Barley Beats Lead: How Two Small Molecules Team Up to Stay Healthy

Lead pollution hurts barley plants in many ways. It slows growth, damages the photosynthetic machinery, and lowers key minerals like calcium and potassium. The plants also suffer from more cell damage, shown by higher levels of harmful molecules such as MDA and hydrogen peroxide. In a separate group that received no lead, the plants stayed strong. Researchers tested whether adding 5‑aminolevulinic acid (ALA) could help. Two doses of ALA, 50 µM and 100 µM, were sprayed on the seedlings. The treated plants grew better than those exposed only to lead. Their leaves kept more calcium and potassium, while the amounts of lead, hydrogen peroxide, and MDA dropped. This suggests ALA protects the plants by keeping their cells less stressed. To find out if nitric oxide (NO) was part of this protection, a second experiment added a chemical that removes NO, called cPTIO. When the seedlings received both ALA and cPTIO, the benefits of ALA vanished. The plants grew poorly again, and lead accumulated in their leaves. This shows that the presence of NO is essential for ALA’s protective effect.The loss of NO also changed other defense enzymes. Normally, ALA boosts antioxidant enzymes such as superoxide dismutase, catalase, and peroxidase. When NO was scavenged, these enzymes fell in activity, while the harmful molecules rose again. Thus, ALA appears to activate NO inside the plant, which then triggers a stronger antioxidant response. The two molecules work together. ALA supplies a signal that increases NO, and the resulting NO helps the plant fight lead toxicity by strengthening its antioxidant system and keeping essential minerals in balance. Without NO, ALA alone cannot protect the barley seedlings. The study shows that combining small‑molecule treatments can be a smart way to help crops survive heavy metal stress. Future work could explore how this strategy works in other plants or under different types of pollution.