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Salt of the Earth

Salt of the Earth
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First Published: Fri, Jul 15 2011. 01 15 AM IST
Updated: Fri, Jul 15 2011. 05 01 PM IST
Stop her, she’s eating rubbish!”
If you have a hyperactive 14-month-old, as I do, this is likely to be the most common exclamation you will hear from her grandparents.
Oh, all right, I confess—I’ve shouted it out too. It’s only natural.
But, really, it’s more natural for children to build resistance by priming their immune systems. They do this by eating or drinking, in small quantities, the very things that could harm them.
My mother clearly remembers how as a toddler I frequently ate mud (she isn’t quite as clear about why she didn’t stop me then, as she does her granddaughter now). I suppose this early acquaintance with the science of immunity continued through my adult life. I can now pretty much each and drink anything, anywhere.
Scientists have long known of natural resistance and used dead or weakened, live viruses as vaccines that help the human body develop an immune response. This is how diseases like small pox and polio were conquered.
Plant scientists, too, adopt this elegant technique, getting inspiration from plants that, in their natural state, respond to and cope with mild stress, such as heat, drought and salinity. This helps them cope with high stress in the future.
The latest example comes from a group of five scientists from the National Centre for Biological Sciences (NCBS), Bangalore, and the University of Bonn, Germany. Their new research paper in the Journal of Experimental Botany explains how they induced a variety of rice to resist the toxic effects of salts by exposing its roots—they call it “conditioning”—to a small amount of those salts.
The stress from salty soils, ironically, is an indication of plenty, a growing problem in poorly drained irrigated lands across great swathes of India and South Asia. In India alone about 6.7 million hectares, nearly twice the area of Goa, are now salt-damaged, according to a report from the Indian Council of Agricultural Research and National Academy of Sciences. Many teams of scientists, Indian and international, work on the problem of soil salinity, and there is an entire scientific institute, the Central Soil Salinity Research Institute in Karnal (Haryana), dedicated to the problem of salty land, but given India’s collapsing agricultural extension services, little has yet reached the farmer.
This is bad news at a time when land-starved India needs to increase its agricultural yield this decade. As irrigation increases, so too will salinity. This is because irrigation water is saltier than rain, and poorly drained irrigated land (nearly half of rice-growing land in India is irrigated) is frequently water-logged, increasing salts to dangerous levels, reducing yields by cutting the amount of oxygen to the roots.
It is the roots that the NCBS and University of Bonn scientists fiddled with. Exposing the roots of IR20, a high-yielding, green-revolution rice variety particularly vulnerable to salt, causes certain root cells to generate a waterproof wax. Salt-laden water is filtered in these cells and only then released into the plant’s plumbing system, or xylem.
The method is simple: Grow young rice plants for a week in a concentration of salt about half the level that would normally be toxic. This is enough to vaccinate—so to say—the rice plant. This implies that existing high-yielding varieties of rice are capable of surviving salt if properly immunized, instead of the infinitely more complicated method of identifying and grafting genes that confer salt resistance.
Such vaccination boosts the effectiveness of the Casparian bands, a network of wax-coated, waterproof barriers sited in the root’s inner core, where the xylem is most concentrated. Before conditioning, the plant allows in all substances dissolved in soil water, good and bad. After conditioning, the filters let in mainly the good.
The scientists also studied a traditional coastal-Kerala variety of rice called Pokkali, which, unlike IR20, was wholly resistant to salt. They found Pokkali already had the filters they induced in IR20, a strong argument for preserving ancestral crop knowledge.
Now, the fine print. Getting the plant to build such filters causes water to move slower through the roots than before, so the plant compensates by growing more roots. Does this reduce the amount of rice produced? There is no answer to that question as yet.
The current study is unlikely to help plants in the ground, but it does help scientists figure out how rice plants mount their response and then see if other things can elicit the same response, especially in seedlings that can then be transplanted into salty fields.
“We do not know at this point as to whether the response can be triggered at so early a stage or how long it lasts (will it stay on long enough to work after transplanting?),” says Prof. M. K. Mathew of the Laboratory of Membrane Biophysics. “These are things worth studying.” Indeed, especially if India hopes to feed its growing millions.
Samar Halarnkar is editor-at-large, Hindustan Times and Mint. This is a fortnightly column that explores the cutting edge of science and technology. Comments are welcome at frontiermail@livemint.com
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First Published: Fri, Jul 15 2011. 01 15 AM IST