Spraying rice with sunscreen particles during heat waves boosts growth

A common sunscreen ingredient, zinc nanoparticles, may help protect rice from heat-related stress, an increasingly common problem under climate change.

Zinc is known to play an important role in plant metabolism. A salt form of the mineral is often added to soil or sprayed on leaves as a fertiliser, but this isn’t very efficient. Another approach is to deliver the zinc as particles smaller than 100 nanometres, which can fit through microscopic pores in leaves and accumulate in a plant.

Researchers have explored such nanoparticle carriers as a way to deliver more nutrients to plants, helping maintain crop yields while reducing the environmental damages of using too much fertiliser. Now Xiangang Hu at Nankai University in China and his colleagues have tested how these zinc oxide nanoparticles affect crop performance under heat wave conditions.

They grew flowering rice plants in a greenhouse under normal conditions and under a simulated heat wave where temperatures broke 37°C for six days in a row. Some plants were sprayed with nanoparticles and others weren’t treated at all.

When harvested, the average grain yield of the plants treated with zinc nanoparticles was 22.1 per cent greater than the plants that had not been sprayed, and this rice also had higher levels of nutrients. The zinc was also beneficial without heat wave conditions – in fact, in these cases, the difference in yield between treated and untreated plants was even greater.

Based on detailed measurements of nutrients in the leaves, the researchers concluded the zinc boosted yields by enhancing enzymes involved in photosynthesis and antioxidants that protect the plants against harmful molecules known as reactive oxygen species.

“Nanoscale micronutrients have tremendous potential to increase the climate resilience of crops by a number of unique mechanisms related to reactive oxygen species,” says Jason White at the Connecticut Agricultural Experiment Station.

The researchers also found the rice treated with zinc nanoparticles maintained more diversity among the microbes living on the leaves – called the phyllosphere – which may have contributed to the improved growth.

Tests of zinc oxide nanoparticles on other crops like pumpkin and alfalfa have also shown yield increases. But Hu says more research is needed to verify this could benefit other crops.