“Maati hi Odan, Maati Bichavan Maati ka Tan Ban Jaayega”
So wrote the Hindi poet Bharat Vyas, in a different context. But it is relevant to us here. A typical man of 70 kg is made up of 43 kg oxygen, 16 kg carbon and just 1 gram of silicon.
Yet he cannot do without this little gram. Without it, his skin would suffer, his bones lose strength. He needs to take in anywhere between 5-20 milligrams of silicon per day, and most, if not all, of it comes through diet.
Research published ten years ago in the West showed that man takes in 30-33 milligrams per day, while a typical woman takes in a bit less, 24-25 mg per day.
Where does this intake come from? Beer, bananas, string beans and cereals. Banana packs in 14 mg per 250 g of the fruit, high grain cereals 10 mg/100 g and green beans 6 mg/250 g. Brown rice has 4 mg/200 g while white rice has 2.5 mg/200g (Gandhiji was right – eat brown rice and high grain cereals. And I like the idea of beer as a silicon supplier).
Plants happen to be the major source of silicon for our needs. But why did they start taking in this element in the first place?
And how do they do it? After all sand, which is silicon dioxide (called silica, to differentiate this compound or molecule from its parent element silicon), is not soluble in water.
The roots of plants must have a mechanism to take silica in the soluble form and transport it to the stem, leaves and other parts.
Strength to stalk
We now know that silica offers strength to the stalk and stem, keeping them from wilting, and to toughen and widen the leaves open so that they may capture light and photosynthesize efficiently. Silica prevents leaves from lodging or falling over, and the husk that covers the seeds has silica.
And the silicon helps warding off invading pests such as the yellow stem borer by killing off their larvae.
Of all plants, rice is the best one to capture silica from the ground and use it for its health. Silica is present to the extent of 10-15 per cent in all parts of the rice plant.
Transported in the soluble form through the roots, it is sent to various parts and processed to diverse morphological forms. In some parts, it is made into tough sheets and in others more granular. Through these specific forms, silica offers protection to the plant from stresses (heat, drought) and attack by pests and fungi, promotes better harvesting of sunlight for fast growth and in packaging the seeds.
We now know that silica is first converted to the soluble silicic acid, in the presence of moisture and the right acidity conditions in the soil. This silicic acid is then transported in plants using proteins called Lsi1 and Lsi2, which belong to what biologists call as the aquaporin family.
The challenge
However, excessive use of fertilizers, insufficient amounts of water, increasing incidence of pests and microbes, and the depletion of soil silicon have all led to a decline in rice production.
It has therefore become important to find ways of enhancing the uptake of available silicon using novel methods.
It is this challenge that Professor S. Ranganathan of the Indian Institute of Chemical Technology, Hyderabad has taken up to address and solve.
A creative organic chemist who successfully practices and propagates the “art of organic synthesis”, he argued that if one can hook on a water-soluble small molecule to the hydroxyl arm of silicic acid, one should be able to enhance the transport of silicon from the soil to the plant via the root.
He had known that people had used a polymer-based molecule to dissolve fine silica from the lungs of affected people.
He then wondered: why not strip the polymer down to its basic active unit (pyridine-N-oxide) and use it to transport silica? He did so and found this simpler version successful in attaching to the silicic acid ( J. Chem. Sci ., 2004, Biologia Plantarum , 2006).
Yet, he was not satisfied, because pyridine N-oxides might lead to soil residual effects. He wanted to try more easily available and naturally occurring small molecules, which do not have ill effects on soil microbial organisms that are beneficial to the plant.
Extensive research
After extensive search, he found simple amino acids like glycine, glutamine, histidine, and even imidazole to enhance silica uptake three times better. And these are natural environment-friendly and easily available ( Crop Protection , 2008, and in the journal called P, S, Si and the Related Elements , 2009, 2010).
The next step was to go from lab to land. Collaborating with the plant physiologist Dr. Voleti Sitapathi Rao of the Directorate of Rice Research (ICMR), Hyderabad, Professor Ranganathan tried his method on rice plants in the green house, field and in normal farmlands.
Not only does silica uptake go up (by 18 per cent in the stalk and 11 per cent in leaves) when imidazole is added, but it also cuts down the damage caused by the pest yellow stem borer by over 50 per cent in three different varieties (Rasi, Kasturi, Krishna hamsa) and reduces fungal damage (blast) remarkably.
Drs. Ranganathan and Sitapathi Rao are now asking that their method be field-tried on a more extensive scale, and I am sure it will be done soon. Here then is a promising example of translational research — sand to lab to land.
dbala@lvpei.org
