BACKGROUND
El Calcium (Ca) is an essential nutrient for plants. After being absorbed by the roots, it is transported via xylem following the perspiration flow and is distributed basically by the same route to all the plant organs. This nutrient intervenes in numerous functions within the plant, acts as a messenger and provides structural stability to the cell wall and membrane.
In terms of its requirement by higher plants, Ca is classified as secondary nutrientHowever, it is involved in numerous biochemical and morphological processes.
Calcium is involved in more than thirty physiological disorders of economic importance in crops, basically due to a poor distribution of the element in organ tissues (Shear, 1975). In tomato, for example, localized calcium deficiency causes blossom end rot and promotes fruit cracking, while excess calcium induces the formation of golden spot. Calcium plays an important role in plant disease resistance by protecting the cell wall from disintegrating enzymes secreted by pathogens.
In cultivated plants, symptoms of calcium deficiency are rarely observed. However, significant losses occur each year due to physiological disorders resulting from inadequate concentrations of this nutrient in leaves, fruits, roots, or tubers.
Calcium has received considerable attention in recent years not only for its relationship with physiological disorders, but also for its beneficial effects, particularly in fruits, in which it can Reduce respiration, delay ripening, increase post-harvest life, as well as improve firmness and vitamin C content.Several experiments indicate that increased calcium in the cell walls of plant tissues decreases the presence or severity of diseases (Villegas et al., 2007b).
In turn, the boron (B) It is a micronutrient that is needed for the nutrition of all plantsThe main functions of boron are related to the Development and resistance of cell walls, cell division, fruit and seed development, sugar transport, and hormone development. Although the essentiality of B as a micronutrient for all vascular plants to achieve high and good quality productions in agricultural practices is well established, knowledge about its metabolic functions in plants remains incomplete. Some research has greatly improved the understanding of some processes in plants regarding their consumption and transport (Takano et al., 2006), cell wall formation (O'Neally et al., 2004), cell membrane functions (Goldbach et al., 2001) and antioxidant defense (Cakmak and Römheld, 1997).
CALCIUM ABSORPTION AND DISTRIBUTION IN THE PLANT
The ca2+ It is transported via the apoplastic pathway to the xylem. Ca transport in the xylem occurs by mass flow of Ca2+ free, some of Organically complexed Ca and by chromatographic movement along Ca exchange sites in the xylem walls. Competition between demand sites intensifies when the Ca concentration2+ In the xylem it is low and transpiration is high (Clarkson, 1984), which can cause nutritional deficiency.
Ca concentration in plants ranges from 0.2 to 3.0% of leaf tissue dry weight, with sufficiency values of 0.3% to 1.0% in the leaves of most crops. The highest concentration is found in older leaves. It has been suggested that total Ca concentration is not a reliable indicator of sufficiency because it accumulates in some plants as calcium oxalate crystals. Therefore, extractable Ca may be a better indicator of sufficiency (Jones et al., 1991).
FUNCTION OF CALCIUM IN CELL STRUCTURE
Ca acts as second messenger in the regulation of a wide variety of physiological and anatomical processesCellular Ca regulation is an essential function, performed by a set of complex processes collectively called Ca homeostasis.
Ca functions predominantly as structural component in cell walls and in maintaining the integrity of the plasma membrane. Deficiency of this nutrient increases membrane permeability, the dissolution of the middle lamella and the associated changes in the cell wall. Most of the Ca entering the plant is accumulated in the cell walls and membranes. In the cell wall, accumulation is facilitated by binding with pectin polymers, particularly in the middle lamella, to form a cell wall network that increases mechanical strength (Gerasopoulos and Chebli, 1999).
Ca constitutes a structural element in membrane architecture: electrostatic bridges formed by Ca and components of the membrane's lipid layer allow for the anchoring and stationarity of integral proteins. Membrane stability, microviscosity, and the state of the lipid phase can all be controlled by Ca (Leshem et al., 1992). Ca preserves membrane integrity in two ways: one, by delaying changes in the lipids that comprise it due to senescence; and another, by increasing restructuring processes. (Gerasopoulos and Chebli, 1999).
While other cations can replace Ca binding sites, they They are not able to replace the latter's function in stabilizing the membrane.. The absence of Ca in the membrane causes it to become porous, and solutes are lost from the cytoplasm. With Ca deficiency, the membrane structure disintegrates. Disorders occur primarily in meristematic tissues such as the root tip, growing points in the upper parts of plants, and storage organs (Kirkby and Pilbeam, 1984).
Ca deficiency modifies the selective action of cations, induces ultrastructural changes and alters the process related to plasma membrane fusion, also causing the separation of the phospholipid phase in artificial membranes (Marmé, 1983).
