Since the 1970s, rare earth elements (REEs), particularly lanthanum (La), have been widely used in agriculture as plant growth stimulants .Previous studies have shown that REEs improve the physiology of plants, but that high concentrations inhibit plant growth. Studies on the physiological roles of REEs in plants have achieved a number of advances in recent years. However, the mechanisms underlying the effects of La on root system development remain unclear. 

Prof. XU Jin and his team from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences investigated the role of reactive oxygen species (ROS, important signaling molecules involved in modulating plant growth and development in response to environmental cues) in La-induced root system architecture (RSA) remodeling. The Arabidopsis ecotype Columbia was used in the study. 

The researchers first examined the effects of La on root system growth. They found that La induced cell death in roots, thereby leading to loss of meristematic cell division potential, stem cell niche activity, and auxin accumulation in primary root (PR) tips, and subsequent cessation of PR growth. La affected uptake and accumulation of elements in plants. 

The researchers then measured ROS levels in PRs of La-treated seedlings, in order to investigate whether ROS signaling is involved in La-mediated PR growth inhibition. They found that La induced ROS accumulation in root tips. 

They further explored the physiological mechanisms underlying the effects of ROS on La-mediated PR growth by applying the ROS scavenger potassium iodide (KI) as well as catalase (CAT).

The results showed that reduced ROS production could alleviate cell death in roots and improve meristem cell division potential and auxin accumulation in root tips, thereby mitigating PR growth inhibition due to La.

Treatment with La resulted in the reorganization and reorientation of the actin microfilaments in the cells of the transition zone in the root tips, indicating that La-induced endocytosis could be modulated by actin microfilaments. 

The study showed that La inhibited PR growth by inducing cell death in PR tips, thereby altering auxin distribution in roots and causing subsequent RSA remodeling, and that ROS were involved in these processes. 

The study entitled “Involvement of reactive oxygen species in lanthanum-induced inhibition of primary root growth” has been published online in Journal of Experimental Botany.