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Agriculture, a highly water-consuming sector, uses about 70 % of potable water for irrigation, which affects the availability of this scarce and limited resource. For decades, the biostimulant action of aqueous extracts of humic substances from cattle manure vermicompost has been demonstrated in numerous crops, and the protective effect against abiotic stress conditions has also been proven. Lettuce (Lactuca sativa L.) is a waterdemanding vegetable that responds to the stimulating effect of humic extracts. For these reasons, the aim of this work was to evaluate the effect of the application of a humic extract of vermicompost (HEV) on lettuce plants grown under low water supply. Experiments were conducted under controlled conditions, treating the plants with a combination of three dilutions of the obtained HEV and two water conditions (25 and 50 % of the maximum water holding capacity (MC), following a completely randomized experimental design. At 42 days after plant emergence, biological productivity indicators and biochemical-physiological indicators were evaluated. The humic extract of vermicompost presented advantageous physicochemical properties for use as a biostimulant. Plants sprayed with dilutions of the extract and under conditions of low water supply showed similar or higher values than the control with adequate water supply (MC 85 %). Increases in proline and leaf protein content were observed, but not in relative chlorophyll content. It is recommended to perform the total characterization of vermicompost extracts and to study the response of lettuce under field conditions. [ABSTRACT FROM AUTHOR]

Plants are frequently subjected to unfavorable situations for their optimal development and operation caused by alterations in the environment. This set of unfavorable situations is known as environmental stress. Biostimulants are substances that by their action can stimulate the plant growth, improve the absorption of nutrients and increase yields under environmental stress conditions regardless of whether they contain nutrients in their composition. There are several categories of specific biostimulants, among them protein hydrolysates, algae extracts, chitosan, humic and fulvic acids, mycorrhizal fungi and growth promoting bacteria. The objective of this review is to inform the biostimulating effect of the application of humic substances in plants under stress conditions. It also synthesizes aspects related to humic substances such as their structural characteristics and classification. Results are shown using humic substances as biostimulants where their potential to stimulate different metabolic and physiological processes in abiotic stress conditions is demonstrated. It concludes that humic substances present a complex structure, a multiplicity of functional groups and small molecules that interact by weak junctions, which makes them exhibit a great variety of beneficial functions among which is their potential to increase the yields and attenuate the effects of abiotic stresses. Therefore they constitute a viable alternative to avoid the consequences of climate change and use natural and environmentally friendly products. [ABSTRACT FROM AUTHOR]

The humic acids (HA) from two different vermicompost were extracted, isolated, purified and partially characterized, to evaluate their possible protection in rice (Oryza sativa L.) plants against an hydric stress. Differences in elemental composition, as the coagulation threshold value and E4/E6 relation in their UV-Vis spectra were found. Two concentrations (40 and 60 mg L-1) of both HA were included in the nutritive solutions for rice plants in controlled conditions. It was verified that the previous treatment with the HA during six days stimulated the root biomass production. Later the HA were excluded and was an hydric deficit induced by adding polietilenglicol (PEG-6000) in the initially treated plants and in a group of those used as control. After 96 hours of this final condition the net radical biomass, the photosynthetic pigments content and the root membrane permeability were evaluated. In the plants previously treated with HA (at the concentration 60 mg HA L-1), the root membrane permeability, the net radical biomass production and the "a" chlorophyll content had no differences when compared with those without stress. It was concluded that the previous treatment with the HA protected the rice plants against a posterior hydric stress that was induced. [ABSTRACT FROM AUTHOR]

The purpose of this research was to evaluate the influence of chitosan on sunflower plants (Helianthus annuus L.) in soils contaminated with high levels of metal ions and to propose an economic, simple and natural alternative. The bioaccumulation of Lead (Pb) and Cadmium (Cd) was evaluated in the cultivated plants in a period of 60 days, for this, treatments were carried out that included the contaminated medium and the foliar application of Quitomax® at different concentrations. At the end of the evaluations, it was evidenced that the sunflower plant absorbs heavy metals, confirming that the application of Quitomax® contributes to solubilizing the Pb and Cd of the soil, in addition to contributing to a greater development of the crop. [ABSTRACT FROM AUTHOR]

