Cerium

Toxicity to terrestrial plants

Administrative data

Endpoint:

toxicity to terrestrial plants

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Data source

Reference

Reference Type:

publication

Title:

Physiological and Biochemical Effects of Rare Earth Elements on Plants and Their Agricultural Significance: A Review

Author:

Zhengyi H, Richter H, Sparovek G, Schnug E,

Year:

2004

Bibliographic source:

Journal of Plant Nutrition Vol. 27, No. 1, pp. 183-220

Materials and methods

Test guideline

Qualifier:

no guideline available

Test material

Test material information

Constituent 1

Reference substance name:

Cerium

EC Number:

231-154-9

EC Name:

Cerium

Cas Number:

7440-45-1

Molecular formula:

Ce

IUPAC Name:

cerium(3+)

Applicant's summary and conclusion

Conclusions:

Studies on the effects of REEs on crop performance have been carried out only in a few countries (China, Australia, former USSR). Until present date these studies have not shown conclusive results. The positive effect of REEs on crop yield reported from a larger number of experiments conducted in China, were not fully confirmed by much smaller number of trials done by Australian research groups. Crop response to REEs depends on a complex combination of many factors, including : soil properties (e.g., pH, organic matter, mineral contents, and parent material), application rate and timing, crop conditions (e.g., type varieties, growth stage), and the purity and pH of the water in which the REEs are dissolved.

Executive summary:

Uptake and Translocation of REEs in Plants

• Soil chelates may influence the uptake of REEs.
• The uptake of REEs may be facilitated by increased levels of nitrogen and potassium fertilization, and decreased by addition of phosphates.
• The Casparian strip in plant roots limits the uptake of REEs.t

The maximum velocity for uptake of nutrients into plants (Vmax) for La is 4,4 times greater than that for Ce. These results indicate that the affinity of cytoplasmatic membrane to Ce is greater than that to La.

REEs are absorbed by root hairs into the xylem, via thin wall cells, and then may be moved to other plant organs. Plants can also rapidly absorb REEs sprayed on foliage. Plant uptake of La and Ce reached at peak value 48h after spraying. After that uptake was decreased, arriving a steady state value 5 days after spraying. The REEs uptake rate for plant via roots was two magnitudes lower than via foliage indicating a physiological barrier for REEs in roots.

Three percent of the total amount of REEs absorbed via the root was translocated to the shoots. The natural translocation rates for REEs from soil to plant are approximately 20%.

Forms and Distribution of REEs in Plants

Usually, the distribution of the amount of REEs in plant tissues are ranked as follows: root>leaf>stem>flower>fruit. The distribution pattern of REEs is varying according to individual REEs. The plants grown in mining areas may be more tolerant to high concentrations of REEs in soils. The absolute majority of REEs sprayed on foliage of wheat was distributed in leaves.

Cytolocalization of REEs in Plants

La cannot penetrate through cell membrane. Ce can not only enter cell, but also be enriched at the cell nucleus.

Effects of REEs on Physiological Functions of Calcium in Plants

It is well known that calcium is an essential nutritional element for plants. REEs have similar characteristics as Ca.

REEs are thought to be analogous to Ca, especially to La, which therefore was nicknamed "super-calcium."

Many enzymes and other functional-proteins have been demonstrated to be inhibited by La3 +.

La3+ can displace Ca2+ from extra-cellular binding sites and can inhibit the efflux of extra-cellular, and part of the intracellular Ca2 +.

REEs can replace Ca from many enzymes, and participate in enzymatic reactions, and thereby interfere with the normal phydiological functions of Ca.

Effects of REEs on the Stability and Function of Cytoplasmatic Membranes

Another major effect of the REEs occours, in a similar way as for Ca2 +, as a result of their effects on the stability and functionality of membranes. La3+ and other REEs may restrict leakiness by changing membrane characteristics, notably membrane fluidity.

Relationship Between REEs and Metabolism of Mineral Nutrient Metabolism in Plants

REEs have important effects on membrane stability and interact strongly with Ca. Therefore, it is not surprising that they strongly affect ionic interactions with the cell.

La3+ and Ce3+ non-conpetitively inhibited the uptake of NO3 -, reducing the uptake of NH4 +.

After using REEs as fertilizer, the absorption of N by rice was increased by 16.4%. The absorption of P by rice increased by 12% after fertilizing with REEs fertilizer.

The absorption of K by rice increased by 8.5% after applying REEs. REEs clearly influence the ionic fluxes into cells in different ways. These fluxes in turn may be expected to affect several plant processes. REEs on nutrients (N, P, and K) uptake by plants. Conflicting data or conclusions may occur because different analytical methods were employed by researchers and also because complex phenomena are involved in influences of REEs on nutrient uptake.

Effects of REEs on Hormonal Interactions

REEs influence many physiological processes of plants, related to the synergistic action of REEs with hormones. The effect on REEs increased the contents of indole acetic acid and tryptophan in the coleoptile.

Effect on REEs on Plant Photosynthesis

The application of mixed RE nitrates turned out to be beneficial for photosynthesis. The supply of REEs to plants increased photosynthesis intensity, and net photosynthetic rate by 11.5 -31.2%.

The effects of REEs on plant photosynthesis are related to chloroplast development, chlorophyll content and enzyme activity.

Effects of REEs on Germination and Growth

The results from the few existing studies on the effect of REEs on plant growth are conflicting. The majority of the reviewed experiments, however, have demonstrated the stimulation of plant growth in the presence of REEs. Application of cerium sulfate enhanced the root and shoot growth.