterium . Alvarez et al. reported the expression in tomato of the Y. pestis F1-Vantigen fusion protein. The immunogenicity of theF1-V transgenic tomatoes was confirmed in mice that were injected subcutaneously with bacterially producedF1-V fusion protein and boosted orally with transgenic tomato fruit. Expression of the plague antigens in the tomato fruit allowed producing an oral vaccine candidate without protein purification and with minimal processing technology, offering a good system for a large-scale vaccination programs in developing countries.

The future of edible plant-based vaccines through transgenic approaches will depend on producing them safely on sufficient amounts. The production of vegetables worldwide tends to be on smaller areas and in more diversified holdings than field crops such as cotton, canola, cereals and soybeans. Vegetables are often in more complex agricultural systems where insects may move from one crop to the next within the same farm. How this will impact the use and effects of transgenic vegetable plants in the agricultural landscape can be complex. Growing multiple insect-resistant transgenic vegetable plants in the same area and exposure of a polyphagous insect to the same Bt protein expressed in the different vegetable species will challenge conventional strategies developed for transgenic cotton or maize cultivars. Thoughtful consideration therefore will be needed before choosing what toxins vegetable plants should express. The selection should be based not only on what will be an effective toxin against the target insect but which toxins are already in use in other vegetable crops that may be hosts for the target insect.Additionally, the difficulty of sampling insect populations for resistant alleles will take on a higher level of complexity in a diversified vegetable system.Further consideration should also be given to the effects on non-target organisms within diversified transgenic vegetable plantings. Hoheisel and Fleischer  investigated the seasonal dynamics of coccinellids and their food  in a vegetable farm system containing plantings of Bt-sweet corn, Bt-potato, and transgenic insect-resistant squash in northeastern USA. Their results indicated that the transgenic vegetable crops provided conservation of coccinellids and resulted in a 25% reduction in insecticide use. In a similar study with these same crops, Leslie et al.  compared the soil surface dwelling communities of Coleoptera and Formicidaein the transgenic crops and their isolines and found no differences in species richness and species composition but found that the transgenic vegetables required fewer insecticide applications. Such results make clear that transgenic technology can be introduced within vegetable integrated pest management  systems and that transgenic vegetables can offer novel and effective ways of controlling insects and the pathogens they transmit.Virus-resistant transgenic plants are particularly valuable if no germplasm source of resistance has been identified or if host plant resistance is difficult to transfer into elite cultivars by traditional breeding methods due to incompatibility barriers or links to undesired traits. In such cases, engineered host plant resistance may be the only viable option to develop virus resistant cultivars. Growers can also use virus-resistant transgenic vegetables as a trap crop by growing it as a border around the non-transgenic vegetable crop and allowing it to cleanse viruliferousaphids.In small, diversified vegetable plantings typical of those found throughout the developing world, the challenges for regulatory oversight of transgenic plants are immense. In these countries, farmers will likely save transgenic seed and move transgenic seed between locations, and some transgenic products may move into markets that do not permit these products. These concerns will be lessened if people consume the produce from transgenic vegetables locally after they are released and grown following national bio-safety guidelines. However,it is likely that violations will occur, and this will challenge legal systems.While each vegetable has its own set of one or more key pests, other pests can also be problematic. Traditional broad-spectrum insecticides often control a suite of pest insects. Thus, when transgenic vegetables are introduced into production systems, other methods of control will have to be applied or developed for secondary pests, e.g., biological control of secondary pests or use of selective insecticides, applied either as seed treatments or foliar sprays, may be necessary.Integrated pest management could benefit from some herbicide-tolerant crops, if alternative non-chemical methods can be applied first to control weeds and the specific herbicide could be used later, only when and where the economic threshold of weeds is surpassed . Herbicide-tolerant transgenic crops can help reducing plough in fields, thereby saving fuel because of less tractor use, which also protects the structure of the soil by reducing its erosion. Repeated use of herbicides in the same area may also create problems of weed herbicide resistance . Although the risk of herbicide-resistant genes in vegetables is globally lower than in field crops because many vegetables are consumed in the vegetative stage. Although transgenic cultivars have proven to be a powerful tool for pest management, and their use has been accompanied by reduced dependence on pesticides, fertilizers and other inputs, and dramatic economic and environmental benefits , many countries are still engaged in discussions about potential negative impacts of these crops on the environment, non-target organisms, food safety, the unintentional spread of transgenic traits into conventionally bred-crop or landrace gene pools of the same species particularly in centers of crop diversity or origin, and questions of seed ownership.

Fear about potential negative effects of transgenic crops has led to the implementation of very stringent regulatory systems in several countries and regulations that are far more restrictive for transgenic crops than for other agricultural technologies . Consumer antagonism has precluded many farmers and consumers from sharing the benefits that these crops can provide. Critics also claim that adoption of transgenic crops benefits multinational seed corporations while hurting small farmers because of the additional investments required for growing these crops successfully. These unfounded concerns are present despite the highly successful and rapid adoption of transgenics in maize, soybeans, canola and cotton in many countries of the world.Farmers and consumers will try to influence political decision making in favor of any technology if they expect to gain from it. The political power of farmers in the developed world was used effectively to gain access to large farm subsidies supported in part by fiscal resources and in part by artificially high consumer prices. Their market power however gradually deteriorated as consumers gained a greater say in the marketplace for food. On the contrary, developing world farmers possess very limited political power and have been taxed rather than subsidized by their governments.Another factor that has led to differential perspectives between rich and poor countries is the relative power possessed by civil society groups including advocacy activists opposed to genetic engineering in food and agriculture.These activists have been very successful in influencing the debate, and consumer and government attitudes towards genetically modified food in Europe and are also gaining power in selected developing countries.While the European governments have tended to follow the expressed desires by advocacy groups and a majority of consumers opposed to genetically engineered food, the USA and Canadian governments support the farm sector and the private sector engaged in the development and deployment of modern biotechnology-crops.