It is in the early stages of the vegetative phase, when the plant manifests its greatest susceptibility to sudden changes in environmental conditions and unleashes adaptive pathways that include changes in the structure of cell membranes, as they are the first to respond to damage. The bean (Phaseolus vulgaris L.) is a crop of agricultural interest that can accumulate heavy metals and therefore, the possibility of developing mechanisms of tolerance to this type of stress. For these reasons, the work aimed to determine the existence of changes in the plasma membrane and in the antioxidant activity of leaves in bean plants germinated in presence of heavy metals. Seeds of the variety CC-25-9-N were germinated under controlled conditions with six specific concentrations of Pb2+, Ni2+ and Cu2+ cations. Fifteen days after seed's germination, the tolerance limit, the lethal dose and changes in the permeability of the leaf membranes were determined through electrical conductivity, pH and the activity of total peroxidases and guaiacol peroxidase. The variability in the membrane permeability was checked from differences in the values of the electrical conductivity and the pH in each of the treatments, which depended on the metal and the concentration under study, as well as on the activity of the enzymes analyzed. These results suggest a possible specificity in the plant - metal interaction that implicate different response mechanisms. [ABSTRACT FROM AUTHOR]

A study was conducted in order to evaluate the performance of the edaphic macrofauna in livestock production soils of the Mayabeque province, Cuba, with different degrees of contamination by heavy metals. In 2012 three plots were sampled dedicated to the cultivation of pasture (Cyperus gigantus L. and Cynodon dactylon L. Pers.), with a concentration gradient of Zn lower than the intervention limit and of available Pb up to 3,5 times higher than the intervention limit; and a non-contaminated plot as control. The rainy season and the 0-10 cm depth were the most favorable for sampling in pastureland ecosystems; and the variations in taxonomic richness, total organisms, relative abundance of each taxon, population density and functional trophic groups for the contaminated ecosystems, were determined through a Union Jack sampling. The taxonomic richness and total organisms significantly decreased wen increasing the concentration of bioavailable Pb and Zn, according to the order Pastureland > Plot 2 > Plot 1 > Ceramic. All the evaluated taxa showed decreases in the relative abundance, and the density of their populations significantly decreased with the increase of the metal concentration, in the order Pastureland > Plot 1 > Plot 2 = Ceramic. The prevailing trophic groups were the predators, and the presence of decomposers diminished. The relative sampling of populations of the Diplopoda class, phytophagous insects of the Coleoptera and Hymenoptera orders and earthworms (Oligochaeta) can be sufficient to indicate the ecological status of the soils. [ABSTRACT FROM AUTHOR]

Bioestimulants of the growth are substances that act as activators of the physiology, absorption of nutrients and to mitigate the stress of salinity. The objective was to evaluate humates of vermicompost as attenuating of the salinity in the emergence and growth of basil (Ocimum basilicum L.). The experimental design was completely randomized with factorial arrangement whose factors were basil varieties (Napoletano and Sweet Genovese), concentrations of NaCl (0.50 and 100 mM) and humates of vermicompost (0 and 1/60 v/v) with six replications. Variance analysis and independent comparisons of means (p ≤ 0.05) were done. The experiment was carried out in 2013 in La Paz, Mexico. The percentage and emergency rate, radicle length, seedling height, fresh and dry biomass of radicle and aerial part were measured. Significant differences were found for all variables (p ≤ 0.05), showing differential response among varieties for emergence rate, emergence percentage and morphometric variables, highlighting the variety Napoletano with biostimulant application as treatment with better results. The humates stimulated all variables under saline conditions, allowing that the tolerant variety improves its emergence and growth and the sensitive variety increases its tolerance to the saline stress. [ABSTRACT FROM AUTHOR]

The contamination by Pb2+ cations and their influence on the food chain is a priority issue for the international scientific community. In field conditions, the tobacco is a species able to accumulate substantial amounts of Pb2+ in their tissues, it credited as a plant accumulator of this metal. It's easy to spread in vitro and management of biotechnology, it is possible to carry out research to understand the mechanisms that occur in plants to stress by heavy metals and extrapolated to other plant species. In this study we have conducted studies of effects on explants of two varieties of tobacco (SL.21 and BH.13), under stress by Pb2+ cation able micropropagation. The explants were kept in contact with three concentrations of Pb2+ (100, 500 and 1000 mg.kg-1) in a culture medium MS. Morphological indicators were assessed as the height of seedlings, leaf number and total number of green leaves, after 15 days of the explants located in the medium. At the stage of the multiplication of both varieties treatments Pb2+ caused damage in all the indicators evaluated, taking the maximum impact of 500 mg.kg-1 and 1000 mg.kg-1, presumably due to Pb2+ of an antagonistic influence on Mg2+, which affected the cellular proliferation and specialization, in addition to a possible use of nitrogen absorbed by seedlings, for the production of peptides that make up the phytochelatins and involved in detoxification processes. [ABSTRACT FROM AUTHOR]