Amelioration of iron toxicity: A mechanism for aluminum-induced growth stimulation in tea plants

• Aluminum up to 300 μM stimulated growth of tea plants.
• Without Al supply young tea leaves accumulated more than 1000 mg Fe kg− 1.
• Al supply reduced Fe uptake and transport.
• Amelioration of Fe toxicity by Al could be a factor in Al-induced growth stimulation.

Tea plants (Camellia sinensis) are well adapted to acid soils with high Al availability. These plants not only accumulate high leaf Al concentrations, but also respond to Al with growth stimulation. Decreased oxidative stress has been associated with this effect. Why tea plants not exposed to Al suffer from oxidative stress has not been clarified. In this study, hydroponically grown tea plants treated with 0 to 300 μM Al were analyzed for growth, Al and Fe accumulation, and Al distribution by means of morin and hematoxylin staining. Roots of control plants stained black with hematoxylin. This indicates the formation of a Fe–hematoxylin complex. Young leaves of controls accumulated more than 1000 mg Fe kg− 1 dry weight. This concentration is above the Fe-toxicity threshold in most species. Supply of Al stimulated growth and reduced Fe uptake and transport. These results indicate that Al-induced growth stimulation might be due to alleviation of a latent Fe toxicity occurring in tea plants without Al supply.

Tea plants tolerate high aluminum concentrations. Moreover, growth in tea is stimulated by this non-essential element. Without Al, tea accumulates high, potentially toxic iron concentrations in young leaves. Aluminum decreases Fe uptake and translocation. Amelioration of Fe toxicity is proposed as a mechanism for Al-induced growth stimulation in tea.Figure optionsDownload as PowerPoint slide