Pesticide guard

PESTICIDES, used to increase yields by protecting plants against a number of diseases, have been known to be harmful for humans. But even plants are not spared from the ill effects of these chemicals. Pesticides sometimes give rise to substances that damage proteins, lipids, carbohydrates and the DNA of plant cells. Certain insecticides like imidacloprid, used to kill aphids and locusts, affect the gene expression of rice plants, making them susceptible to infestation by other pests like brown plant hopper.

Scientists are, therefore, on a constant lookout for naturally-occurring substances that can mitigate the toxic effects of pesticides and make them less harmful. A research team from Guru Nanak Dev University in Amritsar has identified a plant-derived hormone, epibrassinolide (EBL), that can protect rice seeds from the toxic effects of chlorpyrifos, a chlorine-containing pesticide. The study appeared in Ecotoxicology and Environmental Safety on November 1.

The hormone is isolated from bael tree (Aegle marmelos) and belongs to brassinosteroids, a class of chemicals known to protect plants against environmental stresses like chill, drought and toxins. However, its protective effects against toxins produced by pesticides in rice have never been studied earlier. The researchers say such plant-derived chemicals could provide a new way to fight ill-effects of pesticides like chlorpyrifos in plants and humans and pave the way for sustainable agriculture.

This pesticide is used for pest control in a variety of crops. In rice, it is used to check infestations by rice bloodworm, rice stem borer, dragonflies, damselflies and green lacewings. It kills these pests by affecting their nervous system, giving rise to concerns that it could have similar effect on humans and newborns.

For their study, the researchers grew the seeds of Pusa Basmati-1 rice in sand moistened with chlorpyrifos solution. Half of these seeds had previously been soaked in a solution of the plant hormone EBL. The seedlings were removed from the sand after 12 days. They found that in rice seedlings not treated with the plant hormone, the pesticide caused a reduction in chlorophyll content, root and shoot lengths and activity of antioxidant enzymes that counter the effects of harmful chemicals produced by the pesticide. The seedlings pre-treated with EBL were, however, protected against toxic effects of the pesticide. They also showed high level of proline, a key plant protein that protects cell membrane and destroys the harmful substances produced by pesticides. This sped up the repair of cells damaged due to pesticide exposure in these seedlings.

Lead researcher Pratap Kumar Pati says manipulating plants to face various challenges using plant breeding and genetic engineering approaches has its own limitations. He says synthetic pesticides are still an effective method to protect plants and are important for good yields. “Hence our study would be useful in developing acceptable strategies for reducing the adverse effect of pesticides in crop production.”