Bioaccumulation and Effects of Lanthanum on Growth and Mitotic Index in Soybean Plants.

Rare earth elements such as lanthanum (La) have been used as agricultural inputs in some countries in order to enhance yield and improve crop quality. However, little is known about the effect of La on the growth and structure of soybean, which is an important food and feed crop worldwide. In this study, we evaluated the bioaccumulation and the effects of La on the growth and mitotic index of soybean. Soybean plants were exposed to increasing concentrations of La (0, 5, 10, 20, 40, 80, and 160 µM) in nutrient solution for 28 days and plant response to La was evaluated in terms of plant growth, nutritional characteristics, photosynthetic rate, chlorophyll content, mitotic index, modifications in the ultrastructure of roots and leaves, and La mapping in root and shoot tissues. The results showed that the roots of soybean plants can accumulate sixty-fold more La than the shoots. Application of La resulted in increased contents of some essential nutrients (i.e., Ca, P, K, and Mn), while Cu and Fe levels decreased, and S content remained unchanged. The results also demonstrated that low La concentrations (5 and 10 µM) stimulated the photosynthetic rate and total chlorophyll content and promoted a higher incidence of binucleate cells, resulting in a slight increase in roots and shoots. On the other hand, at higher La levels reduced soybean growth was observed, caused by ultrastructural modifications in the cell wall, thylakoids and chloroplasts, and the appearance of c-metaphases.