Rare earth elements activate endocytosis in plant cells

Abstract

It has long been observed that rare earth elements (REEs) regulate multiple facets of plant growth and development. However, the underlying mechanisms remain largely unclear. Here, using electron microscopic autoradiography, we show the life cycle of a light REE (lanthanum) and a heavy REE (terbium) in horseradish leaf cells. Our data indicate that REEs were first anchored on the plasma membrane in the form of nanoscale particles, and then entered the cells by endocytosis. Consistently, REEs activated endocytosis in plant cells, which may be the cellular basis of REE actions in plants. Moreover, we discovered that a portion of REEs was successively released into the cytoplasm, self-assembled to form nanoscale clusters, and finally deposited in horseradish leaf cells. Taken together, our data reveal the life cycle of REEs and their cellular behaviors in plant cells, which shed light on the cellular mechanisms of REE actions in living organisms.activation | endocytic vesicle S ome trace elements, such as rare earth elements (REEs), have been observed for a long time to be beneficial to plant growth (1, 2). REEs are f-block elements in the periodic table, including 15 lanthanides, plus scandium and yttrium (2). The beneficial effect of REEs on plants was first reported in 1917, when it was found that cerium, an REE, improved physiological activities of water-floss (Spirogyra) (3). Since the 1970s, REEs have been widely used in agriculture as plant growth stimulants (4). Currently, more than 100 of crop species have been applied with REEs, which has increased crop yields by 5-15% (4). In addition, REEs also serve to protect plants against certain plant diseases and some stresses, such as drought, cold, acid rain, or heavy metals (2). The wide use of REEs has caused an overaccumulation of REEs in the ecosystem, including soil (5), atmosphere (6), and water (7). Moreover, it was shown that REEs have dual effects on plant growth: low concentrations of REEs exert positive effects on growth and yield of crops, whereas high concentrations of REEs seem to be harmful for plants, indicating that REEs are not absolutely good for plants (2). Therefore, it is imperative to elucidate how REEs act on plant cells to ensure food safety.Despite of many advances achieved in recent years, the action mechanisms of REEs on plant cells still remain poorly understood (2). Several explanations, which are mainly focused on the physiological roles of REEs in plant cells, have been proposed (2). These mechanisms include the possible changes of photosynthesis, mineral nutrient uptake and metabolism, catalytic activities of some enzymes, hormonal balance, and so forth (2). However, these hypotheses are not connected to any cellular or molecular principles and are therefore far from explaining the action mechanisms of REEs in plants (2,8). In addition, little consensus has yet been reached regarding the life cycle of REEs in plant cells. Some studies report that REEs cannot enter the plant cells but only be localized in apoplast (8-14); other st...

Involvement of reactive oxygen species in lanthanum-induced inhibition of primary root growth

“…It has been observed that La activates endocytosis in plant cells, and this process might play a role in La-mediated plant growth and development (Wang et al , 2014). We therefore investigated the effect of La on endocytosis in Arabidopsis roots.…”

“…Since the 1970s, REEs, particularly lanthanum (La), have been widely used in agriculture as plant growth stimulants because they promote crop growth (Hu et al , 2004; Feng et al , 2013). Indeed, REEs protect plants against certain plant diseases and stress conditions (Wang et al , 2014). A low concentration of La 3+ relieves plant growth inhibition, improves leaf water potential and water content, and increases soluble protein and proline contents while decreasing malondialdehyde contents under osmotic or salt stress (Feng et al , 1999; Xu et al , 2007).…”

“…Several mechanisms that explain the effects of REEs have been proposed, including REE-mediated changes in antioxidative enzyme activities, photosynthesis efficiency, mineral nutrient uptake capacity, and phytohormonal balance (Ruíz-Herrera et al, 2012; Wang et al , 2014). Wang et al (2014) showed that REEs enter plant cells via endocytosis. REEs can also activate endocytosis in plant cells, which may be the cellular basis underlying the action of REEs in plants.…”

“…The widespread use of REEs has caused their over-accumulation in soil and water (Wang et al , 2011; Biasioli et al , 2012; Wang et al , 2014). In addition, physiological studies have revealed that REEs have dual effects on plant growth, with low concentrations of REEs improving the growth and yield of crops and high concentrations of REEs having a harmful effect (Wang et al , 2014).…”

“…In addition, physiological studies have revealed that REEs have dual effects on plant growth, with low concentrations of REEs improving the growth and yield of crops and high concentrations of REEs having a harmful effect (Wang et al , 2014). Nonetheless, the molecular mechanisms underlying plant growth and development in response to a high concentration of REE remain poorly understood.…”