Germination and Post-Seminal Development of Mimosa L. (Fabaceae) in Diesel Oil-Contaminated Soil.

Germination and post-seminal development are important stages for the establishment of plants and for determining their tolerance to diesel oil. Diesel-tolerant species can contribute to the recovery of contaminated areas, and leguminous plants are promising in the treatment of contaminated soil through nitrogen fixation. This study identified the effects of diesel oil-contaminated soil on the germination and seedlings of the leguminous species Mimosa bimucronata, M. flocculosa, and M. scabrella var. aspericarpa. The experiment comprised two treatments contaminated (4% concentration) and uncontaminated soil and was performed in a greenhouse for 90 days, with evaluations 30, 60, and 90 days after sowing. Germination was not affected, but most root and aerial system parameters were statistically lower in contaminated soil, indicating low initial development potential in soil contaminated with diesel oil. Moreover, the negative effects increased with higher exposure time to the contaminant.

Morphogenic responses and biochemical alterations induced by the cover crop Urochloa ruziziensis and its component protodioscin in weed species.

Urochloa ruziziensis, a cover plant used in no-till systems, can suppress weeds in the field through their chemical compounds, but the mode of action of these compounds is still unknown. The present study aimed to investigate the effects of a saponin-rich butanolic extract from U. ruziziensis straw (BfUr) and one of its components, protodioscin on an eudicot Ipomoea grandifolia and a monocot Digitaria insularis weed. The anatomy and the morphology of the root systems and several parameters related to energy metabolism and antioxidant defense systems were examined. The IC50 values for the root growth inhibition by BfUr were 108 µg mL-1 in D. insularis and 230 µg mL-1 in I. grandifolia. The corresponding values for protodioscin were 34 µg mL-1 and 54 µg mL-1. I. grandifolia exhibited higher ROS-induced peroxidative damage in its roots compared with D. insularis. In the roots of both weeds, the BfUr and protodioscin induced a reduction in the meristematic and elongation zones with a precocious appearance of lateral roots, particularly in I. grandifolia. The roots also exhibited features of advanced cell differentiation in the vascular cylinder. These alterations were similar to stress-induced morphogenic responses (SIMRs), which are plant adaptive strategies to survive in the presence of toxicants. At concentrations above their IC50 values, the BfUr or protodioscin strongly inhibited the development of both weeds. Such findings demonstrated that U. ruziziensis mulches may contribute to the use of natural and renewable weed control tools.

Increased Gibberellins and Light Levels Promotes Cell Wall Thickness and Enhance Lignin Deposition in Xylem Fibers.

Light intensity and hormones (gibberellins; GAs) alter plant growth and development. A fine regulation triggered by light and GAs induces changes in stem cell walls (CW). Cross-talk between light-stimulated and GAs-induced processes as well as the phenolic compounds metabolism leads to modifications in lignin formation and deposition on cell walls. How these factors (light and GAs) promote changes in lignin content and composition. In addition, structural changes were evaluated in the stem anatomy of tobacco plants. GA3 was sprayed onto the leaves and paclobutrazol (PAC), a GA biosynthesis inhibitor, via soil, at different irradiance levels. Fluorescence microscopy techniques were applied to detect lignin, and electron microscopy (SEM and TEM) was used to obtain details on cell wall structure. Furthermore, determination of total lignin and monomer contents were analyzed. Both light and GAs induces increased lignin content and CW thickening as well as greater number of fiber-like cells but not tracheary elements. The assays demonstrate that light exerts a role in lignification under GA3 supplementation. In addition, the existence of an exclusive response mechanism to light was detected, that GAs are not able to replace.