These novel flavonoids flavones and flavonols-increased threefold, mostly in the Q12 peel, which had higher total antioxidant capacity. These findings add further support to the potential of engineering tomato fruit for accumulation of high levels of beneficial nutrients. Similarly, the poliphenol resveratrol—a stilbenoid—shows cancer chemo-preventative activity and may prevent coronary heart disease and arteriosclerosis. Liu, et al. showed, in a quantitative analysis, that resveratrol in transgenic lettuce plants reached 56.0 ± 5.52 μ/g leaf fresh weight, which is comparable to that in the skin of grape fruit . Flavonoids such as anthocyanins are known as antioxidants in vitro and can reduce the risk of many diseases related to aging. However, some vegetable brassicas, such as cauliflower, are low in anthocyanins. In an attempt to manipulate pigment biosynthesis to increase the health benefits of brassica vegetables, the effect of a regulatory locus of flavonoid content was assessed. Agrobacterium tumefaciens—mediated transformation of a B. oleracea line, selected for high transformation ability by Sparrow, et al., was used to produce plants transgenic for the maize Lc  locus. Lc is a regulatory gene in the anthocyanin pathway, and it is expected that its presence will increase the flavonoid content. Seedling explants were cocultivated with Agrobacterium tumefaciens strain LBA4404 containing a binary vector Q27 with a neomycin phosphotransferase II  gene. Under tissue culture conditions, Lc-containing plants were green with no visible increase in anthocyanin production. However, after transfer to the greenhouse, the exposure to high light intensity led to visible signs of pigmentation within one week.

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. Potato does not normally produce anthocyanin, but germplasm expressing anthocyanin pigment has been developed and is attracting interest from consumers. Stushnoff, et al. in potato identified 27 genes that are differentially expressed in purple and white tuber tissues. One of these genes—which encodes a novel single-domain MYB transcription factor—has the potential to influence anthocyanin-pigment production in potato. The resulting purple potato might offer both novelty and health functionality to consumers, who can also benefit from native Andean potatoes that do not always show desired tuber shapes for both table and processing industry. Several epidemiological studies in Asia, the USA and Europe have suggested that the consumption of vegetables from the Brassicaceae family, notably broccoli, reduce the risk of lung, breast, colon, and prostate cancer. The phytochemicals thought to be responsible for these health benefits are the isothiocyanates sulphoraphane and indole-3-carbinol. Sulphoraphane was initially thought to induce phase II enzymes in humans, which act against potentially carcinogenic compounds entering the body through the digestive system. However, ebb and flow bench it is not clear to what degree the anti-carcinogenic activity of sulphoraphane is achieved by phase II enzyme induction; it also seems that sulphoraphane can induce apoptosis and cell-cycle arrest in a variety of cell types. While research continues into the health-promoting mechanisms of Brassica isothiocyanates, others have developed highglucosinolate broccoli germplasm that results in plants that produce mainly isothiocyanates, compared with standard broccoli cultivars that also produce nitriles. Chromosome segments from a wild ancestor, Brassica villosa, have been introgressed to enhance glucosinolate levels. B. villosa alleles determine whether hydrolysis generates indole-3-carbinol or sulphoraphane. Hence, highglucosinolate broccoli might be suitable for increasing the amount of sulphoraphane in the diet.

The extent to which vegetable brassicas protect against cancer probably depends on the genotype of the consumer, in particular the allele present at the GSTM1 locus. This gene codes for the enzyme glutathione transferase, which catalyses the conjugation of glutathione with isothiocyanates. Approximately 50% of humans carry a deletion of the GSTM1 gene, which reduces their ability to conjugate, process and excrete isothiocyanates. Individuals with two null alleles for GSTM1 might gain less protection from these cultivars of vegetable. The most commonly consumed Brassica vegetable in Asia is Brassica rapa. B. rapa contains different isothiocyanates to B. oleracea and recent evidence suggests that individuals who are null for GSTM1 can gain a protective benefit from B. rapa. This example illustrates another aspect of complexity in breeding for health functionality in vegetable crops: human genetic variability has not generally been considered in the context of plant breeding programmes, but it might have important implications. Thus, when establishing vegetable breeding targets, it is important to explore the extent to which human variability affects the bioavailability and processing of health-functional compounds and influences health outcomes for a particular commodity. Vegetables of the Allium genus such as onion, garlic, leek and chive are among the oldest crops associated with health-related properties. Some of these traits appear to be related to the concentration and activity of organosulphur compounds in these vegetables. 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 Allium species. 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 containing antisense alliinase gene constructs  have been recently produced. Results from the antisense bulb alliinase lines have been much more encouraging, and three lines were produced with barely detectable bulb alliinase levels and activity.

