Zinc limitation and toxicity in crops and effects of Silicon in ameliorating stress response.

Agriculture is the primary food source for human sustainability. The improvement of food provision through agriculture represents a major topic for plant biology. In addition to drought, salinity and starvation, the remediation from soil contaminations by metalloids and heavy metals is important to guarantee food safety. Metalloids are beneficial and necessary elements for higher plants at low concentrations, but high levels of these result severely toxic both for plants and humans. Soil contamination induced by an excess of some metalloids is a widespread problem over the world, causing economic disease and health threatens by human consumption. In addition to metalloids, heavy metal pollution is rapidly increasing and present many environmental problems. Among heavy metals, some metals such as cadmium (Cd), lead (Pb) and chromium (Cr) have no known biological role while others such as copper (Cu), manganese (Mn) and zinc (Zn) are required in small amount for normal plant growth and developments but are extremely toxic to plants and animals slightly larger than the required concentrations. While some metalloids and heavy metals effects are largely identified, a number of potential ameliorative effects of silicon (Si) are actually discussed. In fact, the silicon utilization as fertilizer is a recent suggestion to guarantee a compatible and sustainable agriculture inducing plant growth and to improve biotic and abiotic stress tolerance, such as metalloids deficiency or toxicity. In the present doctoral thesis, we analyzed three horticultural plants of great agronomic importance, exhibiting different tolerance to Zn, Lactuca sativa cv. Phillipus, Brassica oleracea cv. Bronco, and barley (Hordeum vulgare). These species were exposed to Zn toxicity and deficiency in order to evaluate the contribution of compatible osmolytes, in the mechanism(s) of tolerance to Zn stress. As further control, the effects of a heavy metal such as cadmium were tested on barley plants in order to discriminate and confront the damages induced by polluting metals with those caused by limitation or excess of a nutritional microelement as zinc. Furthermore, we studied the possible beneficial effect of Si on ameliorating plant stress conditions in Hordeum vulgare. In conclusion, this project suggests that metals excess and/or deficiency induces in crops substantially similar responses depending on their capability to manage the stress induced by pollutants. Furthermore, stress symptoms induced by metals are clearly mitigated by Si supply, thus improving plant tolerance mechanisms such as photosynthesis and photorespiratory systems

Improvement of the physiological response of barley plants to both Zinc deficiency and toxicity by the application of calcium silicate

V.P. Acknowledges Erasmus traineeship program by the University of Naples "Federico II". Funding for open access charge: Universidad de Granada / CBUA.An adequate availability of Zinc (Zn) is crucial for plant growth and development given the essentiality of this element. Thus, both Zn deficiency and Zn toxicity can limit crop yields. In plants, the responses to Zn imbalances involve important physiological aspects such as reactive oxygen species (ROS) accumulation, phytohormone balance, tricarboxylic acid cycle (TCA) metabolism, and organic acids (OAs) accumulation. However, a way to improve tolerance to stresses such as those produced by nutritional imbalances is the application of beneficial elements such as silicon (Si). In this study, we grew barley plants in hydroponics under Zn deficiency and toxicity conditions, applying Si in the form of CaSiO3 in order to assess its effectiveness against Zn imbalances. Parameters related to plant growth, oxidative stress, TCA enzyme activities, phytohormones and OAs accumulation were analyzed. Both Zn deficiency and toxicity reduced leaf biomass, increased ROS accumulation, and affected phytohormone and OAs concentrations and TCA enzyme activities. CaSiO3 treatment was effective in counteracting these effects enhancing Zn accumulation under Zn deficient conditions and limiting its accumulation under toxic conditions. In addition, this treatment decreased ROS levels, and improved ascorbate/glutathione and phytohormonal responses, citrate synthase activity, and malate/oxalate ratio. Therefore, this study enhanced the notion of the efficacy of CaSiO3 in improving tolerance to Zn imbalances.Universidad de Granada / CBU

Calcium silicate ameliorates zinc defciency and toxicity symptoms in barley plants through improvements in nitrogen metabolism and photosynthesis

This work was supported by the PAI programme (Plan Andaluz de Investigacion, Grupo de Investigacion AGR282). V. P. Acknowledges Erasmus traineeship program by the University of Naples "Federico II". The results presented in this paper are based on the PhD Thesis by Paradisone ( 2018).Zinc (Zn) deficiency causes serious issues to plant growth and development, negatively affecting crops in many world regions. On the other hand, Zn toxicity impairs plant growth, producing physiological alterations, and even cell death. In plants, two of the processes that most determine growth are nitrogen (N) metabolism and photosynthesis. In the last decades, several authors proved that silicon (Si) and calcium (Ca) mitigate the effects of various abiotic and biotic stresses in plants. The objective of this research is to study the effect of Si application to barley (Hordeum vulgare cv. Nure) plants grown under Zn deficiency and Zn toxicity. Hence, barley plants were grown in hydroponics and supplied with a low Zn dose (0.01 mu M ZnSO4) and a high Zn dose (100 mu M ZnSO4) and were supplied with CaSiO3. Parameters related to Zn accumulation, N metabolism, and photosynthesis were measured. Zn stress affected leaf Zn concentration and reduced biomass in barley plants. Both Zn toxicity and deficiency inhibited N metabolism and enhanced photorespiration, increasing stress symptoms. CaSiO3 mitigated Zn stress effects, probably regulating Zn levels in plant cells and enhancing N metabolism and photosynthesis. We conclude that CaSiO3 could be beneficial to grow barley plants in soils with high or low availability of Zn.PAI programme (Plan Andaluz de Investigacion, Grupo de Investigacion) AGR28

Improvement of the physiological response of barley plants to both Zinc deficiency and toxicity by the application of calcium silicate

An adequate availability of Zinc (Zn) is crucial for plant growth and development given the essentiality of this element. Thus, both Zn deficiency and Zn toxicity can limit crop yields. In plants, the responses to Zn imbalances involve important physiological aspects such as reactive oxygen species (ROS) accumulation, phytohormone balance, tricarboxylic acid cycle (TCA) metabolism, and organic acids (OAs) accumulation. However, a way to improve tolerance to stresses such as those produced by nutritional imbalances is the application of beneficial elements such as silicon (Si). In this study, we grew barley plants in hydroponics under Zn deficiency and toxicity conditions, applying Si in the form of CaSiO in order to assess its effectiveness against Zn imbalances. Parameters related to plant growth, oxidative stress, TCA enzyme activities, phytohormones and OAs accumulation were analyzed. Both Zn deficiency and toxicity reduced leaf biomass, increased ROS accumulation, and affected phytohormone and OAs concentrations and TCA enzyme activities. CaSiO treatment was effective in counteracting these effects enhancing Zn accumulation under Zn deficient conditions and limiting its accumulation under toxic conditions. In addition, this treatment decreased ROS levels, and improved ascorbate/glutathione and phytohormonal responses, citrate synthase activity, and malate/oxalate ratio. Therefore, this study enhanced the notion of the efficacy of CaSiO in improving tolerance to Zn imbalances.V.P. Acknowledges Erasmus traineeship program by the University of Naples “Federico II”. Funding for open access charge: Universidad de Granada / CBUA. This work was supported by the PAI programme (Plan Andaluz de Investigación, Grupo de Investigación AGR282). The results presented in this paper are based on the PhD Thesis by Paradisone (2018)