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‘Golden’ lettuce could be used to fight micronutrient deficiencies‘Golden’ lettuce could be used to fight micronutrient deficiencies

Researchers from Spain have discovered a way to increase levels of beta (β)-carotene – a precursor to vitamin A – in lettuce by up to 30 times.

Tessa Wiles, Content Editor

October 29, 2024

6 Min Read
‘Golden’ lettuce could be used to fight micronutrient deficiencies
© AdobeStock/Cherry

In doing so, the green leaves of the lettuce turned a golden colour, indicating boosted β-carotene and nutritional enhancement.

The enhancement can potentially improve certain plant species' nutrition, alongside presenting biofortification opportunities for the food industry.

The team of researchers, from the Institute of Molecular and Cell Biology (IBMCP) at the Polytechnic University of Valencia and the Spanish National Research Council, developed a method to significantly increase β-carotene content in lettuce leaves.

The study, published in The Plant Journal, outlines the biotechnological techniques and high-light intensity treatments used by the team to discover and develop new places to store β-carotene in lettuce leaves without impacting photosynthesis.

Through this method, the team claims to have successfully increased levels of accessible β-carotene in the leaves 30-fold, compared with controls.

Powerful properties of β-carotene

β-carotene, naturally found in plants and photosynthetic organisms, is a precursor to vitamin A. This means that in its original form, the compound is inactive. However, once ingested, the body transforms it into an active form of vitamin A.

The carotenoid has an essential role in the body, including in vision, immune function, and processes on the cellular level, including cell differentiation and proliferation. It has also been shown to possess immunostimulant, antioxidant, and cognitive-enhancing properties.

Over half of the global population is micronutrient-deficient  

The human body requires micronutrients – essential vitamins and minerals – in small amounts to function and develop properly. Unlike classical hunger, defined as macronutrient deficiencies, hidden hunger (micronutrient deficiencies) is, as demonstrated by its name, more insidious, often going unnoticed and untreated despite its potentially devastating effects.

A 2024 study published in The Lancet Global Health found that over half of the global population consumes inadequate levels of micronutrients, a finding the authors described as “alarming”.

The challenge of biofortifying green leafy vegetables with β-carotene

The IBMCP team noted that incorporating vitamin A or β-carotene into food could help fight micronutrient deficiencies. However, these fortified food products are often expensive for the end consumer, leaving them unavailable to those who need them most.

Another strategy that can be used to enhance crops with micronutrients is biofortification. Carotenoid biofortification has been reported successfully in non-photosynthetic tissues, such as potato tubers, seeds, or rice endosperm.

While the crops themselves may be boosted with high β-carotene levels, it only solves part of the challenge. Bioavailability often remains low in these genetically modified crops, meaning it is difficult for the human body to digest and utilise the compound.

The team aimed to bridge this gap by improving both the levels of β-carotene and its bioaccessibility in lettuce leaves.

Increasing β-carotene without impacting photosynthesis

The study authors noted that manually changing carotenoid levels in leaves has posed a challenge in the past, due to the need to strike a delicate balance between increased β-carotene accumulation and the maintenance of photosynthesis.

Excess amounts of β-carotene often disrupt photosynthesis processes, potentially leading to chloroplast dysfunction and cell death. Chloroplasts are plant cell organelles that, via photosynthesis, convert light energy into chemical energy.

To address this challenge, the study authors devised two key objectives: to significantly increase the β-carotene levels in lettuce leaves, and to enable β-carotene to be stored within plant tissues without adversely impacting essential processes such as photosynthesis.

The primary crop of interest was the Lactuca sativa species of edible lettuce, chosen for its practical applicability and commercial viability.

The team, however, first used the tobacco plant Nicotiana benthamiana as a model organism to explore the mechanisms behind β-carotene biosynthesis and accumulation. Only after this initial exploration did the researchers apply their findings to L. sativa.

They initially applied genetic modification techniques to the model organism N. benthamiana. Using agroinfiltration, the team introduced genetic material into the plant cells, stimulating the carotenoid biosynthesis pathway and targeting β-carotene production. This process provided insights into how plants' cellular systems could be manipulated to increase β-carotene levels.

Combining techniques to increase β-carotene levels in lettuce leaves

After successfully increasing β-carotene levels in N. benthamiana, the team shifted their focus to L. sativa. Using a combination of biotechnological techniques and high-intensity light treatment, the team successfully elevated β-carotene levels in the lettuce leaves.

Biotechnological techniques, specifically agroinfiltration, was used by the researchers to direct β-carotene into the cytosolic vesicles, or “storage structures” located in the cell’s cytosol, outside of the chloroplasts. This process allowed genetic modifications to adapt the plants' metabolic pathways and enabled the accumulation of β-carotene within the cytosol.

The team then used high-intensity light treatment to stimulate the formation of plastoglobules – lipoprotein particles inside chloroplasts that do not commonly store carotenoids.

The key here was that by directing the β-carotene to the plastoglobules and the cytosolic vesicles, the researchers completely avoided and did not interfere with the photosynthetic process. Therefore, β-carotene accumulation was maximised, while avoiding potential disruptions to the photosynthesis process, which typically happens with excessive levels of β-carotene.

Manuel Rodríguez Concepción, lead author of the study, discussed this development in a press release.

He said: “Leaves need carotenoids such as β-carotene in the photosynthetic complexes of chloroplasts for their proper functioning.

“When too much or too little β-carotene is produced in the chloroplasts, they stop functioning, and the leaves eventually die. Our work has successfully produced and accumulated β-carotene in cellular compartments where it is not normally found by combining biotechnological techniques and treatments with high light intensity.”

Improved bioavailability and golden colour

The team found that by combining the biotechnological techniques and high-intensity light treatments, β-carotene levels could be increased by up to 30 times compared with untreated control leaves.

In plants, β-carotene is usually stored within the photosynthetic complexes of chloroplasts, where it is tightly bound to pigment-protein complexes, meaning when it is digested, the release of β-carotene is difficult.

By storing β-carotene in the plastoglobules and the cytosolic vesicles, or in other words the non-photosynthetic compartments of the plants, the team successfully increased bioaccessibility. Increased digestibility was possible as carotenoids within these structures are not as tightly bound, which makes for easier release and absorption.  

The team also found that the green leaves of the lettuce turned a “golden” colour. Generally, the more vividly orange a plant is coloured, the higher levels of β-carotene, thus indicating the leaves had achieved significantly increased levels of β-carotene, and nutritional enhancement.

Commercial viability and societal acceptance may be the new challenge

The researchers noted their method “represents a very significant advance for improving nutrition through biofortification of vegetables such as lettuce, chard, or spinach without giving up their characteristic scent and flavour”.

While the initial challenge of the study – enhancing β-carotene levels in lettuce leaves – was achieved, and the scientific potential and feasibility of the biofortification method holds promise, the next stage – towards widespread adoption and commercial viability – has its own set of hurdles.

The team acknowledged that commercial success is not so straightforward and depends on other factors, including societal and political acceptance of genetically engineered and enhanced crops.   

About the Author

Tessa Wiles

Content Editor , Informa Markets

Tessa Wiles is a content editor for Ingredients Network, Food Ingredients Global Insights, and Vitafoods Insights. She writes about food and ingredient innovations, product development, R&D, nutraceuticals, consumer trends, and more.

Always looking for industry insights, Tessa invites connections to explore the latest developments in the food and beverage sector.

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