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Thursday, September 23, 2021

A nutrient-rich weed for a climate stressed world

Purslane is known for its phytochemicals such as alkaloids, flavonoids, catecholamines and carotenoids.

Written by Ritvik Chaturvedi | Bengaluru |
Updated: July 23, 2021 6:58:02 pm
Purslane, a crop historically consumed through much of the Old World, but has of-late been dismissed as a peripheral, if not an outright useless byproduct (Wikimedia Commons)

Climate change has brought to the fore concerns of ensuring food security for a growing population in a sustainable manner. In recent years, attention has turned to plants that are naturally drought resilient and consume less water. Many of these are ‘orphan’ crops – those that are historically and indigenously important, but have recently been put on the back burner due to a dietary homogenisation brought about by globalisation. Examples familiar to the workaday Indian would include small grasses like sorghum, pearl millet, finger millet; and tubers like elephant yams and sweet potatoes.

An upcoming, comprehensive study in Frontiers in Sustainable Food Systems from the Department of Plant Science, Central University of Kerala, puts the spotlight on purslane (Portulaca oleracea), a crop historically consumed through much of the Old World (Europe, Africa, Asia), but has of-late been dismissed as a peripheral, if not an outright useless byproduct. Its nicknames include duck’ weed’ and fat weed.

Authors of the study – and others before them – maintain that purslane could be a key ‘climate smart’ crop in a drying environment.

Magic mechanisms

Purslane is a C4 plant which means that it fixes atmospheric CO2 as a 4-carbon molecule (the other photosynthetic pathway is C3, which fixes CO2 as a 3-carbon molecule). While C3 plants (e.g. wheat, barley, and oats) grow at higher latitudes with high winter rainfall, C4 plants (e.g. most millets, maize, sugarcane) are found in warmer, low latitudes.

Purslane can also switch to special photosynthesis called Crassulacean acid metabolism (CAM) photosynthesis according to environmental conditions like salinity, day length, night temperature and water stress. CAM photosynthesis is an adaptation to arid conditions, whereby plants fix atmospheric CO2 at night and perform photosynthesis during the day. This photosynthetic pathway is present in xerophytic plants such as cactus.

Purslane, unlike many crops, has a unique ability of a C4-CAM switch. It can adopt a C4 pathway under normal irrigation conditions and switch to a CAM pathway when faced with aridity.

Salt tolerance

The plant also exhibits natural resilience to salinity, and it is argued that it could be an important biosaline crop. Purslane responds to salinity stress by increasing the expression of a gene called the pyrroline-5-carboxylate synthetase (PC5S) gene.

Previous studies have established that purslane – like other biosaline crops – manages to keep up its photosynthetic activity, albeit at the cost of its growth potential. Nevertheless, researchers note that while stress impacts the germination potential of the plant, it has no effect on the production of a high number of seeds.

As a species, purslane exhibits a wide range of phenotypic plasticity, which is the ability of an individual to adapt easily to a change in the environment.

The paper further discusses various subspecies/cultivars with their own strengths:

  • Cultivars from Turkey have the lowest amount of antinutrients
  • Eritrea and Egypt cultivars have the highest drought tolerance
  • Iranian cultivars have the highest biomass yield
  • Dutch varieties have high levels of omega-3-fatty acids
  • Greek varieties exhibit high levels of crude protein

Stress resistance

It is argued that identification of the genetic pathways responsible for these individual stress-resilient traits can be used in genetic engineering programmes to create even more superior varieties.

Besides its stress resilience, the crop is known for its nutritive phytochemicals such as alkaloids, flavonoids, catecholamines, lignans, terpenoids, betalains, carotenoids, vitamins.

In addition to the high biomass, “purslane takes up very little space and time to grow and contains omega-3-fatty acids that are lacking in a vegetarian/vegan diet.” Ajay Kumar, the author of the study, said in an email conversation with IE.com. Consumption of purslane should therefore be promoted among vegetarians and vegans.

“Considering the vulnerabilities associated with the mainstream globalised foods that travel long distances before reaching the kitchens, it is important to prospect those orphan crops which have regional and local importance and are easily available. Such crops are especially important during the pandemics such as COVID 19 and civil wars when supply-chains are disrupted,” he adds.

The author is a freelance science communicator. (mail@ritvikc.com)

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