Cadmium and nickel accumulation in rice plants. Effects on mineral nutrition and possible interactions of abscisic and gibberellic acids
Rice plants accumulate high quantities of Cd and Ni when grown for 10 days in a medium containing these heavy metals. Accompanying Cd and Ni uptake, a decrease in shoot and root length was observed, though dry matter accumulation was not affected accordingly. Metal treatments also induced a decrease in K, Ca and Mg contents in the plants, particularly in the shoots, indicating that Cd and Ni interfered not only with nutrient uptake but also with nutrient distribution into the different plant parts. Addition of abscisic acid (ABA) or gibberellic acid (GA3) to the external solution could not overcome the depressing effects of the metals on nutrient acquisition, and even induced a further decr…
La evaluación y seguimiento del estudiante de forma telemática: el proyecto Cuestionarios
En la mayor parte de las ciencias, los ejercicios practicos son la mejor manera de adquirir y evaluar, tanto conocimientos cientificos como las habilidades y competencias necesarias para su aplicacion. Es un entrenamiento que, como en el mundo del deporte, resulta imprescindible y mejora el rendimiento. La resolucion de problemas exige una gran dedicacion del profesorado y, en este aspecto, la utilizacion de cuestionarios on-line puede ser de gran ayuda. Sin embargo, este tipo de cuestionarios tambien presentan una dificultad, que es el esfuerzo inicial necesario. Para reducir esta dificultad se planteo la elaboracion de una base de datos de cuestiones y un protocolo de exportacion.
Morpho-physiological variations in response to NaCl stress during vegetative and reproductive development of rice
The complex nature of plant resistance to adverse environmental conditions, such as salinity and drought requires a better understanding of the stress-induced changes that may be involved in tolerance mechanisms. Here we investigate stress-related morpho-physiological effects during vegetative and reproductive growth in two Japonica rice cultivars (Bomba and Bahia) exposed to a range of NaCl concentrations from the seedling stage. The stress-related detrimental effects were observed either earlier or to a higher extent in cv. Bomba than in Bahia. Damages to the photosynthetic apparatus were related to loss of chlorophyll (Chl) and to a decrease of the maximum potential efficiency of PSII (F…
Modulation of copper deficiency responses by diurnal and circadian rhythms in Arabidopsis thaliana
Highlight Cyclic expression of copper transport and the responses to copper deficiency are integrated into the light and circadian–oscillator signalling in plants.
Defective copper transport in the copt5 mutant affects cadmium tolerance.
Cadmium toxicity interferes with essential metal homeostasis, which is a problem for both plant nutrition and the consumption of healthy food by humans. Copper uptake is performed by the members of the Arabidopsis high affinity copper transporter (COPT) family. One of the members, COPT5, is involved in copper recycling from the vacuole toward the cytosolic compartment. We show herein that copt5 mutants are more sensitive to cadmium stress than wild-type plants, as indicated by reduced growth. Exacerbated cadmium toxicity in copt5 mutants is due specifically to altered copper traffic through the COPT5 transporter. Three different processes which have been shown to affect cadmium tolerance ar…
A relationship between tolerance to dehydration of rice cell lines and ability for ABA synthesis under stress
Plant dehydration is commonly caused by some adverse environmental conditions such as salinity, drought and freezing. As the plant hormone abscisic acid (ABA) is involved in responses to water stress, we studied its putative relationship with the degree of tolerance to these abiotic stresses. For this purpose we used cell lines that had been established from mature embryos of rice (Oryza sativa L, cvs. Bahia and Bomba), and selected by their high (L-T) or low (L-S) levels of tolerance to each type of stress. Tolerance of rice calli to either osmotic, saline, or freezing stress was generally improved by a previous treatment with ABA. This ABA effect was evident in those callus lines with low…
Ni2+ toxicity in rice: effect on membrane functionality and plant water content.
The heavy metal nickel is an essential mineral trace nutrient found at low concentrations in most natural soils. However, it may reach toxic levels in certain areas and affect a number of biochemical and physiological processes in plants. Wilting and leaf necrosis have been described as typical visible symptoms of Ni(2+) toxicity. The plasma membrane (PM) of root cells constitutes the first barrier for the entry of heavy metals but also a target of their toxic action. This work studies the relationship between disturbances of membrane functionality and the development of the typical symptoms of Ni(2+) toxicity. Rice plants (Oryza sativa L. cv. Bahia) grown in nutrient medium containing 0.5m…
Evaluation of Arsenate- and Vanadate-Associated Changes of Electrical Membrane Potential and Phosphate Transport inLemna gibbaG1
Interference of arsenate and vanadate with phosphate uptake in Lemna gibba L. was studied by measuring voltage changes and (32P)phosphate uptake. Arsenate proved to be competitive with the highand low-affinity phosphate uptake system. It induced transient membrane potential changes of up to 120 mV which were similar to those induced by phosphate and indicated a cotransport mechanism with at least 2H+/H2As04. The amplitude of the transient arsenate-induced membrane depolarization was strongly influenced by phosphate starvation. A permanent membrane depolarization to the diffusion potential was achieved within 2 to 6 h in P-starved plants. Thus, arsenate is indeed a strongly competitive physi…
Distinctive phytotoxic effects of Cd and Ni on membrane functionality.
Metal ions essential for plant growth, such as Fe, Mn, Ni, Cu or Zn, are taken up by plants from the soil solution through metal transporters at the plasma membrane, mainly of the ZIP and Nramp families. These transport systems, however, can also give entry to other metals (Al, Cd, Hg, Pb). Non-nutritive elements, as well as the essential nutrients at higher than metabolic concentrations, can cause phytotoxicity. We have studied previously the effects of an essential (Ni) and a non essential (Cd) heavy metal on root cell plasma membranes, the first selective barrier encountered when entering the plant, using rice as model plant. Distinctive effects of Cd and Ni on membrane function (i.e., E…
Temporal aspects of copper homeostasis and its crosstalk with hormones
To cope with the dual nature of copper as being essential and toxic for cells, plants temporarily adapt the expression of copper homeostasis components to assure its delivery to cuproproteins while avoiding the interference of potential oxidative damage derived from both copper uptake and photosynthetic reactions during light hours. The circadian clock participates in the temporal organization of coordination of plant nutrition adapting metabolic responses to the daily oscillations. This timely control improves plant fitness and reproduction and holds biotechnological potential to drive increased crop yields. Hormonal pathways, including those of abscisic acid, gibberellins, ethylene, auxin…
Interaction Between ABA Signaling and Copper Homeostasis inArabidopsis thaliana
ABA is involved in plant responses to non-optimal environmental conditions, including nutrient availability. Since copper (Cu) is a very important micronutrient, unraveling how ABA affects Cu uptake and distribution is relevant to ensure adequate Cu nutrition in plants subjected to stress conditions. Inversely, knowledge about how the plant nutritional status can interfere with ABA biosynthesis and signaling mechanisms is necessary to optimize stress tolerance in horticultural crops. Here the reciprocal influence between ABA and Cu content was addressed by using knockout mutants and overexpressing transgenic plants of high affinity plasma membrane Cu transporters (pmCOPT) with altered Cu up…