EFFECT OF A HIGH CALCIUM CONCENTRATION ON PLANTS
Ca is a relatively non-toxic cation in large quantities and plants can adapt to a wide range of supply.. Toxicity develops slowly and can usually be attributed to an indirect effect involving other ions (Nonami et al., 1995). Among the effects that can occur in plants when subjected to high calcium concentrations are: growth arrest due to the impediment of cell wall extension, rigidity of the cell membrane, and an increase in insoluble deposits in walls and vacuoles (Hanson, 1984). High concentrations of Ca2+ exceeding physiological tolerance decrease photosynthesis and disrupt KXNUMX+ fluxes.+ (Marschner, 2002).
In contrast to other macronutrients, a high proportion of the total calcium in plant tissues is frequently located in cell walls due to the large number of binding sites found there, as well as the reduced transport of calcium to the cytoplasm. In the middle lamella, it is bound to the carboxyl groups of polygalacturonic acids (pectins) in a relatively exchangeable form. In dicotyledonous plants, which have a high cation exchange capacity (CEC), more than 50% of the total calcium is bound to pectates (Marschner, 2002).
CALCIUM DEFICIENCY DISEASES
Problems associated with Ca deficiency in plants are characterized in two areas:
- those related to the inability to absorb Ca from the solution due to low absolute concentration or low Ca/other cation ratios
- those related to inadequate distribution of Ca to actively growing tissues after absorption. The upward movement of Ca in the xylem and its ultimate distribution are largely dependent on the bulk flux associated with transpiration. Ca transport through the xylem is controlled by the density of negative charges in the vessels, the concentration of other cations in this tissue, and the capacity of the cells.
adjacent to remove Ca from the exchange sites (Marschner, 2002).
Disorders associated with Ca deficiency include diverse symptoms. The blossom end rot They begin at the opposite pole to the peduncle, with the formation of numerous small necroses that eventually form an almost circular, depressed spot with well-defined edges, which can cover half the fruit. Blossom end rot, which correlates with the collapse of the middle lamellae of the pulp cells, is related to low Ca concentrations in the distal tissue and rapid fruit growth (Ho et al., 1999). The symptoms of fruit cracking These consist of cracks extending from the insertion point with the calyx, almost always appearing in ripe fruit and sometimes during ripening. They are usually caused by water deficiency at high ambient temperatures followed by a rapid change in the moisture supplied to the plants. However, this phenomenon can be exacerbated by the reduction in cell wall rigidity caused by low Ca concentrations (Resh, 2001).
THE ROLE OF CALCIUM IN PLANT RESISTANCE TO BIOTIC DISEASES
The infective capacity of microorganisms that develop in plant cells is determined by their ability to hydrolyze cell walls.Without this condition, the penetration of an infectious agent into a group of cells affected by a wound would not be accompanied by the spread of the infection to neighboring cells; for this reason, a very important aspect in the pathogenesis of plant diseases is the chemical mechanism by which the pathogen penetrates and colonizes its tissues (Cornide et al., 1994).
Pathogens secrete enzymes that cause softening of cell wallsThe role of these enzymes in pathological processes is of undeniable importance, especially in young plants, since the primary wall of plants is rich in pectin, while the secondary wall, characteristic of mature tissues, is more abundant in cellulose and hemicellulose (Cornide et al., 1994).
Several experiments indicate that increasing Ca in the cell walls of plant tissues can reduce the presence or severity of diseases.
In a study in which the role of Ca in protecting pumpkin fruit tissues from infection was evaluated Botrytis cinerea, it was determined that Ca applied to the fruit increased the concentration of this element in the cell walls and thus decreased the digestion of pectin by the pectinolytic enzymes of the fungus. (Chardonnet and Doneche, 1995).
Increases in Ca concentration in potatoes, significantly improved quality and storage life by reducing damage caused by Erwinia carotovora (Conway and Gross, 1987). In fruit tissues with high Ca concentration, changes in cell wall composition were generally smaller due to infection, compared to those observed in fruits with low Ca content. The results of this investigation indicated that The effect of Ca in reducing rot is associated with the stability of the cell wall structure (Tobias et al., 1993).
BORON IN THE CELL WALL AND MEMBRANE
The cell wall is fundamental in determining the growth and development of the plant cell, which involves a dynamic and continuous modification during cell differentiation (Pérez Almeida and Carpita, 2006), where Boron plays an important role in forming borate bridges for the formation of the B-RGII dimer, a fundamental component in the architecture of the cell wall. (Goldbach and Wimmer, 2007). The role of B is also correlated with the development and lignification of cell walls. (Matsunaga et al., 2004).
Extensive studies have demonstrated the importance of B for the complete functionality of different processes at the cellular level in plants, where a variety of enzymes and other plasma proteins participate, in addition to the processes of transport through the membrane and its integrity (Bronw et al., 2002). B deficiency alters the membrane potential (Blaser-Grill et al., 1989), reduces ATPase activity in proton pumping, and consequently the proton gradient across the plasma membrane (Obermeyer et al., 1996), and reduces Fe-reductase activity (Ferrol and Donaire, 1992).
