Encapsulation Reduces the Deleterious Effects of Salicylic Acid Treatments on Root Growth and Gravitropic Response.

The role of salicylic acid (SA) on plant responses to biotic and abiotic stresses is well documented. However, the mechanism by which exogenous SA protects plants and its interactions with other phytohormones remains elusive. SA effect, both free and encapsulated (using silica and chitosan capsules), on Arabidopsis thaliana development was studied. The effect of SA on roots and rosettes was analysed, determining plant morphological characteristics and hormone endogenous levels. Free SA treatment affected length, growth rate, gravitropic response of roots and rosette size in a dose-dependent manner. This damage was due to the increase of root endogenous SA concentration that led to a reduction in auxin levels. The encapsulation process reduced the deleterious effects of free SA on root and rosette growth and in the gravitropic response. Encapsulation allowed for a controlled release of the SA, reducing the amount of hormone available and the uptake by the plant, mitigating the deleterious effects of the free SA treatment. Although both capsules are suitable as SA carrier matrices, slightly better results were found with chitosan. Encapsulation appears as an attractive technology to deliver phytohormones when crops are cultivated under adverse conditions. Moreover, it can be a good tool to perform basic experiments on phytohormone interactions.

Efficient strategies for controlled release of nanoencapsulated phytohormones to improve plant stress tolerance.

Climate change due to different human activities is causing adverse environmental conditions and uncontrolled extreme weather events. These harsh conditions are directly affecting the crop areas, and consequently, their yield (both in quantity and quality) is often impaired. It is essential to seek new advanced technologies to allow plants to tolerate environmental stresses and maintain their normal growth and development. Treatments performed with exogenous phytohormones stand out because they mitigate the negative effects of stress and promote the growth rate of plants. However, the technical limitations in field application, the putative side effects, and the difficulty in determining the correct dose, limit their widespread use. Nanoencapsulated systems have attracted attention because they allow a controlled delivery of active compounds and for their protection with eco-friendly shell biomaterials. Encapsulation is in continuous evolution due to the development and improvement of new techniques economically affordable and environmentally friendly, as well as new biomaterials with high affinity to carry and coat bioactive compounds. Despite their potential as an efficient alternative to phytohormone treatments, encapsulation systems remain relatively unexplored to date. This review aims to emphasize the potential of phytohormone treatments as a means of enhancing plant stress tolerance, with a specific focus on the benefits that can be gained through the improved exogenous application of these treatments using encapsulation techniques. Moreover, the main encapsulation techniques, shell materials and recent work on plants treated with encapsulated phytohormones have been compiled.

Improvement of salicylic acid biological effect through its encapsulation with silica or chitosan.

Attacks of necrotrophic and biotrophic fungi affect a large number of crops worldwide and are difficult to control with fungicides due to their genetic plasticity. Encapsulation technology is a good alternative for controlling fungal diseases. In this work, encapsulated samples of salicylic acid (SA) with silica (Si:SA) or chitosan (Ch:SA) at three different ratios were prepared by spray drying, and morphological and physicochemical characterised. Therefore, size distribution, specific surface area, thermal stability, encapsulation efficiency, and in-vitro SA release were determined. Biological activity of encapsulated samples were tested against different fungi of agricultural interest at various concentrations (0-1000 µM). Treatments prepared with the lowest ratios for both capsules, were found to have the best antifungal effect in an in vitro system, inhibiting the mycelial growth of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum and Geotrichum candidum. Similarly, treatments with the lowest ratios of both encapsulated samples reduced free SA toxicity on Arabidopsis thaliana seeds. In this system, plants treated with capsules had higher root and rosette development than those treated with free SA. In conclusion, a product with a great potential in agriculture that shows high antifungal capacity and low toxicity for plants have been developed through a controlled and industrially viable process.