Progress has been confounded by the poor survival of transgenic plants. Transgenic hybrid onion seed from these transgenic lines has been developed by crossing a nontransgenic openpollinated parental line with a transgenic parental plant carrying a single transgene in the hemizygous state. Some resulting seed produced by the nontransgenic parents will be hemizygous for the transgene and can be selected to obtain F1 heterozygous individuals containing the transgene. Self-fertilization of these individuals produces homozygous, hemizygous, and null F2 progeny for the transgene locus. These homozygous individuals can then be used to generate the bulk seed required for the production of commercial transgenic onion lines with less bitter taste. When onions are cut, two compounds are formed: propanethial sulphoxide—also known as the lachrymatory factor—and 1-propanesulphenic acid. The lachrymatory factor reacts with nerve-cell membranes in the eye to produce tears, causing the familiar crying when cutting onions. In normal conditions, levels of 1-propanesulphenic acid are low because it is rapidly converted to the lachrymatory factor. Recently, Eady, et al. silenced the gene for the lachrymatory factor enzyme by using RNAinterference, to produce tearless onions: 1-propanesulphenic acid self-condenses to 1-propenyl 1-propenethiosulphinate, 4x8ft rolling benches which then undergoes further reactions. This feat of genetic engineering reduces levels of lachrymatory factor up to 30-fold but does not diminish the overall levels of organosulphur compounds in the bulb. These “tearless onions” have potential health benefits for consumers as they do not produce tears, but retain their health-promoting properties. 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, which is 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, which is active at extremely low concentrations, as a food sweetener. The first successful study conducted to engineer genetically 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 from T2 transgenic plants tasted sweeter than the control plants, leaving a unique and sweet-specific after taste. Fructans and fructose polymers, sometimes known as inulin, might also have health-functional properties because they promote the growth of beneficial microbes in the gut, add sweetness without adding calories, and contribute to the fibre content of foods. Hellwege, et al., developed transgenic potato plants that produce inulin by the expression of the 1-SST  and 1-FFT  genes from globe artichoke. The results suggested that these enzymes might be sufficient to produce inulin molecules of various lengths in plants. Another approach to improving the health functionality of vegetable crops is to reduce the concentration of antinutritional factors. These are naturally occurring compounds with inhibitory effects on the nutritive potential of plants. In many cases, anti-nutritional factors are produced in planta for pest control, but have secondary effects on human nutrition. 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 Africa where this starchy root crop is the base of their diet. Faba bean  contains condensed tannins that reduce the value of the inherently high protein levels of the crop. Tannins can be removed by the activity of two genes, zt-1 and zt-2, which are pleiotropic for white-flowered plants. Gutierrez, et al. have identified a sequence characterized amplified repeat  marker linked to the zt-2 gene that is associated with increased protein levels and reduced fibre content of faba bean seeds, which should facilitate the development of tannin-free faba cultivars. Calcium oxalate is another common anti-nutritional factor in plants. It is most commonly found as deposits in the vacuole of specialized cells called idioblasts. The specific function of calcium oxalate accumulation in plants is not known; it might have a role in calcium regulation, ion balance, plant protection, detoxification or light gathering. There have been several attempts to reduce the amount of calcium oxalate in plant tissues by using molecular approaches. Nakata and McConn identified mutants of barrel clover  that are deficient in calcium oxalate and not compromised in growth. This suggests that it might be possible to genetically engineer plants with low or very low calcium oxalate levels; however, if calcium oxalate has a role in plant protection, low-calcium oxalate crops would require other protection strategies. Some vegetables, mainly tomato, have also been genetically modified to be used as vaccine delivery.Oral vaccines also offer the hope of more convenient immunization strategies and a more practical means of implementing universal vaccination programs worldwide. Tomato has been tested for expression of vaccines that can address human health issues of the developing world. 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, lasmalemma, 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 to 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.