Rare earth elements(REEs)as nonessential trace elements are enriched in living organisms and threaten their health.To early detect and reduce REE enrichment in living organisms,scientists are focused on clarifying the enrichment process of REEs in living organisms and its risks.However,the enrichment process of REEs in edible plant cells has remained unclear.Herein,by using interdisciplinary methods and techniques,the enrichment process of lanthanum(La(Ⅲ))in the leaf cells of lettuce(Lactuca sativa L.)was investigated.(1)When La(Ⅲ)exposure dose is 0.5-5μmol/L,La(Ⅲ)is enriched outside the plasma membrane(PM).In this zone,La(Ⅲ)is bound to vitronectin-like protein(VN)to form La-VN complexes;(2)When La(Ⅲ)exposure dose is 5-20μmol/L,besides the zone outside the PM,La(Ⅲ)is also enriched on the PM and bound to arabinogalactan proteins(AGPs)to form La-AGPs complexes;(3)When La(Ⅲ)exposure dose is 20-140μmol/L,besides the zone outside and on the PM,La(Ⅲ)is enriched inside the PM;(4)When La(Ⅲ)exposure dose is 60-140μmol/L,malondialdehyde content(an important indicator of invisible damage)significantly increases.Thus,as La(Ⅲ)exposure dose increases,La(Ⅲ)gradually migrates from outside the PM to the PM and inside the PM,enriching in these zones in turn.The enriched La(Ⅲ)will cause invisible damage to lettuce leaf cells and even enter human bodies along food chains.These results provide references for investigating the enrichment process of REEs in plants and its environmental risks,and finding strategies to early detect and reduce REE enrichment in plants.
The harmful effect of low-concentration lanthanum [La(Ⅲ)] on plants was investigated by choosing horseradish as a representative of plants and using the methods of physics, analytical chemistry and biology. The results show that the genetic expressions related to glucosinolates(GLS, the marker of plant resisting harmful effects) synthesis are significantly increased after the endocytosis in leaf cells is initiated by low-concentrations La(Ⅲ). Consequently, the activities in the key enzymes for catalyzing the GLS synthesis are promoted. Meanwhile, the contents of the precursors and substrates in GLS synthesis are increased. All the above changes accelerate the GLS synthesis and result in the maximum increase in GLS content by 14%. Finally, the uptake of nutrient elements in horseradish is enhanced, and the yield of horseradish is maximally increased by 25%. Therefore, low-concentration La(Ⅲ) is harmful to plants, and plants can promote growth to resist the harmful effects of low-concentration La(Ⅲ) by regulating GLS content. The results show a new insight into how rare earth elements stimulate plant growth, and provide a reference for the risk assessment of rare earth elements.
