Climate change is a scary reality. As global temperatures rise and water becomes an ever scarcer commodity, we fear that many of our common crop species may not survive to feed the relentlessly growing human population.
Through the process of photosynthesis green plants combine carbon dioxide (CO2) and water in the presence of sunlight to make food (carbohydrates) for themselves and for those that eat them. However, rising world temperatures puts plants under survival stress.
Some plants have evolved a variety of different mechanisms to improve photosynthesis. For instance, maize and sugarcane evolved so-called C4 photosynthesis, which allows the plant to remain productive under high temperatures. Succulents such as cacti and agaves use another type called Crassulacean Acid Metabolism (CAM) photosynthesis, which helps them survive in deserts and other areas with little water. Both C4 and CAM serve different functions, but they use the same basic biochemical pathway of photosynthesis, acting as “add-ons” to regular photosynthesis.
CAM is particularly interesting. In most plants CO2 enters the plant from the atmosphere through little openings in the leaf called stomata. The plant also loses water through the same stomata. Photosynthesis happens during the day when the sun shines and the stomata are open for CO2 to enter. However, in hot, dry climates the plant cannot afford to have constantly open stomata during the heat of the day, lest it loses too much water. This is where CAM comes to the rescue. The plant keeps its stomata closed during the heat of the day and opens them at night when the sun doesn’t shine. The CO2 absorbed at night is “fixed” in the form of malate. During the day when the sun is shining the malate is broken down to release the CO2 so that normal photosynthesis can take place.
What if these C4 and CAM photosynthesis adaptations could be combined in the same plant to make it resistant to both heat and drought? It’s the sort of perfect outcome that plant genetic engineers dream of.
No need for them to dream – there is already such a plant. It’s probably growing in your back yard and you may have been pulling up what is usually considered a pesky weed for decades! I’m talking about Portulaca oleracea, commonly known as purslane.
Purslane – Portulaca oleracea
Scientists from Yale University have recently described their discovery: “This is a very rare combination of traits and has created a kind of ‘super plant’—one that could be potentially useful in endeavours such as crop engineering.
“What makes the weed purslane unique is that it possesses both of these evolutionary adaptations—which allows it to be both highly productive and also very drought tolerant, an unlikely combination for a plant.”
Until now, most scientists believed that C4 and CAM operated independently within the leaves of purslane. But the Yale team conducted a spatial analysis of gene expression within the leaves of purslane and found that C4 and CAM activity are totally integrated in them. They operate in the same cells, with products of CAM reactions being processed by the C4 pathway. This system provides unusual levels of protection for a plant in times of heat and drought.
This is an amazing adaptation in a common weed, but what makes it more exciting is that purslane is an edible (and palatable) weed with scores of health and medicinal benefits.
According to WebMD, purslane has vitamins, minerals, and antioxidants that can provide important health benefits. For example, vitamin A helps your eyes remain healthy as well as improve your immune system, and is also critical to the health of your organs because it supports healthy cell division. Purslane is also rich in vitamin C, which is important to keep your collagen and blood vessels in good shape, as well as helping injuries heal. This weed is full of beta-carotene, the pigment responsible for the reddish colour of its stems and leaves. Beta-carotene is one of many antioxidants found in purslane. These antioxidants have been found to reduce the number of free radicals in the body, which may help reduce the risk of cellular damage.
Purslane salad – IzzyCooking
Purslane is one of the few vegetables that’s rich in omega-3 fatty acids, which are important to support healthy arteries and can help prevent strokes, heart attacks, and other forms of heart disease. In fact, purslane has the highest-recorded levels of omega-3 fatty acids of any land-based plant.
Purslane is also a good source of two minerals that are important for bone health: calcium and magnesium.
So why are you still eradicating this weed? Just eat it! Eat it raw in salads, stir-fried with other greens, or in soups and sauces. It’s the new super-food!
Cautionary note: Purslane contains oxalates, which have been linked to the formation of kidney stones. People prone to kidney stones should be careful when eating purslane, especially the seeds.
Portulaca grandiflora – a popular garden relative