Effects of lanthanum on growth and accumulation in roots of rice seedlings

Abstract

Hormetic effects on the growth were found in the roots of rice (Oryza sativa L. cv. Shengdao 16) exposed to increasing concentrations of La 3+ (0.05, 0.1, 0.5, 1.0, and 1.5 mmol/L). The results indicated that La 3+ promoted the growth of rice roots at 0.05 mmol/L, but inhibited the growth at 1.0 and 1.5 mmol/L La 3+ after 13 days of exposure. Transmission electron microscope showed that La 3+ was mainly deposited in the cell walls of the roots. In addition, the accumulation of K, Mg, Ca, Na, Fe, Mn, Zn, Cu, and Mo in the roots was also affected with the exposure of different La 3+ treatments. It showed that La 3+ affected the nutritional status of roots and further regulated the growth of rice.

Rare Earth Elements in the Soil Environment

“…These destructuring processes are commonly verified in cell walls [125,142] and also occur frequently in chloroplasts, mitochondria, and nuclei that lose their original format [102,106,140]. The main reports of REE effects on membrane stability are associated to alterations of stability, functionality, and permeability [120,138,140,150,151].…”

“…Hypotheses supporting the beneficial effects of REE in plant metabolism include stimulation of the antioxidant system, increased nutrient absorption, increased nitrogen and CO 2 fixation, and positive effects on biomass production by induction of a higher photosynthetic rate, due to an increase in electron transport rate in the photochemical phase of photosynthesis [105]. Regarding the plant structural level, the hypotheses vary from the substitution of Ca in cell wall structure, in cytoskeleton, and in membranes and cytoplasmatic organelles [106,107], to modifications in size and density of anatomic structures such as stomata, trichomes, and tissue thickness [103]. At the cytogenetic level, the REE-associated benefits are linked to an increase in the mitotic index [102, (a) show a trend of REE depletion in soils relative to UCC, whereas countries on the right (b) show a trend of REE enrichment relative to UCC.…”

“…Inside the vascular tissues, the REE can bind reversibly to anions such as COOH − , with the degree of bonding varying according to the atomic number of the element of interest [97], which may also influence the accumulation of these elements [97,147]. Inside the plants, most REE are bonded to cell walls [106,148]. However, some REE can cross the cell membrane, accumulating in organelles as crystals such as BREE oxalates [ 102,107] or even in root cortical tissues, which also avoids translocation to plant shoots.…”

“…The REE, La in special, can act as Ca replacements, mainly in plant structure, bonding with cell walls in which Ca would be part of the composition and replacing it in its function as a secondary messenger [106]. Due to the fact that La and Ca are chemically and physically similar, the manner that they act is similar in plants, inducing the competition and substitution of Ca by La [20,149].…”

“…Due to the fact that La and Ca are chemically and physically similar, the manner that they act is similar in plants, inducing the competition and substitution of Ca by La [20,149]. This replacement in general promotes structural modifications [106,120], such as loss of structuring in the medium lamella. La can also replace Ca in the protoplasm, chloroplasts, mitochondria, and cytoplasmatic membranes [102,107].…”