Soil flooding and its outcome on cadmium and nutrient uptake affect photosynthetic activity in Inga laurina plants.

Urban areas next to mangroves are subject to progressive heavy metal contamination. Treelets of Inga laurina were collected in this ecosystem and cultivated for 30 days in waterlogged conditions and closed pots (WC) and at field capacity (FC), while exposed to different Cd concentrations (0, 50 and 100 mg·kg-1). Soil water conditions did not affect total Cd in plants, with Cd accumulating in roots and WC inducing less leaf chlorophyll while increasing carotenoids and chlorophyll ratio. Higher net photosynthesis, stomatal conductance, transpiration, and Ci/Ca ratio were observed under the highest Cd concentration and WC, while being conservative in water consumption as shown by the reduction in both water use efficiencies. Nutritional uptake behaved differently for each element, with N, Mg and Ca not being affected by Cd under WC but K increasing with Cd. At FC, plants showed higher values than WC, with the highest Cd concentration at FC showing the highest values overall. Nutrient allocation in organs was affected by WC in N, Mg, K, P and Ca but only P by Cd, with WC reducing nutrients overall and N, Mg and Ca behaving the same in both soil conditions while K was lowered in leaves and increased in roots under WC. P allocation under WC was not hindered by Cd even showing higher values in it than FC in some treatments. Altogether, results indicate that I. laurina can be considered a Cd-tolerant species, especially in WC and it presents a potential to be used as a phytoremediator plant.

Morphophysiological, ultrastructural, and nutritional changes induced by Cu toxicity in young Erythrina fusca plants.

Erythrina fusca is an important legume used for shade cover in cacao plantations in Brazil. Cacao plantations receive large quantities of copper (Cu)-containing agrochemicals, mainly for control of diseases. Therefore, Cu toxicity was investigated in seedlings grown in hydroponics with increasing concentrations of Cu (0.005-32 mg L-1) in a greenhouse. Ultrastructural analyses showed cell plasmolysis in the root cortical area and changes in thylakoid membranes at 8 mg Cu L-1 and higher. There were changes in epicuticular wax deposition on the leaf surface at the 16 and 32 mg Cu L-1 treatments. Leaf gas exchanges were highly affected 24 hours after application of treatments beginning at 8 mg Cu L-1 and higher Cu concentrations. Chemical analyses showed that Cu content in E. fusca roots increased as Cu concentration in the nutrient solution increased, whereas the shoot did not show significant changes. It is also observed that excess Cu interfered with Zn, Fe, Mn, Mg, K, P, and Ca content in the different E. fusca organs. Investigation of Cu toxicity symptoms focusing on morphophysiological, ultrastructural, gas exchange, and nutritional changes would be useful to alleviate Cu toxicity in E. fusca under field conditions, an important agroforestry species in cacao plantation.

Compartmentalization and ultrastructural alterations induced by chromium in aquatic macrophytes.

The aim of the present study was to identify the sites of accumulation of Cr in the species of macrophytes that are abundant in the Cachoeira river, namely, Alternanthera philoxeroides, Borreria scabiosoides, Polygonum ferrugineum and Eichhornia crassipes. Plants were grown in nutritive solution supplemented with 0.25 and 50 mg l(-1) of CrCl(3)·6H(2)O. Samples of plant tissues were digested with HNO(3)/HCl in a closed-vessel microwave system and the concentrations of Cr determined using inductively-coupled plasma mass spectrometry (ICP-MS). The ultrastructure of root, stem and leaf tissue was examined using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) in order to determine the sites of accumulation of Cr and to detect possible alterations in cell organelles induced by the presence of the metal. Chromium accumulated principally in the roots of the four macrophytes (8.6-30 mg kg(-1) dw), with much lower concentrations present in the stems and leaves (3.8-8.6 and 0.01-9.0 mg kg(-1) dw, respectively). Within root tissue, Cr was present mainly in the vacuoles of parenchyma cells and cell walls of xylem and parenchyma. Alterations in the shape of the chloroplasts and nuclei were detected in A. philoxeroides and B. scabiosoides, suggesting a possible application of these aquatic plants as biomarkers from Cr contamination.

Morphophysiological responses and programmed cell death induced by cadmium in Genipa americana L. (Rubiaceae).

Cadmium (Cd) originating from atmospheric deposits, from industrial residues and from the application of phosphate fertilizers may accumulate in high concentrations in soil, water and food, thus becoming highly toxic to plants, animals and human beings. Once accumulated in an organism, Cd discharges and sets off a sequence of biochemical reactions and morphophysiological changes which may cause cell death in several tissues and organs. In order to test the hypothesis that Cd interferes in the metabolism of G. americana, a greenhouse experiment was conducted to measure eventual morphophysiological responses and cell death induced by Cd in this species. The plants were exposed to Cd concentrations ranging from 0 to 16 mg l(-1), in a nutritive solution. In TUNEL reaction, it was shown that Cd caused morphological changes in the cell nucleus of root tip and leaf tissues, which are typical for apoptosis. Cadmium induced anatomical changes in roots and leaves, such as the lignification of cell walls in root tissues and leaf main vein. In addition, the leaf mesophyll showed increase of the intercellular spaces. On the other hand, Cd caused reductions in the net photosynthetic rate, stomatal conductance and leaf transpiration, while the maximum potential quantum efficiency of PS2 (Fv/Fm) was unchanged. Cadmium accumulated in the root system in high concentrations, with low translocation for the shoot, and promoted an increase of Ca and Zn levels in the roots and a decrease of K level in the leaves. High concentrations of Cd promoted morphophysiological changes and caused cell death in roots and leaves tissues of G. americana.