Melatonin a balm for drought-affected maize

Melatonin, recently found to be involved in many physiological processes in plants, has been shown to have pronounced effects on photosynthesis efficiency in maize^1,2. The finding, from researchers at Northwest A&F University in Shaanxi, China, highlights a promising approach to enhancing drought resilience and improving yields of this globally critical crop.

“Melatonin is a familiar animal hormone that was first isolated from the bovine pineal gland, but has since been found to be an important growth regulator in plants,” says Ren-He Zhang from the research team. “Treatment of maize with extra melatonin has been shown to improve the crop’s ability to withstand harsh environmental conditions including drought, but the exact molecular and physiological mechanisms are unclear.”

The global production of maize exceeds that of both rice and wheat, and is a staple in many parts of the world, particularly in developing countries. Yet while demand for maize in developing countries is expected to double by 2050, yields are anticipated to decline due to the impacts of climate change.

In their study published in the Russian Journal of Plant Physiology, Zhang and his colleagues grew from seed a series of maize plants with and without melatonin treatment at various concentrations under normal and drought conditions. Once the first full leaves had developed, they analysed the first full leaves using a plant efficiency analyser, which gave the critical parameters of photosynthesis including energy conversion efficiency and changes in reduction-oxidation state.

“We found that drought stress damages the photosystem apparatus in maize by reducing the function of reaction centres responsible for energizing the chlorophyll electrons that drive photosynthesis,” says Zhang. “This resulted in a lower electron transport rate and lower energy conversion efficiency or quantum yield of the photosystems. We also found that the glutathione-ascorbate cycle is responsible for cleaning up the reaction oxygen molecules produced by photosynthesis and other plant metabolic functions.”

Seedlings treated with exogenous melatonin, however, showed normal photosynthetic function and higher photosynthetic capacity, as well as reduced cell membrane damage as reflected by significantly decreased levels of oxidized ascorbate, superoxide anions and hydrogen peroxide.

“Our studies provide detailed evidence that treatment of maize seedlings with 100 micromoles of melatonin is effective for alleviating damage to the photosynthetic apparatus due to drought stress,” says Zhang. “Melatonin also upregulated gene expression for enzymes related to the glutathione-ascorbate cycle. Interestingly, the effects of melatonin were more conspicuous in the tolerant cultivar than in a more sensitive cultivar.”