Abstract
Salinity is an abiotic stress that affects agriculture by severely impacting crop growth and, consequently, final yield. Considering that sea levels rise at an alarming rate of >3 mm per year, it is clear that salt stress constitutes a top-ranking threat to agriculture. Among the economically important crops that are sensitive to high salinity is tomato (Solanum lycopersicum L.), a cultivar that is more affected by salt stress than its wild counterparts. A strong body of evidence in the literature has proven the beneficial role of the quasi-essential metalloid silicon (Si), which increases the vigor and protects plants against (a)biotic stresses. This protection is realized by precipitating in the cell walls as opaline silica that constitutes a mechanical barrier to the entry of phytopathogens. With respect to Si accumulation, tomato is classified as a non-accumulator (an excluder), similarly to other members of the nightshade family, such as tobacco. Despite the low capacity of accumulating Si, when supplied to tomato plants, the metalloid improves growth under (a)biotic stress conditions, e.g., by enhancing the yield of fruits or by improving vegetative growth through the modulation of physiological parameters. In light of the benefits of Si in crop protection, the available literature data on the effects of this metalloid in mitigating salt stress in tomato are reviewed with a perspective on its use as a biostimulant, boosting the production of fruits as well as their post-harvest stability.
Highlights
Plants are sessile organisms and, they are continuously exposed to the surrounding environment
Soil salinization is defined as the accumulation of salts in the soil solution that can be measured as the total dissolved solids (TDS) or the electrical conductivity [16], while sodicity is the predominance of Na+ ions that saturate the ion exchange sites in the soil instead of other ions, such as Mg2+ and Ca2+ [17]
Results concerning the protective impact of Si on the photosynthetic machinery were obtained by Muneer and colleagues who performed a proteome analysis on tomato chloroplasts after supplying high concentrations of Si (2.5 mM), which is beyond the solubility limit [83]
Summary
Plants are sessile organisms and, they are continuously exposed to the surrounding environment. If the non-optimal conditions become common in a specific location, plants need to adopt strategies to exploit their new environment in the most efficient manner and transmit these changes to their progeny. In this case, evolutionary adaptation takes place [9]. Stresses are generally divided into two different classes, depending on whether they entail the interaction with a living organism or not The latter includes abiotic stresses that are caused by environmental changes, such as water stress, exposure to extreme temperatures, excess or lack of nutrients, high salinity, presence of heavy metals and ultraviolet radiation. The paragraphs will treat (1) the problem of salt stress with the physiological impairments it causes to plants; (2) the response of cultivated tomato (Solanum lycopersicum L.) as an example of an economically relevant crop sensitive to excessive salinity; and (3) the mitigatory effects of silicon (Si) in S. lycopersicum, a Si non-accumulator
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