Indian basmati rice is world famous. But the seeds are vulnerable to environmental stresses and show reduced germination with time. Recently, many metal nanoparticles have been tried for improving seed germination and the healthy growth of various crops.
Shadma Afzal at the Motilal Nehru National Institute of Technology Allahabad has been working on metal nanoparticles in plant growth and fortification. Would nano-iron oxides improve rice germination, she wondered.
Iron is an important nutrient for plant growth. But large quantities can be harmful. To prime seeds, however, small quantities of iron suffice. Iron oxide nanoparticles are reported to improve respiration and DNA synthesis in wheat seeds. So, Shadma and her mentors embarked on a series of experiments.
Iron oxide nanoparticles can be toxic but, capped with plant metabolites, they are safer and seem to have many useful properties. So the team engineered iron oxide nanoparticles and capped them using flower extracts of Cassia occidentalis. Phytoconstituents in the plant reduced and activated iron atoms for the rapid formation of stable nanoparticles. Particles of about 30 nanometres had a negative charge due to the capping with the plant’s secondary metabolites.
The team selected Pusa basmati, an early flowering variety. They primed seeds by soaking them in an aqueous solution of nanoparticles for a day. Laboratory tests showed that priming improved germination. While the control started germinating on the third day, about a quarter of the seeds, primed with 20 milligrams per litre of the nanoparticles, germinated on the second day. The final germination percentage was 95 per cent, whereas, for control seeds, the maximum germination was only 89 per cent.
Primed seeds showed faster elongation of root hair. And root hairs had increased alpha amylase activity, indicating a boost in carbohydrate metabolism. This extra shot in the arm to root metabolism better equips the plant to grow and assimilate nutrients.
“Priming with the reduced form of nano-iron oxide improves water absorption by seeds. This solubilises gibberellic acid, a plant growth hormone in seeds, and increases amylase activity, hydrolysing starch into sugars to meet energy requirements for germination”, explains Nand K Singh, NIT Allahabad.
“Priming also led to a significant increase in antioxidant activity in germinating seeds”, adds Deepa Sharma, his colleague.
This nano-oxide method involves trace amounts of iron. At higher amounts, effects are reduced. And the primer treatment ensures that the nanomaterial does not contaminate soil in any significant manner. So the method is within the safety guidelines for nano-agriproducts.
“Iron ions seem to cross the seed coat and improve iron content. So, in a way, we are fortifying crops with the essential mineral”, says Shadma Afzal, NIT Allahabad.
“With minimum inputs, rice seed companies can now ensure that their products have high germination and fast growth,” adds Nand K Singh, her mentor.
Manish Kumar Tekam
Holkar Science College, Indore
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