Arsenic contamination is a serious problem in many parts of India. The toxic metal finds its way through water to plants to food and to the human body. How can we reduce the uptake of the metal by plants?
Bishwajit Kumar Kushwaha, a young plant physiologist and his mentor, Vijay Pratap Singh, from a college in Allahabad teamed up with a group of researchers from Saudi Arabia to investigate whether 2-oxoglutarate can help alleviate arsenic toxicity. The chemical, 2-oxoglutarate, is a key intermediate in the metabolic pathways of sugars and amino-acids and acts as bridge between them. It is also involved in the pathways for energy production and stress response.
The duo dipped tomato seeds in different concentrations of 2-oxoglutarate, for different durations. Bishwajit kept the seeds in darkness for sprouting and, once they germinated in sterilized sand, the seeds were primed in 2-oxoglutarate for 24 hours before exposing them to sodium arsenate in an environmentally equivalent concentration.
In plants exposed to arsenate, the roots do not grow well. Arsenic accumulates in roots and interferes with nitrogen assimilation. So, cell death rate in roots is high.
But in plants from primed seeds, accumulation of arsenic in roots was less than half that found in those that were not treated. Nitrogen assimilation was near normal. Cell death in roots was also found to be lower. And the reduction in root weight was minor.
Image: Karon Magwood
Normally, the chlorophyll content of the leaves of plants exposed to arsenate is reduced. But priming with 2-oxoglutarate retained most of the photosynthetic activity.
The researchers also observed reduced superoxide radicals in root tissue indicating that physiological stress due to arsenate is lower in treated than in untreated plants.
“All these effects could be due to nitric oxide”, says Bishwajit. In plants exposed to arsenate, nitric oxide in roots is lower. But, plants primed with 2-oxoglutarate had higher amounts of nitric oxide”.
Nitric oxide is a regulator of plant development and could explain the differential expression of antioxidant enzymes, lower cell death and better plant growth in primed seeds.
“Priming seeds is an easy technique. Now we need field experiments to test the impact on the productivity of crops in arsenic contaminated areas”, says Vijay P. Singh, his mentor at the University of Allahabad.
Physiologia Plantarum, DOI: 10.1111/ppl.13168
Gujarat Arts and Science College, Ahmedabad
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