Most of us don’t eat enough fruits and veggies, but with a broad and varied diet, nutrient deficiencies are relatively rare. However, billions of people on Earth don’t have the luxury of a broad and varied diet. Vitamin A deficiency, for instance, is a huge problem. An estimated 250,000-500,000 children who are vitamin A-deficient become blind every year, and half of them die within 12 months of losing their sight.
Lettuce, one of the least attractive leafy vegetables, could end up playing a key role in this problem. A team of scientists from the Institute for Plant Molecular and Cell Biology in Valencia, Spain have engineered a new “Golden Lettuce” with 30 times more nutrients than commercial lettuce.
IBMCP.
Vitamin A deficiency is a widespread health crisis, particularly in developing countries, disproportionately affecting children and malnourished populations across the world. While supplementing diets with vitamin A or fortified foods is an effective solution, this approach is often unaffordable or simply impractical.
A promising alternative is biofortification — the process of increasing the nutrient content of food crops.
A leafy solution
In principle, this isn’t a new approach. It’s been done through agronomic techniques like selective breeding for millennia. But in recent years, researchers have been taking a more direct approach, increasing selective nutrients through genetic biofortification.
However, genetic biofortification efforts typically focus on non-photosynthetic tissues, such as seeds and tubers. This time, researchers focused on the leafy parts themselves, increasing the content of carotenoids.
Carotenoids, which include beta-carotene (a precursor to vitamin A), are critical for photosynthesis in plants. In leaves, carotenoids help absorb light and protect chloroplasts from damage caused by excess sunlight. However, bioengineering leaves to increase carotenoid levels has been challenging because it risks disturbing the delicate balance between carotenoids and chlorophylls, which can negatively affect plant growth and photosynthesis.
The research team used two main approaches. The first involved producing beta-carotene in the cytosol (the fluid part) of leaf cells, rather than in the chloroplasts where photosynthesis happens. This way, they avoided disturbing the chloroplasts’ balance of carotenoids.
The second approach focused on turning chloroplasts into chromoplasts, which are storage centers for carotenoids found in parts of plants like carrot roots and tomato fruits. To do this, the researchers used a bacterial enzyme called crtB, which stopped the chloroplasts from performing photosynthesis and turned them into carotenoid storage sites. By combining both strategies, the team was able to increase beta-carotene levels by five times.
The innovation achieved an increase in beta-carotene content in the model plant Nicotiana benthamiana and edible lettuce (Lactuca sativa). Moreover, by enhancing how plants store these nutrients, they dramatically improved the bioaccessibility — the portion of a nutrient that the body can absorb and use — of beta-carotene.
Light and lettuce
While engineering carotenoid biosynthesis and storage improved beta-carotene levels, the researchers found that exposing the plants to high-intensity light further amplified the results. Intense light promoted the proliferation of plastoglobules — structures that store compounds like carotenoids. These plastoglobules became the primary storage sites for beta-carotene, and their proliferation under high-light conditions led to a 30-fold increase in bioaccessible beta-carotene.
The researchers chose lettuce as it is a common staple in many diets and already contains some carotenoids, including a unique one called lactucaxanthin. The fact that lettuce can be grown in a number of different climates and conditions makes it all the more promising.
Perhaps most importantly, the technique could also be used on a number of different leafy greens.
The implications of this research are vast. By biofortifying leafy vegetables like lettuce, the researchers have created a scalable solution to improve nutrition without relying on costly supplements or fortification programs.
Of course, GM foods are notoriously unpopular. A classical example is the Flavr Savr tomato, the first genetically modified food approved for sale in the U.S. in 1994. It was engineered to have a longer shelf life and better flavor by suppressing a gene that causes tomatoes to rot quickly. However, despite initial excitement, Flavr Savr faced significant pushback from anti-GMO activists and concerns over potential health risks. Production costs were high, and consumer acceptance was low. The tomato was eventually pulled from the market.
However, the use of high-intensity light to enhance nutrient storage and bioaccessibility offers a practical, low-cost method that could be adopted by farmers worldwide. This approach does not require the use of genetically modified organisms (GMOs), which could make it more acceptable in regions with strict regulations on GM crops.
The research was published in The Plant Journal.
