Potential of Panicum aquanticum Poir. (Poaceae) for the phytoremediation of aquatic environments contaminated by lead.

Aquatic environments contaminated by lead (Pb) are a problem in many regions of world. Since Pb has high toxicity, the identification of species for phytoremediation is important for the recovery of these areas. Thus, the phytoremediation potential of Panicum aquaticum Poir. (Poaceae) was evaluated. The anatomical and physiological responses of P. aquaticum were assessed under different concentrations of Pb [0.0, 0.5, 1.0, 2.0, 4.0, and 8.0 mM of Pb(NO3)2]. Plant growth, anatomy of roots and leaves, root uptake, root to shoot translocation, and the concentration and accumulation of Pb in organs were analyzed. Regarding leaf anatomy, Pb treatment led to changes in epidermis thickness, stomatal density, stomatal diameter, and sclerenchymal area. Endoderm thickness was increased at the highest concentrations of Pb, which may be related to reduced translocation and shoot accumulation. The roots of P. aquaticum presented increased absorption (2279 µg g-1 DW-1 of Pb). In conclusion, P. aquaticum was found to have potential for the phytoremediation of areas contaminated with Pb.

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, bioaccumulation of La and its effects on the growth and mitotic index of soybean was evaluated. Soybean plants were exposed to increasing concentrations of La (0, 5, 10, 20, 40, 80, and 160 µM) in nutrient solution for 28 days. 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 shoots. La deposition occurred mainly in cell walls and in crystals dispersed in the root cortex and in the mesophyll. When La was applied, it resulted in increased contents of some essential nutrients (i.e., Ca, P, K, and Mn), while Cu and Fe levels decreased. Moreover, low La concentrations stimulated the photosynthetic rate and total chlorophyll content and lead to a higher incidence of binucleate cells, resulting in a slight increase in roots and shoot biomass. At higher La levels, soybean growth was reduced. This was caused by ultrastructural modifications in the cell wall, thylakoids and chloroplasts, and the appearance of c-metaphases.

Aerenchyma, gas diffusion, and catalase activity in Typha domingensis: a complementary model for radial oxygen loss.

Radial oxygen loss is a physical phenomenon that occurs naturally in aquatic plants. Typha domingensis was chosen as a model plant because it possesses basic morphological characteristics, such as a stem (rhizome) that produces leaves and adventitious roots, which are present in many aquatic plants. This study aimed to evaluate the following: the relevance of the anatomy of T. domingensis on gas diffusion among organs; the influence of plant parts on radial oxygen loss; the role of catalase in radial oxygen loss; and the proposition of a novel explanation for the downward diffusion of oxygen through the organs of this aquatic macrophyte and into the environment. Typha domingensis plants were cultivated in a greenhouse under different conditions: plants with intact leaves, plants with leaves cut in half, and plants without leaves. Furthermore, we evaluated the percentage of aerenchyma in different vegetative organs, the minimum pressure required for radial oxygen loss, the daily variations of dissolved oxygen, and the roots' catalase activity. The results demonstrated that certain cellular features contributed to decreased oxygen diffusion among the organs, specifically, those found in the leaf-rhizome and root-rhizome interfaces as well as the suberin and lignin layers in these regions. Additionally, our experiments with a catalase activator and inhibitor validated that a significant amount of the oxygen released in radial oxygen loss could not, in fact, be exclusively supplied by the atmosphere. Thus, a complementary model is proposed in which catalase activity is an important component of radial oxygen loss.