OTHER PROCESSES INVOLVED IN THE BORON-PLANT RELATIONSHIP AT THE CELLULAR LEVEL
Some studies have shown that B deficiency affects the photosynthesis process in plants. The primary mechanisms of B function in photosynthesis are unknown, but it may affect functions at the level of chloroplast membranes by disrupting electron transport and the energy gradient across the membrane, resulting in photoinhibition (Goldbach and Wimmer, 2007).
Other studies indicate the existence of a close relationship between B and Ca where both co-act at the level of the cell membrane by interactions that are still unknown (Bolaños et al., 2004). In this regard, evidence from various investigations indicates that this relationship is a determining factor in genetic expression (Redondo Nieto, 2002), in addition to the fact that the participation of Ca is important in the stabilization of B complexes (Wimmer and Goldbach, 1999). Additionally, Ca reduces the effects of B deficiency on nodule development (Redondo Nieto et al., 2002) even under salt stress (El-Hamdaoui et al., 2003).
BORON MANAGEMENT IN AGRICULTURAL SYSTEMS
Imbalances caused by B deficiency and toxicity are problems that exist in many agricultural regions of the world, and their identification and correction are necessary not only through a good understanding of the processes involved in its absorption, mobilization and distribution in the plant (Brown and Hu, 1998).
In general, sampling techniques for diagnosing B status in plants are based on the premise that B is immobile, it does not move in the phloem, as it happens in most speciesHowever, it is now known that B is mobile in those species that use polyols (simple sugars) as a primary photosynthetic metabolite with high affinity to bind B for subsequent transport in the phloem to areas of active accumulation, such as vegetative or reproductive meristems (Brown et al., 2002). In species that do not produce significant amounts of polyols, B once translocated with the flow of transpiration to the leaves, remains immobile without being able to re-enter the phloem, accumulating in the terminal parts of the leaf veins (Brown and Hu, 1998).
The difference in B mobility influences the diagnosis of its status to correct its deficiency and toxicity in plants, taking into account its mobility in the phloem when selecting the tissue to sample. This is because B does not accumulate in older leaves, but it does in younger leaves in species where it is mobile; while on the contrary, in species where it is immobile, its accumulation is greater in older leaves., compared to younger women, due to greater perspiration (Brown and Hu, 1998).
B fertilization must be managed very carefully to avoid contamination problems in the crop, taking into account plant mobility patterns. According to experimental evidence, Foliarly applied B is retranslocated to growing organs in species where it is mobile (Christensen et al., 2006). However, in species where B is immobile, its foliar application does not translocate it from the applied site, as its requirements cannot be met in tissues that are not yet formed. Therefore, deficiency correction is achieved by direct application to the target sites. Thus, in fruit trees where B is immobile but essential for the flowering process, applications are effective directly to flower buds or flowers (Brown and Hu, 1998).
CONCLUSIONS
The study of calcium from the perspective of plant physiology is essential to understand more precisely the role it plays in the development and production of crops, which allows the design of methodologies in which the knowledge generated can be applied in order to improve the response of plants and impact the increase in yields and their quality. The absolute concentration of calcium and its relationship with other ions in the nutrient solution is essential to reduce the Physiological disorders caused by poor distribution of this element in plant organs (Villegas et al., 2007a).
Calcium increases plant resistance to diseases by protecting the cell wall. against the action of disintegrating enzymes secreted by pathogens (Villegas et al., 2007b).
El boron stands out as a dynamic element that affects an exceptionally large number of biological functions involved in a wide spectrum of processes encompassed in plants (Malavé and Carrero, 2007).
It is essential to know the relative mobility of boron in the species for tissue sampling, the analysis of which will indicate the boron status of the plant and the consequent strategy of applying or not applying fertilization, taking into account the narrow margin between deficiency and toxicity (Malavé and Carrero, 2007).
CULTIFORT RECOMMENDATION
At Cultifort, we offer a wide range of zero-waste nutritional formulations, manufactured with the highest quality raw materials that guarantee maximum product stability, the best possible assimilation, and improved plant physiological processes.
Within our range of organic amendments and deficiency correctors, you will find CULTIFORT CALCIUM y CULTIBORO PLUS.
CULTIFORT CALCIUM It is a liquid fertilizer with High calcium content complexed with organic acids and formulated with organic matter and carbohydratesOrganic acids facilitate the assimilation of calcium by the plant (via leaves and roots) and organic matter and carbohydrates ensure its efficient translocation into the interior, avoiding nutritional imbalances caused by high transpiration rates (high temperatures) that divert the flow of sap towards the leaves, causing nutritional deficiencies in the fruits.
CULTIBORO PLUS It is a liquid formulation of boron complexed with ethanolamine and reducing sugars, which guarantee their rapid assimilation, both through leaves and roots. CULTIBORO PLUS helps Regulate the plant's hormonal levels, improving root growth and cell division in stems and leaves. As well guarantees the transport of sugars in the plant and facilitates breathing
The relationship between CULTIBORO PLUS y CULTIFORT CALCIUM (B/Ca) plays a very important role at the structural level and in signal transduction. Both formulations mutually improve their translocation inside the plant, multiplying the efficiency of the applications.
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